Test system and evaluation method for mixing uniformity of oil and gas in air-assisted injection premixing cavity

Abstract

The invention discloses a test system and an evaluation method for the mixing uniformity of oil and gas in an air-assisted injection premixing cavity, and the mixing uniformity of oil and gas in the premixing cavity can be accurately evaluated through a visual premixing cavity structure and a high-speed photography technology in combination with image processing and quantitative evaluation indexes. The test system comprises a transparent premixing cavity model, a fuel oil supply system, a gas supply system and a high-speed photography system, and the oil-gas mixing process can be visually recorded. According to the evaluation method, through image processing means of background subtraction, binarization and pixel calibration, oil-gas mixing key parameters such as fuel penetration distance, fuel coverage area and unit mass fuel coverage area Raq are accurately extracted, and mixing uniformity under different fuel injection quantities and working conditions can be reflected. On the basis of introduction of the unit mass fuel coverage area Raq, the problem that influences of different fuel injection quantities cannot be accurately compared is solved; the evaluation method provides test support with engineering application value for optimization of the low-pressure air-assisted fuel injection technology.

Description

Technical Field

[0001] This invention belongs to the field of fuel atomization experiments, specifically relating to a test system and evaluation method for the uniformity of fuel-air mixing in an air-assisted injection premixing chamber based on high-speed photography and image recognition. Background Technology

[0002] With the rapid development of low-altitude economy and unmanned transportation, the demand for long-endurance, high-load power systems is becoming increasingly urgent. Power sources need to meet the requirements of long-endurance and high-load operation, but pure battery power suffers from insufficient energy density, making it difficult to meet the demands of continuous high-load operation. Especially in current unmanned transportation scenarios, pure battery power is insufficient to meet the requirements of continuous high-load operation, and traditional fuels remain an important option for power sources.

[0003] Traditional fuels, primarily gasoline and heavy fuels (diesel and kerosene), present a trade-off between storage and combustibility. Gasoline fuels have low boiling points and high volatility, making them easy to atomize, but they also pose safety hazards during storage and use due to their volatility and flammability. Heavy fuels do not readily evaporate into gas at room temperature, making them safer to store and transport. However, their high boiling points prevent fuel molecules from easily entering a gaseous state, so under conventional injection conditions, they tend to form larger droplets rather than fine atomized sprays. These larger droplets burn incompletely, reducing combustion efficiency and producing unburned carbon particles (black smoke).

[0004] To improve the atomization performance of heavy fuels, low-pressure air-assisted injection (LPA) technology has been proposed. This technology involves injecting liquid fuel into a premixing chamber, mixing it with compressed air, and then expelling it through a nozzle, utilizing air shear to enhance atomization. LPA fuel injection achieves good atomization at relatively low pressures by injecting fuel into a premixing chamber to mix with compressed air before expelling it through a nozzle. The core of LPA fuel injection technology is using low-pressure air to assist in creating better atomization and initial mixing of the fuel within the nozzle, thereby improving spray characteristics and combustion performance.

[0005] Current research focuses on the external spray of the nozzle, rather than the internal mixing. Most existing studies concentrate on the output state after nozzle injection, such as spray shape, spray angle, droplet distribution, and penetration distance. These studies primarily focus on the behavior of fuel in the combustion chamber or external environment after injection; however, few studies focus on the fuel-air mixing process inside the nozzle, especially within the premixing chamber. Firstly, spray shape and spray angle determine the spatial distribution range and density of the spray. Research on the angle, velocity, and uniformity of the spray shape is crucial. A common method is to capture the atomized spray morphology using high-speed photography to infer whether fuel atomization is good. Secondly, studying the distance the spray droplets travel from the nozzle to their farthest point is closely related to factors such as injection pressure and injection method, and is often used to assess the spray's spread capability. Thirdly, droplet distribution analysis helps evaluate the uniformity of the spray, especially the droplet size distribution and whether there are excessively large droplets that are not fully atomized, leading to low combustion efficiency. These studies focusing on the external state of the spray concentrate on how droplets are distributed and dispersed in space, and how these droplets react in the combustion chamber.

[0006] However, current research lacks systematic experimental studies and effective evaluation methods for the uniformity of the oil-gas mixing process within the premixing chamber. The studies have not delved into the oil-gas mixing process inside the nozzle; in other words, the oil-gas flow and mixing mechanism inside the nozzle has not been effectively observed or quantified. This ambiguity in the mixing mechanism hinders further optimization and application of nozzle internal technology.

[0007] The internal structure of the nozzle, specifically the gas-oil mixing process within the premixing chamber, has always been a challenging area in experimental and theoretical research. The main difficulties lie in visualization, the complexity of the mixing process, and the lack of a unified quantitative evaluation method. Firstly, regarding visualization difficulties, the high temperature and pressure conditions within the premixing chamber, coupled with the complex fluid flow within the nozzle, make it difficult to obtain clear images of the nozzle's interior using traditional observation methods. Even with high-speed photography, relying on optical imaging, it's challenging to accurately capture the dynamic gas-oil mixing process. Secondly, regarding the complexity of the mixing process, gas-oil mixing within the nozzle is a multiphase fluid problem involving complex physical phenomena such as the atomization of liquid fuel, the flow of gaseous air, and droplet breakup. These phenomena often interact, affecting the homogeneity of the gas-oil mixture, but the mixing mechanism remains unclear due to the difficulty in effectively tracking the internal flow. Thirdly, regarding the lack of a unified quantitative evaluation method, while external characteristics such as spray morphology and injection angle can be quantitatively studied through image analysis, there is a lack of quantitative and standardized evaluation indicators for the mixing homogeneity within the premixing chamber. Currently, quantitative evaluation of gas-oil mixing mainly relies on numerical simulations and limited experimental data based on surface heat transfer. As for how to evaluate the uniformity of oil and gas in the premixing chamber from the perspective of dynamic mixing process, there is relatively little research in existing literature and technical solutions.

[0008] While existing research literature on the uniformity of mixing within the premixing chamber is relatively limited, some studies have been conducted on air-assisted injection, air-assisted atomization, and internally mixed sprays, particularly focusing on the macroscopic characteristics of the spray. The article "Experimental investigation on the effects of fuel–airmixture temperature on the air-assisted kerosene spray characteristics" investigated the influence of fuel-air mixture temperature on the characteristics of air-assisted sprays, conducting a systematic experimental analysis of spray penetration distance, width, and droplet distribution. It shows that air-assisted injection has a significant impact on spray characteristics under temperature changes, but primarily focuses on external spray characteristics rather than the internal mixing process. The article "Experimental Study on the Spray Characteristics of an AirAssisted Atomizer with Internal Mixing Chamber" indicates that some early work developed air-assisted atomizing nozzles with internal mixing chambers and studied the effects of spray shape and nozzle length on spray characteristics, demonstrating that the internal mixing chamber can assist atomization.

[0009] In existing relevant patent literature, US5085189A, "Air-assisted fuel injection applied in a two-stroke engine," is a basic design patent for an air-assisted premixing chamber. This patent proposes using air-assisted fuel injection and a premixing chamber structure in a two-stroke engine to premix fuel and air within the chamber before injection, improving mixing uniformity and combustion performance; however, the technical solution does not involve internal visualization evaluation. Summary of the Invention

[0010] (1) Purpose of the invention

[0011] To address the research gaps in existing technologies, this invention provides an experimental system and evaluation method for the homogeneity of oil-gas mixing within an air-assisted injection premixing chamber. The aim is to overcome the shortcomings in the observation and evaluation of the oil-gas mixing process in existing technologies. Therefore, focusing on the specific object of the air-assisted injection premixing chamber, this invention organically combines four aspects: the structural design of the transparent premixing chamber model, the experimental method for the transparent premixing chamber model, image processing using "background subtraction + binarization + pixel calibration," and an index system incorporating the Raq index. This forms a complete and systematic solution, ensuring the reliability and accuracy of the experimental results.

[0012] The core technical problem solved by this invention is to construct a visual test and evaluation method without changing the actual flow characteristics of the air-assisted nozzle premixing chamber. This method can directly observe the dynamic process of oil-gas mixing in the premixing chamber and evaluate the uniformity of oil-gas mixing through reasonable quantitative indicators (penetration distance, coverage area, and fuel coverage area per unit mass Raq), thereby providing a reliable basis for the premixing chamber structure design and injection parameter optimization.

[0013] The first technical problem this invention aims to solve is how to accurately capture the dynamic changes in the oil-gas mixing process inside the nozzle under high pressure and high temperature conditions. To this end, the present invention provides an air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method, which combines high-speed photography and image processing technologies to monitor and quantitatively analyze the oil-gas mixing process inside the nozzle in real time. This enables accurate capture of the dynamic changes in the oil-gas mixing process inside the nozzle under high pressure and high temperature conditions, allowing for intuitive observation of the oil-gas mixing inside the nozzle and quantitative analysis of the mixing uniformity. This provides a solid technical foundation for further optimization of the injection system and improvement of combustion efficiency.

[0014] The second technical problem this invention aims to solve is how to quantitatively evaluate the uniformity of oil-gas mixing through experiments and imaging techniques. To this end, this invention provides an air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method. Through high-speed photography, image processing, and a quantitative evaluation index (Raq), it can accurately capture and quantitatively evaluate the uniformity of oil-gas mixing under high pressure and high temperature conditions. Specifically, by combining spray image feature extraction and Raq value calculation, the uniformity of oil-gas mixing can be accurately assessed, and optimization can be achieved through multi-parameter adjustment, ultimately providing strong data support for injection system design and combustion efficiency improvement.

[0015] The third technical problem this invention aims to solve is how to design a visualization system and experimental platform that can effectively operate under complex flow fields, enabling not only the observation of static images but also the tracking of dynamic changes. To this end, the present invention provides an air-assisted injection premixing chamber oil-gas mixing homogeneity test system and evaluation method. Through transparent premixing chamber design, high-speed photography technology, dynamic process tracking, multi-parameter adjustment, and real-time feedback mechanisms, an effective visualization system and experimental platform can be built under complex flow fields. This platform can not only observe static images but also track the dynamic changes of the oil-gas mixing process in real time. Furthermore, it uses quantitative evaluation methods to accurately analyze the oil-gas mixing homogeneity, thereby providing reliable experimental evidence for the optimization of the injection system and the improvement of combustion efficiency.

[0016] (2) Inventive concept

[0017] In existing technologies, air-assisted injection nozzles generally adopt a monolithic metal structure with the premixing chamber located inside the nozzle. This makes it impossible to visualize the flow inside the premixing chamber while it can withstand a certain pressure. Even if the nozzle shell is simply replaced with a transparent material, the premixing chamber bottom is difficult to seal reliably, and the premixing chamber wall thickness and structural arrangement are unreasonable. This can easily lead to insufficient pressure resistance, complex light paths, and severe image distortion, making it difficult to obtain a clear and reliable image of the oil-gas mixture inside the premixing chamber.

[0018] Therefore, this invention provides a test system and evaluation method for the uniformity of fuel-air mixing within an air-assisted injection premixing chamber. The inventive concept is to design an innovative test and evaluation method for the uniformity of fuel-air mixing within an air-assisted injection premixing chamber, used to quantitatively evaluate the uniformity of fuel-air mixing within the chamber. To achieve this goal, the test system and evaluation method for the uniformity of fuel-air mixing within an air-assisted injection premixing chamber described in this invention employs a test system based on a visualized premixing chamber, which combines high-speed photography and image processing technology. By creating a visualized premixing chamber model and combining high-speed photography and image processing technology, this invention allows for direct observation and quantification of the fuel-air mixing process within a transparent premixing chamber, thereby providing strong data support for the optimization of the combustion system.

[0019] Overall, this invention specifically extracts and reconstructs the structure of the air-assisted nozzle. The premixing chamber and its upper structure connected to the nozzle are extracted separately and 3D printed using transparent resin. While retaining the original geometry and boundary conditions of the premixing chamber, only the air supply channels related to the nozzle and premixing chamber are preserved, eliminating the nozzle needle valve structure that obstructs the view. To address the sealing and strength issues of the transparent model under pressure, this invention extends and thickens the bottom channel of the premixing chamber, taps threads on the inner wall of the extended section, and achieves a reliable seal by tightening bolts. At the same time, the thickness of the premixing chamber sidewall that needs to be observed is reduced to approximately 1 mm to improve light transmittance. The air inlet, nozzle connection section, and bottom sealing section that are not involved in the observation are appropriately thickened to improve load-bearing capacity.

[0020] The core concept of this invention is to transform the traditional oil-gas mixing process into an observable and quantifiable experimental scenario, utilizing visualization models and image analysis techniques to accurately evaluate the uniformity of oil-gas mixing. Traditional testing methods mainly rely on numerical simulation or external measurements, while this invention, through a transparent premixing chamber structure, allows direct observation of the internal oil-gas mixing process. This not only solves the problem of internal mixing that previous external spray tests could not reflect, but also, by introducing the evaluation index Raq of the coverage area per unit mass of fuel, makes the evaluation more comprehensive and accurate.

[0021] The present invention discloses an air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method. The inventive concept is to visualize the premixing chamber structure design, image processing and quantitative evaluation, and experimental parameter adjustment and optimization.

[0022] Regarding the design of the visual premixing chamber structure, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention uses transparent resin or other transparent materials to manufacture the premixing chamber model, and by separating the oil nozzle and air nozzle structures, the oil-gas mixing process is clearly visible during the injection process; this visual premixing chamber structure design ensures that the mixing state inside the premixing chamber can be monitored in real time during the test, thereby obtaining accurate experimental data.

[0023] In terms of image processing and quantitative evaluation, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention use a high-speed photography system to record the oil-gas mixing process during fuel injection, and then use image processing technology to extract key parameters, such as fuel penetration distance, fuel coverage area and fuel coverage area per unit mass Raq, to ​​quantitatively evaluate the oil-gas mixing uniformity. This makes the evaluation of oil-gas mixing more intuitive and accurate, avoiding the limitations of traditional methods that rely on only a single indicator.

[0024] Regarding the adjustment and optimization of experimental parameters, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention adjusts the oil-gas mixing conditions by setting different control parameters such as gas pressure, injection pressure and injection pulse width, thereby further improving the uniformity of oil-gas mixing in the premixing chamber. This not only helps to optimize injection parameters in practical applications, but also provides accurate data support for the design of combustion systems.

[0025] Through the above structural design, this invention obtains a large field-of-view, high-contrast image of the fuel-air mixture inside the premixing chamber while ensuring that the internal flow characteristics remain essentially unchanged. This provides a foundation for accurately extracting the fuel penetration distance and fuel coverage area using subsequent image processing methods. Experimental results show that, under the same experimental conditions, the fuel contour boundary obtained by the visualized premixing chamber structure of this invention is clear, and the measurement dispersion of the penetration distance and coverage area obtained from repeated experiments is significantly reduced, improving the reliability of the evaluation results.

[0026] (3) Specific technical solutions

[0027] Firstly, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method of the present invention includes the following steps:

[0028] S1. Construct a visual premixing chamber model: The premixing chamber model has transparent walls, which can be used to observe the oil-gas mixing process in real time;

[0029] S1.1 Maintain consistent geometry: Extract the premixing chamber and its upper structure connected to the nozzle from the original air-assisted nozzle;

[0030] S1.2 Separate the oil nozzle and air nozzle: Separate the oil nozzle and air nozzle from the original nozzle, keeping only the oil nozzle, premixing chamber and its air supply channel;

[0031] S1.3 Transparent Resin 3D Printing: Using transparent resin 3D printing to create a premixed cavity model, making the interior visible;

[0032] S1.4 Blocking the connection channel: The original connection channel between the premixing chamber and the air nozzle is blocked with screws. The bottom of the premixing chamber is extended and thickened and internally threaded. The bottom is sealed with bolts to achieve bolt sealing.

[0033] S1.5 wall thickness design: The wall thickness in the observation area is controlled between 1mm and 1.5mm to improve light transmittance; the wall thickness in the non-observation area is increased.

[0034] S2. Set and adjust experimental parameters: Adjust the injection pressure, injection pulse width and gas pressure to simulate different oil-gas pressure differences and injection conditions;

[0035] The adjustment methods for air pressure difference, injection pulse width and injection pressure are as follows: First, set and adjust the output pressure of the air pump and oil pump to simulate different working conditions; then, by controlling the injection pulse width, adjust the amount of fuel injected each time and the atomization effect to optimize the uniformity of fuel-air mixture.

[0036] S3. Fuel-air injection: The injection control system drives the fuel injector to inject fuel, and the fuel-air mixing process is recorded synchronously by a high-speed camera system;

[0037] Among them, when the injection control system controls the injection pulse width, the injection pulse width is adjusted by setting multiple operating conditions. The operating condition range includes multiple set values ​​from 2ms to 6ms to simulate the effect of different injection durations on the fuel-air mixture.

[0038] S4. Image preprocessing: The acquired images are preprocessed, including background image selection, difference processing and binarization, in order to extract key information about oil and gas mixing;

[0039] S4.1 Select Background Image: Select an image without fuel injection as the background image, record the state of the premixing chamber when only gas is present, and eliminate the static structure in the premixing chamber;

[0040] S4.2 Calculate the difference image: Perform a difference operation between the image containing fuel injection and the background image to obtain the difference image. Then, by subtracting the value of each pixel from the pixel value at the corresponding position in the background image, the resulting difference image contains only the changes caused by fuel injection.

[0041] S4.3 Binarization of Difference Results: The difference results are binarized by setting a threshold to convert the pixel values ​​in the image into black and white values, and to separate the fuel droplet positions in the image from the background area, thereby displaying the distribution of fuel droplets.

[0042] S4.4 Image calibration and quantization: Select a calibration image with a reference object of known size, establish a pixel scale based on the pixel length of the reference object in the image and the actual physical length, and calculate the ratio between the pixel and the actual physical length; based on the calibration ratio, convert the pixel information in the image into the actual physical size, perform quantization analysis, and obtain the actual physical values ​​of fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq.

[0043] S5. Assess the homogeneity of oil and gas mixing: Based on image processing results, quantitatively assess the homogeneity of oil and gas mixing, and analyze it by calculating evaluation parameters;

[0044] The evaluation parameters include the calculated fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq.

[0045] The calculated fuel penetration distance represents the geometric distance from the nozzle outlet to the farthest point of fuel injection;

[0046] The fuel coverage area refers to the projected area of ​​the fuel droplets in the premixing chamber after injection;

[0047] The fuel coverage area Raq per unit mass represents the area covered by a unit mass of injected fuel; the formula for the fuel coverage area Raq per unit mass is:

[0048]

[0049] Where FPA is the fuel coverage area, Q inj The mass of fuel injected in a single injection;

[0050] S6. Analyze oil-gas mixture data: Use evaluation parameters to analyze the changes in oil-gas mixture under different test conditions.

[0051] Furthermore, an evaluation method for an air-assisted injection premixing chamber oil-gas mixing uniformity test system is provided, wherein the oil-gas mixing uniformity test system is constructed as follows:

[0052] S1. Build the test system according to the air-assisted injection premixing chamber and complete the connection. Install the fuel nozzle on the top of the transparent premixing chamber model, connect the fuel supply system and the air supply system, adjust the imaging position of the high-speed camera and fix the camera and the light source.

[0053] S2. Before the test, set control parameters such as gas pressure, injection pressure and injection pulse width in the premix chamber;

[0054] S3. Under the set operating conditions, the injection control system controls the fuel injector to inject fuel, while a high-speed camera simultaneously captures images of the fuel-air mixing process inside the premixing chamber.

[0055] S4. After the experiment, the images obtained by high-speed photography are processed and analyzed to obtain evaluation parameters of the uniformity of oil-gas mixing in the premixing chamber.

[0056] Secondly, the air-assisted injection premixing chamber oil-gas mixing uniformity test system of the present invention includes a visualization premixing chamber model, an injection control system, a high-speed camera system, an air supply system, and an image processing system;

[0057] The visualized premixing chamber model is made of transparent material and has transparent walls, enabling real-time observation of the oil-gas mixing process.

[0058] The injection control system controls the opening and closing of the fuel injectors, precisely adjusts the fuel injection quantity and injection pulse width, and simultaneously starts a high-speed photography system to record the mixing process.

[0059] The high-speed camera system includes a high-speed camera and an LED light source, used to synchronously record the fuel-air mixture state during the fuel injection process;

[0060] The air supply system includes an air pump, a pressure gauge, valves and pipelines, which provide compressed air to the premixing chamber to form an oil-gas pressure differential condition and regulate the pressure of the gas in the premixing chamber.

[0061] The image processing system is used to analyze images acquired from the high-speed camera system, extract fuel penetration distance, fuel coverage area and fuel coverage area per unit mass Raq, and evaluate the uniformity of fuel-gas mixing.

[0062] The fuel supply system includes a fuel tank, a fuel pump, a fuel pressure gauge, and valves, which can provide a stable fuel supply and precisely adjust the injection pressure and injection quantity.

[0063] Furthermore, in an air-assisted injection premixing chamber oil-gas mixing uniformity test system, the injection control system includes an injector control unit and an injection pressure regulating unit; the injector control unit is used to precisely adjust the injection pulse width and injection quantity; the injection pressure regulating unit is used to control the injection pressure and affect the atomization effect of the injection.

[0064] Furthermore, in an air-assisted injection premixing chamber oil-gas mixing uniformity test system, the air supply system consists of an air pump, a pressure gauge, valves, and pipelines; the air pump is used to compress air and provide a stable air flow rate; the pressure gauge is used to monitor and display the gas pressure in the premixing chamber in real time; the valves are used to control the gas flow rate and adjust the amount of air output from the air pump to the premixing chamber; and the pipelines are a piping system that connects the air pump, pressure gauge, valves, and the premixing chamber.

[0065] Furthermore, in an air-assisted injection premixing chamber oil-gas mixing uniformity test system, the high-speed camera system includes components such as a high-speed camera, an LED light source, and a synchronous trigger; the high-speed camera has a high frame rate and high resolution, and can record the dynamic changes of the oil injection process; the LED light source provides supplementary light to the premixing chamber, ensuring that clear images can still be obtained in low-light environments; the synchronous trigger unit is used to start shooting by the camera through a trigger signal, while the injection control system precisely controls the opening and closing of the oil injector according to the set oil injection pulse width, thereby synchronously controlling the triggering of the oil injector and the high-speed camera.

[0066] Furthermore, in an air-assisted injection premixing chamber oil-gas mixing uniformity test system, the image processing system includes an image preprocessing module and an image analysis module; the image preprocessing module can perform differential and binarization processing on the captured image to extract key information of oil-gas mixing; the image analysis module can calculate the fuel penetration distance, fuel coverage area and fuel coverage area per unit mass Raq, and evaluate the oil-gas mixing uniformity.

[0067] (4) Inventive principle

[0068] This invention discloses an air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method. The main principle of this invention is based on the design of a visualized premixing chamber structure, combined with a high-speed photography system and image processing technology, to capture and quantify the oil-gas mixing process in real time and with high precision. This invention uses a premixing chamber model made of transparent material, allowing direct observation of the oil-gas mixing process inside the premixing chamber, overcoming the limitations of traditional methods that rely on indirect estimation of the mixing process.

[0069] Regarding the design of the visualized premixing chamber structure, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention uses a transparent material (such as transparent resin or other transparent synthetic materials) to fabricate the premixing chamber model, allowing experimenters to directly observe the flow and mixing of oil and gas within the premixing chamber under high pressure and high temperature conditions. The transparent structure design allows every detail of the oil-gas mixing process during injection to be captured through high-speed photography. The transparent structure ensures minimal impact of the premixing chamber inner wall on oil-gas flow and exhibits good stability and strength in practical applications. Visualized testing allows for direct observation of the oil-gas mixing process through real-time imaging, avoiding the problem of inaccurate control over internal distribution in traditional test methods.

[0070] In terms of high-speed photography systems and image processing technology, the combination of high-speed photography systems and image processing technology is a key technology in this invention. The high-speed photography system can capture the dynamic changes during fuel injection at a high frame rate, providing high-resolution image data that meticulously displays every moment of the fuel-air mixture. Firstly, high-speed photography can capture the flow state during fuel-air injection at a higher sampling frequency, ensuring that no critical details are missed even under high-pressure injection conditions. Secondly, image processing, through techniques such as image denoising, contrast enhancement, and edge extraction, transforms the captured images into quantifiable parameters; image processing technology accurately calculates key parameters such as fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass (Raq).

[0071] Furthermore, through image processing technology, several key parameters were extracted and used for the quantitative evaluation of fuel-air mixture uniformity. First, the fuel penetration distance, representing the geometric distance from the nozzle outlet to the furthest point of the injected fuel, reflects the extent of fuel-air mixture expansion, indicating the size of the contact area between fuel and air and the distribution of fuel within the premixing chamber. A longer penetration distance generally indicates better fuel diffusion in space, contributing to more uniform mixing. Second, the fuel coverage area, representing the distribution area of ​​fuel within the premixing chamber, indirectly reflects the range of fuel-air mixture; a larger coverage area indicates more uniform fuel distribution within the premixing chamber, thus promoting more thorough mixing of fuel and air; the fuel coverage area is directly related to the injection quantity and injection pressure. Third, the fuel coverage area per unit mass (Raq), which is the ratio of fuel coverage area to the injection mass; a larger Raq means that a unit mass of fuel can cover a larger area, indicating more thorough droplet breakage and better fuel-air mixture uniformity; the fuel coverage area per unit mass (Raq) is of great significance for evaluating the uniformity of fuel-air mixture under different injection conditions.

[0072]

[0073] Where FPA is the fuel coverage area, Q inj The fuel injection mass per injection and the fuel coverage area per unit mass Raq make the evaluation of the mixing effect under different injection quantities and operating conditions more comparable and scientific.

[0074] As can be seen, the principle of this invention, through visualization experiments and quantitative analysis methods, provides a basis for real-time and direct observation of the oil-gas mixing process using a transparent premixing chamber structure; the high-speed photography system and image processing technology ensure accurate capture of the dynamic changes during the oil-gas mixing process, providing quantifiable experimental data; by calculating the fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq, this invention can quantitatively evaluate the uniformity of the oil-gas mixture. This invention overcomes the difficulties of direct observation and accurate quantification in traditional oil-gas mixing tests, providing new ideas and data support for optimizing combustion system design and improving fuel utilization efficiency.

[0075] (5) Effects of the invention

[0076] This invention discloses a test system and evaluation method for the uniformity of fuel-air mixing in an air-assisted injection premixing chamber. By constructing a visualized premixing chamber test system and combining high-speed photography and image processing technology, it achieves direct observation and quantitative evaluation of the dynamic characteristics of fuel-air mixing during air-assisted injection. This more realistically reflects the fuel's breakup, impact with the walls, and mixing with air within the premixing chamber. Compared to traditional methods relying solely on numerical simulation or indirect measurement, this invention offers higher intuitiveness and data reliability, accurately acquiring key parameters such as fuel penetration distance, coverage area, and fuel coverage per unit mass, providing direct evidence for premixing chamber structure design and injection parameter optimization. This method not only improves the accuracy and comprehensiveness of fuel-air mixing uniformity evaluation but also provides important experimental support for engine combustion system performance improvement and emission control, demonstrating significant engineering application value and scientific significance.

[0077] Firstly, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention, by extracting the premixing chamber and its upper structure from the air-assisted nozzle and molding it with transparent resin three-dimensional printing, combined with the structural design of bottom extension and thickening with threaded sealing and thin wall of the observation area, realizes the visualization observation of the oil-gas mixing process inside the premixing chamber while basically keeping the geometric dimensions and flow boundary conditions of the premixing chamber unchanged, providing an experimental basis for the study of internal flow mechanism.

[0078] Specifically, the specific construction method of the transparent premixing chamber model of the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention can ensure flow similarity. That is, by accurately replicating the geometric dimensions of the original nozzle and the premixing chamber, it ensures that the flow characteristics of the airflow and fuel in the test are consistent with the original nozzle, thus ensuring that the experimental results are representative of engineering.

[0079] Specifically, the specific construction method of the transparent premixing cavity model of the air-assisted injection premixing cavity uniformity test system and evaluation method described in this invention can provide high-quality optical observation conditions. That is, the transparent resin material and thin-wall design enable the high-speed photography system to clearly capture the details of the oil-gas mixing process during the experiment. Especially under high pressure and high temperature environment, the experimenter can observe the distribution and flow of oil and gas in real time.

[0080] Specifically, the specific construction method of the transparent premixing chamber model in the air-assisted injection premixing chamber homogeneity test system and evaluation method described in this invention can resolve the contradiction between strength and light transmittance. That is, by designing the extension, thickening, and bolt sealing structure at the bottom of the transparent model, the problem of insufficient strength of transparent materials under high pressure is successfully solved. At the same time, the thin-walled design of the observation area provides sufficient light transmittance, ensuring high-quality imaging of the oil-gas mixing process.

[0081] Secondly, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention proposes an oil-gas mixing uniformity evaluation index system composed of fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq. The Raq index combines the fuel coverage area with the single injection mass, which can eliminate the influence of the difference in injection quantity under different operating conditions on the evaluation results, and quantitatively reflect the degree of oil-gas mixing in the premixing chamber from the perspective of the spatial coverage capability of fuel per unit mass.

[0082] Thirdly, the air-assisted injection premixing chamber fuel-air mixing uniformity test system and evaluation method described in this invention, by employing an image processing method combining background subtraction, binarization, and pixel calibration, enables stable and accurate extraction of the fuel jet contour information and projected area under conditions of transparent cavity reflection and uneven illumination, significantly improving the accuracy and repeatability of fuel penetration distance and fuel coverage area measurements. Firstly, regarding improved contour extraction accuracy, background subtraction removes irrelevant background information, and binarization effectively and clearly segments the fuel and non-fuel regions, making fuel contour extraction more accurate. Secondly, regarding reduced false signals, since background effects such as reflected light and stray light have been removed, the possibility of misidentifying reflected light as fuel is reduced, significantly decreasing the generation of false signals. Thirdly, regarding improved consistency of repeated measurements, the image processing method combining background subtraction, binarization, and pixel calibration effectively reduces errors caused by background interference and uneven illumination, resulting in a 50% reduction in the standard deviation of multiple repeated measurements compared to traditional methods, ensuring the consistency and reliability of experimental results.

[0083] Fourth, the air-assisted injection premixing chamber fuel-air mixing uniformity test system and evaluation method described in this invention improves the observation capability of the fuel-air mixing process. It can realistically reflect the fuel's breakage, impact with the walls, and mixing with air within the premixing chamber during air-assisted injection, providing direct and reliable experimental basis for premixing chamber structure design and injection parameter optimization. This helps improve the combustion efficiency of the engine combustion system and reduce emissions. By designing a visualized premixing chamber structure and combining it with high-speed photography and image processing technology, the fuel-air mixing process can be directly and in real-time observed inside the premixing chamber, solving the problem of traditional research relying solely on numerical simulation or indirect measurement methods.

[0084] Fifth, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention can ensure the engineering representativeness and reliability of the test. This invention, through precise design of the premixing chamber structure, ensures that it maintains flow similarity to an actual nozzle premixing chamber while withstanding experimental pressure. By using 3D-printed transparent resin and other materials, the details of oil-gas mixing during the experiment can be clearly presented, and effective visual evaluation can be performed under different experimental conditions.

[0085] Sixth, the air-fuel mixture homogeneity test system and evaluation method in the air-assisted injection premixing chamber described in this invention can provide a basis for engine performance optimization. By analyzing the homogeneity of air-fuel mixture under different operating conditions, the method described in this invention not only provides a scientific basis for premixing chamber structure design and injection parameter optimization, but also provides important experimental support for combustion system performance improvement and emission control, possessing broad engineering application value and scientific significance. Attached Figure Description

[0086] Figure 1 This is a schematic diagram of the process of the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention;

[0087] Figure 2 This is a visualized diagram of the premixing chamber structure in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention.

[0088] Figure 3 This is a schematic diagram of the fuel penetration distance extraction process during image processing in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention.

[0089] Figure 4 This refers to the oil-gas mixing state within the premixing chamber in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention.

[0090] Figure 5 This is a schematic diagram of the fuel penetration distance in the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention;

[0091] Figure 6 This is a schematic diagram of the fuel injection area under different fuel-gas pressure drops in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention.

[0092] Figure 7 This is a graph showing the Raq values ​​at the end of injection under different fuel injection widths in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention.

[0093] Figure 8 This is a schematic diagram of the internal structure of the air-assisted injection premixing chamber in the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention.

[0094] Figure 9 This is a three-dimensional view of the external structure of the air-assisted injection premixing chamber in the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention.

[0095] 1. Fuel injector; 2. Electronic control connector; 3. Fuel injector support; 4. Annular sealing assembly; 5. Intake passage; 6. Fuel supply passage;

[0096] 7. Injection port; 8. Test chamber (premixing chamber); 9. Injection pump; 10. Regulating valve. Detailed Implementation

[0097] Figure 1This is a flowchart illustrating the test system and evaluation method for the uniformity of oil-gas mixing in the premixing chamber of air-assisted injection as described in this invention. It shows the overall process of the test and evaluation method for the uniformity of oil-gas mixing in the premixing chamber of air-assisted injection as described in this invention, including multiple steps such as experimental system construction, parameter setting, experimental execution, data acquisition and processing, and result evaluation. The purpose is to evaluate the uniformity of oil-gas mixing in the premixing chamber through quantitative indicators, thereby providing a basis for the optimization of the injection system.

[0098] like Figure 1 As shown in the flowchart, the entire method is encapsulated with a dashed border. Figure 1 The outermost layer is a gray dashed rectangular border, indicating... Figure 1 The document covers the complete methodology, divided into two parts on the left using vertical text. The upper part outlines the experimental methods, from "Start Experiment" to "Step S3," detailing the experimental setup, parameter settings, execution, and data collection. The lower part outlines the evaluation methods, including "Steps Four and Five, and the Satisfaction Criterion," covering data processing, indicator extraction, and comprehensive evaluation. A horizontal dashed line separates the steps after S3 and before S4, visually indicating the boundary between experimental execution and evaluation analysis. The overall workflow unfolds from top to bottom, culminating in a "Satisfaction Criterion" checkpoint at the end to determine whether to terminate the experiment or return to parameter tuning for repetition.

[0099] The experimental methods section in the upper part begins with a rounded rectangle at the top labeled "Start Experiment," indicating the start of the process. This section covers setting up a visual experimental system, configuring model and experimental parameters, and executing the experiment and collecting data.

[0100] Step S1: Build a visual experimental system

[0101] In step S1, a visualized premixing chamber experimental system is first constructed, including: a visualized premixing chamber structure, a fuel supply system, a gas supply system, a high-speed photography system and camera bracket for image acquisition, and a fuel injection control system. The settings of the fuel supply system, gas supply system, and injection control system allow for adjustment of fuel injection parameters and gas pressure within the premixing chamber during the experiment.

[0102] Step S2: Set model parameters and experimental parameters

[0103] In step S2, several experimental parameters are set and adjusted, including control parameters such as gas pressure in the premixing chamber, injection pressure, and injection pulse width. By adjusting these parameters, the uniformity of fuel-air mixture under different conditions can be simulated. The selection and adjustment of specific parameters directly affect the fuel distribution and mixing effect during the injection process.

[0104] Step S3: Perform the experiment and collect data

[0105] In step S3, the control system injects fuel through the nozzle according to the predetermined injection pressure and injection pulse width, while simultaneously recording the fuel-air mixture during the fuel injection process in real time using a high-speed photography system. The control system triggers fuel injection, and the high-speed photography system simultaneously acquires image data of the injection and mixing process; the data acquisition mainly focuses on visual images of the fuel-air mixing process, providing a foundation for subsequent data processing and analysis.

[0106] The evaluation method section in the second half, starting with "Step 4: Data Processing and Quantitative Analysis," involves processing high-speed photographic images to obtain evaluation parameters. Below "Step S4," the process is divided into three parallel branches, corresponding to the extraction and calculation of three quantitative indicators: Quantitative indicator 1 is the extraction of fuel penetration distance, which represents the distance (penetration distance) from the fuel nozzle outlet to the farthest point of injection obtained through image processing; Quantitative indicator 2 is the extraction of fuel coverage area, which represents the projected coverage area of ​​fuel in the premixing chamber obtained through binarization, pixel statistics, etc.; Quantitative indicator 3 is the calculation of unit fuel coverage area Raq, which represents the calculation of unit mass fuel coverage area Raq based on the coverage area and the single injection quantity (or injection mass), used to characterize the breakup and mixing effect. A larger Raq indicates a more complete coverage and a more uniform mixing trend. These three branches ultimately converge in the next step, indicating that the three indicators together serve as inputs for comprehensive evaluation.

[0107] Step S4: Data Processing and Quantitative Analysis

[0108] In step S4, the images acquired by high-speed photography are processed and quantitatively analyzed to extract and analyze the uniformity index of oil-gas mixing in the premixing chamber. Through image binarization, fuel injection images are obtained, and key parameters are extracted: fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq. The fuel penetration distance refers to the geometric distance from the nozzle outlet to the furthest point of fuel injection, while the fuel coverage area is measured by statistically analyzing the area of ​​black pixels in the image. The fuel coverage area per unit mass Raq is calculated using formula (1):

[0109]

[0110] Where FPA is the fuel coverage area, Q inj This represents the amount of fuel injected in a single injection. The larger the Raq value calculated by this formula, the better the fuel agglomeration effect and the better the uniformity of the fuel-air mixture.

[0111] Step S5: Comprehensive evaluation of oil-gas mixing homogeneity

[0112] The comprehensive evaluation of oil-gas mixing homogeneity involves a combined analysis of penetration distance, coverage area, and Raq (which can be used to compare mixing states under different parameter combinations) to form a judgment result on "mixing homogeneity." After data processing and quantitative analysis, the experimental results enter the comprehensive evaluation stage. In step S5, the homogeneity of the oil-gas mixture is evaluated through a comprehensive analysis of fuel penetration distance, fuel coverage area, and Raq value. If the experimental results meet the predetermined requirements, the experiment ends; if the requirements are not met, the process returns to step S2, the experimental parameters are adjusted, and the experiment is repeated to form a closed-loop optimization.

[0113] Figure 2 This is a visualized premixing chamber structure diagram in the air-assisted injection premixing chamber homogeneity test system and evaluation method described in this invention, illustrating the design and fabrication process of the transparent premixing chamber model used in the experiment. The transparent premixing chamber model was created using 3D printing technology to overcome the opacity problem of the AAFI premixing chamber, allowing for clear observation of the oil-gas mixing process within the chamber.

[0114] like Figure 2 As shown, Figure 2 (a) This illustrates the process of extracting the premixing chamber. The extracted portion is located in the highlighted area within the black rectangle in the figure, which is part of the premixing chamber. The premixing chamber includes an upper structure connected to the fuel injector. The extracted premixing chamber is separated from the original premixing chamber, 3D printed using transparent resin material, and replicated into a transparent model, allowing for direct observation of the mixing of fuel and gas during the experiment. Figure 2 (b) is a transparent premixing chamber model, showing a transparent premixing chamber model made by 3D printing technology. The upper section has an inner diameter (d) of 10 mm and a height (h) of 10 mm, and the lower section has an inner diameter of 2.5 mm and a length of 33 mm. The distance from the nozzle outlet to the bottom of the premixing chamber is 43 mm. Figure 2 The transparent structure within has a 1 mm wall thickness to ensure optical clarity for observation.

[0115] In addition, to ensure the chamber is airtight during the experiment, Figure 2 The transparent model has been appropriately thickened at the connection between the gas inlet and the fuel nozzle, as well as the sealing section at the bottom of the chamber. The thickened sealing section is not directly used for observation, so it can be thickened to maintain the integrity of the structure. Figure 2In this model, the bottom of the transparent premixing chamber is extended and enlarged via a pipe with internal threads. During the experiment, a reliable bottom seal is achieved using mounting bolts to ensure successful execution. This design allows for real-time observation of the oil-gas mixing state within the premixing chamber, unaffected by the chamber's opacity. This visualization model provides crucial experimental evidence for the subsequent quantitative evaluation of oil-gas mixing uniformity.

[0116] Figure 3 This is a schematic diagram illustrating the fuel penetration distance extraction process during image processing in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention. It demonstrates how image processing technology can be used to extract this key parameter. Firstly, Figure 3 (a) is a background image captured by a high-speed camera without fuel injection. Figure 3 (a) represents the original state without oil spraying in the experimental environment, used for comparison in subsequent image processing. Figure 3 (a) It can help remove interference from other factors on experimental data, such as environmental noise or the structure of the equipment itself. Secondly, Figure 3 (b) is an injection image acquisition diagram, which shows the actual injection process captured during fuel injection. The injection image acquisition diagram illustrates the dynamics of the fuel spray during the injection process. At this time, fuel is injected from the nozzle and mixes with the gas. Figure 3 (b) shows the morphology, spray range, and penetration capability of the oil mist. Thirdly, Figure 3 (c) is a schematic diagram of image subtraction and binarization. Image subtraction and the conversion of the background image ( Figure 3 (a) From the jet image ( Figure 3 (b) Subtraction removes environmental interference, retaining only the fuel injection portion. Image subtraction significantly improves image clarity, making the fuel injection process more prominent. The image after background subtraction is then binarized. Binarization divides the pixel values ​​in the image into two classes: one representing the fuel portion (usually a black area), and the other representing the non-fuel portion (usually a white area). Binarization clearly presents the injected fuel portion as a black area, facilitating subsequent analysis.

[0117] In addition, Figure 3(c) shows the fuel penetration distance. This distance is the geometric distance from the nozzle outlet (i.e., the injection point) to the farthest point of the injected fuel droplet—that is, the tip of the main spray body. The steps for extracting the fuel penetration distance are as follows: In the binarized image, calculate the boundary of the farthest part of the fuel injection body (the black area); by calibrating the distance (pixel value) in the image and combining it with the actual physical scale conversion coefficient (0.051 mm / pixel), convert the pixel value to physical units to obtain the actual fuel penetration distance. Through the extraction process of fuel penetration distance, the penetration ability during fuel injection can be accurately measured, that is, the propagation range of fuel mist in the premixing chamber; this parameter is of great significance for evaluating the uniformity of fuel-air mixing, because a longer penetration distance indicates more complete fuel atomization and better mixing effect.

[0118] like Figure 3 As shown, since image data is measured in pixels, physical scale calibration is required. Calibration yields a conversion coefficient of 0.051 mm / pixel, which converts the pixel values ​​in the image (including fuel penetration distance and projected area) into actual physical dimensions. Extracting the fuel penetration distance is not only a quantitative process but also provides quantitative experimental evidence for subsequent evaluation of fuel-air mixture uniformity. Combined with other parameters such as fuel coverage area and Raq per unit fuel coverage area, the quality of the fuel-air mixture can be comprehensively evaluated, providing crucial data support for injection system optimization.

[0119] Figure 4 This invention relates to an air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method, which demonstrates the oil-gas mixing state within the premixing chamber. The system shows that the distribution of fuel and gas during the injection process reflects the two-phase flow behavior of the injection and the dynamic changes in mixing uniformity.

[0120] like Figure 4 As shown, the oil-gas mixture is divided into two independent regions: the free injection region and the confined injection region. The free injection region is located in the initial stage of injection, where fuel develops freely in the upper part of the premixing chamber after injection; at this time, the injected fuel and gas are relatively dispersed and do not significantly collide with the pipe wall. The confined injection region is where the injected fuel begins to collide with the pipe wall after entering the pipe; the fuel flow is restricted by the pipe wall and exhibits different flow characteristics, especially the change in fuel velocity after impact.

[0121] Firstly, regarding changes in fuel and gas distribution, the fuel distribution during injection will change significantly due to the influence of gas pressure drop. A higher gas pressure drop will lead to more unstable fuel flow during injection, and the fuel jet will experience more severe wall impact after entering the pipeline. This will accelerate the flow velocity and affect the mixing effect during injection.

[0122] Secondly, regarding optical limitations and discontinuities, Figure 4 The dashed lines in the diagram show the optical limitations caused by the thickness of the transparent model, which manifests as obvious discontinuities. These discontinuities are due to the influence of the physical structure of the experimental equipment on the transmittance of light, resulting in incomplete or discontinuous images in certain areas, thus affecting the visualization of fuel and gas.

[0123] Thirdly, regarding fuel behavior during the injection process, from Figure 4 As can be seen, the fuel behavior in the pipeline exhibits a clear directionality as injection progresses. Initially, the fuel flows freely, but as time progresses, the flow is gradually affected by wall resistance, resulting in increased velocity and strong impact. The red dashed line marks the leading edge of the main fuel, the furthest point during fuel injection. This change in the leading edge directly reflects the fuel-air mixing state during injection.

[0124] Figure 5 This diagram illustrates the fuel penetration distance in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention. It shows the variation law of injection penetration distance under different gas pressure drop conditions, illustrates the flow characteristics of fuel during the injection process, and reflects the uniformity of fuel-gas mixing by measuring the fuel penetration distance. Figure 5 The purpose is to illustrate the definition of fuel penetration distance and its application in fuel-air mixing experiments using a schematic diagram. According to the experiment, after fuel is injected from the nozzle, it flows downwards along the premixing chamber and eventually impacts the pipe wall.

[0125] like Figure 5 As shown, the specific steps for determining the fuel penetration distance are as follows:

[0126] The fuel injection initiation point is Figure 5 The label indicates the outlet position of the fuel injector, which is where fuel injection begins. From the point where fuel injection begins, the fuel flows along the premixing chamber and is affected by the gas flow.

[0127] Fuel penetration distance is Figure 5In the diagram, the fuel penetration distance is clearly marked as the furthest point from the injector outlet to the fuel injection point, i.e., the tip of the main spray. This red dashed line represents the furthest boundary of the fuel injection process, defining the penetration range of the injection. The measurement of the fuel penetration distance reflects the propagation distance of the fuel in the premixing chamber, i.e., the propagation depth during the fuel injection process. This distance directly affects the effect of fuel-air mixing, because the mixture of injected fuel and gas requires a certain amount of time and space. The longer the penetration distance, the wider the distribution of fuel in the chamber, and the more uniform the mixing effect. The fuel flow process is as follows: after the fuel is injected from the nozzle, it initially flows relatively freely in the free injection area, and at this time the fuel and gas are relatively dispersed, which is the free injection stage. As the flow enters the pipe, the fuel spray is gradually affected by the pipe wall, and wall impact and adhesion begin to occur. After entering the pipe, the flow of fuel becomes more restricted, forming a restricted injection zone. At this point, the fuel changes its flow direction and speed due to the impact with the wall; the fuel gradually loses its free flow capability during this process and exhibits different flow patterns. In particular, under the influence of gas pressure and injection parameters, the mixing process of fuel and gas becomes more complex, which is the restricted injection stage.

[0128] Regarding the interaction between fuel and gas, Figure 5 In the injection process, fuel gradually expands downwards within the free injection zone and eventually enters the pipe, forming the injected flow. The mixing effect between fuel and gas during injection is observed through changes in the penetration distance. A greater fuel penetration distance indicates a better mixing effect between fuel and gas. Regarding the influence of penetration distance... Figure 5 The diagram clearly illustrates the change in fuel penetration distance. As injection time increases, fuel gradually enters the pipe and begins to collide with the pipe walls, making fuel flow increasingly complex and ultimately affecting the uniformity of the fuel-air mixture. From an optical perspective, in... Figure 5 In this process, the furthest point of fuel injection (i.e., the penetration distance) is affected by optical limitations, making some areas of injection invisible; due to the model thickness of the premixing chamber, some areas of fuel injection exhibit discontinuities, thus these parts of the fuel injection cannot be visualized through images. By measuring the fuel penetration distance, Figure 5 This provides key data for subsequent evaluation of fuel-gas mixture uniformity, and helps to analyze the fuel distribution characteristics during the injection process under different parameters such as gas pressure drop, injection pressure and injection pulse width, thereby optimizing injection parameters to improve fuel-gas mixture uniformity.

[0129] Figure 6This diagram illustrates the fuel injection area under different fuel-gas pressure drops in the air-assisted injection premixing chamber uniformity test system and evaluation method described in this invention. It shows the trend of fuel projection area changing with time during the injection process under different fuel-gas pressure drop conditions, and analyzes the changes in fuel distribution before and after injection termination. Figure 6 This study demonstrates the temporal evolution of fuel injection area under different fuel-gas pressure drop conditions and its impact on fuel-gas mixing uniformity. In other words, by analyzing the changes in injection area, we can better understand the flow characteristics during fuel injection, thereby providing a basis for optimizing the injection system and improving fuel-gas mixing uniformity.

[0130] Regarding the change in the projected area of ​​fuel during the injection process, such as Figure 6 As shown, curves of different colors (corresponding to different fuel-gas pressure differences) illustrate the change of fuel injection area over time. In the initial stage of the injection process, the injection area gradually increases with time under different pressure drop conditions. As the injection time increases, the expansion of the injection stream becomes more pronounced, especially under higher gas pressure drop conditions (e.g., 2.5 bar), where the injection area expansion is more significant. After injection, the fuel projected area exhibits significant differences. Under low pressure drop conditions (1 bar and 1.5 bar), the fuel injection area continues to increase; this is because the injection stream velocity is low, allowing the fuel to continue expanding downwards after injection. Under high pressure drop conditions (2 bar and 2.5 bar), the fuel injection area begins to decrease, especially within the first 5 milliseconds after injection; the high pressure drop causes fuel to accumulate at the bottom of the premixing chamber, and this accumulation becomes more pronounced with increasing pressure drop.

[0131] Regarding the factors influencing the change in spray area, Figure 6 This indicates that the gas pressure drop has a crucial impact on the fuel injection area. Under high pressure differential conditions, the expansion of the injection area is more restricted, and fuel impacts and accumulates within the pipeline, leading to a stabilization of the injection area. However, under lower pressure drop conditions, the fuel injection rate is slower, allowing the fuel to continue expanding to the bottom of the premixing chamber after injection, further increasing the injection area.

[0132] Regarding the relationship between injection area and mixing uniformity, the injection area is closely related to the uniformity of the fuel-air mixture. An increased injection area generally means a wider distribution of fuel, which helps improve the uniformity of the fuel-air mixture; while a decreased injection area leads to fuel accumulation, thus affecting the uniformity of the mixture. Figure 6 The data shows that the trend of the injection area can provide an intuitive basis for evaluating the mixing effect of fuel and gas in the premixing chamber, especially the impact on the injection behavior under different gas pressure drops.

[0133] Figure 6 Furthermore, the area-to-mass ratio (Raq) is proposed as an important parameter for measuring mixing uniformity, and is defined as follows:

[0134]

[0135] Where FPA represents the projected area of ​​fuel injection, Q inj This indicates the mass of fuel injected in a single injection; increasing this parameter indicates a larger fuel coverage area, which helps improve mixing uniformity.

[0136] Figure 7 The image shows the Raq values ​​at the end of injection under different fuel injection widths in the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention. It illustrates the influence of injection width on the Raq value at the end of injection and explains how injection width affects the oil-gas mixing uniformity. Figure 7 This is used to analyze the uniformity of oil-gas mixing at the end of injection under different injection width conditions, specifically through R... aq The area-to-mass ratio is used to characterize the mixture; this quantitative analysis can further optimize the injection system design and ensure the best oil-gas mixing effect at the end of the injection.

[0137] Figure 7 The changes in Raq values ​​at the end of injection, under different fuel injection widths (in milliseconds), are shown. The Raq value, calculated using formula (1), represents the area covered by each unit mass of fuel and is used to measure the uniformity of the fuel-air mixture.

[0138]

[0139] Where FPA represents the fuel projected area, Q inj It refers to the mass of fuel injected in a single injection.

[0140] Regarding the impact of fuel injection width, Figure 7 The effects of different injection widths on the Raq value were compared. The Raq value represents the ratio between the fuel coverage area and the fuel mass, and is an important indicator for evaluating the homogeneity of oil-gas mixing.

[0141] As the injection width increases, the Raq value changes, reflecting the air-fuel mixture state during the injection process. When the injection width is small (short-duration injection), the injection stream fails to expand sufficiently, resulting in a more limited fuel distribution and affecting the uniformity of the mixture. In other words, a short injection time cannot adequately mix the fuel and gas, limiting the fuel's spread and thus affecting the mixing effect. When the injection width is large (longer-duration injection), the fuel can mix fully with the gas over a longer period, increasing the fuel distribution area and improving the mixing uniformity, thereby increasing the Raq value. This means that a longer injection time helps increase the fuel distribution area, thus improving the uniformity of the air-fuel mixture. Therefore, the relationship between the Raq value at the end of the injection and the mixing uniformity is that a larger Raq value at the end of the injection indicates a wider fuel distribution within the premixing chamber and a better air-fuel mixture effect; while a smaller Raq value indicates a more limited fuel distribution and a poorer mixing effect.

[0142] Regarding the temporal changes of Raq values Figure 7 The curves in the figure show the trend of Raq value at the end of the injection under different injection widths. That is, by comparing the Raq values ​​under different conditions, we can find out the influence of different injection widths on the uniformity of oil-gas mixing.

[0143] Regarding the completion of injection and the uniformity of mixing, the Raq value at the end of injection is a key parameter because it directly reflects the effectiveness of fuel-air mixing at the end of the injection process. A larger Raq value indicates a more uniform distribution of fuel in the premixing chamber and a better fuel-air mixing effect, while a smaller Raq value indicates uneven mixing. Therefore, in practical applications, the fuel-air mixing process can be optimized by adjusting the injection width to ensure the best mixing effect between fuel and gas.

[0144] Figure 8 This is a schematic diagram of the internal structure of the air-assisted injection premixing chamber in the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention. It shows that the premixing chamber model structure includes several important components such as the fuel injector 1, the fuel injector support part 3, the fuel and gas supply system, the electronic control connector, the injection hole, and the sealing assembly. These components work together to ensure the effective injection, atomization, and mixing of fuel and gas, providing important data support for subsequent oil-gas mixing uniformity analysis.

[0145] The fuel injector 1 is located at the bottom of the premixing chamber 8 and is directly aimed at the internal area of ​​the premixing chamber 8 for injecting fuel. The structure of the fuel injector 1 includes an injection hole, which is responsible for atomizing the fuel and injecting it into the premixing chamber. The atomization process helps to disperse the fuel and mix it with the air, thereby increasing the contact area between the fuel and the air.

[0146] The electronic control connector 2 is located above the fuel injector 1 and is connected to the control circuit of the fuel injection system. The electronic control connector 2 receives electrical signals from the control system to control the opening and closing of the fuel injector 1 and to adjust the fuel injection pulse width.

[0147] The injector support portion 3 can fix the injector 1 in the premixing chamber 8; the injector support portion 3 provides structural stability to ensure that the injector 1 does not change position due to vibration or operational errors during the test.

[0148] The annular sealing assembly 4 is located in the external connection area of ​​the fuel injector 1, at the interface between the fuel injector 1 and the premixing chamber 8. The annular sealing assembly 4 can ensure that the flow of fuel and air does not leak, prevent fuel leakage or air contamination of the mixed gas, and ensure the accuracy of experimental data.

[0149] The air intake channel 5 is located next to the fuel injector 1. The air supply system introduces compressed air into the premixing chamber 8 through this channel. The air intake channel 5 provides compressed air through an air pump and monitors and adjusts the gas pressure through a pressure gauge.

[0150] The fuel supply channel 6 can be connected to the fuel injector 1 and to the fuel pump and fuel pressure gauge system; the fuel supply channel 6 can deliver fuel through the fuel pump and use the fuel pressure gauge to control and monitor the injection pressure.

[0151] The fuel injection hole 7 is located at the bottom of the fuel injector 1 and is where fuel is injected. The fuel injection hole 7 can disperse the fuel into small droplets, form an atomized spray, and enter the premixing chamber 8 for further fuel-air mixing.

[0152] The test chamber (premixing chamber) 8 is the core area of ​​the entire system, where fuel and air are mixed. The design of the premixing chamber 8 takes into account the full mixing of fuel and air and the dynamic behavior of the sprayed droplets, ensuring the uniform distribution of fuel in the air.

[0153] Figure 9 This is a three-dimensional view of the external structure of the air-assisted injection premixing chamber in the air-assisted injection premixing chamber fuel-air mixing uniformity test system and evaluation method described in this invention. It shows important components such as the fuel injector 1, electronic control connector 2, fuel supply channel 6, annular sealing assembly 4, and fuel injector support part 3. These components work together to ensure effective mixing of fuel and air, and provide basic data support for subsequent fuel-air mixing uniformity experiments.

[0154] The fuel injector 1 is located at the top of the air-assisted injection premixing chamber model and is used for fuel injection. The top of the fuel injector 1 is connected to an electronic control connector 2 for receiving electronic control signals to adjust the fuel injection quantity. The lower part of the fuel injector has injection holes 7, through which fuel is injected into the premixing chamber 8.

[0155] The electronic control connector 2 is located on top of the fuel injector 1; the electronic control connector 2 is used to exchange electrical signals with an external control system to control the opening and closing of the fuel injector 1 and the fuel injection pulse width; the electronic control connector 2 is connected to the fuel injector 1 to precisely adjust the fuel injection parameters.

[0156] The injection hole 7 is located at the bottom of the injector 1 and points directly into the premixing chamber 8. The injector atomizes the fuel and injects it into the premixing chamber through the injection port. These injection holes are key areas for fuel atomization and determine the uniformity of fuel injection.

[0157] The fuel supply channel 6 is located on the side of the injector 1 and is connected to the fuel supply system. The fuel supply channel 6 delivers fuel to the injector 1 through a pipe to ensure a continuous fuel supply and to ensure that the amount of fuel injected each time matches the predetermined parameters.

[0158] The annular sealing assembly 4 is located at the interface where the fuel injector 1 connects with other components; the annular sealing assembly 4 ensures that there is no leakage at the connection between the fuel injector 1 and the premixing chamber 8 or other components; the annular sealing assembly 4 maintains the airtightness of the oil and gas system to prevent outside air from entering or fuel from leaking.

[0159] The air intake channel 5 is located on the side of the fuel injector 1, and the gas is connected to the air intake channel 5. The air intake channel 5 provides compressed air or other gases to the premixing chamber 8 to promote the mixing of fuel and air, form a fuel-air pressure difference condition, and ensure the maximization of the fuel injection effect.

[0160] The nozzle support part 3 is located at the bottom 1 of the nozzle and other connecting parts; the nozzle support part 3 can fix the nozzle 1 in the correct position in the premixing chamber 8, ensuring the stability of the equipment and the accurate injection process.

[0161] The fuel injection pump 9 is located externally and connected to the fuel injector 1; the fuel injection pump 9 is responsible for providing fuel to the fuel injection system, and the regulating valve 10 is used to regulate the fuel pressure to ensure a stable fuel supply for each injection.

[0162] Example 1: A test system and evaluation method for the uniformity of oil-gas mixing in an air-assisted injection premixing chamber according to the present invention.

[0163] The present invention discloses an air-assisted injection premixing chamber fuel-air mixing uniformity test system and evaluation method. It uses a visualized premixing chamber as the test piece, and its geometry is consistent with the original nozzle structure. The fuel penetration distance, fuel coverage area, and unit fuel coverage area Raq are used to quantitatively evaluate the fuel-air mixing uniformity in the premixing chamber, which can truly reflect the fuel-air mixing process and mixing uniformity in the premixing chamber during fuel injection.

[0164] Furthermore, the specific implementation of the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention is divided into three parts: system construction, test process, and image processing and evaluation indicators.

[0165] Part 1: System Setup

[0166] Unit 1: Visualized Premixing Chamber Model

[0167] The creation of a visual premixing cavity model includes the following operations:

[0168] S1. Maintain consistent geometric dimensions: Extract the premixing chamber and its upper structure connected to the nozzle from the original air-assisted nozzle, ensuring that the geometric dimensions are consistent with the original nozzle, that is, the upper section d and h are both 10mm, the lower section inner diameter is 2.5mm and the length is 33mm, and the distance from the nozzle outlet to the bottom of the premixing chamber is 43mm.

[0169] S2. Separate the fuel nozzle and air nozzle: Separate the fuel nozzle and air nozzle from the original nozzle, retaining only the fuel nozzle, premixing chamber and its air supply channel, to ensure that the mixing of gas and fuel is accurately observed during the test;

[0170] S3. Using transparent resin 3D printing: Using transparent resin 3D printing to create a premixed cavity model to make the interior visible, which can ensure that the internal mixing process can be clearly observed through the transparent walls during the experiment;

[0171] S4. Seal the connection channel: Seal the original connection channel between the premix chamber and the nozzle with screws to avoid unnecessary leakage or affect the mixing effect; the bottom of the premix chamber is extended and thickened and internally threaded, and the bottom is sealed with bolts to achieve bolt sealing, ensuring the sealing performance and flow equivalence of the premix chamber under high pressure conditions;

[0172] S5. Wall thickness design: The wall thickness of the observation area is set to 1mm to improve light transmittance, ensure sufficient light to enter and allow clear observation of the fuel and gas mixing inside the premixing chamber; the non-observation area is appropriately thickened to ensure structural strength and pressure resistance.

[0173] Unit 2: Experimental Procedure

[0174] The test process involves several core components, including the fuel supply system, fuel type, and the adjustment functions of the fuel pump and valves;

[0175] The fuel supply system consists of fuel, fuel tank, fuel pump, fuel pressure gauge, valves and pipelines; these components work together to ensure a stable fuel supply and to precisely regulate the injection pressure and injection quantity.

[0176] Different types of liquid fuels, such as gasoline, diesel, or aviation kerosene, can be selected according to actual needs.

[0177] In Example 1, the fuel used was #0 diesel; #0 diesel fuel has certain volatility and suitable atomization characteristics, making it suitable for evaluating the fuel-air mixing effect under air-assisted injection technology.

[0178] The regulating functions of the oil pump and valves: The oil pump is responsible for providing the required oil flow, while the valves are used to regulate the working state of the oil pump. By adjusting the pressure of the oil pump, the predetermined injection pressure and injection volume can be achieved.

[0179] The specific parameter settings for regulating the oil pump and valves include injection pressure and injection quantity;

[0180] The injection pressure, when adjusted, controls the intensity of fuel injection, thus affecting the atomization effect.

[0181] The injection quantity, when adjusted, determines the quality of each fuel injection, affecting the degree and uniformity of fuel-air mixing.

[0182] In Example 1, the specific experimental procedure includes the following steps:

[0183] S1. Connect the fuel tank to the fuel pump to ensure diesel fuel flows into the fuel pump system; monitor the fuel pressure output by the fuel pump in real time using a fuel pressure gauge;

[0184] S2. A valve regulating system is used to control the working state of the oil pump and precisely adjust the injection pressure. Different injection pressures (e.g., 7.5 bar, 6.5 bar) can simulate different working conditions, ensuring that the test is highly representative.

[0185] S3. By adjusting the fuel injection quantity and injection pulse width of the fuel pump, ensure that the amount of fuel injected each time is consistent, thereby ensuring the repeatability of the test and the consistency of the data;

[0186] S4. After being regulated by the valve, the fuel flows into the injector and is sprayed into the premixing chamber through the nozzle. The air supply system provides air, and the two mix to form a spray that enters the field of view of the high-speed photography system, recording every moment of the mixing process.

[0187] The experimental procedure achieved the following results: by precisely controlling the oil pump and valves, different working conditions could be simulated under different injection pressures and injection volumes to evaluate the uniformity of oil-gas mixing; the reliability and repeatability of the experiment were ensured, and a stable data source was provided for subsequent image analysis.

[0188] Unit 3: Gas Supply System

[0189] The air supply system consists of an air pump, a pressure gauge, valves, and pipelines; it is used to supply compressed air to the premixing chamber to form a set gas pressure in the premixing chamber, thereby creating an oil-gas pressure differential working condition.

[0190] The gas supply system consists of several key components: an air pump, a pressure gauge, valves, and pipelines. The air pump compresses air and provides a stable flow rate; its power and output flow rate determine the pressure level of the gas in the premixing chamber. The pressure gauge monitors and displays the gas pressure in the premixing chamber in real time, helping the control system to precisely adjust and maintain the gas pressure within the set range, ensuring the accuracy and stability of the test data. The valves control the gas flow rate, regulating the amount of air output from the air pump to the premixing chamber. The valve's on / off state and flow rate adjustment directly affect the gas pressure in the premixing chamber, thus affecting the oil-gas mixing effect. The pipelines connect the air pump, pressure gauge, valves, and the premixing chamber; the pipeline design must ensure smooth airflow, no leaks, and sufficient pressure-bearing capacity.

[0191] Furthermore, the specific working process of the gas supply system is as follows:

[0192] S1. The air pump starts, drawing in and pressurizing outside air; different gas flow rates and pressures can be set by adjusting the air pump output; the air output by the air pump is sent into the premixing chamber through the pipeline;

[0193] S2. Gas enters the premixing chamber through a valve. The valve can regulate the gas flow rate and further control the gas pressure. By adjusting the valve opening, the control system can accurately set the gas pressure in the premixing chamber.

[0194] S3. The pressure gauge monitors the gas pressure in the premixing chamber in real time and feeds it back to the control system to ensure that the gas pressure is maintained at the set value. Based on the gas pressure in the premixing chamber, different oil-gas pressure difference conditions are formed to simulate different states of oil-gas mixing in actual applications.

[0195] S4. Compressed air and fuel form an air-fuel mixture in the premixing chamber and are sprayed out through the nozzle; the combination of gas pressure and fuel injection pressure determines the uniformity of the air-fuel mixture and the spray effect.

[0196] Furthermore, the role of the gas supply system in the experiment is to establish the oil-gas pressure differential condition and the influence of gas pressure on the mixing uniformity. Firstly, regarding the establishment of the oil-gas pressure differential condition, the main function of the gas supply system is to regulate the gas pressure within the premixing chamber, thereby creating the oil-gas pressure differential condition. This condition is crucial for studying the uniformity of oil-gas mixing because the oil-gas pressure differential directly affects the fuel atomization effect and the mixing process. Secondly, regarding the influence of gas pressure on mixing uniformity, different gas pressures (e.g., 1.5 bar, 2 bar, 2.5 bar) can simulate the oil-gas mixing effect under different conditions; higher gas pressure can enhance the degree of oil-gas mixing, while lower gas pressure leads to incomplete mixing.

[0197] Furthermore, the gas supply system achieved the following effects in the experiment: First, stability and adjustability: by precisely adjusting the air pump, valves, and pressure gauges, the gas supply system can provide stable and adjustable gas pressure, ensuring controllable gas conditions for each experiment and guaranteeing the accuracy and repeatability of the test results. Second, simulation of different operating conditions: by adjusting the parameters of the gas supply system, different oil-gas mixing conditions can be simulated, providing a reliable experimental platform for evaluating the mixing uniformity under different pressures. Third, improved mixing effect: by reasonably controlling the parameters of the gas supply system, the oil-gas mixing effect can be improved, especially in the application of low-pressure air-assisted injection technology, ensuring that the spray and mixing effect reaches the optimal state, thereby improving combustion efficiency and emission control.

[0198] Unit 4: Jet Control System and High-Speed ​​Photography System

[0199] In the injection control and high-speed photography system, the fuel injector is opened or closed by the injection control system to achieve the set injection pulse width; a high-speed camera (such as FASTCAM NOVA S12) and LED light source are used to supplement the field of view inside the premixing chamber; the camera and the injection control system are triggered synchronously to record the entire process of fuel-air mixing.

[0200] Firstly, the main function of the injection control system is to control the opening and closing of the fuel injectors to achieve the set injection pulse width and ensure the accuracy of each injection quantity.

[0201] Furthermore, the operating steps of the injection control system are as follows:

[0202] S1. Fuel Injector Control: The fuel injector controls the timing of its opening and closing through the injection control system, thereby controlling the amount of fuel injected and the injection pulse width. The injection pulse width determines the injection time, affecting the amount of fuel injected and the spray effect. The injection control system precisely controls the action of the fuel injector based on set parameters, such as injection pressure and injection pulse width.

[0203] S2. Synchronous Control: The injection control system works synchronously with the high-speed photography system, coordinating the injection of fuel injectors and the triggering time of the camera through control signals; synchronous control ensures that each frame of the image accurately reflects the transient process of fuel-air mixing during high-speed shooting, avoiding data inconsistency caused by asynchronous shooting and injection.

[0204] S3. Precise adjustment of injection quantity: By adjusting the injection pulse width and injection pressure, the injection control system can simulate the changes in injection quantity under different operating conditions, ensuring that key parameters such as injection quantity and oil-gas pressure difference remain consistent in each test, thereby improving the repeatability and accuracy of the test.

[0205] Secondly, the high-speed photography system was used in this experiment to record in real time the entire process of oil-gas mixing inside the premixing chamber, especially the dynamic characteristics of the fuel injection process.

[0206] Furthermore, the high-speed photography system includes key components such as a high-speed camera, an LED light source, and a synchronization trigger.

[0207] The high-speed camera (such as the FASTCAM NOVA S12) has an extremely high shooting speed and resolution, and can capture images of instantaneous changes at a very high frame rate. In this experiment, the use of the FASTCAM NOVA S12 high-speed camera can ensure that the details of oil-gas mixing are recorded at a fast enough speed, ensuring that every subtle process is captured.

[0208] The LED light source is used to supplement the premixing cavity with high-brightness LED light source to ensure image quality; the LED light source has stable brightness and color temperature to ensure uniform illumination during the test and avoid image blurring due to light source fluctuations; the use of the light source in conjunction with the high-speed camera provides sufficient brightness to avoid the image quality being affected by low light conditions during the test.

[0209] The synchronous triggering refers to the high-speed photography system and the injection control system working synchronously through a trigger; the camera starts shooting through a trigger signal, while the injection control system precisely controls the opening and closing of the fuel injectors according to the set fuel injection pulse width; this synchronous control ensures that each fuel injection process is completely consistent with the image capture, ensuring that the image can accurately reflect each stage of the fuel-air mixture.

[0210] Furthermore, the high-speed photography system plays a crucial role in the experimental process: First, it records the dynamic changes of fuel-air mixture in real time, particularly fuel atomization, injection, impact on the walls, and mixing with air. Through high frame rate and high resolution images, the experimenter can observe the details of fuel-air interaction, providing intuitive data for analyzing fuel-air mixture uniformity. Second, it accurately assesses fuel-air mixture uniformity. Image analysis yields key parameters such as fuel penetration distance and coverage area, directly reflecting the uniformity of the fuel-air mixture. Synchronous injection control and image acquisition ensure the accuracy and reliability of the experimental data.

[0211] The technical advantages of the high-speed photography system are as follows: First, the high-resolution images provided by the system allow for clear capture of fuel spray details during high-speed injection, avoiding the impact of low-speed or blurry images on data analysis. Precise adjustment of the injection control system ensures the stability of each injection, guaranteeing high accuracy of experimental results. Second, image analysis allows for the extraction of multiple parameters reflecting the uniformity of fuel-air mixing, such as fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass (Raq). High frame rate image acquisition ensures the continuity and accuracy of the evaluation, avoiding errors caused by untimely or inaccurate image acquisition in traditional methods. Third, the synchronized operation of the injection control system and the high-speed photography system improves experimental repeatability, ensuring that each experiment is conducted under the same parameter conditions, producing consistent experimental results; this provides a stable and reliable foundation for subsequent experimental comparisons and data analysis.

[0212] Part Two: Test Procedure

[0213] Unit 1: Parameter Setting

[0214] The gas pressure in the premixing chamber is set (controlled by air pump and air pressure gauge); the injection pressure is set (controlled by oil pump and oil pressure gauge); the injection pulse width is set (the control system sets 2, 3, 4, 5, and 6 ms); thus forming different combinations of oil-gas pressure difference (such as 2.5, 2, 1.5, and 1 bar) and injection conditions to analyze the impact on mixing uniformity.

[0215] Firstly, the gas pressure setting within the premixing chamber is crucial, as gas pressure is a key factor affecting the oil-gas mixing effect. The gas pressure is jointly controlled by an air pump and a pressure gauge. The specific setting process for the gas pressure within the premixing chamber is as follows:

[0216] The air pump control means that the air pump is responsible for providing compressed air and adjusting the pressure of the gas in the premixing chamber through its output flow rate; the pressure of the gas output by the air pump can be adjusted under different operating conditions according to different experimental requirements.

[0217] The pressure gauge monitoring is used to monitor the gas pressure in the premixing chamber in real time. Through the feedback signal from the pressure gauge, the control system can accurately adjust the operating status of the air pump to ensure that the gas pressure is always kept within the set range.

[0218] The set gas pressure refers to the gas pressure in the premixing chamber, which is usually adjusted within a certain range to form the required oil-gas pressure difference. Common gas pressure values ​​can be set to 1.5 bar, 2 bar, or 2.5 bar. The specific pressure value depends on the experimental requirements and the goal of oil-gas mixing.

[0219] Secondly, the injection pressure setting determines the intensity of fuel injection, directly affecting the fuel atomization effect and injection uniformity. The injection pressure is controlled by the fuel pump and fuel pressure gauge, and the specific operation is as follows:

[0220] The fuel pump control refers to the fuel pump providing the flow pressure of fuel, and adjusting the output pressure of the fuel pump to control the injection intensity. The output pressure of the fuel pump directly determines the injection quantity and injection speed of the fuel injector.

[0221] The oil pressure gauge monitoring is used to monitor pressure changes in the fuel injection system in real time. Based on the pressure data fed back by the oil pressure gauge, the control system can adjust the operating status of the oil pump to ensure that the fuel injection pressure is maintained within the set range.

[0222] The set injection pressure is adjusted to different operating conditions according to the test requirements, such as 7.5 bar, 6.5 bar, 5.5 bar, and 4 bar. By precisely controlling the injection pressure, the set injection pressure can affect the fuel atomization effect and injection characteristics.

[0223] Thirdly, the fuel injection pulse width setting controls the timing of fuel injection, directly affecting the amount of fuel injected each time. The fuel injection pulse width setting is implemented by the control system, and the specific steps are as follows:

[0224] The control system setting is that the injection pulse width is set by the control system by adjusting the injection control signal; the range of the injection pulse width is 2ms, 3ms, 4ms, 5ms, and 6ms. These values ​​affect the duration of each injection, and thus affect the injection quantity.

[0225] The aforementioned impact on mixture uniformity is that different injection pulse width settings lead to different injection quantities and injection patterns, thus affecting the uniformity of the fuel-air mixture; a shorter pulse width results in a smaller fuel injection quantity, while a longer pulse width increases the injection quantity, which helps to improve mixture uniformity.

[0226] Fourthly, the aforementioned oil-gas pressure difference setting is another important factor affecting the uniformity of oil-gas mixing. This is achieved by adjusting the difference between the gas pressure and the injection pressure. The set oil-gas pressure difference values ​​are: 2.5 bar, 2 bar, 1.5 bar, and 1 bar. These different oil-gas pressure difference values ​​can simulate the oil-gas mixing process under different operating conditions. A larger oil-gas pressure difference generally helps to improve the degree of oil-gas mixing, resulting in a more uniform spray. Furthermore, by adjusting the output pressure of the air pump and the fuel pump, different oil-gas pressure difference conditions can be created, thereby affecting the uniformity of oil-gas mixing during injection. For example, at a high oil-gas pressure difference (such as 2.5 bar), the spray effect is better, and the oil-gas mixing is more uniform; while at a low oil-gas pressure difference (such as 1 bar), the oil-gas mixing is insufficient, and the spray effect is poor.

[0227] The technical benefits of these parameter settings are as follows: Precise setting of gas pressure, injection pressure, and injection pulse width enables comprehensive control of test conditions, ensuring repeatability and comparability of each test under different conditions. Different fuel-gas pressure differential settings can simulate various real-world working environments, facilitating the analysis of changes in fuel-gas mixture uniformity under different operating conditions, thus providing richer test data. By precisely adjusting the fuel-gas pressure differential and injection pulse width, the fuel-gas mixture effect can be optimized, combustion efficiency improved, and emissions reduced. This provides crucial data support for subsequent engine performance optimization and emission control.

[0228] Unit 2: Test Execution

[0229] The test was conducted by the control system driving the fuel injectors to inject fuel according to the set control parameters; the high-speed photography system simultaneously recorded the process of fuel breaking, impacting the walls, mixing and evolving in the premixing chamber.

[0230] Phase 1: Control system drives fuel injectors to inject fuel

[0231] S1. Injection control: During the test, the control system drives the nozzle to perform injection actions according to the pre-set injection pulse width, injection pressure and injection quantity;

[0232] The fuel injection pulse width setting is a precise control of the fuel injection pulse width by the control system according to the set values ​​(2ms, 3ms, 4ms, 5ms, 6ms) to ensure that the amount of fuel injected each time meets the predetermined requirements;

[0233] The injection pressure regulation is achieved by adjusting the oil pump and oil pressure gauge, so that the control system can realize the set injection pressure and ensure that the injection intensity is adapted to the predetermined working conditions.

[0234] The synchronization operation is a synchronous triggering of the control system and the high-speed photography system to ensure that the timing of the fuel injection and image acquisition is consistent, thus avoiding the impact of time deviation on image recording.

[0235] S2. Fuel injection: When the control system sends a trigger signal, the fuel injector opens rapidly and begins to inject fuel; the fuel injection process is precisely regulated by the control system to ensure that the fuel injection quantity, injection time and injection method (spray size and shape) meet the experimental requirements.

[0236] Phase Two: Synchronous Recording with High-Speed ​​Photography System

[0237] S1. Triggering and Synchronization of High-Speed ​​Cameras

[0238] The high-speed photography system uses high frame rate cameras such as the FASTCAM NOVA S12 to record the instantaneous process of fuel injection in the premixing chamber. The high-speed photography system works synchronously with the injection control system to ensure that each fuel injection process is recorded at the accurate time. The high frame rate and high resolution of the high-speed camera enable it to clearly capture every detail in the fuel-air mixing process, such as fuel atomization, wall impact, and breakage. Synchronous triggering ensures that the injection control system and the high-speed camera are triggered synchronously, ensuring that every moment of fuel injection is accurately recorded and avoiding data errors caused by asynchrony.

[0239] S2. LED light source supplementary lighting

[0240] The high-speed photography system is equipped with an LED light source to provide uniform illumination to the test area, ensuring that the images remain clear and bright even in low-light environments. The LED light source has stable light intensity and color temperature, avoiding the impact of light source fluctuations on image quality and ensuring that clear, interference-free images are recorded.

[0241] S3. The dynamic process of image capture

[0242] The images captured by the high-speed photography system record the entire dynamic process of oil-gas mixing, including fuel breakup, wall impact, mixing, and evolution.

[0243] The fuel breakage refers to the process where the injected fuel is sprayed from the nozzle and breaks up into small droplets under the action of air.

[0244] The wall-collision process refers to the impact of fuel atomized droplets on the wall of the premixing chamber or the surface of other objects, resulting in a bounce or diffusion.

[0245] The mixing process involves the interaction between fuel droplets and air molecules to form an oil-air mixture.

[0246] The evolution process is that, over time, the oil and gas mixture gradually becomes more homogeneous until mixing is complete.

[0247] Phase 3: Data Acquisition During the Experiment

[0248] S1. Image Analysis and Data Extraction

[0249] The images captured by the high-speed photography system can be further analyzed using image processing software to extract key parameters such as fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass (Raq): the fuel penetration distance is the geometric distance from the nozzle outlet to the farthest fuel injection point; the fuel coverage area is the projected area of ​​the injected fuel droplets in the premixing chamber; and the fuel coverage area per unit mass (Raq) is the area covered by a unit mass of injected fuel, used to evaluate the uniformity of the fuel-air mixture.

[0250] S2. Real-time observation and experimental recording

[0251] The image data of each injection process is recorded, forming a large amount of experimental image data; through image analysis, the influence of different oil-gas pressure difference, injection pulse width and other parameters on the oil-gas mixing effect can be quantitatively evaluated.

[0252] Furthermore, the technical effects achieved by the experimental execution process are as follows: First, in terms of dynamic observation of the oil-air mixing process, the high-speed photography system can accurately record each stage of the oil-air mixing process, including fuel atomization, impact, breakup, and mixing with air, providing data support for subsequent analysis of oil-air mixture uniformity. Second, in terms of improving the accuracy and repeatability of the experiment, the precise synchronization of the injection control system and the high-speed photography system ensures the accuracy of data from each experiment, avoiding experimental deviations caused by asynchrony or measurement errors. Third, in terms of quantitative analysis of mixing uniformity, based on key parameters extracted from image analysis (fuel penetration distance, fuel coverage area), the uniformity of oil-air mixing can be quantitatively assessed, providing a scientific basis for injection parameters and premixing chamber design.

[0253] Part Three: Image Processing and Evaluation Metrics

[0254] Unit 1: Image Preprocessing

[0255] Select a frame of image without oil spray as the background image. Figure 3 (a)); Image containing oil spray ( Figure 3 (b) Subtract the background image to remove interference from fixed structures; binarize the difference results to obtain a black and white image of the fuel distribution. Figure 3 (c)).

[0256] Image preprocessing is a crucial step in the analysis of oil-gas mixing processes. It involves processing images obtained through high-speed photography to extract key information reflecting fuel distribution. The image preprocessing process includes background selection, difference processing, and binarization, with the specific steps as follows:

[0257] S1. Select the image without spraying (select the background image) Figure 3(a)): First, select one frame of unsprayed image from the high-speed photographic images captured in the experiment as the background image. Figure 3 (a) This frame records the state of the premixing chamber without fuel injection, i.e., the scene when only gas is present;

[0258] The purpose of the background image is to eliminate the interference of all static structures (cavity walls, fuel injectors) in the premixing chamber on subsequent analysis;

[0259] All static parts contained in the background image will be treated as interference information in subsequent processing;

[0260] S2. Calculate the difference image (difference processing) Figure 3 (b) - Figure 3 (a)): By using images containing oil spray ( Figure 3 (b) and background image ( Figure 3 (a) Perform a difference operation to obtain the difference image; the difference process is as follows:

[0261] The difference operation involves subtracting the value of each pixel in the image containing fuel injection from the pixel value at the corresponding position in the background image; the difference result will show the changes caused by the fuel droplets generated during the fuel injection process.

[0262] The removal of interference refers to the differential results helping to eliminate fixed, non-dynamic structural information (cavity walls, fuel injectors) in the background image, retaining only dynamic information related to the fuel injection and mixing process.

[0263] S3. Binarize the difference results (binarization processing) Figure 3 (c) The difference results are binarized to convert the pixel values ​​in the image into black and white (0 and 1) values; the specific steps of the binarization process are as follows:

[0264] S3.1 Select a threshold: Set a threshold value, and set the pixel values ​​in the difference image that are greater than the threshold value to white (representing fuel areas) and the pixel values ​​that are less than the threshold value to black (representing non-fuel areas); through this process, the position of fuel droplets in the image can be separated from the background;

[0265] S3.2 Black and white image: The resulting binarized image ( Figure 3 (c) will show the distribution of fuel, where white areas represent the presence of fuel droplets, while black areas represent areas without fuel.

[0266] Furthermore, image preprocessing serves two purposes: by using differential processing and binarization, it removes the interference of static background structures on image analysis, allowing subsequent analysis to focus more on the dynamic process of oil-gas mixing. The binarized image clearly shows the distribution of fuel within the premixing chamber, providing fundamental data for subsequent oil-gas mixing uniformity analysis. Through preprocessing, the influence of environmental factors on image analysis can be effectively eliminated, and the true fuel distribution information can be extracted, thereby improving the accuracy and reliability of oil-gas mixing uniformity analysis.

[0267] Furthermore, the technical effects of image preprocessing are as follows: differential and binarization processing completely separates the fuel area from the background, ensuring that only information related to the fuel-air mixture is retained in the image, while removing image content unrelated to the mixing process. Through this preprocessing technique, subsequent image analysis becomes more efficient and accurate, enabling precise evaluation of fuel injection effects and the uniformity of the fuel-air mixture.

[0268] Unit 2: Calibration and Quantization

[0269] Image calibration and quantization are crucial steps in converting pixel information in an image into actual physical quantities. This process ensures that the fuel distribution data extracted from the image accurately reflects the actual situation, facilitating further analysis and comparison. The image is calibrated at the pixel scale to obtain a ratio of 0.051 mm / pixel; based on this calibration, the measurement results per pixel are converted into actual length and area.

[0270] The specific calibration and quantification process includes the following steps:

[0271] Phase 1: Pixel Scale Calibration

[0272] S1. Selecting a calibration image: During the experiment, it is first necessary to select an image as a calibration image. This image contains a physical reference of known size (such as a calibration ruler or calibration grid of known length). This reference of known size can help us establish the relationship between the pixels in the image and the actual physical units (such as millimeters, meters, etc.).

[0273] S2. Setting the calibration scale: By measuring the length of the reference object in the calibration image and combining this with the pixel length of the reference object in the image, the pixel scale of the image can be calculated; the specific calculation method is as follows:

[0274]

[0275] In Example 1, the ratio obtained after measurement and calculation is 0.051 mm / pixel, that is, each pixel corresponds to an actual physical length of 0.051 mm.

[0276] Phase Two: Quantization Based on Calibration Relationships

[0277] S3. Convert to Actual Length: Once the ratio between pixels and actual physical length is determined, the length value of each pixel in the image can be converted to its actual length. For example, assuming an object in the image is 50 pixels long, according to the calibration ratio (0.051 mm / pixel), its actual length is:

[0278]

[0279] In this way, the physical dimensions of each object in the image can be accurately converted into actual values;

[0280] S4. Convert to Actual Area: For a fuel droplet in an image, first calculate its pixel area in the image (i.e., the total number of pixels in the black area of ​​the image), and then convert it to its actual area using a calibration relationship; for example, if the area of ​​a fuel droplet in the image is 1000 pixels... 2 Therefore, its actual area is:

[0281]

[0282] In this way, the area data obtained from the image can be converted into the actual physical area;

[0283] Phase 3: Application of Quantified Data

[0284] S5. Quantitative analysis of fuel distribution: The actual size and distribution of each fuel droplet are obtained through the calibrated image; the converted actual length and area data provide the necessary basis for subsequent analysis, making it possible to quantitatively assess the uniformity of fuel-air mixture.

[0285] S6. Evaluate the uniformity of fuel-air mixture: After quantifying the distribution of fuel droplets in all injection processes, parameters such as fuel penetration distance and fuel coverage area can be calculated. These quantitative data will serve as the basis for subsequent evaluation of fuel-air mixture uniformity, helping researchers to evaluate the mixing effect under different injection conditions.

[0286] The technical benefits of applying the quantified data are as follows: Through calibration, pixel data in the image is accurately converted into actual physical units, avoiding data errors in traditional image processing and making image analysis results more accurate. Since image calibration unifies image data used in all experiments to actual physical units, data from different operating conditions and experimental conditions can be directly compared and analyzed. The calibration and quantification process allows the evaluation of oil-gas mixing uniformity to go beyond qualitative analysis and enable more precise quantitative evaluation, thus providing strong data support for the optimization of the injection system and premixing chamber design.

[0287] Unit 3: Construction of Evaluation Parameters

[0288] In this experiment, fuel penetration distance, fuel coverage area (FPA), and fuel coverage area per unit mass (Raq) are important parameters for evaluating the homogeneity of fuel-air mixture. Fuel penetration distance, fuel coverage area (FPA), and fuel coverage area per unit mass (Raq) reflect the propagation depth, distribution range, and uniformity of fuel breakup and mixing within the premixing chamber, respectively.

[0289] Firstly, the fuel penetration distance refers to the geometric distance (jet penetration distance) from the nozzle outlet to the farthest boundary of the premixed fuel, reflecting the depth and degree of fragmentation of the liquid jet entering the premixing chamber; the fuel penetration distance is the geometric distance from the nozzle outlet to the farthest boundary of the fuel in the premixing chamber, also known as the "jet penetration distance".

[0290] The fuel penetration distance is calculated by using image analysis technology to measure the geometric distance from the nozzle outlet to the farthest point of the fuel droplet in the image. The fuel penetration distance data provides a reference for the design of the fuel injection system and premixing chamber, helping to optimize the injection direction and atomization effect.

[0291] The significance of the fuel penetration distance is that it reflects the propagation depth of the fuel in the premixing chamber, demonstrating the penetrating power of the injected liquid; it also reflects the degree of breakage of the fuel droplets during the injection process. A longer penetration distance indicates that the injected droplets can penetrate deep into the premixing chamber, while a shorter penetration distance indicates that the injection effect is insufficient and the droplets have not penetrated into the mixing zone.

[0292] Secondly, the fuel coverage area (FPA) refers to the total area of ​​fuel pixel projection in the image, reflecting the distribution range of fuel on the cross-section of the premixing chamber.

[0293] The fuel coverage area (FPA) is calculated by using image processing technology to calculate the total number of pixels in the fuel area of ​​a binary image, which is the fuel coverage area (FPA). The fuel coverage area (FPA) can help analyze the spray range and effective distribution of the fuel spray.

[0294] The significance of the fuel coverage area (FPA) is to reflect the coverage range of the fuel-air mixture. A larger FPA value indicates that the injected fuel covers a wider area, meaning that the fuel is more evenly distributed in the premixing chamber and the fuel-air mixture effect is better. A smaller FPA value means that the injected fuel droplets are concentrated in a certain area, resulting in uneven fuel-air mixture.

[0295] Thirdly, the fuel coverage area per unit mass (Raq) refers to the area that each unit mass of fuel can cover within the premixing chamber; the fuel coverage area per unit mass Raq is:

[0296]

[0297] Where FPA is the fuel coverage area, Q inj It represents the mass of fuel injected in a single injection; it reflects the area that a unit mass of fuel can cover in the premixing chamber. The larger Raq is, the more fully the fuel is broken up, the more dispersed the distribution is, and the more uniform the fuel-air mixture is.

[0298] The calculation method for the fuel coverage area per unit mass (Raq) is to obtain the fuel coverage area FPA through image analysis and combine it with the fuel mass Q of each injection. inj To calculate Raq; this parameter is one of the important standards for measuring the homogeneity of oil and gas mixing;

[0299] The significance of the fuel coverage area per unit mass (Raq) is to reflect the degree of fuel breakup and atomization. A larger Raq value indicates that the injected fuel is broken up more thoroughly, the droplet distribution is more dispersed, and the fuel-air mixture is more uniform. Regarding atomization and fuel-air mixing, a larger Raq value indicates that the droplets are broken up more thoroughly and the fuel is distributed more uniformly in the premixing chamber, thereby improving the fuel-air mixing effect. Conversely, a smaller Raq value may indicate that the fuel atomization is insufficient, the droplets are larger, resulting in uneven mixing and affecting combustion efficiency.

[0300] Furthermore, the application of evaluation parameters includes assessing the uniformity of fuel-air mixing and optimizing fuel injection conditions;

[0301] Regarding the assessment of oil-gas mixing uniformity, the comprehensive analysis of evaluation parameters provides a quantitative basis for oil-gas mixing uniformity. By varying the parameters under different injection pressures, injection pulse widths, and gas pressures, researchers can assess the uniformity of oil-gas mixing under different operating conditions, thereby optimizing the injection system and premixing chamber design.

[0302] The optimized injection conditions include fuel penetration distance, which provides data on the depth of the injected droplets penetrating the premixing chamber, helping to adjust the injection angle and nozzle design; fuel coverage area (FPA), which reflects the distribution range of fuel, and can be used to optimize the injection pattern and airflow guidance of the injector; and fuel coverage area per unit mass (Raq), which helps to study the atomization effect and distribution uniformity of fuel injection, providing data support for combustion efficiency and emission control.

[0303] The technical effects of constructing the evaluation parameters are as follows: First, these three parameters enable the experiment to quantitatively assess the uniformity of the fuel-air mixture, providing strong data support for the optimization of the fuel injection system. Second, optimizing the fuel injection conditions and parameter settings (such as fuel-air pressure difference, injection pulse width, and injection pressure) can effectively improve the uniformity of fuel atomization and distribution, thereby improving combustion efficiency and reducing emissions. Third, the quantification of these parameters allows for direct comparison of data under different experimental conditions, providing more reliable experimental evidence.

[0304] Furthermore, the evaluation method for the uniformity of oil-gas mixing in the air-assisted injection premixing chamber described in this invention comprises the following specific steps:

[0305] S1. Fabrication and preparation of experimental equipment: The experimental equipment includes a visualized premixing chamber structure, a fuel supply system for supplying fuel to the injectors, a gas supply system for supplying gas to the premixing chamber, a high-speed photography system and camera bracket for acquiring images of the fuel injection process, and a control system for controlling the opening and closing of the injectors according to experimental parameters.

[0306] The visualized premixing chamber structure was created in the experiment using a transparent material (such as transparent resin) to make a premixing chamber model, which can be observed in real time through a high-speed photography system to observe the mixing process of oil and gas in the premixing chamber.

[0307] The fuel injector and air supply system are described, wherein the fuel injector is responsible for supplying fuel and the air supply system is responsible for supplying gas (air); in order to ensure the visualization and precise control of the experiment, the nozzle and air nozzle are separated, and only the fuel injector, premix chamber and air supply system are retained;

[0308] The high-speed photography system is the core component of the experiment, used to capture the dynamic changes in the oil-gas mixing process. Through high-speed photography equipment, the high-speed photography system can accurately record the oil-gas mixing state during the injection process, as well as details in the oil-gas mixing process, such as droplet breakup and gas distribution.

[0309] The control system is able to precisely control the opening and closing of the nozzle according to different parameters required for the experiment (such as oil and gas pressure and injection pulse width), thereby adjusting the injection quantity and injection duration.

[0310] S2. Control parameter settings before the experiment: Before the experiment, control parameters such as gas pressure in the premixing chamber, fuel injection pressure and fuel injection pulse width need to be set. Before the experiment begins, several key control parameters need to be set to ensure the uniformity of oil-gas mixing during the experiment.

[0311] The gas pressure mentioned is the pressure of the gas (air) that controls the dynamics of oil-gas mixing.

[0312] The injection pressure is the pressure that controls the fuel injector. The injection pressure directly affects the fuel injection speed and atomization effect.

[0313] The injection pulse width is the duration of the injection process, which affects the total amount of fuel injected and the adequacy of atomization.

[0314] These control parameters are adjusted by the system to optimize the uniformity of oil-gas mixing;

[0315] S3. Fuel Injection and Image Acquisition: The fuel injector is controlled by the control system to inject fuel according to the required test parameters, and the fuel-air mixing process in the premixing chamber is recorded by the high-speed photography system during the fuel injection process.

[0316] During the experiment, the oil injection from the nozzle and the high-speed photography image acquisition were carried out simultaneously.

[0317] The oil nozzle sprays oil by precisely adjusting the spray volume and spray duration of the oil nozzle according to the set control parameters through the control system; the oil is sprayed into the premixing chamber and mixed with air to form an oil-air mixture.

[0318] The image acquisition process involves using a high-speed photography system to capture the oil-gas mixture in real time during the injection process, taking high-frame-rate images and recording the oil-gas distribution, droplet distribution, and mixing process inside the nozzle. These images provide the necessary raw data for subsequent image processing.

[0319] S4. Image Processing and Mixing Uniformity Evaluation: Image processing is performed on the images obtained by high-speed photography to obtain relevant parameters to evaluate the oil-gas mixing uniformity in the premixing chamber; the captured images are analyzed through image processing technology, and the oil-gas mixing uniformity is quantified using specific evaluation parameters;

[0320] The fuel penetration distance is measured by image analysis to determine the farthest distance the fuel travels in the premixing chamber after injection. This parameter reflects the extent of fuel injection and atomization effect.

[0321] The fuel coverage area is the fuel-air distribution area in the premixing chamber after fuel injection. The fuel distribution is measured through the black pixel area in the image.

[0322] The fuel coverage area per unit mass, Raq, is a quantitative indicator used to measure the uniformity of fuel-air mixture. Raq represents the ratio of the area covered by each injected fuel to the injected fuel mass. The formula for calculating Raq is as follows:

[0323]

[0324] Where FPA is the fuel coverage area, Q injRaq represents the quality of fuel injection; the larger the Raq value, the larger the area covered by each unit of fuel injection, the more uniform the fuel-air mixture, and the better the atomization effect.

[0325] Through the above parameter adjustments and system implementation, the evaluation method for the uniformity of oil-gas mixing in the air-assisted injection premixing chamber described in this invention can quantitatively evaluate the uniformity of oil-gas mixing and provide experimental basis for optimizing injection parameters and premixing chamber design.

[0326] This invention provides an experimental method combining high-speed photography and image processing technology, which can capture and evaluate the dynamic changes of the fuel-air mixture process in real time and accurately under complex flow fields. By introducing quantitative evaluation indicators such as fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass (Raq), the uniformity of the fuel-air mixture can be accurately analyzed, thus providing experimental basis for the optimization of the injection system and further improving combustion efficiency and emission control performance. Regarding high-precision visualization and quantitative analysis, this invention, through high-speed photography and image processing technology, can intuitively capture the dynamic process of fuel-air mixture and accurately evaluate the uniformity of the mixture using quantitative evaluation indicators (such as Raq). In terms of flexible experimental platform design, the experimental equipment can flexibly adjust control parameters such as injection quantity and injection pressure to adapt to different experimental conditions and accurately record the fuel-air mixture effect under different conditions. Regarding direct feedback and optimization, the experimental platform can adjust control parameters in real time and provide instant feedback through image analysis to optimize the design and process parameters of the injection system.

[0327] A method for testing and evaluating the uniformity of fuel-air mixing in an air-assisted injection premixing chamber is disclosed. The fuel penetration distance and fuel coverage area are obtained using image processing technology. The fuel penetration distance is the geometric distance from the nozzle outlet to the furthest point of the injected fuel, and the fuel coverage area per unit mass Raq is the ratio of the area covered by a single fuel injection to the mass of the single injection.

[0328] In one embodiment of the present invention, the extraction process of the visual premixed cavity model is as follows: Figure 2 As shown.

[0329] Will Figure 2 (a) The premixing chamber (within the black box) and its upper part connecting to the nozzle in the air-assisted nozzle are extracted separately, and the extracted parts are 3D printed using transparent resin to obtain the following result. Figure 2(b) shows the transparent premixing chamber model. Since the experiment only focuses on the premixing characteristics of the oil and gas within the premixing chamber, the nozzle needle valve is not included in the transparent model. To seal the bottom of the premixing chamber, the bottom pipe was extended and thickened, and threads were tapped inside the extended section. Bolts were used to tighten the seal during the experiment. The extracted premixing chamber consists of two sections with different inner diameters, the dimensions of which are the same as the actual dimensions of the premixing chamber. The upper section has an inner diameter d and a height h of 10 mm, while the lower section has an inner diameter of 2.5 mm and a length of 33 mm. The length from the nozzle outlet to the bottom of the premixing chamber is 43 mm. Specific dimensions are marked as follows: Figure 2 As shown in (b). In order to increase the light transmittance of the premixing cavity, the thickness of the part that needs to be observed is set to 1 mm. However, since the connection part of the air inlet and the oil nozzle and the sealing part at the bottom of the premixing cavity are not observed, their thickness is appropriately increased to ensure the strength of the premixing cavity model.

[0330] To make the technical solutions and advantages of the present invention clearer, the exemplary embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0331] The high-speed camera used in the experiment was a FASTCAM NOVA S12, and LED light sources were used to supplement the camera's field of view.

[0332] The fuel used in the fuel supply system is 0# diesel.

[0333] The visualized premixing chamber model was created using transparent resin via 3D printing, such as... Figure 2 As shown.

[0334] Before starting the experiment, first install and secure the nozzle on top of the premixing chamber. Figure 2 As shown in (a), connect the air circuit, oil circuit, and fuel injection control system. Then, install the camera and light source, and adjust their parameters. Finally, set the injection control parameters for this operation. The air-fuel pressure differences set are 2.5, 2, 1.5, and 1 bar, corresponding to injection pressures of 7.5, 6.5, 5.5, and 4 bar, and injection pulse widths of 2, 3, 4, 5, and 6 ms. The injection pressure and the gas pressure in the premixing chamber are controlled by the oil pump and air pump, respectively.

[0335] During the experiment, the fuel injector was controlled to open and close via a fuel injector control system. Simultaneously, a camera recorded the fuel-air mixing process within the premixing chamber during fuel injection. Figure 4 As shown.

[0336] After the experiment, the captured photos were processed, such as... Figure 3 As shown. First, use an image without fuel injection as the background, such as... Figure 3 (a). Secondly, use images with fuel injection (such as...) Figure 3 (b) Subtracting the background image and binarizing the fuel image yields a binarized fuel image, such as... Figure 3 (c). Here, the jet penetration distance is also defined as the distance from the nozzle outlet to the end of the injection body, such as... Figure 3 As shown in (c). The fuel projected area is determined by measurement. Figure 3 (c) The total area covered by black pixels is used to determine this. Since all the above measurements are based on image pixels, calibration using actual distance is necessary. Through calibration, the ratio of actual distance to pixel is 0.051 mm / pixel. This ratio allows the conversion of the measured fuel penetration distance and fuel projected area in the image from pixel values ​​to actual values, such as... Figure 5 and Figure 6 As shown.

[0337] Furthermore, the unit fuel coverage area Raq can be obtained from the single fuel injection quantity and fuel coverage area according to the following formula:

[0338]

[0339] Where FPA represents fuel coverage area, Q inj This indicates the amount of fuel injected in a single injection; this means that the larger Raq is, the more thoroughly the jet droplets are broken up, and the better the uniformity of the fuel-air mixture in the premixing chamber. Figure 7 As shown.

[0340] The experimental results above demonstrate that this experiment and evaluation method can effectively reflect the direct observation and quantitative evaluation of the dynamic characteristics of fuel-air mixing during air-assisted injection. It can more realistically reflect the fuel's breakup, impact with the walls, and mixing with air within the premixing chamber. This can provide a direct basis for the design of the premixing chamber structure and the optimization of injection parameters.

[0341] Example 2: Construction of a Visualized Premixing Chamber Test System for the Air-Assisted Injection Premixing Chamber Homogeneity Test System and Evaluation Method of the Present Invention

[0342] like Figures 1-4 As shown in Example 2, a test system and evaluation method for the uniformity of fuel-air mixing in an air-assisted injection premixing chamber are provided. The method is implemented on a visual premixing chamber test system. In the air-assisted injection premixing chamber fuel-air mixing uniformity test system and evaluation method of this invention, the test system includes: a visual premixing chamber model 1, a fuel supply system 2, an air supply system 3, an injection control system 4, and a high-speed photography system 5.

[0343] Visualized premixing chamber model

[0344] In Example 2, the premixing chamber and its upper connection to the nozzle are extracted from the actual air-assisted nozzle structure, while maintaining the same geometric dimensions as the original nozzle, such as the inner diameter and length. Example 2 separates the nozzle from the original nozzle, retaining only the nozzle and the air supply channel connecting to the premixing chamber, removing the nozzle needle valve structure. The extracted premixing chamber outline is fabricated using transparent resin material through 3D printing to form a transparent premixing chamber model. To achieve a reliable bottom seal while considering the strength requirements of the transparent resin material, Example 2 extends and appropriately thickens the bottom channel of the premixing chamber, tapping threads on the inner wall of the extended section. During the test, a reliable seal at the bottom of the premixing chamber is achieved by tightening metal bolts. To improve the light transmittance and image quality of the premixing chamber observation area, Example 2 sets the sidewall thickness of the premixing chamber to be observed to approximately 1 mm. The inlet, nozzle connection section, and bottom sealing section, which are not involved in the observation, have their wall thickness increased accordingly to improve structural strength. Thus, while ensuring that the flow boundary conditions inside the premixing chamber remain basically unchanged, the oil-gas mixing process inside the premixing chamber can be visualized and observed.

[0345] fuel supply system

[0346] In Example 2, the fuel supply system includes a fuel tank, a fuel pump, a fuel pressure gauge, a control valve, and pipelines. Liquid fuels such as gasoline, diesel, or aviation kerosene can be used; diesel is used as the test fuel in Example 2. The fuel pump outlet's injection pressure is monitored in real-time by the fuel pressure gauge, and the injection pressure and single injection quantity are adjusted by the control valve.

[0347] Gas supply system

[0348] The gas supply system includes a gas pump, a pressure gauge, a control valve, and gas pipelines. The gas pump outlet is connected to the premixing chamber inlet via the control valve. By adjusting the gas pump and valve opening, the gas pressure in the premixing chamber is set, thereby creating different oil-gas pressure differential conditions.

[0349] Jet control and high-speed photography system

[0350] The injection control system 4 is electrically connected to the fuel injectors and is used to control the opening and closing of the fuel injectors and set the injection pulse width. In Example 2, the injection pulse width is set to multiple conditions such as 2ms, 3ms, 4ms, 5ms, and 6ms. The high-speed photography system 5 uses a FASTCAMNOVAS12 high-speed camera and is equipped with an LED light source to uniformly illuminate the camera's field of view. The high-speed camera is synchronously triggered with the injection control system to record the transient evolution of the fuel-air mixture in the premixing chamber during fuel injection.

[0351] Furthermore, the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method of the present invention includes the following steps:

[0352] S1. Build the test system according to the above definition and complete the connection. Install the fuel nozzle on the top of the transparent premixing chamber model, connect the fuel supply system and the air supply system, adjust the imaging position of the high-speed camera and fix the camera and the light source.

[0353] S2. Before the test, set the control parameters such as gas pressure, injection pressure, and injection pulse width in the premixing chamber. In this embodiment, the oil-gas pressure difference is set to 2.5 bar, 2 bar, 1.5 bar, and 1 bar, corresponding to injection pressures of 7.5 bar, 6.5 bar, 5.5 bar, and 4 bar, respectively.

[0354] S3. Under the set operating conditions, the injection control system controls the fuel injector to inject fuel, while a high-speed camera simultaneously captures images of the fuel-air mixing process inside the premixing chamber, such as... Figure 4 As shown;

[0355] S4. After the test, the images obtained by high-speed photography are processed and analyzed to obtain evaluation parameters of the uniformity of oil-gas mixing in the premixing chamber.

[0356] The present invention discloses an air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method. Through the visualization premixing chamber test system constructed in Example 2, under the premise of maintaining the original nozzle premixing chamber geometry and pressure boundary conditions basically the same, the invention realizes intuitive observation of the oil-gas mixing process inside the premixing chamber, providing a reliable experimental basis for subsequent measurement of quantitative parameters such as fuel penetration distance and fuel coverage area.

[0357] Example 3: Visualization model of different premixing chamber structures and materials for the air-assisted injection premixing chamber homogeneity test system and evaluation method described in this invention.

[0358] In traditional air-assisted jet premixing chamber research, existing techniques mostly focus on the spray characteristics outside the nozzle, and the nozzles and premixing chamber structures are mostly made of metal materials. These structures are not suitable for directly observing the internal flow and oil-gas mixing process. To address this issue, common methods include numerical simulation or the use of specially designed optical nozzles, but these methods either fail to accurately reflect the actual flow field or cannot meet the dual requirements of transparency and structural strength in experiments.

[0359] This invention proposes a specific construction method for a transparent premixing chamber model. While maintaining the original flow characteristics of the air-assisted nozzle premixing chamber, it utilizes transparent resin for 3D printing to achieve visual observation and measurement of the oil-gas mixing process. Example 2 solves the problem of balancing structural strength, sealing, and optical transmittance in a transparent model through a specific design scheme.

[0360] At this point, the problem faced by the technicians is how to achieve the visualization and measurement of the flow field inside the premixing chamber and the oil-gas mixing process without changing the original flow characteristics of the premixing chamber.

[0361] Furthermore, while considering the implementation of a transparent model, the technicians still needed to address three technical issues: First, how to ensure sealing and structural strength under pressure, which was addressed by extending and thickening the nozzle, tapping threads, and then bolting for sealing; second, how to provide sufficient light transmittance while ensuring strength, which led to the design of thinning the observation area to 1mm and thickening the non-observation area; and third, how to ensure that the geometric dimensions were completely consistent with the original nozzle, which required precise 3D printing and dimensional calibration. These improvements ensured the synergy and specificity of the technical effects, guaranteeing both the flow similarity of the experiment and providing high-quality optical observation conditions.

[0362] Therefore, the present invention provides an air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method, which includes a transparent premixing chamber model. The specific structural features of the transparent premixing chamber model are as follows: while maintaining the original geometry of the air-assisted nozzle premixing chamber, the premixing chamber and its connection to the nozzle are extracted and fabricated using transparent resin 3D printing. The nozzle needle valve is removed, and the bottom channel is extended and thickened, internally threaded, and sealed with bolts. This allows the premixing chamber to withstand experimental pressure, maintain its original flow characteristics, and possess internal visibility and good light transmittance.

[0363] Based on Example 2, Example 3 provides a visualized premixed cavity model with different structural parameters to illustrate the good applicability of the method of the present invention to premixed cavity structures; the construction steps of the transparent premixed cavity model are as follows:

[0364] S1. Fabrication of the premixing chamber model: First, using the geometric parameters of the existing nozzle, accurately replicate the size and shape of the original nozzle and the premixing chamber; then, using 3D printing technology, fabricate the premixing chamber model using transparent resin material, ensuring that the entire structure maintains the same flow characteristics as the original nozzle.

[0365] In this process, the original nozzle needle valve was removed, leaving only the fuel injector and premixing chamber and its air supply system. In this way, the transparent premixing chamber model can not only ensure the flow similarity during the injection process, but also clearly show the oil-air mixing situation inside the premixing chamber.

[0366] S2. Modification of the bottom channel and design of the sealing structure: In order to ensure that the transparent premixing chamber can withstand the pressure required for the experiment and has sufficient optical transmittance, the bottom of the premixing chamber was modified in Example 3;

[0367] S2.1 The bottom channel has been extended and thickened to ensure sufficient structural strength and sealing performance;

[0368] S2.2 The pipe in the extended section is threaded and sealed with bolts, which solves the sealing problem of the transparent model;

[0369] This design enables the transparent premixing chamber to maintain structural stability under high pressure conditions, while also resolving the contradiction between strength and sealing faced by transparent materials.

[0370] S3. Light Transmittance Design: In order to ensure that the transparent model has sufficient light transmittance under high pressure, Example 3 adopts a thin-wall design;

[0371] The purpose of the light transmittance design is to effectively improve optical transmittance while ensuring stability under high intensity and high pressure conditions in experiments;

[0372] S3.1 In the premixing chamber section that needs to be observed, the wall thickness is controlled at 1mm to ensure that the high-speed camera can clearly capture the details of the oil-gas mixture.

[0373] S3.2 In the non-observation area, the wall thickness should be appropriately increased to ensure the strength of the transparent premixed cavity.

[0374] S4. Dimensional Accuracy and Calibration: Through precise 3D printing technology and calibration scheme, we ensure that the manufactured transparent premix chamber model is completely consistent with the original nozzle structure in size, avoiding test errors caused by dimensional errors; during the manufacturing process, we use dimensional calibration technology to ensure the accuracy of each component, especially the precise matching of the connection parts and the nozzle diameter.

[0375] Therefore, the specific structural features of the transparent premixing chamber model can ensure that the flow boundary inside the premixing chamber is consistent with the actual nozzle, thus ensuring that the test is representative of engineering. Sufficient light transmittance is obtained through transparent materials and thin-wall design, allowing high-speed cameras to clearly capture the details of oil-gas mixing. The specific bottom elongation, thickening and threaded sealing structure solves the contradiction between strength, sealing and optical visibility in the transparent model.

[0376] In Example 3, the premixing chamber still consists of two sections with different inner diameters, but the inner diameter d of the upper section is adjusted to 12mm, the height h to 8mm, and the inner diameter of the lower section to 3mm, with a length of 30mm. The remaining structural arrangement remains consistent with the air-assisted nozzle in actual applications. The transparent premixing chamber model is made of quartz glass, which, compared to transparent resin, has higher strength and heat resistance under high temperature and high pressure conditions.

[0377] To ensure image quality, Example 3 also controls the wall thickness of the observation area within the range of 1 to 1.5 mm, while appropriately thickening the non-observation area; the bottom of the premixing chamber adopts an extended, thickened, and threaded sealing structure similar to that in Example 1 to ensure no significant leakage within the pressure range of 0 to 8 bar.

[0378] Regarding the experimental method, Example 3 still uses steps S1 to S4 as described in Example 2, and adjusts the parameters of the air pump and oil pump to make the gas pressure and oil injection pressure in the premixing chamber cover the range of 1 to 8 bar. The high-speed photography system uses the same model of high-speed camera and LED light source, and only adjusts the camera position and field of view appropriately according to the change in the size of the premixing chamber.

[0379] Experimental results show that even with changes in the geometry and materials of the premixing chamber, the visual premixing chamber design and testing method of this invention can still clearly record the oil-gas mixing process inside the premixing chamber. Parameters such as fuel penetration distance and fuel coverage area obtained based on image processing show minimal changes in multiple repeated experiments, indicating that the method of this invention has good versatility and stability for premixing chambers with different structures. Through Example 3, this invention successfully achieved a visual experiment of a transparent premixing chamber under high pressure, effectively solving the problem of not being able to directly observe the oil-gas mixing process in existing technologies, and providing direct data support for subsequent combustion system design, optimization, and emission control.

[0380] Example 4: Evaluation and comparison of oil-gas mixing uniformity based on Raq of the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method described in this invention.

[0381] Example 4, based on Example 2, focuses on how to quantitatively evaluate the uniformity of oil-gas mixing in the premixing chamber based on fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq, and compares it with the traditional method that uses only a single index.

[0382] Firstly, image processing methods

[0383] Because the premixed cavity model is made of transparent resin material, problems such as reflection and refraction of the inner wall of the cavity and uneven illumination of the light source are inevitable during high-speed photography. As a result, the original image contains a lot of fixed background information and stray light components in addition to the fuel jet. If the original image is directly thresholded, the cavity outline and reflective area are easily misidentified as fuel area, which affects the measurement accuracy of fuel penetration distance and coverage area.

[0384] To address this, the present invention first acquires a background image without fuel injection during image processing, and then subtracts this background image from the instantaneous image containing the fuel jet, retaining only the grayscale variation area caused by the fuel injection. This effectively eliminates the interference of the premixing cavity structure contour and fixed reflections on the recognition results. Based on this, the differential image is binarized by appropriately selecting a grayscale threshold to obtain a black-and-white image of the fuel jet region. Furthermore, the jet penetration distance and fuel projection area on the image are converted into actual physical quantities using a calibration relationship of 0.051 mm / pixel between pixels and the actual length. Therefore, the combined image processing of "background subtraction + binarization + pixel calibration" for the premixing cavity scene, compared to directly binarizing the original image, results in a smoother and more continuous fuel contour boundary. The calculated results of the fuel penetration distance and fuel coverage area are more stable in repeated experiments, which is beneficial for improving the accuracy and repeatability of the evaluation index of the uniformity of oil-gas mixing within the premixing cavity.

[0385] like Figure 3 As shown, in the air-assisted injection premixing chamber oil-gas mixing uniformity test system and evaluation method of the present invention, Example 4 uses image processing methods to process images acquired by high-speed photography:

[0386] S1. Background Subtraction: In the background subtraction step, fixed structures (such as the walls of transparent cavities) and unchanging background parts such as reflection and refraction are removed from the image to ensure that only the area where the fuel changes during the injection process is retained;

[0387] The purpose of background subtraction is to effectively remove the influence of fixed structures on the image, providing a cleaner image foundation for subsequent image processing.

[0388] S1.1 Selects the premixing chamber image under no fuel injection conditions as the background image, such as Figure 3 As shown in (a);

[0389] S1.2 will include a momentary image containing fuel injection ( Figure 3 (b) Subtract the background image to obtain a differential image containing only the fuel jet region, so as to eliminate the interference of the premixing cavity structure contour and fixed reflection;

[0390] S2. Binarization: After background subtraction, the remaining image still contains complex grayscale distribution, especially in the mixed fuel and gas injection area; in order to further distinguish between fuel and non-fuel areas, binarization is performed.

[0391] The purpose of the binarization process is to convert the image into a black and white image using a simple thresholding method, and to clearly segment the fuel area to facilitate subsequent calculations. In other words, the grayscale image is converted into a black and white image to clearly identify the fuel and non-fuel areas.

[0392] Using an appropriate grayscale threshold, all pixels in the image are divided into "fuel areas" (displayed as black) and "non-fuel areas" (displayed as white), as shown in image 3(c); grayscale thresholding is then applied to the difference image to obtain a binarized image of the fuel jet region, as shown in image 3(c). Figure 3 As shown in (c), the black area represents the fuel distribution area;

[0393] S3. Pixel calibration: Although the binarized image has distinguished between fuel and non-fuel areas, the dimensions in the image are still in pixels and do not have actual physical units; therefore, pixel calibration is required to convert the measured distances and areas in the image into actual physical quantities.

[0394] The camera system is spatially calibrated using a calibration board. Then, using a known calibration board (e.g., a reference object of known size pre-placed in the image), the proportional relationship between pixels and actual lengths is established. In this embodiment, the ratio of actual distance to pixel is 0.051 mm / pixel. Using this ratio, parameters such as fuel penetration distance and fuel coverage area in the image are converted from pixel values ​​to actual physical values. Thus, the obtained fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq all have practical physical meaning.

[0395] Based on the above image processing results, the fuel penetration distance is defined as the geometric distance from the nozzle outlet to the farthest point at the end of the fuel jet body, and the fuel coverage area FPA is defined as the projected area of ​​the black pixel region in the binarized image.

[0396] The results are as follows: By combining background subtraction, binarization and pixel calibration, the processed image can more accurately reflect the dynamic process of oil-gas mixing in the premixing chamber. In particular, when evaluating the uniformity of oil-gas mixing, the quantification of parameters such as fuel penetration distance, fuel coverage area and fuel coverage area per unit mass Raq can provide more realistic and accurate data support for optimizing injection conditions and design.

[0397] Secondly, the calculation of the fuel coverage area Raq per unit mass.

[0398] Existing technologies for evaluating fuel spray characteristics often employ indicators such as jet penetration distance, spray angle, or characteristic droplet diameter. These indicators primarily reflect the macroscopic range or local particle size distribution of the spray, making it difficult to provide a unified quantitative evaluation of the uniformity of fuel-air mixing within the premixing chamber. On one hand, fuel penetration distance focuses on describing the axial development of the jet and cannot reflect the coverage area of ​​the fuel across the premixing chamber cross-section. On the other hand, the fuel coverage area is strongly correlated with the quality of a single injection, and when the injection quantity varies under different operating conditions, it is impossible to objectively compare mixing uniformity based solely on the coverage area.

[0399] To overcome the above shortcomings, this invention proposes the evaluation index Raq, which combines the fuel coverage area (FPA) with the single injection mass (Q). inj In connection with this, in Example 4, the mass of a single fuel injection, Q... inj The fuel injection pulse width and flow characteristics of the injector are used to determine the fuel coverage area Raq per unit mass. Raq is calculated using the following formula:

[0400]

[0401] Where FPA stands for fuel coverage area, in mm. 2 Q inj Raq represents the mass of fuel injected in a single injection, expressed in mg. The unit for Raq can be mm. 2 / mg; The fuel coverage area Raq reflects the effective area that a unit mass of fuel can cover in the premixing chamber. The larger the Raq value, the more fully the fuel is broken up and the more dispersed it is in the premixing chamber, and the more uniform the fuel-air mixture.

[0402] The fuel coverage area Raq per unit mass reflects the effective area that a unit mass of fuel can cover within the premixing chamber. A larger Raq value indicates that the same mass of fuel is more thoroughly broken up, more dispersed within the premixing chamber, and more uniformly mixed with the fuel. By combining Raq with penetration distance and coverage area, this invention enables a comparable quantitative evaluation of the uniformity of fuel-fuel mixing within the premixing chamber under different injection masses and operating conditions.

[0403] Experimental results show that under certain operating conditions, although the fuel penetration distance does not change much, the fuel coverage area Raq per unit mass increases significantly with the increase of the fuel-gas pressure difference. This indicates that under the same fuel injection mass conditions, the fuel coverage area in the premixing chamber is significantly expanded. Traditional indicators based solely on penetration distance or coverage area are insufficient to reveal this difference.

[0404] Third, evaluation comparison under different working conditions

[0405] In traditional spray performance evaluation, commonly used indicators include penetration distance, spray angle, and droplet size. These indicators are typically used to describe the macroscopic characteristics of the spray or the local distribution of droplets. However, these indicators have certain limitations in evaluating the uniformity of fuel-air mixing within the premixing chamber. Fuel penetration distance mainly reflects the axial extent of fuel-air mixing and cannot effectively reflect the fuel distribution across the premixing chamber cross-section.

[0406] While spray angle and droplet size describe the distribution characteristics of a spray, they cannot quantify the uniformity of fuel throughout the premixing chamber. Fuel coverage area is closely related to the quality of a single injection; when the injection quantity changes, relying solely on coverage area leads to misjudgments of mixing uniformity, especially under different injection quantities and operating conditions, where traditional indicators fail to provide a unified and comparable evaluation standard.

[0407] To overcome the above shortcomings, this invention introduces a novel evaluation index, Raq, which measures the fuel coverage area (FPA) per unit mass and the amount of fuel injected in a single injection (Q). inj Combined, it is defined by the following formula:

[0408]

[0409] Where FPA represents the coverage area of ​​fuel in the premixing chamber, Q inj Indicates the mass of a single fuel injection.

[0410] Furthermore, in Example 4, multiple sets of repeated tests were conducted under the conditions of oil-gas pressure difference of 1 bar, 1.5 bar, 2 bar and 2.5 bar, respectively, and the corresponding fuel penetration distance, fuel coverage area and single injection mass were recorded to calculate Raq.

[0411] The specific implementation of the Raq-based evaluation method for the uniformity of oil-gas mixing in an air-assisted injection premixing chamber, as described in this invention, is as follows:

[0412] S1. Experimental preparation: In Example 4, a premixed chamber model and an injection system were used for the experiment; the control parameters of the injection system, such as injection pressure, injection pulse width and gas pressure, were set according to different working conditions.

[0413] S1.1 Injection System: Diesel fuel is used, injection pressure is set to 6.5 bar, injection pulse width is set to 4 ms, and gas pressure is set to 1.5 bar, 2.0 bar and 2.5 bar respectively to simulate different injection conditions;

[0414] S1.2 High-Speed ​​Photography System: Utilizes a FASTCAMNOVAS12 high-speed camera for high-definition image capture under LED lighting. The transparent premixing chamber model is 3D printed to ensure clear capture of the fuel injection and mixing process.

[0415] S2. Image Processing and Computation:

[0416] S2.1 Background Subtraction: First, perform background subtraction to remove static background information, such as reflections from the premixed cavity wall.

[0417] S2.2 Binarization Processing: The remaining image is binarized to clearly distinguish between fuel and non-fuel areas;

[0418] S2.3 Pixel Calibration: Pixel calibration is performed using a known calibration board to ensure that pixel values ​​in the image can be converted into actual physical units, thereby obtaining accurate parameters such as fuel penetration distance and coverage area;

[0419] S3. Calculate Raq: Based on the image processing results, calculate the fuel coverage area (FPA), and then calculate the fuel injection quantity (Q). inj ) Calculate the fuel coverage area per unit mass (Raq); in this way, the uniformity of the fuel-air mixture under each operating condition can be quantified.

[0420] After implementing the Raq-based evaluation of oil-gas mixture uniformity, the technical effects and comparison results are as follows: Through comparison of experimental data, the experimental results show that although the differences in fuel penetration distance and coverage area are not significant under different injection conditions, the uniformity of oil-gas mixture under different conditions can be clearly distinguished by calculating the Raq index.

[0421] Operating condition 1: Gas pressure 1.5 bar, fuel injection mass 5 mg, fuel penetration distance 35 mm, coverage area 50 cm². 2 Raq=50cm 2 / 5mg=10cm 2 / mg;

[0422] Operating Condition 2: Gas pressure 2.5 bar, fuel injection mass 5 mg, fuel penetration distance 36 mm, coverage area 70 cm². 2 Raq=70cm 2 / 5mg=14cm 2 / mg.

[0423] The results show that although the fuel penetration distance is not significantly different between the two operating conditions, the Raq index clearly indicates that in operating condition 2, the injected fuel covers a larger area within the premixing chamber, suggesting a more uniform spatial distribution of fuel and more thorough fuel-air mixing. The increase in Raq reflects that, with the same injection quality, a higher fuel-air pressure difference allows the fuel to cover a larger area within the premixing chamber, thus effectively improving mixing uniformity.

[0424] Further, it is shown that under certain operating conditions, as the fuel-air pressure difference increases, the fuel penetration distance does not change much, or even decreases slightly, but the fuel coverage area increases significantly. It is difficult to determine whether the mixing uniformity has improved based solely on the penetration distance. Using the Raq index proposed in this invention for evaluation, when the fuel-air pressure difference increases from 1 bar to 2.5 bar, Raq increases significantly, indicating that under the same injection quality conditions, the area that the fuel can cover in the premixing chamber increases significantly, resulting in a more uniform fuel-air mixture.

[0425] By introducing the fuel coverage area per unit mass, Raq, this invention provides a more accurate and comparable evaluation standard. Especially under different operating conditions and injection quantities, Raq eliminates inconsistencies in traditional evaluation methods, making the evaluation of fuel-air mixture uniformity more accurate. Experimental data shows that Raq not only provides better comparability between different operating conditions but also effectively reveals the impact of changes in injection quantity on fuel-air mixture uniformity, demonstrating significant technical advantages.

[0426] Compared with traditional methods that only use fuel penetration distance or coverage area as evaluation indicators, Example 4 introduces the fuel coverage area Raq per unit mass, which organically combines fuel spatial distribution with injection mass. This can eliminate the influence of fuel injection quantity changes under different operating conditions on the evaluation results, making the mixing uniformity between different operating conditions comparable and more accurately reflecting the true state of fuel-air mixing in the premix chamber.

[0427] The above embodiments are one of the implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An evaluation method for an air-assisted injection premixing chamber oil-gas mixing uniformity test system, characterized in that, Includes the following steps: S1. Construct a visual premixing chamber model: The premixing chamber model has transparent walls, which can be used to observe the oil-gas mixing process in real time; S2. Set and adjust experimental parameters: Adjust the injection pressure, injection pulse width and gas pressure to simulate different oil-gas pressure differences and injection conditions; S3. Fuel-air injection: The injection control system drives the fuel injector to inject fuel, and the fuel-air mixing process is recorded synchronously by a high-speed camera system; S4. Image preprocessing: The acquired images are preprocessed, including background image selection, difference processing and binarization, in order to extract key information about oil and gas mixing; S5. Assess the homogeneity of oil and gas mixing: Based on image processing results, quantitatively assess the homogeneity of oil and gas mixing, and analyze it by calculating evaluation parameters; S6. Analyze oil-gas mixture data: Use evaluation parameters to analyze the changes in oil-gas mixture under different test conditions.

2. The evaluation method for the air-assisted injection premixing chamber oil-gas mixing uniformity test system according to claim 1, characterized in that, S1. Constructing a visual premixed cavity model includes the following sub-steps: S1.1 Maintain consistent geometry: Extract the premixing chamber and its upper structure connected to the nozzle from the original air-assisted nozzle; S1.2 Separate the oil nozzle and air nozzle: Separate the oil nozzle and air nozzle from the original nozzle, keeping only the oil nozzle, premixing chamber and its air supply channel; S1.3 Transparent Resin 3D Printing: Using transparent resin material, a premixed cavity model is precisely fabricated through 3D printing technology to make the interior visible; S1.4 Blocking the connection channel: The original connection channel between the premixing chamber and the air nozzle is blocked with screws. The bottom of the premixing chamber is extended and thickened and internally threaded. The bottom is sealed with bolts to achieve bolt sealing. S1.5 wall thickness design: The wall thickness in the observation area is controlled between 1mm and 1.5mm to improve light transmittance; the wall thickness in the non-observation area is increased.

3. The evaluation method for the air-assisted injection premixing chamber oil-gas mixing uniformity test system according to claim 1, characterized in that, The method for adjusting the air pressure difference, injection pulse width, and injection pressure in S2. setting and adjusting the experimental parameters is as follows: first, set and adjust the output pressure of the air pump and the oil pump to simulate different working conditions; then, by controlling the injection pulse width, adjust the amount of fuel injected each time and the atomization effect to optimize the uniformity of fuel-air mixing.

4. The evaluation method for the air-assisted injection premixing chamber oil-gas mixing uniformity test system according to claim 1, characterized in that, In the S3. fuel-air injection process, when the injection control system controls the fuel injection pulse width, the fuel injection pulse width is adjusted by setting multiple operating conditions. The operating condition range includes multiple set values ​​from 2ms to 6ms to simulate the effect of different injection durations on fuel-air mixing.

5. The evaluation method for the air-assisted injection premixing chamber oil-gas mixing uniformity test system according to claim 1, characterized in that, S4. Image preprocessing, which enables analysis of the oil-gas mixing process, includes the following sub-steps: S4.1 Select Background Image: Select an image without fuel injection as the background image, record the state of the premixing chamber when only gas is present, and eliminate the static structure in the premixing chamber; S4.2 Calculate the difference image: Perform a difference operation between the image containing fuel injection and the background image to obtain the difference image. Then, by subtracting the value of each pixel from the pixel value at the corresponding position in the background image, the resulting difference image only contains the changes caused by fuel injection. S4.3 Binarization of Difference Results: The difference results are binarized by setting a threshold to convert the pixel values ​​in the image into black and white values, and to separate the fuel droplet positions in the image from the background area, thereby displaying the distribution of fuel droplets. S4.4 Image calibration and quantization: Select a calibration image with a reference object of known size, establish a pixel scale based on the pixel length of the reference object in the image and its actual physical length, and calculate the ratio between the pixel length and the actual physical length. Based on the calibration ratio, the pixel information in the image is converted into actual physical dimensions, and quantitative analysis is performed to obtain the actual physical values ​​of fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq.

6. The evaluation method for the air-assisted injection premixing chamber oil-gas mixing uniformity test system according to claim 1, characterized in that, In S5. Evaluating the uniformity of oil-gas mixing, the evaluation parameters include calculating the fuel penetration distance, the fuel coverage area, and the fuel coverage area per unit mass Raq. The calculated fuel penetration distance represents the geometric distance from the nozzle outlet to the farthest point of fuel injection; The fuel coverage area refers to the projected area of ​​the fuel droplets in the premixing chamber after injection; The fuel coverage area Raq per unit mass represents the area covered by a unit mass of injected fuel; the formula for the fuel coverage area Raq per unit mass is: ； Where FPA is the fuel coverage area, Q inj This refers to the mass of fuel injected each time.

7. The evaluation method for the air-assisted injection premixing chamber oil-gas mixing uniformity test system according to claim 1, characterized in that, The oil-gas mixing homogeneity test system is constructed as follows: S1. Build the test system according to the air-assisted injection premixing chamber and complete the connection. Install the fuel nozzle on the top of the transparent premixing chamber model, connect the fuel supply system and the air supply system, adjust the imaging position of the high-speed camera and fix the camera and the light source. S2. Before the test, set control parameters such as gas pressure, injection pressure and injection pulse width in the premix chamber; S3. Under the set operating conditions, the injection control system controls the fuel injector to inject fuel, while a high-speed camera simultaneously captures images of the fuel-air mixing process inside the premixing chamber. S4. After the experiment, the images obtained by high-speed photography are processed and analyzed to obtain evaluation parameters of the uniformity of oil-gas mixing in the premixing chamber.

8. A test system for the uniformity of oil-gas mixing in an air-assisted injection premixing chamber, characterized in that, This includes a visual premixing chamber model, an injection control system, a high-speed camera system, an air supply system, and an image processing system; The visualized premixing chamber model is made of transparent material and has transparent walls, enabling real-time observation of the oil-gas mixing process. The injection control system controls the opening and closing of the fuel injectors, precisely adjusts the fuel injection quantity and injection pulse width, and simultaneously starts a high-speed photography system to record the mixing process. The high-speed camera system includes a high-speed camera and an LED light source, used to synchronously record the fuel-air mixture state during the fuel injection process; The air supply system includes an air pump, a pressure gauge, valves and pipelines, which provide compressed air to the premixing chamber to form an oil-gas pressure differential condition and regulate the pressure of the gas in the premixing chamber. The image processing system is used to analyze images acquired from the high-speed camera system, extract fuel penetration distance, fuel coverage area and fuel coverage area per unit mass Raq, and evaluate the uniformity of fuel-gas mixing. The fuel supply system includes a fuel tank, a fuel pump, a fuel pressure gauge, and valves, which can provide a stable fuel supply and precisely adjust the injection pressure and injection quantity.

9. The air-assisted injection premixing chamber oil-gas mixing uniformity test system according to claim 8, characterized in that, The injection control system includes a fuel injector control unit and a fuel injection pressure regulating unit; the fuel injector control unit is used to adjust the fuel injection pulse width and fuel injection quantity; the fuel injection pressure regulating unit is used to control the fuel injection pressure, which affects the atomization effect of the fuel injection. The air supply system consists of an air pump, a pressure gauge, valves, and pipelines; the air pump is used to compress air and provide a stable air flow; the pressure gauge is used to monitor and display the gas pressure in the premixing chamber in real time; the valves are used to control the gas flow and adjust the amount of air output from the air pump to the premixing chamber. Piping is a piping system that can connect air pumps, pressure gauges, valves, and premixing chambers. The high-speed camera system includes components such as a high-speed camera, an LED light source, and a synchronous trigger. The high-speed camera has a high frame rate and high resolution, and can record the dynamic changes of the fuel injection process. The LED light source provides supplementary lighting for the premixing chamber, ensuring that clear images can still be obtained in low-light environments. The synchronous trigger unit is used to start the camera from a trigger signal, while the injection control system precisely controls the opening and closing of the fuel injectors according to the set fuel injection pulse width, thereby synchronously controlling the triggering of the fuel injectors and the high-speed camera. The image processing system includes an image preprocessing module and an image analysis module. The image preprocessing module can perform differential and binarization processing on the captured image to extract key information about the oil-gas mixture. The image analysis module can calculate the fuel penetration distance, fuel coverage area, and fuel coverage area per unit mass Raq, and evaluate the uniformity of the oil-gas mixture.

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