Experimental device and method for researching thermal delay fusion mechanism of liquid drops

Abstract

The invention discloses an experimental device and method for researching a droplet thermal delay fusion mechanism, and belongs to the technical field of droplet impact fusion research. Comprising ultra-white glass, a heating assembly and a liquid drop generator are arranged above the ultra-white glass, the heating assembly is used for increasing the temperature when liquid drops drop, the liquid drop outlet end of the liquid drop generator is located in the heating assembly, and the dropping path of the liquid drops is perpendicular to the center of the ultra-white glass. A single-color high-speed camera, an LED lamp and an infrared camera are arranged outside the side face of the ultra-white glass, the acting ends of the single-color high-speed camera, the LED lamp and the infrared camera all point to the upper surface of the ultra-white glass, and the single-color high-speed camera is used for shooting impact images generated when liquid drops impact the ultra-white glass. And the infrared camera is used for monitoring the temperature of the liquid drops when the liquid drops are about to collide with the ultra-white glass. The technical scheme is used for researching the influence of the liquid drop temperature on the thickness of the formed gas film, and provides guidance for application of spray combustion.

Description

Technical Field

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

[0002] The dynamics study of a single fuel droplet impact plays a vital role in the design and optimization of the internal combustion engine fuel injection system. When the droplet hits the wall, a very thin air film will be squeezed at the bottom of the droplet, causing the fuel droplet to rebound after hitting the wall oil film. This rebound prevents the generation of more fuel droplets attached 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 study of droplet impact fusion, the study of the thickness of the air film at the bottom of the droplet is particularly important, as it can change the fusion process of the droplets 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 droplet impacting the wall, the thickness of the air film during the impact fusion process is affected by many factors, such as internal pressure, droplet diameter, and droplet temperature. The prior art has already conducted some research on the effects of internal pressure and droplet diameter on the thickness of the air film, but there are few studies on the effects of droplet temperature on the thickness of the air film during the impact fusion process. At the same time, most of the experimental devices in the prior art can only study the macroscopic phenomenon of droplet impact, and it is difficult to analyze the microscopic air 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 thermal delayed fusion of droplets, so as to study the influence of droplet temperature on the thickness of formed gas film and provide theoretical guidance for the application of spray combustion.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention discloses an experimental device for studying the mechanism of thermal delayed fusion of droplets, comprising ultra-white glass. A heating component and a droplet generator are arranged above the ultra-white glass. The heating component is used to increase the temperature of the droplets when they fall. The droplet outlet end of the droplet generator is located inside the heating component, and the droplet falling path is arranged perpendicular to the center of the ultra-white glass. A monochrome high-speed camera, an LED lamp and an infrared camera are arranged outside the side of the ultra-white glass. The action ends of the monochrome high-speed camera, the LED lamp and the infrared camera are all arranged to point to the upper surface of the ultra-white glass. The monochrome high-speed camera is used to shoot an impact image when the droplets hit the ultra-white glass. The infrared camera is used to monitor the temperature of the droplets when they are about to hit the ultra-white glass. A color high-speed camera, a metal halide lamp and a semi-transparent and semi-reflective mirror are arranged below the ultra-white glass. The semi-transparent and semi-reflective mirror is inclined 45 degrees toward the metal halide lamp. The action end of the color high-speed camera and the center of the droplet are on the same axis, the center of the semi-transparent and semi-reflective mirror and the metal halide lamp are on the same horizontal line, and the color high-speed camera is used to shoot interference fringes of an air film during the impact of the droplet with the ultra-white glass.

[0006] Furthermore, an aerogel insulation board is provided between the heating component and the ultra-white glass, and a through hole is provided on the aerogel insulation board directly below the liquid droplet to facilitate the liquid droplet to pass through.

[0007] Furthermore, the heating component heats the droplets by means of thermal radiation.

[0008] Furthermore, the working fluid in the droplet generator is silicone oil.

[0009] An experimental method for an experimental device for studying the mechanism of thermal delayed fusion of droplets, comprising the following experimental steps: S1. Adjust the height of the liquid outlet end of the droplet generator relative to the ultra-white glass, then control the droplet generator to emit droplets toward the surface of the ultra-white glass, and then use the blocking component to block the irregular droplets falling in the early stage until the droplet generator discharges continuous and regular spherical droplets; S2, turning 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, thereby forming heated droplets; S3, before the heated droplet collides with the ultra-white glass, an infrared camera takes a temperature image of the droplet before it collides with the ultra-white glass, and the captured image is processed by a Matlab program to obtain the surface temperature of the droplet, and then the average temperature of the central area of ​​the droplet surface is calculated to obtain the temperature of the heated droplet; S4. When the heated droplet collides with the ultra-white glass, the light emitted by the LED lamp illuminates the droplet impact process, and then a monochrome high-speed camera records the macroscopic morphological changes of the droplet 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; S5. When the heated droplet collides with the ultra-white glass, the white light emitted by the metal halide lamp is reflected to the ultra-white glass after passing through the semi-transparent and semi-reflective mirror. Part of the light is reflected from the upper surface of the ultra-white glass, and the other part of the light passes through the ultra-white glass to illuminate 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-white glass and the bottom of the droplet interfere to form interference fringes of different colors, which pass through the semi-transparent and semi-reflective mirror, and then pass through the plane mirror to enter the color high-speed camera, and obtain the interference fringes of the micron-level air film, which are then processed to obtain the true thickness curve of the air film at the bottom of the heated droplet.

[0010] Further, in step S5, the method for obtaining the air film thickness curve at the bottom of the heated droplet is: An optical lens with known curvature is used as a calibration tool. The interference fringes of the air film at the bottom of the lens are obtained by photographing, and the interference fringes corresponding to the thickness of the air film are obtained. The interference fringes are then tangentially averaged, and the thickness of the air film is calculated based on the lens contour. Then, the color of the interference fringes is corresponded to the thickness of the air film. In the process of processing the real air film at the bottom of the droplet, the interference image of the real air film thickness is converted from the RGB mode to the CIE1976 mode, and the color difference is calculated by the Euclidean distance. A continuous curve can be obtained from the color difference image. 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 can be obtained.

[0011] The beneficial effects of the present invention are: The present invention proposes an experimental device that can simultaneously obtain the macroscopic contours of millimeter-level droplets and the microscopic morphology of micrometer-level air films during the process of delayed thermal fusion of droplets, realize experimental measurements of millimeter-level droplets and micrometer-level air films at different time and space scales, obtain the flow, heat and mass transfer laws in the air film, reveal the rupture mechanism of the air film at the bottom of the droplet, and finally realize the regulation of delayed thermal 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 air film during delayed thermal fusion of droplets, and ultimately provide theoretical guidance for the application of spray combustion.

[0012] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration: Figure 1 It is a schematic plan view of the experimental device of the present invention; Figure 2 This is the distribution diagram of the gas film thickness formed 21.6 ms after the droplets of different temperatures hit the wall in the present invention; Figure 3 It is a schematic diagram of a copper heating wire embedded in a copper block in a heating assembly of the present invention and a liquid droplet located in a U-shaped through groove.

[0014] The following are marked in the accompanying drawings: 1. Droplet generator; 2. Droplet tube; 3. Droplet; 4. Heating component; 5. Monochrome high-speed camera; 6. Aerogel insulation board; 7. LED lamp; 8. Ultra-white 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 groove; 15. Copper heating wire. DETAILED DESCRIPTION

[0015] like Figure 1~Figure 2 As shown, the present invention is an experimental device for studying the mechanism of delayed thermal fusion of droplets. The specific device components include: a droplet generator 1, a droplet 3, a heating component 4, an ultra-white 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 radiantly heated by the heating component 4. Under the heating component 4, an aerogel insulation board 6 with a circular 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 insulation board 6 so that the heated droplet 3 can fall from the circular hole on the aerogel insulation board 6.

[0016] Transparent materials such as organic ultra-white glass 8 are used as the impacted wall surface to achieve the capture of the air film at the bottom of the droplet 3 during the impact of the droplet 3; silicone oil is selected as the working medium for the impact of the droplet 3, because the viscosity of the silicone oil will gradually decrease when heated, that is, the fluidity will gradually increase, thereby ensuring its residence time in the heating component 4 and ensuring the heating effect of thermal radiation.

[0017] Silicone oil droplets 3 are squeezed out through the droplet generator 1 (syringe), and the viscosity of the silicone oil is 200 cSt. The impact velocity of the droplet 3 is changed by the distance between the droplet generator 1 and the wall surface. The side view image taken is processed by a custom Matlab program to measure the actual impact velocity of the heated droplet 3.

[0018] An infrared camera 12 (INFRATEC ImageIR 8355BBhp) was used to capture the temperature image of the heated droplet 3 before it hit the liquid film, and the captured image was processed by a Matlab program to obtain the surface temperature of the droplet 3. The surface temperature of the droplet 3 was measured by a thermocouple, and the emissivity of the surface of the silicone oil droplet 3 captured by the infrared camera 12 was obtained. The temperature of the droplet 3 after heating can be obtained by calculating the average temperature of the central area of ​​the surface of the droplet 3.

[0019] Two high-speed cameras were used to simultaneously capture the impact process of droplet 3 from the side and bottom. The frame rate of both cameras was 5000 frames / s and the resolution was 1024×1024 pixels. A high-speed black-and-white camera (Photron Fastcam SA-1.1) was used with a macro lens (Nikon ED AF Micro Nikkor 200 mm f / 4D) to capture the impact image of heated droplet 3 from the side. An LED cold light source (Hecho S5000) was 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) were used to capture the interference fringes of the air film during the impact process of droplet 3 from the bottom. The color high-speed camera 10 was placed vertically and on the same axis as the center of droplet 3; the center of the semi-transparent and semi-reflective mirror 9 was on the same horizontal line as the metal halide lamp 11 and 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. A part of the light is reflected from the bottom surface with the glass, and the other part of the light passes through the glass and enters 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 with each other 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.

[0020] The heating temperature range of the heating component 4 is 30~550°C, which is used for radiant heat transfer to the droplet 3, thereby achieving the purpose of non-contact heating of the droplet 3. The heating temperature range of the droplet 3 is 30~180°C. Preferably, an electric heating method is used to heat the copper block 13 embedded with the copper heating wire 15. Specifically, the copper block 13 has a U-shaped groove 14, and the droplet 3 is located in the U-shaped groove 14. The copper block 13 radiates heat to the droplet. After each experiment, the copper block 14 is removed to avoid the droplet 3 from continuing to fall after being heated.

[0021] use Figure 1 The experimental device in the figure can obtain the interference fringes of the micron-level air film during the impact of the heated droplet 3 on the wall. It is also necessary to extract the thickness of the micron-level air film through the interference fringes. The specific operation steps are: use an optical lens with a known curvature as a calibration tool, and Figure 1 The device shown captures the interference fringes of the air film at the bottom of the lens, and obtains the interference fringes corresponding to the thickness of the air film. The interference fringes are tangentially averaged, and the thickness of the air film is calculated based on the lens profile. Then, the color of the interference fringes is matched to the thickness of the air film. During the processing of the real air film at the bottom of the droplet 3, the interference image with the real air film thickness is converted from the RGB mode to the CIE1976 mode. The color difference is calculated by the Euclidean distance. From the color difference image, a continuous curve can be obtained, which is composed of the darkest points. By connecting these dark points, the real thickness of the air film at the bottom of the droplet 3 can be obtained.

[0022] Before the heated droplet 3 merges with the wall, the gas at the bottom of the droplet 3 is compressed to form a dimple-shaped air film. The thickness of the air 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 distribution diagram of the air film thickness 21.6 ms after the droplet 3 hits the wall at different temperatures is obtained. From the figure, it can be concluded that as the temperature of the droplet 3 increases, the air film becomes thicker, and a thicker air film can hinder the fusion of the droplet 3 with the wall. That is, the heated droplet 3 produces a thicker air film, which has a better rebound effect on the fusion of the droplet 3 and the wall, which is equivalent to hindering the generation of droplets 3 attached to the wall and improving the combustion effect.

[0023] An experimental method for an experimental device for studying the mechanism of thermal delayed fusion of droplets 3, comprising the following experimental steps: S1, adjusting the height of the liquid outlet end of the droplet generator 1 relative to the ultra-white glass 8, and then controlling the droplet generator 1 to emit droplets 3 toward the surface of the ultra-white glass 8, and then blocking the irregular droplets 3 falling in the early stage by a blocking component (blocking plate), 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 droplet 3 collides with the ultra-white glass 8, the infrared camera 12 takes a temperature image of the droplet 3 before it collides with the ultra-white glass 8, and processes the image through the Matlab program to obtain the surface temperature of the droplet 3, and then calculates the average temperature of the central area of ​​the surface of the droplet 3, that is, the temperature of the heated droplet 3 can be obtained; 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 speed of the heated droplet 3; S5. When the heated droplet 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. 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 to irradiate 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, 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 the interference fringes of the micron-level air film, and then process the interference fringes to obtain the true thickness curve of the air film at the bottom of the heated droplet 3.

[0024] It should be noted that each component in the present technical solution can be fixed by a separate bracket or the like, thereby forming the positional relationship required in the present technical solution. The specific support and fixing method will not be described in detail here.

[0025] 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 it. 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 arranged below the ultra-white glass (8), the semi-transparent and semi-reflective mirror (9) is arranged to be inclined at 45 degrees 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).

2. The experimental device for studying the mechanism of thermal delayed fusion of droplets according to claim 1, characterized in that: 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 liquid droplet (3) to facilitate the liquid droplet (3) to pass through.

3. The experimental device for studying the mechanism of delayed thermal fusion of droplets according to claim 1, characterized in that: The heating component (4) heats the droplets (3) by means of thermal radiation.

4. The experimental device for studying the mechanism of thermal delayed fusion of droplets according to claim 1, characterized in that: The working fluid in the droplet generator (1) is silicone oil.

5. An experimental method for an experimental device for studying the mechanism of delayed thermal fusion of droplets according to any one of claims 1 to 4, 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). 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) 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 the interference fringes of the micron-level air film. The interference fringes are then processed to obtain the true thickness curve of the air film at the bottom of the heated liquid drop (3).

6. The experimental method of the experimental device for studying the mechanism of thermal delayed fusion of droplets according to claim 5, characterized in that: In step S5, the method for obtaining the air film thickness curve at the bottom of the heated droplet (3) is as follows: 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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