An experimental device and method for studying the mechanism of droplet thermal delay fusion

Abstract

The present invention discloses an experimental device and method for studying the mechanism of droplet thermal delay fusion, belonging to the technical field of droplet impact fusion research. It includes ultra-clear glass, above which a heating component and a droplet generator are provided. The heating component is used to increase the temperature of the droplet when it drips. The droplet outlet end of the droplet generator is located inside the heating component, and the dripping path of the droplet is set perpendicular to the center of the ultra-clear glass. On the outer side of the ultra-clear glass, a monochromatic high-speed camera, an LED lamp and an infrared camera are provided. The acting ends of the monochromatic high-speed camera, the LED lamp and the infrared camera all point to the upper surface of the ultra-clear glass. The monochromatic high-speed camera is used to capture the impact image when the droplet impacts the ultra-clear glass, and the infrared camera is used to monitor the temperature of the droplet when it is about to impact the ultra-clear glass. This technical solution is used to study the influence of droplet temperature on the thickness of the formed gas film, providing guidance for the application of spray combustion.

Description

Technical Field

[0001] The present invention belongs to the technical field of droplet impact fusion research, and particularly relates to an experimental device and method for studying the mechanism of droplet thermal delay fusion. Background Art

[0002] The kinetic study of a single fuel droplet impact plays a crucial role in the design and optimization of the internal combustion engine fuel injection system. During the process of a droplet impacting a wall surface, a very thin gas film will be squeezed and formed at the bottom of the droplet, resulting in the rebound of the fuel droplet after it impacts the wall-attached oil film. This rebound hinders the generation of more fuel droplets attaching to the wall, which is beneficial to the reduction of unburned hydrocarbons (HC) and has a certain positive effect on improving environmental pollution. Therefore, it is of great significance to deeply understand the evolution characteristics and mechanism of the droplet impact fusion process.

[0003] However, in the research of droplet impact fusion, the study of the gas film thickness at the bottom of the droplet is particularly important, as it can change the fusion process of the droplet and is of great significance to the spray combustion process. The interior of an internal combustion engine is a complex system. During the process of a droplet impacting a wall surface, the gas film thickness during its impact fusion process is affected by many factors, such as internal pressure, droplet diameter, and droplet temperature. In the prior art, there has been some research on the influence of internal pressure and droplet diameter on the gas film thickness, but during the impact fusion process, there is less research on the influence of droplet temperature on the formed gas film thickness. At the same time, most of the experimental devices in the prior art can only study the macroscopic phenomena of droplet impact and it is difficult to analyze the microscopic gas film thickness during the droplet fusion process. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an experimental device and method for studying the mechanism of droplet thermal delay fusion, so as to study the influence of droplet temperature on the formed gas film thickness and provide theoretical guidance for the application of spray combustion.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] An experimental device for studying the mechanism of thermal delay fusion of droplets, comprising a ultra-clear glass. Above the ultra-clear glass, there are a heating component and a droplet generator. The heating component is used to raise the temperature of the droplets when they drip. The droplet outlet end of the droplet generator is located inside the heating component, and the dripping path of the droplets is set perpendicular to the center of the ultra-clear glass. Outside the side of the ultra-clear glass, there are a monochrome high-speed camera, an LED lamp and an infrared camera. The acting ends of the monochrome high-speed camera, the LED lamp and the infrared camera all point to the upper surface of the ultra-clear glass. The monochrome high-speed camera is used to capture the impact images when the droplets impact the ultra-clear glass. The infrared camera is used to monitor the temperature of the droplets when they are about to impact the ultra-clear glass. Below the ultra-clear glass, there are a color high-speed camera, a metal halide lamp and a semi-transparent and semi-reflective mirror. The semi-transparent and semi-reflective mirror is inclined at 45° towards the metal halide lamp. The acting end of the color high-speed camera is on the same axis as the center of the droplet. The center of the semi-transparent and semi-reflective mirror is on the same horizontal line as the metal halide lamp. The color high-speed camera is used to capture the interference fringes of the air film during the process of the droplets impacting the ultra-clear glass.

[0007] Further, an aerogel heat insulation board is provided between the heating component and the ultra-clear glass, and a through hole for the droplets to pass through is provided on the aerogel heat insulation board directly below the droplets.

[0008] Further, the heating component heats the droplets by means of thermal radiation.

[0009] Further, the working fluid in the droplet generator is silicone oil.

[0010] An experimental method for an experimental device for studying the mechanism of thermal delay fusion of droplets, comprising the following experimental steps:

[0011] S1. Adjust the height of the liquid outlet end of the droplet generator relative to the ultra-clear glass, then control the droplet generator to emit droplets towards the surface of the ultra-clear glass, and first block the irregular droplets falling in the early stage through a blocking component until the droplet generator discharges continuous and regular spherical droplets;

[0012] S2. Turn on the heating component to heat the droplets on the liquid outlet end of the droplet generator until the heating temperature meets the experimental requirements to form heated droplets;

[0013] S3. Before the heated droplets impact the ultra-clear glass, the infrared camera captures the temperature image of the droplets before impacting the ultra-clear glass, and the captured image is processed by the Matlab program to obtain the surface temperature of the droplets, and then by calculating the average temperature of the central area of the droplet surface, the temperature of the heated droplets can be obtained;

[0014] S4. When the heated droplet impacts the ultra-clear glass, the process of droplet impact is illuminated by the light emitted by the LED lamp. Then, a monochromatic high-speed camera records the macroscopic morphological changes during the droplet impact process from the side. Subsequently, it is processed by a custom Matlab image processing program to obtain the actual impact velocity of the heated droplet.

[0015] S5. When the heated droplet impacts the ultra-clear glass, the white light emitted by the metal halide lamp is reflected onto the ultra-clear glass after passing through a semi-transparent and semi-reflective mirror. Part of the light is reflected from the upper surface of the ultra-clear glass, and the other part of the light passes through the ultra-clear glass and irradiates the bottom surface of the heated droplet, and is reflected from the bottom surface of the heated droplet. The two beams of light reflected from the ultra-clear glass and the bottom of the droplet interfere to form interference fringes of different colors. The interference fringes pass through the semi-transparent and semi-reflective mirror, then enter the color high-speed camera through a plane mirror, and the interference fringes of the micron-scale gas film are obtained. Then, these interference fringes are processed to obtain the true thickness curve of the gas film at the bottom of the heated droplet.

[0016] Furthermore, in step S5, the method for obtaining the thickness curve of the gas film at the bottom of the heated droplet is as follows:

[0017] An optical lens with a known curvature is used as a calibration tool. By photographing, the interference fringes of the gas film at the bottom of the lens are obtained, and the interference fringes corresponding to the gas film thickness are obtained. Then, tangential averaging processing is performed on the interference fringes, and the gas film thickness is calculated according to the lens contour. Then, the interference fringe color is corresponded to the gas film thickness. During the processing of the true gas film at the bottom of the droplet, the interference image of the true gas film thickness is converted from the RGB mode to the CIE1976 mode, and its color difference is calculated through the Euclidean distance. A continuous curve can be obtained from the color difference image. This curve is composed of the points with the darkest color. Connecting these dark points can obtain the true thickness curve of the gas film at the bottom of the droplet.

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention proposes an experimental device capable of simultaneously obtaining the macroscopic contour of millimeter-scale droplets and the microscopic morphology of micron-scale gas films during the thermal delay fusion process of droplets, realizing experimental measurements of millimeter-scale droplets and micron-scale gas films at different time and space scales, obtaining the laws of fluid flow, heat transfer, and mass transfer in the gas film, revealing the rupture mechanism of the gas film at the bottom of the droplet, and ultimately realizing the regulation of the thermal delay fusion of droplets. The invention of this experimental device will further enrich and improve the existing droplet impact theory, deepen the understanding of the evolution characteristics of the bottom gas film during the thermal delay fusion process of droplets, and ultimately provide theoretical guidance for the application of spray combustion.

[0020] Other advantages, objects, and features of the present invention will be set forth in the following description, and to some extent will be apparent to those skilled in the art, or can be taught from the practice of the present invention. The objects and other advantages of the present invention can be achieved and obtained through the following description. Brief Description of the Drawings

[0021] In order to make the objectives, technical solutions, and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0022] Figure 1 It is a schematic plan view of the experimental device of the present invention;

[0023] Figure 2 It is a distribution diagram of the gas film thickness formed 21.6 ms after droplets of different temperatures in the present invention impact the wall surface;

[0024] Figure 3 It is a schematic diagram of a copper block embedded with a copper heating wire in the heating component of the present invention and a droplet located in a U-shaped through groove.

[0025] The reference signs in the drawings are as follows:

[0026] 1. Droplet generator; 2. Dripping tube; 3. Droplet; 4. Heating component; 5. Monochrome high-speed camera; 6. Aerogel heat insulation board; 7. LED lamp; 8. Ultra-clear glass; 9. Semi-transparent and semi-reflective mirror; 10. Color high-speed camera; 11. Metal halide lamp; 12. Infrared camera; 13. Copper block; 14. U-shaped through groove; 15. Copper heating wire. Detailed Embodiments

[0027] As Figures 1 - 2 shown, an experimental device for studying the mechanism of droplet thermal delay fusion according to the present invention specifically includes: a droplet generator 1, a droplet 3, a heating component 4, an ultra-clear glass 8, a monochrome high-speed camera 5, an LED lamp 7, a color high-speed camera 10, a metal halide lamp 11, a semi-transparent and semi-reflective mirror 9, and an infrared camera 12. The heating component 4 uses a PID (Proportional Integral Derivative) temperature control device to control its temperature. The droplet 3 is radiatively heated by the heating component 4 with a heater. Below the heating component 4, an aerogel heat insulation board 6 with a round hole is fixed. The purpose is to prevent the liquid film from being heated by the heating component 4. A circular through hole is processed on the aerogel heat insulation board 6 so that the heated droplet 3 can fall from the round hole on the aerogel heat insulation board 6.

[0028] Use transparent materials such as organic ultra-white glass 8 as the impacted wall surface to achieve the shooting of the gas film at the bottom of the droplet 3 during the impact of the droplet 3; select silicone oil as the working medium for the impact of the droplet 3 because the viscosity of silicone oil will gradually decrease when heated, that is, its fluidity will gradually increase, which can ensure its residence time in the heating component 4 and ensure the heating effect of thermal radiation.

[0029] The silicone oil droplet 3 is extruded by the droplet generator 1 (syringe), and the viscosity of the silicone oil is 200 cSt. The impact speed of the droplet 3 is changed by the distance between the droplet generator 1 and the wall surface. The side-view images taken are processed by a custom Matlab program, and the actual impact speed of the heated droplet 3 can be measured.

[0030] An infrared camera 12 (INFRATEC ImageIR 8355BBhp) is used to take the temperature image of the droplet 3 before it impacts the liquid film after heating, and the taken images are processed by a Matlab program to obtain the surface temperature of the droplet 3. By measuring the surface temperature of the droplet 3 with a thermocouple, the emissivity of the surface of the silicone oil droplet 3 taken by the infrared camera 12 is obtained. By calculating the average temperature in the central region of the surface of the droplet 3, the temperature of the heated droplet 3 can be obtained.

[0031] Two high-speed cameras are used to simultaneously shoot the impact process of the droplet 3 from the side and the bottom. The frame rate of both cameras is 5000 frames per second, and the resolution is 1024×1024 pixels. A high-speed black-and-white camera (Photron Fastcam SA-1.1) is used with a macro lens (Nikon ED AF Micro Nikkor 200 mm f / 4D) to shoot the impact image of the heated droplet 3 from the side. An LED cold light source (Hecho S5000) is used as the illumination light source. A high-speed color camera (PhotronFastcam SA-1.1) and an inverted microscope (Nikon Ti-U with 10× magnification) are used to shoot the interference fringes of the gas film during the impact process of the droplet 3 from the bottom. The color high-speed camera 10 is placed vertically and is on the same axis as the center of the droplet 3; the center of the semi-transparent and semi-reflective mirror 9 is on the same horizontal line as the metal halide lamp 11 and is at a 45-degree angle to the horizontal direction. The white light emitted by the metal halide lamp 11 passes through the semi-transparent and semi-reflective mirror 9 and reaches the bottom surface of the glass. Part of the light is reflected from the bottom surface of the glass with the glass, and the other part of the light passes through the glass and is incident on the bottom of the droplet 3 and is reflected from the bottom surface of the droplet 3. The two beams of light reflected from the glass and the bottom surface of the droplet 3 interfere to form interference fringes of different colors, pass through the semi-transparent and semi-reflective mirror 9, and then enter the color high-speed camera 10.

[0032] The heating temperature range of the heating component 4 is 30~550 °C for radiative heat transfer to the droplet 3, so as to achieve the purpose of non-contact heating of the droplet 3. The heating temperature range of the droplet 3 is 30~180 °C. Preferably, the copper block 13 embedded with the copper heating wire 15 is heated by an electric heating method. Specifically, the copper block 13 is provided with a U-shaped through groove 14, and the droplet 3 is located in the U-shaped through groove 14. The copper block 13 radiatively heats the droplet. After each experiment, the copper block 14 is moved away to avoid the continuous dropping of the droplet 3 after heating.

[0033] The Figure 1 experimental device in can obtain the interference fringes of the micron-scale gas film during the process of the heated droplet 3 impacting the wall surface. It is also necessary to extract the thickness of the micron-scale gas film from these interference fringes. The specific operation steps are as follows: An optical lens with a known curvature is used as a calibration tool. Through Figure 1 the device shown in, the interference fringes of the gas film at the bottom of the lens are photographed to obtain the interference fringes corresponding to the gas film thickness. The interference fringes are subjected to tangential averaging processing, and the gas film thickness is calculated according to the lens contour. Then, the interference fringe color is corresponded to the gas film thickness. During the processing of the real gas film at the bottom of the droplet 3, the interference image corresponding to the real gas film thickness is converted from the RGB mode to the CIE1976 mode. Its color difference is calculated by the Euclidean distance. A continuous curve can be obtained from the color difference image. This curve is composed of the points with the darkest color. Connecting these dark points can obtain the real thickness of the gas film at the bottom of the droplet 3.

[0034] Before the heated droplet 3 fuses with the wall surface, the gas at the bottom of the droplet 3 is compressed to form a dimple-shaped gas film. The thickness of the gas film has an important influence on the residence time of the droplet 3. Figure 2 After analyzing and processing the data collected by the experimental device, the gas film thickness distribution map of the droplet 3 at 21.6 ms after impacting the wall surface at different temperatures is obtained. It can be concluded from the figure that as the temperature of the droplet 3 increases, the gas film becomes thicker. A thicker gas film can hinder the fusion of the droplet 3 with the wall surface. That is, the heated droplet 3 generates a thicker gas film, which has a better rebounding effect on the fusion of the droplet 3 with the wall surface, and thus equivalently hinders the generation of the droplet 3 adhering to the wall, improving the combustion effect.

[0035] An experimental method for an experimental device for studying the thermal delay fusion mechanism of the droplet 3 includes the following experimental steps:

[0036] S1. Adjust the height of the liquid outlet end of the droplet generator 1 relative to the ultra-white glass 8, then control the droplet generator 1 to emit the droplet 3 towards the surface of the ultra-white glass 8, and first block the irregular droplets 3 falling in the early stage through a blocking component (a blocking plate is sufficient) until the droplet generator 1 discharges continuous and regular spherical droplets 3;

[0037] S2. Turn on the heating component 4 to heat the droplet 3 at the liquid outlet end of the droplet generator 1 until the heating temperature meets the experimental requirements, forming the heated droplet 3.

[0038] S4. Before the heated droplet 3 impacts the ultra-white glass 8, the infrared camera 12 takes the temperature image of the droplet 3 before it impacts the ultra-white glass 8, and the captured image is processed by the Matlab program to obtain the surface temperature of the droplet 3. Then, by calculating the average temperature of the central region on the surface of the droplet 3, the temperature of the heated droplet 3 can be obtained.

[0039] S7. When the heated droplet 3 impacts the ultra-white glass 8, the light emitted by the LED lamp 7 irradiates the impact process of the droplet 3. Then, the monochromatic high-speed camera 5 records the macroscopic morphological changes during the impact process of the droplet 3 from the side, and then processes it through a custom Matlab image processing program to obtain the actual impact speed of the heated droplet 3.

[0040] S10. When the heated droplet 3 impacts the ultra-white glass 8, the white light emitted by the metal halide lamp 11 is reflected by the semi-transparent and semi-reflective mirror 9 onto the ultra-white glass 8. Part of the light is reflected from the upper surface of the ultra-white glass 8, and the other part of the light passes through the ultra-white glass 8 and irradiates the bottom surface of the heated droplet 3, and is reflected from the bottom surface of the heated droplet 3. The two beams of light reflected from the ultra-white glass 8 and the bottom of the droplet 3 interfere to form interference fringes of different colors, pass through the semi-transparent and semi-reflective mirror 9, and then enter the color high-speed camera 10 through the plane mirror, and the interference fringes of the micron-scale air film are obtained. Then, these interference fringes are processed to obtain the true thickness curve of the air film at the bottom of the heated droplet 3.

[0041] It should be noted that in this technical solution, each component can be fixed by means of a separate bracket or the like, so as to form the positional relationship required in this technical solution. The specific support and fixing method will not be elaborated here.

[0042] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. An experimental device for studying the mechanism of thermal delayed fusion of droplets, characterized in that: The invention comprises an ultra-white glass (8), wherein a heating component (4) and a droplet generator (1) are arranged above the ultra-white glass (8), wherein the heating component (4) is used to increase the temperature of the droplets (3) when they are dripping, wherein the droplet (3) outlet end of the droplet generator (1) is located inside the heating component (4), and the droplet (3) dripping path is arranged perpendicular to the center of the ultra-white glass (8), and a monochrome high-speed camera (5), an LED light (7) and an infrared camera (12) are arranged on the outside of the side of the ultra-white glass (8), wherein the action ends of the monochrome high-speed camera (5), the LED light (7) and the infrared camera (12) are all arranged to point to the upper surface of the ultra-white glass (8), and the monochrome high-speed camera (5) is used to photograph the droplets. (3) an impact image when the droplet (3) impacts the ultra-white glass (8), the infrared camera (12) is used to monitor the temperature of the droplet (3) when it is about to impact the ultra-white glass (8), a color high-speed camera (10), a metal halide lamp (11) and a semi-transparent and semi-reflective mirror (9) are provided below the ultra-white glass (8), the semi-transparent and semi-reflective mirror (9) is arranged to be inclined at 45° toward the metal halide lamp (11), the active end of the color high-speed camera (10) and the center of the droplet (3) are on the same axis, the center of the semi-transparent and semi-reflective mirror (9) and the metal halide lamp (11) are on the same horizontal line, and the color high-speed camera (10) is used to photograph the interference fringes of the air film during the impact of the droplet (3) and the ultra-white glass (8); The working fluid in the droplet generator (1) is silicone oil; the heating component (4) heats the droplet (3) by means of thermal radiation, and uses an electric heating method to heat a copper block (13) embedded with a copper heating wire (15); the copper block (13) is provided with a U-shaped through groove (14), and the droplet (3) is located in the U-shaped through groove (14); an aerogel insulation board (6) is provided between the heating component (4) and the ultra-white glass (8), and a through hole is provided on the aerogel insulation board (6) directly below the droplet (3) for facilitating the droplet (3) to pass through.

2. The experimental method of the experimental device for studying the mechanism of thermal delayed fusion of droplets according to claim 1, characterized in that: The experimental steps include the following: S1, adjusting the height of the liquid outlet end of the droplet generator (1) relative to the ultra-white glass (8), then controlling the droplet generator (1) to emit droplets (3) toward the surface of the ultra-white glass (8), and then using a blocking component to first block the irregular droplets (3) that fall in the early stage, until the droplet generator (1) discharges continuous and regular spherical droplets (3); S2, turning on the heating component (4) to heat the droplets (3) on the liquid outlet end of the droplet generator (1) until the heating temperature meets the experimental requirements, thereby forming heated droplets (3); S3, before the heated liquid droplet (3) collides with the ultra-white glass (8), an infrared camera (12) takes a temperature image of the liquid droplet (3) before it collides with the ultra-white glass (8), and processes the image using a Matlab program to obtain the surface temperature of the liquid droplet (3), and then calculates the average temperature of the central area of ​​the surface of the liquid droplet (3), thereby obtaining the temperature of the heated liquid droplet (3); S4, when the heated droplet (3) collides with the ultra-white glass (8), the light emitted by the LED lamp (7) illuminates the impact process of the droplet (3), and then the monochrome high-speed camera (5) records the macroscopic morphological changes of the droplet (3) during the impact process from the side, and then processes it through a custom Matlab image processing program to obtain the actual impact velocity of the heated droplet (3); S5. When the heated liquid drop (3) collides with the ultra-white glass (8), the white light emitted by the metal halide lamp (11) is reflected to the ultra-white glass (8) after passing through the semi-transparent and semi-reflective mirror (9). A part of the light is reflected from the upper surface of the ultra-white glass (8), and another part of the light passes through the ultra-white glass (8) to irradiate the bottom surface of the heated liquid drop (3), and is reflected from the bottom surface of the heated liquid drop (3). The two beams of light reflected from the ultra-white glass (8) and the bottom of the liquid drop (3) interfere with each other to form interference fringes of different colors, which pass through the semi-transparent and semi-reflective mirror (9), and then pass through the plane mirror to enter the color high-speed camera (10), and obtain interference fringes of the micron-level air film. The interference fringes are then processed to obtain a true thickness curve of the air film at the bottom of the heated liquid drop (3); Wherein, in step S5, the method for obtaining the air film thickness curve at the bottom of the heated droplet (3) is: An optical lens with a known curvature is used as a calibration tool. The interference fringes of the air film at the bottom of the optical lens are obtained by photographing, and the interference fringes corresponding to the thickness of the air film are obtained. The interference fringes are then averaged tangentially, and the thickness of the air film is calculated based on the contour of the optical lens. Then, the color of the interference fringes is matched with the thickness of the air film. During the processing of the real air film at the bottom of the droplet (3), the interference image of the real air film thickness is converted from the RGB mode to the CIE1976 mode, and its color difference is calculated by the Euclidean distance. From the color difference image, a continuous curve can be obtained. The curve is composed of the darkest points. By connecting these dark points, the real thickness curve of the air film at the bottom of the droplet (3) can be obtained.

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