A turbulent constant-volume bomb flame speed measuring device based on laser light scattering

Abstract

The present application relates to combustion experiment measurement technology, aims at providing a turbulent constant volume bomb flame speed measuring device based on laser Mie scattering. The device comprises a turbulent constant volume bomb, an ignition needle, an ignition control system, an oil droplet generator, a high-speed laser, a lens group, a high-speed camera and four fan motor assemblies; four fan shaft interfaces are arranged on the spherical cavity and are connected to form a regular tetrahedron; the high-speed laser and the lens group are arranged outside an optical window in sequence, and the high-speed camera is arranged outside another optical window; the high-speed camera and the high-speed laser are connected to a delay generator through signal lines respectively. The present application can simulate the combustion experiment of the coupling of turbulent flame and chemical reaction under the isotropic uniform turbulent flow field, realize the isotropic turbulent flow field with different intensities, and is used for studying the interaction of the coupling of turbulent flame and chemical reaction under different turbulent intensities and the influence on the flame propagation speed.

Description

Technical Field

[0001] This invention relates to the field of combustion experiment measurement technology, and in particular to a device and method for measuring the flame velocity of a turbulent constant-volume combustion bomb based on laser Mie scattering. Background Technology

[0002] Flame propagation speed is an important parameter reflecting the intrinsic reaction rate of fuel premixed gas, including both laminar combustion speed and turbulent combustion speed. In real gasoline and diesel engine combustors and gas turbine combustors, high-temperature and high-pressure turbulent combustion often occurs in a confined space, which makes the propagation speed of turbulent flame a long-term focus of scientific research and engineering practice.

[0003] Turbulent flame velocity reflects the overall combustion propulsion speed resulting from the coupling of turbulence and chemical reaction. It is higher than laminar flame velocity and reflects the actual ability of the flame to propagate in the flow field. In burner design, the size, shape, position, height of the combustion zone, and characteristics such as backfire and extinguishing are highly dependent on turbulent flame velocity.

[0004] Currently, the main experimental methods for measuring flame velocity both domestically and internationally include the Bunsen burner method, the planar flame method, the opposed flame method, and the spherical flame method. Among these, the opposed flame method involves complex flow field configurations and its effectiveness is limited at high Reynolds numbers. The Bunsen burner and planar flame methods suffer from significant heat loss, affecting the combustion rates of laminar and turbulent flames. The spherical flame method, with its quasi-one-dimensional flame structure, low heat loss, and suitability for creating isotropic, uniform turbulent flow fields, is therefore suitable for measuring the velocities of laminar and turbulent flames.

[0005] The spherical flame method is a study of the propagation characteristics of spherical flames using a constant-volume combustion bomb. The constant-volume combustion bomb is its core experimental apparatus; however, existing constant-volume combustion bombs still have many shortcomings. For example, they typically involve static premixing of fuel gas after introduction, lacking an external turbulent flow field and thus failing to obtain the turbulent flame combustion velocity. Furthermore, they often employ orifice plates and varying jet velocities to achieve turbulence intensity variations, leading to complex configurations and inhomogeneous turbulent flow fields. Simultaneously, flame velocity measurement methods using conventional constant-volume combustion bombs are mostly based on the schlieren method. While simple to operate, this ignores the fact that the schlieren method obtains a flame front with overlapping lines of sight, failing to capture an accurate two-dimensional flame propagation structure, which negatively impacts the measurement results.

[0006] Therefore, proposing new solutions to address these problems has become a widespread and urgent need. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a device for measuring the flame velocity of a turbulent constant-volume combustion bomb based on laser Mie scattering.

[0008] To solve the technical problem, the solution of the present invention is:

[0009] A device for measuring the flame velocity of a turbulent constant-volume combustion bomb based on laser Mie scattering is provided, comprising a turbulent constant-volume combustion bomb for flame combustion testing, as well as an ignition needle, an ignition control system, an oil droplet generator, a high-speed laser, a lens group, a high-speed camera, and a fan motor assembly.

[0010] The spherical cavity of the turbulent constant-volume combustion bomb is equipped with two electrode interfaces, one oil droplet generator interface, at least two optical windows, four fan shaft interfaces, and multiple gas interfaces; the lines connecting each fan shaft interface form a regular tetrahedron, the center of which coincides with the center of the spherical cavity; the center lines of each optical window form a cross, and the intersection point coincides with the center of the spherical cavity.

[0011] Two ignition needles are fixed to the electrode interface via an adapter. The ignition electrode at the front end of the ignition needle extends into the spherical cavity, and the ends of the ignition electrodes are arranged alternately at the center of the cavity. The tail end of each ignition needle is connected to the ignition control system via a cable.

[0012] The oil droplet generator is fixed to the oil droplet generator interface via an adapter, and the multi-hole injector at its end extends into the spherical cavity with the nozzles facing the center of the cavity.

[0013] A high-speed laser and a lens group are arranged sequentially outside one of the optical windows. The point light source emitted by the high-speed laser is expanded into a sheet light source by the lens group and then enters the spherical cavity. A high-speed camera is arranged outside the other optical window, forming a 90° angle with the center line of the high-speed laser, and is used to acquire images of the combustion process inside the spherical cavity. The high-speed camera and the high-speed laser are respectively connected to a delay generator through signal lines. The delay generator is connected to the ignition control system through signal lines to synchronize the timing of the high-speed laser, the high-speed camera, and the ignition control system.

[0014] In the fan motor assembly, the drive motor is fixed to the fan shaft interface via an adapter on the bushing, and its shaft extends into the spherical cavity and the fan is installed at the end; the intersection of the extended lines of the shaft in each fan motor assembly coincides with the center of the spherical cavity;

[0015] The gas interface has at least three parts, which are respectively connected to the vacuum pump, the fuel gas storage cylinder and the oxidant gas storage cylinder through pipelines.

[0016] As an improvement to the present invention, it also includes an optical window serving as an observation window, which forms a 90° angle with the center line of each high-speed laser.

[0017] As an improvement of the present invention, the high-speed laser, the lens group and the center of the spherical cavity are all located on the center line of the same optical window, which passes through the center of one side of the regular tetrahedron.

[0018] As an improvement of the present invention, the lens group includes a plano-convex lens and a plano-concave lens, and the laser emitted by the high-speed laser passes through the plano-convex lens, the plano-concave lens and the optical window in sequence.

[0019] As an improvement of the present invention, the electrode interface, the oil drop generator interface and the fan shaft interface are all flange surfaces. The adapter refers to the flange structure provided on the ignition needle and the oil drop generator housing or the bushing. The flange structure of the adapter and the interface flange surface are fixedly connected by bolts.

[0020] As an improvement of the present invention, a ball bearing is provided between the drive motor shaft and the bushing, and a water-cooled outer shell with a water-cooling cavity is provided circumferentially outside the bushing at the ball bearing; the bushing extends into the spherical cavity and the seal between the bushing and the shaft is achieved by a lip seal ring.

[0021] As an improvement of the present invention, the ignition needle includes a rod-shaped body that penetrates the center of the metal shell, most of the rod-shaped body extending into the cavity of the turbulent constant volume combustion bomb, its surface being covered with a ceramic shell, and its end being an ignition electrode; the metal shell is provided with a plurality of circumferentially arranged through holes for passing through fixing bolts, and a sealing ring is provided on the inner side of the metal shell; a power cable is led out from the end of the rod-shaped body located on the outer side of the metal shell.

[0022] As an improvement of the present invention, the vacuum pump is connected in sequence to a three-way valve and a gas interface through a pipeline, and the other port of the three-way valve is connected to the atmospheric environment through a pipeline.

[0023] The present invention further provides a method for measuring the flame velocity of a turbulent constant-volume incendiary bomb based on laser Mie scattering using the aforementioned apparatus, comprising the following steps:

[0024] (1) Install and connect the components according to the structural relationship of the device to ensure that the inside of the turbulent constant volume combustion bomb is clean, the optical window is clean, and all electrical equipment is ready;

[0025] (2) Use a vacuum pump to evacuate the cavity of the turbulent constant volume combustion bomb, and then fill the cavity with fuel gas according to the partial pressure ratio designed in the test plan.

[0026] (3) Using an oil drop generator, first inject oxidant gas carrying atomized oil droplets into the fuel gas inside the cavity, then turn off the oil drop generator and continue to introduce the remaining oxidant gas; the injection amount of atomized oil droplets and oxidant gas is controlled according to the partial pressure ratio designed in the test plan;

[0027] (4) Start the drive motor in the fan motor assembly and set the speed of the four fans according to the preset turbulence scheme;

[0028] (5) A high-voltage electric field is formed between the ignition electrodes by the ignition control system, which generates an electric spark to ignite the premixed fuel gas; the delay generator triggers the high-speed laser and the high-speed camera to start working in the same sequence at the same time when it receives the ignition signal; the point light source emitted by the high-speed laser is expanded into a sheet light source and uniformly illuminates the flame under turbulent conditions; when the size of the tiny particles generated during combustion is comparable to the laser wavelength, Mie scattering occurs, and the scattered light signal is collected by the high-speed camera to form a continuous image;

[0029] (6) After the test, the internal cavity of the turbulent constant volume combustion bomb is connected to the atmospheric environment to release the high-temperature exhaust gas generated by combustion. The next set of experiments is carried out after the turbulent constant volume combustion bomb has completely cooled down.

[0030] (7) Perform grayscale and binarization batch processing on multiple sets of continuous images obtained by the high-speed camera, calculate particle velocity motion based on the particle image velocimetry principle and cross-correlation method, and then invert the velocity distribution of the combustion flow field.

[0031] As an improvement of the present invention, the laser frequency of the high-speed laser is 10KHz, and the shooting frequency of the high-speed camera is 10kHz.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1. The flame velocity measuring device of the present invention can simulate combustion experiments in which turbulent flame and chemical reaction are coupled under an isotropic uniform turbulent flow field. Due to the use of a larger volume spherical chamber, compared with the cylindrical chamber used in traditional turbulent constant volume combustion bombs, the turbulent flow field distribution is more spatially symmetrical, ensuring overall pressure stability and conforming to the quasi-one-dimensional flame propagation assumption.

[0034] 2. This invention, by incorporating a fan within a turbulent constant-volume combustion bomb and adjusting the fan speed, can achieve isotropic turbulent flow fields of varying intensities. This is used to study the interaction between turbulent flames and chemical reactions under different turbulence intensities and their impact on flame propagation speed. The motor-driven fan has a wide range of speed adjustment and precise control, which can generate a uniform and controllable turbulent flow field.

[0035] 3. This invention employs laser Mie scattering measurement technology, overcoming the limitation of the schlieren method, which can only measure overlapping flame surfaces. By combining it with particle image velocimetry, the two-dimensional distribution of the turbulent flow field within the observation area can be accurately calculated, allowing for a more intuitive observation of the impact of turbulent flame propagation on the turbulent flow field. Compared to the traditional schlieren method, this invention can measure real two-dimensional spherical flame structures, obtaining more accurate two-dimensional spherical flame structures without line-of-sight overlap; it can also study parameters such as flame brush thickness and flame surface density in greater detail, thereby obtaining the true turbulent flame propagation velocity, improving experimental accuracy, and making the measurement results more practically significant.

[0036] 4. This invention is applicable to the measurement of turbulent flame propagation velocity of various gaseous fuels. It can obtain the turbulent flame propagation velocity of various fuels under different pressures, turbulence intensities, and equivalence ratios. The measurement data can be widely applied to the research, design, and production practice of real gasoline and diesel engine and gas turbine combustors. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structural principle of the system of the present invention.

[0038] Figure 2 This is a schematic diagram of the turbulent constant-volume combustion chamber structure in the present invention.

[0039] Figure 3 This is a schematic diagram of the fan shaft structure in this invention.

[0040] Figure 4 This is a schematic diagram of the ignition electrode structure in this invention.

[0041] Figure 5 This is a flowchart of the method of the present invention.

[0042] Figure 6 This is a diagram of Mie scattering image processing and analysis.

[0043] Reference numerals: 1-Turbulent constant volume combustion bomb, 2-Drive motor, 3-Fan, 4-Optical window, 5-Vacuum pump, 6-Three-way valve, 7-Drop generator, 8-Ignition control system, 9-High-speed laser, 10-Planto-convex lens, 11-Planto-concave lens, 12-Delay generator, 13-High-speed camera, 14-Fan shaft interface, 15-Electrode interface, 16-Drop generator interface, 17-Shaft, 18-Lip seal, 19-Ball bearing, 20-Water cooling cavity, 21-Water cooling shell, 22-Ignition needle metal shell, 23-Sealing ring, 24-Ceramic shell, 25-Ignition electrode. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention.

[0045] 1. Structural description of the testing device in this invention

[0046] Turbulent constant-volume combustion bomb flame velocity measuring device, such as Figures 1 to 4 As shown, it includes a turbulent constant-volume combustion bomb 1 for flame combustion testing, as well as an ignition needle, an ignition control system 8, an oil droplet generator 7, a high-speed laser 9, a lens group, a high-speed camera 13, and a fan motor assembly.

[0047] The spherical cavity of the turbulent constant-volume combustion bomb 1 is equipped with two electrode interfaces 15, one oil droplet generator interface 16, at least two optical windows 4, four fan shaft interfaces 14, and multiple gas interfaces. The electrode interfaces 15, oil droplet generator interfaces 16, and fan shaft interfaces 14 are all flanged. Adapters with flange structures are respectively provided on the ignition needle, the housing of the oil droplet generator, or the bushing of the fan motor assembly. The flange structure is fixedly connected to the interface flange surface by bolts.

[0048] The lines connecting the various fan shaft interfaces 14 form a regular tetrahedron, the center of which coincides with the center of the spherical cavity. The lines connecting the centers of the various optical windows 4 intersect each other, and the intersection point coincides with the center of the spherical cavity. This special design enables a uniform three-dimensional spatial intensity distribution of the flow field. Unlike traditional techniques that use orifice plates and change the jet velocity to achieve variations in turbulence intensity, this invention utilizes a specially positioned fan, requiring a simple equipment structure, convenient speed control, and the ability to adjust the turbulence velocity in each direction according to the experimental requirements. Compared to orifice plates and changing the jet velocity, this invention can achieve an isotropic turbulent flow field.

[0049] The ignition needle comprises a rod-shaped body penetrating the center of a metal casing, which also serves as an adapter for mounting. Multiple circumferentially arranged through holes allow for the passage of fixing bolts. An electrical cable extends from the end of the rod-shaped body located on the outside of the metal casing to connect to the ignition control system 8. A sealing ring 23 is provided on the inside of the metal casing. Most of the rod-shaped body extends into the cavity of the turbulent constant-volume incendiary bomb 1, its surface covered by a ceramic casing, and its end is an ignition electrode 25. Two ignition needles are respectively fixedly mounted at the electrode interface 15, and the ends of the two ignition electrodes 25 are arranged alternately at the center of the cavity.

[0050] The oil droplet generator 7 is fixed to the oil droplet generator interface 16 via an adapter, and its multi-hole injector extends into the spherical cavity with the nozzles facing the center of the cavity. The adapter is a flange structure, and is fixedly connected to the flange face at the oil droplet generator interface 16 by bolts.

[0051] In the fan motor assembly, the drive motor 2 is fixed to the fan shaft interface 14 via an adapter mounted on the bushing. Its shaft 17 extends into the spherical cavity and a fan 3 is mounted at its end. The intersection of the extended shaft lines in each fan motor assembly coincides with the center of the spherical cavity. The adapter is a flange structure, and is fixedly connected to the flange face at the fan shaft interface 14 by bolts. A ball bearing 19 is provided between the shaft 17 and the bushing. A water-cooled outer shell 21 with a water-cooling cavity 20 is circumferentially arranged outside the bushing at the ball bearing 19. The bushing extends into the spherical cavity and is sealed to the shaft 17 by a lip seal 18.

[0052] There are at least three gas interfaces, which are respectively connected to the vacuum pump 5, the fuel gas storage cylinder, and the oxidizer gas storage cylinder via pipelines, and valves are installed on the pipelines. Among them, the vacuum pump 5 is connected to a three-way valve 6 and a gas interface in sequence via pipelines, and the other end of the three-way valve 6 is connected to the atmospheric environment via pipelines.

[0053] A high-speed laser 9 and a lens group are sequentially arranged outside one of the optical windows 4. The lens group includes a plano-convex lens 10 and a plano-concave lens 11. The laser emitted by the high-speed laser 9 passes sequentially through the plano-convex lens 10, the plano-concave lens 11, and the optical window 4, causing the emitted point light source to be expanded into a sheet light source by the lens group before entering the spherical cavity. The high-speed laser 9, the lens group, and the center of the spherical cavity are all located on the center line of the same optical window 4. This center line passes through the center of one side of the regular tetrahedron. This special design allows the sheet light source to capture the trajectory of an oil droplet on a two-dimensional plane located at the center of the spherical cavity. Unlike the schlieren method that uses line-of-sight overlap in traditional technology, this invention captures the two-dimensional trajectory of the flame by sheet light source and then compares the Mie scattering signal intensity between the burned and unburned areas to distinguish the flame surface contour, achieving true two-dimensional turbulent flame propagation imaging without line-of-sight overlap.

[0054] A high-speed camera 13 is positioned outside another optical window 4, forming a 90° angle with the centerline of the high-speed laser 9, to acquire images of the combustion process within the spherical cavity. The high-speed camera 13 and the high-speed laser 9 are connected to a delay generator 12 via signal lines. The delay generator 12 is connected to the ignition control system 8 via a signal line to synchronize the timing of the high-speed laser 9, the high-speed camera 13, and the ignition control system 8. To facilitate adjustment of the mounting position and angle of the fan, ignition electrode 25, and oil droplet generator, as well as observation of the experimental process and progress, at least one additional optical window is provided as an observation window. This optical window forms a 90° angle with the centerline of the high-speed laser to prevent laser injury to observers.

[0055] In this invention, "high-speed" in the high-speed laser 9 refers to a laser device with characteristics such as high pulse frequency, short pulse duration, and high modulation bandwidth. Such lasers can emit pulsed light at extremely short time intervals (e.g., microseconds). For example, the pulse width of an Nd:YAG laser can be as low as 10-100 ns, and the pulse repetition frequency (PRF) can reach over 10 kHz, ensuring the capture of transient changes in the combustion process. The shorter the pulse width, the higher the time resolution. For example, femtosecond lasers (such as Ti:Sapphire) have pulse widths of only a few femtoseconds (10 ns). -15 (seconds), capable of freezing ultra-high-speed combustion phenomena (such as Mach 7 shock waves). The frequency response of directly modulated lasers can reach the GHz level, supporting high-precision detection of Doppler frequency shift (such as the bandwidth of laser Doppler velocimeters needs to be >100MHz).

[0056] In this invention, "high-speed" in the high-speed camera 13 refers to a photographic device with characteristics such as ultra-high frame rate, nanosecond-level exposure time, and synchronization control precision. Such photographic devices typically have frame rates ranging from thousands to millions of frames per second (fps), for example, the industrial-grade Photron Fastcam Nova S20 reaches 1.1 million fps (1024×8 pixels resolution), which can be used to capture flame propagation and particle motion. Shutter speed can be reduced to nanoseconds (10... -9 High-speed cameras with nanosecond-level exposures can avoid dynamic blurring caused by high-speed motion (such as shock waves from explosions). They can support sub-microsecond synchronization with lasers and triggers, ensuring the timing consistency of optical signals and image acquisition. For example, in wind tunnel experiments, the camera and PIV system synchronously record particle displacement.

[0057] Both the high-speed laser 9 and the high-speed camera 13 are commercially available products that can be used directly.

[0058] 2. Method of using the device of the present invention

[0059] Using the aforementioned device, the flame velocity of a turbulent constant-volume incendiary bomb based on laser Mie scattering can be measured. This measurement method specifically includes the following steps:

[0060] (1) Install and connect the components according to the structural relationship of the device to ensure that the interior of the turbulent constant volume combustion bomb 1 is clean, the optical window is clean, and all electrical equipment is ready;

[0061] (2) Use vacuum pump 5 to evacuate the cavity of turbulent constant volume combustion bomb 1, and then fill the cavity with fuel gas according to the partial pressure ratio designed in the test plan.

[0062] (3) First, inject oxidant gas carrying atomized oil droplets into the fuel gas inside the cavity using the oil droplet generator 7, and then turn off the oil droplet generator 7 and continue to introduce the remaining oxidant gas; the injection amount of atomized oil droplets and oxidant gas is controlled according to the partial pressure ratio designed in the test plan;

[0063] (4) Start the drive motor 2 in the fan motor assembly and set the speed of the four fans 3 according to the preset turbulence scheme;

[0064] (5) A high-voltage electric field is formed between the ignition electrodes 25 by the ignition control system 8, which generates an electric spark to ignite the premixed fuel gas; the delay generator 12 triggers the high-speed laser 9 and the high-speed camera 13 to start working in the same sequence at the same time when it receives the ignition signal; the point light source emitted by the high-speed laser 9 is expanded into a sheet light source and uniformly illuminates the flame under turbulent conditions; when the size of the tiny particles generated during combustion is comparable to the laser wavelength, Mie scattering occurs, and the scattered light signal is collected by the high-speed camera 13 to form a continuous image;

[0065] (6) After the test, the internal cavity of the turbulent constant volume combustion bomb 1 is connected to the atmospheric environment to release the high-temperature exhaust gas generated by combustion. The next set of experiments is carried out after the turbulent constant volume combustion bomb 1 has completely cooled down.

[0066] (7) Perform grayscale and binarization batch processing on multiple sets of continuous images obtained by high-speed camera 13, calculate particle velocity based on the correlation between Doppler frequency shift and particle velocity, and then invert the velocity distribution of combustion flow field.

[0067] 3. A specific application example

[0068] The measuring device in this example includes a turbulent constant-volume combustion bomb 1, a motor control system, an ignition control system 8, an intake and exhaust control system, an oil droplet generator 7, and a high-speed laser Mie scattering measurement system.

[0069] like Figure 1 As shown, the turbulent constant-volume combustion bomb cavity 1 is spherical, made of 316L stainless steel, and has an inner diameter of 440 mm. Four optical windows 4, each 150 mm in diameter, are opened in three mutually perpendicular radial directions. One window is used to receive incident laser light, one to collect Mie scattering signals, and the other two are used as observation windows. The optical windows 4 are bolted to the annular cover and glass cover plate, and are sealed to the bomb body using graphite gaskets. Four fan shaft interfaces 14 are distributed on the bomb body, and their connections form a regular tetrahedron. An oil droplet generator interface 16 and two electrode interfaces 15 are also arranged on the bomb body. The initial pressure range of the turbulent constant-volume combustion bomb 1 can be set between 0.05-1 MPa, and the initial temperature range is 273-600 K.

[0070] like Figure 2 As shown, the turbulent constant-volume incendiary bomb 1 has four built-in rotating fans 3, which are installed at the fan shaft interfaces 14. The fans 3 are rigidly connected to the drive motor 2 via a rotating shaft 17. The drive motor 2 is connected to a speed controller, allowing for speed adjustment from 0 to 10,000 rpm. The intake and exhaust control system consists of a three-way valve 6 and a vacuum pump 5. The three-way valve 6 is connected to the bottom of the bomb body, the vacuum pump 5, and the atmospheric environment, respectively. An oil droplet generator 7 extends into the bomb body, generating silicone oil droplets with a particle size of 1-2 micrometers using a pressurized spray method. A pair of high-voltage ignition electrodes 25 are symmetrically arranged at the center of the bomb body. The tail of the ignition needle is connected to the ignition control system 8 via a wire. The ignition control system 8 includes a high-voltage pulse generator and an ignition coil. The high-voltage pulse generator has a voltage range of 0 to 100 kV and a square wave current waveform. The diameter of the ignition electrodes 25 is 2.5 mm. The high-speed laser Mie scattering measurement system includes a high-speed laser 9, a plano-convex lens 10, a plano-concave lens 11, a high-speed camera 13, and a time delay generator 12. The high-speed laser 9 and the two sets of lenses are arranged in front of the turbulent constant-volume combustion bomb 1. The power of the high-speed laser 9 is set to 35W and the frequency to 10kHz. The high-speed camera 13 is arranged to the left of the turbulent constant-volume combustion bomb 1, and the shooting frequency is set to 10kHz. The time delay generator 12 receives the trigger signal from the ignition control system 8 and is connected to the high-speed laser 9 and the high-speed camera 13. The point light source is expanded into a sheet light source after passing through the lens group, uniformly illuminating the oil droplets filling the turbulent constant-volume bomb. The Mie scattering light signal generated by the oil droplets is collected frame by frame by the high-speed camera 13.

[0071] like Figure 3 As shown, the shaft 17 is sealed to the projectile body of the turbulent constant-volume incendiary bomb 1 by a lip seal ring 18. This dynamic sealing method can ensure the sealing performance of the shaft 17 at high speeds. A ball bearing 19 is provided between the shaft 17 and the water-cooled housing 21 to fix the fan position. The water-cooled housing 21 is provided on the shaft 17, and the water-cooled housing 21 has a water-cooling cavity 20. During operation, circulating cooling water at 10°C to 20°C is introduced to cool the ball bearing 19.

[0072] like Figure 4 As shown, the main body of the ignition electrode 25 extends into the internal cavity of the turbulent constant-volume incendiary bomb 1, and this part is covered by a ceramic shell 24, which serves as an insulating protective sleeve. The ignition needle is installed through the metal shell 22, which is fixed to the ignition electrode interface 15 by bolts and sealed with the bomb body by an O-ring 23.

[0073] like Figure 5 As shown, the specific workflow of this invention includes the following steps:

[0074] (1) Connect the turbulent constant volume incendiary bomb 1 and all related equipment, check the inside of the bomb body to ensure it is clean, wipe all optical windows 4 clean, and ensure that the related equipment and control system are ready;

[0075] (2) Adjust the three-way valve 6 to connect the cavity and the vacuum pump 5, and turn on the vacuum pump 5 to evacuate the cavity into a vacuum;

[0076] (3) Fuel gas is first introduced into the cavity of the turbulent constant volume combustion bomb 1 according to the partial pressure ratio;

[0077] (4) Turn on the oil drop generator 7 and introduce oxidant gas carrying atomized oil droplets at a specified pressure into the turbulent constant volume combustion bomb 1; then turn off the oil drop generator 7 and introduce the remaining oxidant gas to reach the experimental set pressure.

[0078] (5) According to the experimental settings for turbulence, turn on the drive motor 2 and set the speed of the four fans 3 to be the same;

[0079] (6) The ignition control system 8 forms a high voltage electric field between the ignition electrodes 23 to generate an electric spark to ignite the premixed fuel gas. At the same time, the delay generator 12 receives the ignition signal and triggers the high-speed laser 9 and the high-speed camera 13 to start working.

[0080] (7) After a set of experiments is completed, adjust the three-way valve 6 to connect the cavity and the atmospheric environment to discharge the high-temperature exhaust gas inside the turbulent constant volume combustion bomb 1. After the temperature cools down to the initial temperature, continue the next set of experiments according to the same operating procedure.

[0081] (8) Analyze experimental data: Perform batch image processing such as grayscale conversion and binarization on the continuous images obtained by the high-speed camera 13 after successful ignition. Obtain frequency shift data from the images, calculate particle velocity motion based on the particle image velocimetry principle and cross-correlation algorithm, and then invert the velocity distribution of the combustion flow field.

[0082] Particle image velocimetry (PIV) is a method that measures flow velocity by recording the positions of particles in a flow field through multiple photographs and analyzing the captured images. Its basic principle involves scattering tracer particles in the flow field and using a pulsed laser sheet as the incident light source in the area to be measured. Through two or more consecutive exposures, the particle images are recorded on a PIV film or a CCD camera. Using autocorrelation or cross-correlation methods, the images recorded on the PIV film or CCD are processed point-by-point to obtain the flow field velocity distribution, and thus the combustion flow field velocity distribution.

[0083] A real-world test example:

[0084] A typical methane and air mixture was sequentially injected into the cavity of the turbulent constant-volume combustion bomb at a volume ratio of 1:9.52. The speed of the four fans was controlled at 750 rpm to make the turbulent pulsation velocity 0.585 m / s. Figure 6 This is a Mie scattering image of a turbulent spherical flame with methane and air at an equivalence ratio of 1. After image grayscale processing and binarization, the current equivalent flame radius is 30 mm, and the turbulent flame velocity is 2.25 m / s. After PIV processing, the turbulent pulsation velocity within a 5 mm profile of the flame front is obtained as 0.75 m / s. Figure 6 In the image, (a) is the outline of the flame scattering by laser Mie scattering, and (b) is the local gas velocity distribution map.

[0085] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A device for measuring the flame velocity of a turbulent constant-volume combustion bomb based on laser Mie scattering, characterized in that, It includes a turbulent constant-volume combustion bomb for flame combustion testing, as well as an ignition needle, ignition control system, oil droplet generator, high-speed laser, lens group, high-speed camera and fan motor assembly; The spherical cavity of the turbulent constant-volume combustion bomb is equipped with two electrode interfaces, one oil droplet generator interface, at least two optical windows, four fan shaft interfaces, and multiple gas interfaces; the lines connecting each fan shaft interface form a regular tetrahedron, the center of which coincides with the center of the spherical cavity; the center lines of each optical window form a cross, and the intersection point coincides with the center of the spherical cavity. Two ignition needles are fixed to the electrode interface via adapters. The ignition electrodes at the front end of the ignition needles extend into the spherical cavity, and the ends of the ignition electrodes are arranged alternately at the center of the cavity. The tail ends of each ignition needle are connected to the ignition control system via cables. The ignition needle includes a rod-shaped body that penetrates the center of the metal shell. Most of the rod-shaped body extends into the cavity of the turbulent constant volume incendiary bomb. Its surface is covered with a ceramic shell, and the end is the ignition electrode. The metal shell has multiple circumferentially arranged through holes for the fixing bolts to pass through. A sealing ring is provided on the inner side of the metal shell. The end of the rod-shaped body located on the outer side of the metal shell leads out a power cable. The oil droplet generator is fixed to the oil droplet generator interface via an adapter, and the multi-hole injector at its end extends into the spherical cavity with the nozzles facing the center of the cavity. A high-speed laser and a lens group are sequentially arranged outside one of the optical windows. The point light source emitted by the high-speed laser is expanded into a sheet light source by the lens group and then enters the spherical cavity. The centers of the high-speed laser, the lens group, and the spherical cavity are all located on the center line of the same optical window, which passes through the center of one side surface of the regular tetrahedron. A high-speed camera is arranged outside another optical window, forming a 90° angle with the center line of each of the high-speed lasers, and is used to acquire images of the combustion process inside the spherical cavity. The high-speed camera and the high-speed laser are respectively connected to a delay generator via signal lines. The delay generator is connected to the ignition control system via signal lines to synchronize the timing of the high-speed laser, the high-speed camera, and the ignition control system. In the fan motor assembly, the drive motor is fixed to the fan shaft interface via an adapter mounted on the bushing. Its shaft extends into the spherical cavity and a fan is installed at its end. The intersection of the extended lines of the shafts in each fan motor assembly coincides with the center of the spherical cavity. A ball bearing is provided between the drive motor shaft and the bushing, and a water-cooled outer shell with a water-cooling cavity is provided circumferentially outside the bushing at the ball bearing. The bushing extends into the spherical cavity and a lip seal is used to achieve a seal between the bushing and the shaft. The gas interface has at least three parts, which are respectively connected to the vacuum pump, the fuel gas storage cylinder and the oxidant gas storage cylinder through pipelines.

2. The apparatus according to claim 1, characterized in that, It also includes an optical window used as an observation window, which forms a 90° angle with the center line of each high-speed laser.

3. The apparatus according to claim 1, characterized in that, The lens group includes a plano-convex lens and a plano-concave lens. The laser emitted by the high-speed laser passes through the plano-convex lens, the plano-concave lens and the optical window in sequence.

4. The apparatus according to claim 1, characterized in that, The electrode interface, oil drop generator interface, and fan shaft interface are all flange faces. The adapter refers to the flange structure located on the ignition needle and the oil drop generator housing or bushing. The flange structure of the adapter is fixedly connected to the interface flange face by bolts.

5. The apparatus according to claim 1, characterized in that, The vacuum pump is connected in sequence to a three-way valve and a gas port via a pipeline, and the other port of the three-way valve is connected to the atmospheric environment via a pipeline.

6. A method for measuring the flame velocity of a turbulent constant-volume incendiary bomb based on laser Mie scattering using the apparatus described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Install and connect the components according to the structural relationship of the device to ensure that the inside of the turbulent constant volume combustion bomb is clean, the optical window is clean, and all electrical equipment is ready; (2) Use a vacuum pump to evacuate the cavity of the turbulent constant volume combustion bomb, and then fill the cavity with fuel gas according to the partial pressure ratio designed in the test plan. (3) Using an oil drop generator, first inject oxidant gas carrying atomized oil droplets into the fuel gas inside the cavity, then turn off the oil drop generator and continue to introduce the remaining oxidant gas; the injection amount of atomized oil droplets and oxidant gas is controlled according to the partial pressure ratio designed in the test plan; (4) Start the drive motor in the fan motor assembly and set the speed of the four fans according to the preset turbulence scheme; (5) A high-voltage electric field is formed between the ignition electrodes by the ignition control system, which generates an electric spark to ignite the premixed fuel gas; the delay generator triggers the high-speed laser and the high-speed camera to start working in the same sequence at the same time when it receives the ignition signal; the point light source emitted by the high-speed laser is expanded into a sheet light source and uniformly illuminates the flame under turbulent conditions; when the size of the tiny particles generated during combustion is comparable to the laser wavelength, Mie scattering occurs, and the scattered light signal is collected by the high-speed camera to form a continuous image; (6) After the test, the internal cavity of the turbulent constant volume combustion bomb is connected to the atmospheric environment to release the high-temperature exhaust gas generated by combustion. The next set of experiments is carried out after the turbulent constant volume combustion bomb has completely cooled down. (7) Perform grayscale and binarization batch processing on multiple sets of continuous images obtained by the high-speed camera, calculate particle velocity motion based on the particle image velocimetry principle and cross-correlation method, and then invert the velocity distribution of the combustion flow field.

7. The method according to claim 6, characterized in that, The high-speed laser has a laser frequency of 10kHz, and the high-speed camera has a shooting frequency of 10kHz.

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