Calculation Method for Discriminating Liquid Fuel Spray Region and Transient Evaporation Rate Based on Ballistic Light Imaging

Abstract

The present invention proposes a method for discriminating the spray region of liquid fuel and calculating the transient evaporation amount based on ballistic light imaging, which relates to the field of spray measurement and calculation of internal combustion engines; the method for discriminating the spray region of liquid fuel in the present invention mainly includes the division of the liquid column region and the droplet region; the method for calculating the transient evaporation amount of liquid fuel in the present invention mainly includes the calculation of the liquid phase mass in the liquid column region, the calculation of the liquid phase mass in the droplet region and the calculation of the total fuel injection amount, and finally obtains the transient evaporation amount during the liquid fuel spray process; compared with the existing technology, the present invention does not need to set temperature and pressure sensors, nor does it need to obtain the droplet velocity. In addition to obtaining conventional parameters such as spray cone angle and penetration distance, it can also simply and accurately obtain the states of the spray liquid column and droplet region, as well as the instantaneous evaporation amount of the spray.

Description

Technical Field

[0001] The present invention relates to the technical field of measuring the transient evaporation process during fuel spraying, and in particular to a discriminant calculation method for judging the transient spraying process of liquid fuel by ballistic light imaging. Background Art

[0002] The power of motor vehicles in China mainly relies on internal combustion engines, consuming a large amount of fossil fuels. In 2019, China's dependence on foreign oil rose to 70%. Diesel engines emit a large amount of NO x , particulate matter and other emissions, which cause great harm to the environment and human health. These pollutants can be controlled by improving spray combustion, thereby contributing to alleviating the energy crisis and environmental problems. The combustion of fuels with different components is also different. Therefore, it is necessary to carry out research on the fuel spraying process. The calculation of the instantaneous evaporation amount of fuel spraying helps to evaluate the formation effect of the mixture.

[0003] Previously, high-speed microphotography was mostly used to observe the near-field area of the spray. However, with the application of technologies such as high supercharging and high injection pressure in internal combustion engines, the in-cylinder pressure and temperature of internal combustion engines have been continuously increasing. The ambient pressure and temperature when hydrocarbon fuels are injected into the cylinder have exceeded the critical pressure and temperature of most hydrocarbon fuels and ambient gases, and the fuel reaches the supercritical state. Therefore, conventional optical measurement methods cannot obtain effective information on the liquid core of the spray. Ballistic light imaging can obtain the liquid core information of the actual spray near-field area through methods such as spatial filtering and time gating.

[0004] Compared with the existing technologies, the present invention does not require setting temperature and pressure sensors, nor obtaining the droplet velocity. In addition to obtaining conventional parameters such as spray cone angle and penetration distance, it can also simply and accurately obtain the state of the spray liquid column and droplet area, as well as the mass of the spray liquid column area, the mass of the spray droplet area, and the instantaneous evaporation amount of the spray. Summary of the Invention

[0005] Aiming at the deficiencies in the prior art, the present invention proposes a discriminant method for the spray area of liquid fuel based on ballistic light imaging and a calculation method for the transient evaporation amount. The fuel spray image is captured by a ballistic light imaging device, the spray area is discriminated according to the discriminant method proposed by the invention, and the instantaneous evaporation amount of the spray is calculated according to the calculation method proposed by the invention, so as to calculate the instantaneous evaporation amount during the spray process.

[0006] The technical solution of the present invention is as follows: A discriminant and transient evaporation amount calculation method for the spray area of liquid fuel based on ballistic light imaging, comprising the following steps:

[0007] Step 1: Use a ballistic light imaging device to obtain the spray image of the liquid fuel; Step 2: Use the gray function processing method and the curvature optimization method to divide the captured spray image into a liquid column area and a droplet area; Step 3: Calculate the transient evaporation amount based on the spray image after the area division is completed.

[0008] Further, the specific process of Step 2 is as follows:

[0009] Step 2.1: Use a ballistic light imaging device to obtain the spray field imaging picture, denoted as T;

[0010] Step 2.2: Preprocess the image T; for the preprocessing of the image T, use the clipping algorithm in the matlab toolbox to remove the invalid black border; use the maximum value method to grayscale the image T, and select the maximum value of the three-component brightness in the RGB image as the grayscale value; further use the Gaussian filtering method to remove the image noise, and the processed image is denoted as T1;

[0011] Step 2.3: Further set a threshold to perform binary processing on the image; the pixel points with a grayscale value greater than the threshold are regarded as interference elements and deleted; the area with a grayscale value of 0 is regarded as the ambient gas and deleted, and the processed image is denoted as T2;

[0012] Step 2.4: Calculate the gray function I = f(x, y) of the image T2, where x and y are the horizontal and vertical coordinates of the image respectively, and I is the grayscale value at the image coordinate (x, y);

[0013] Step 2.5: Based on the grayscale values of each pixel point of the image T2 obtained in Step 2.4, form a grayscale matrix; use the contour analysis algorithm to screen the contour lines of the liquid column area in the image T2; the contour analysis algorithm is to perform liquid column contour feature discrimination on the grayscale matrix from the axis of the liquid column area to both sides, and initially divide the area where the grayscale value drops steeply into the contour lines of the liquid column or droplet;

[0014] Step 2.6: Based on the contour lines of the liquid column or droplet initially divided in Step 2.5, use the curvature optimization method for further precise division; the curvature optimization method is to perform optimization using a square grid with a side length of E millimeters on both sides of the initially divided contour line; E = 10d0; d0 is the initial value of the droplet diameter assumed based on experience;

[0015] Step 2.7: Further divide the contour lines of the liquid column or droplet with J square grids with a side length of E millimeters, and calculate the curvature radius of each figure within these J square grids;

[0016] When calculating the curvature radius of each figure in the jth (j = 1, 2, 3... J) grid, it is necessary to first calculate the average curvature radius of the figure near the jth grid;

[0017] Step 2.9: The steps for calculating the average curvature radius of the figure near the jth grid are as follows: randomly select 10 square units with a side length of E mm in a semicircle with the jth grid as the center and a radius of 5E; calculate the average curvature radius of the droplets in these 10 units (repeat the calculation 12 times to reduce the error); further calculate the average curvature radius of these 120 units and standard deviation s, then the standard error Assume that the significance level α is set to 0.05, and check the normal distribution z value table to know that the standard score z = 1.96; then the confidence interval is

[0018] Step 2.10: Calculate the curvature radius of each figure in the jth (j=1,2,3…J) grid

[0019] Step 2.11: Set the J grids with a curvature radius greater than further connect all the marked graphics and record them as the contour line of the liquid column area;

[0020] Step 2.12: At this point, the contour line of the droplet area is divided. The area inside the contour line is the liquid column area, recorded as L; the area outside the contour line is the droplet area, recorded as K.

[0021] Further, in step 2.10:

[0022] When the curvature radius of each shape in the grid All less than When , it is considered that the grid is located in the droplet area;

[0023] When there is a curvature radius of a graphic in the grid Greater than When , the grid is considered to be located in the liquid column area;

[0024] Further, the specific process of step 3 is:

[0025] Step 3.1: Calculate the instantaneous fuel mass M0 based on the fuel injection law;

[0026] Step 3.2: Calculate the liquid phase mass in the spray column region; Denote the nozzle as point a, the demarcation line as point b, and the spray end as point c; Denote the mass of the liquid phase fuel in the spray column region as M1; The fuel temperature at the nozzle is close to room temperature, and the fuel temperature in the liquid column region is close to the ambient gas temperature. Then denote the density of the liquid phase fuel at the nozzle as ρ1, and the density at the end of the liquid column region as ρ2. After weighted processing of the overall density of the liquid column, it is ρ = 2 / 3ρ1 + ρ2; The fuel density in the droplet region is the density of the fuel at the ambient gas temperature; Fit the spray contour line in the spray column region to f(x) through the matlab program, then

[0027] Step 3.3: Divide the droplet region into grids. Divide the droplet region into m sub-regions with a side length of E millimeters, and use m i to represent the i-th sub-region, and η i to represent the number of droplets in the i-th sub-region, and d i to represent the average diameter of the droplets in the i-th sub-region (i = 1…m);

[0028] The average number of droplets in the m sub-regions of the droplet region

[0029] The volume average diameter of the droplets in the m sub-regions of the droplet region is

[0030] Step 3.4: Convert the volume average diameter of the droplets into the volume V of the droplets through the relationship between gravitational acceleration and surface tension m ,

[0031] where α, β are constants, and γ is the surface tension;

[0032] Step 3.5: Fit the spray contour line in the droplet region to g(x) through the matlab program; The volume of a grid cube is E 3 ; Further, the number of grids in the droplet region is

[0033] Step 3.6: The liquid phase mass in the droplet region is M2 = ρNηV m ;

[0034] Step 3.7: The transient evaporation amount M of the liquid fuel e = M0 - M1 - M2.

[0035] Furthermore, the ballistic light imaging device includes: a femtosecond laser, a beam splitter, a frequency doubler, a band-pass filter 1, a mirror 1, a constant volume bomb, a mirror 2, a lens 1, a polarizer 1, a dichroic mirror, an optical Kerr medium, a band-pass filter 2, a polarizer 2, a lens 2, and a high-speed camera;

[0036] The optical path of the ballistic light imaging device is a femtosecond laser, which outputs laser pulses. After passing through a frequency amplifier, the beam splitter divides the laser pulses into a switching beam and an imaging beam; the ratio of the two beams is 7:3; the imaging beam is converted to 400 nm after passing through a frequency doubler; the frequency doubler is a barium metaborate crystal; the imaging beam passes through a band - pass filter 1 and then passes through a mirror 1 to pass through a constant - volume combustion bomb to obtain spray field information; there is an elliptical quartz glass window on each side of the cavity of the constant - volume bomb; after the imaging beam obtains the spray field information, it passes through a mirror 2, a lens 1, a polarizer 1 and a dichroic mirror and then converges with the switching beam in a Kerr medium; the lens 1 plays a role in spatial filtering; the polarizer 1 plays a role in polarization filtering; the Kerr medium is filled with CS2 liquid; the CS2 liquid is an isotropic transparent liquid when no switching beam passes through; when a switching beam passes through, the dipole moment of CS2 molecules is arranged along the polarization direction of the switching beam under the strong electromagnetic field of the laser pulse, causing the CS2 liquid to produce the Kerr effect and twist the polarization of the imaging beam; using the Kerr effect, ballistic photons can be separated from the imaging beam; the imaging beam passes through a band - pass filter 2, a polarizer 2 and a lens 2 and then irradiates a high - speed camera.

[0037] Furthermore, the femtosecond laser outputs laser pulses with a wavelength of 800 nm, a pulse width of 100 fs, a single - pulse energy of 4 mJ, and a frequency of 1000 Hz.

[0038] Furthermore, the effective pixels of the high - speed camera are 1024×1024, the camera shutter time is 100 μs, and the acquisition time is 1 ms ASOI.

[0039] The beneficial effects of the present invention are as follows:

[0040] Compared with the existing technology, the present invention does not need to set temperature and pressure sensors, nor does it need to obtain the droplet velocity. In addition to obtaining conventional parameters such as spray cone angle and penetration distance, it can also simply and accurately obtain the state of the spray liquid column and droplet area, as well as the instantaneous evaporation amount of the spray. Description of the Drawings

[0041] Figure 1 is the ballistic light imaging device

[0042] Figure 2 is the schematic diagram of the division of the spray area

[0043] Figure 3 is the flow chart of the spray area discrimination

[0044] Figure 4 is the flow chart of the calculation of the transient evaporation amount Detailed Embodiments

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0046] Both the discrimination method and the calculation method of the present invention are based on a ballistic light imaging device. Ballistic light imaging means using the optical Kerr effect to image the acquired ballistic photons; ballistic photons are photons that are not scattered and maintain their original propagation direction, containing information about the liquid core; clear images of the spray can be obtained.

[0047] Such as Figure 1 , the ballistic light imaging device mainly includes a femtosecond laser, a frequency amplifier, a beam splitter, a frequency doubler, band-pass filter 1, band-pass filter 2, a constant volume bomb, lens 1, lens 2, polarizer 1, polarizer 2, a dichroic mirror, an optical Kerr medium, and a high-speed camera.

[0048] The constant volume bomb increases the high-pressure air with stable flow through an external air compressor; the high-pressure air flows vertically through the inside of the constant volume bomb after being heated by an electric heating wire; the pressure inside the constant volume bomb is composed of high-pressure air and can reach up to 9 MPa; the temperature inside the constant volume bomb can reach up to 900 K; there is an elliptical quartz glass window on each side of the cavity of the constant volume bomb; the lens plays a role in spatial filtering of the light beam; the polarizer plays a role in polarizing filtering of the light beam; the effective pixels of the high-speed camera are 1024×1024, the shutter time is 100 us, and the acquisition time is 1 ms ASOI.

[0049] The optical path propagation of the ballistic light imaging device is that the femtosecond laser outputs a laser pulse with a wavelength of 800 nm, a pulse width of 100 fs, a single pulse energy of 4 mJ, and a frequency of 1000 Hz; the beam splitter divides the laser pulse into a switching beam and an imaging beam, and the ratio of the two beams is 7:3; the imaging beam is converted to 400 nm after passing through the frequency doubler; the frequency doubler is a barium metaborate crystal; the imaging beam passes through the constant volume combustion bomb after frequency doubling and converges with the switching beam in the optical Kerr medium; the optical Kerr medium is filled with CS2 liquid; the CS2 liquid is an isotropic transparent liquid when no switching beam passes through; when a switching beam passes through, the dipole moments of CS2 molecules are arranged along the polarity direction of the switching beam under the strong electromagnetic field of the laser pulse, causing the CS2 liquid to generate the Kerr effect and twist the polarity of the imaging beam; the optical Kerr effect can separate the ballistic photons from the imaging beam; the imaging beam directly irradiates the high-speed camera after passing through lens 2.

[0050] Such as Figures 2-4 , after obtaining the spray image, it is necessary to first discriminate the liquid fuel spray area and divide the spray into a liquid column area and a droplet area. The spray area discrimination method is as follows:

[0051] Step 1: Use the ballistic light imaging device to obtain an imaging picture of the spray field, denoted as T.

[0052] Step 2: Preprocess the image T; for the preprocessing of the image T, use the clipping algorithm in the matlab toolbox to remove the invalid black borders; use the maximum value method to perform grayscale processing on the image T, and select the maximum value of the three-component brightness in the RGB image as the grayscale value; further use the Gaussian filtering method to remove image noise, and the processed image is denoted as T1;

[0053] Step 3: Further set a threshold to perform binary processing on the image, regard the pixel points with grayscale values greater than the threshold as interference elements and delete them, and regard the pixel points with grayscale value of 0 as the ambient gas and delete them; the processed image is denoted as T2;

[0054] Step 4: Calculate the grayscale function I = f(x, y) of the image T2, where x and y are the horizontal and vertical coordinates of the image respectively, and I is the grayscale value at the image coordinate (x, y);

[0055] Step 5: Based on Step 4, obtain the grayscale values of each pixel point of the image T2 to form a grayscale matrix; use the contour analysis algorithm to screen the contour lines of the liquid column area in the image T2; the contour analysis algorithm is to perform liquid column contour feature discrimination on the grayscale matrix from the axis of the column area to both sides; the liquid column contour feature discrimination is to initially divide the area where the grayscale value drops steeply into the contour lines of the liquid column or liquid droplet;

[0056] Step 6: Based on the contour lines of the liquid column or liquid droplet initially divided in Step 5, use the curvature optimization method for further precise division; the curvature optimization method is to perform optimization using a square grid with a side length of E millimeters on both sides of the initially divided contour line; E = 10d0; d0 is the initial value of the liquid droplet diameter assumed based on experience; taking diesel as an example, the initial value range of the liquid droplet diameter of diesel spray is 80 - 120 μm, and in this implementation case, d0 = 100 μm is selected.

[0057] Step 7: Further divide the contour lines of the liquid column or liquid droplet with J square grids with a side length of E millimeters, and calculate the curvature radius of each figure within these J square grids;

[0058] Step 8: When calculating the curvature radius of each figure in the j-th (j = 1, 2, 3... J) grid, it is necessary to first calculate the average curvature radius of the figure near the j-th grid;

[0059] Step 9: The calculation steps of the average curvature radius of the figure near the j-th grid are as follows: randomly select 10 square units with a side length of E millimeters within a semi-circle with a radius of 5E centered on the j-th grid; calculate the average curvature radius of the liquid droplets within these 10 units (repeat the calculation 12 times to reduce errors); further calculate the average value of the curvature radii of these 120 units and the standard deviation s, then the standard error Let the significance level α be set to 0.05. Looking up the table, the standard score z = 1.96; then the confidence interval is

[0060] Step 10: Calculate the radius of curvature of each figure within the j-th (j = 1, 2, 3... J) grid When the radius of curvature of each figure in the grid is less than at this time, it is considered that the position where the grid is located is the droplet area; when there is a figure in the grid whose radius of curvature is greater than at this time, it is considered that the position where the grid is located is the liquid column area;

[0061] Step 11: Mark the figures with a radius of curvature greater than in the J grids in Step 7; further connect all the marked figures, which is denoted as the contour line of the liquid column area;

[0062] Step 12: So far, the division of the droplet area contour line is completed. The area inside the contour line is the liquid column area, denoted as L; the area outside the contour line is the droplet area, denoted as K;

[0063] After the spray area is discriminated, the calculation method of the transient evaporation amount of the liquid fuel spray of the present invention can calculate the transient evaporation amount of the liquid fuel spray at different times; mainly including fuel injection mass calculation and liquid phase mass calculation; the difference between the fuel injection mass and the liquid phase mass is the transient evaporation amount;

[0064] Step 13: The fuel injection mass calculation is to calculate the mass of the fuel instantaneously ejected based on the fuel injection law, denoted as M0;

[0065] Step 14: The liquid phase mass calculation includes the liquid phase mass in the liquid column area and the liquid phase mass in the droplet area; the calculation method of the liquid phase mass in the liquid column area L is to rotate the liquid column area L around the axis with the nozzle center as the axis to obtain a rotating body; denote the nozzle as a, the dividing line as b, and the spray end as c;

[0066] Denote the mass of the liquid phase fuel in the spray column area as M1; the fuel temperature at the nozzle is close to room temperature, and the fuel temperature in the liquid column area is close to the ambient gas temperature. Then denote the density of the liquid phase fuel at the nozzle as ρ1, and the density at the end of the liquid column area as ρ2. After weighted processing of the overall density of the liquid column, it is ρ = 2 / 3ρ1 + ρ2; the fuel density in the droplet area is the fuel density at the ambient gas temperature, ρ2; fit the spray contour line in the spray column area to f(x) through the matlab program, then

[0067] Step 15: The method for calculating the liquid phase mass in the droplet region K is to rotate the droplet region K around the axis to obtain a rotating body. Further, the droplet region is divided into grids, and the droplet region is divided into m sub-regions with a side length of E millimeters. Use m i to represent the i-th sub-region, and η i to represent the number of droplets in the i-th sub-region, and d i to represent the average diameter of the droplets in the i-th sub-region (i = 1…m). Further, calculate the average number of droplets in the droplet region K Further, calculate the volume average diameter of the droplets in the droplet region Ki as d vm , then

[0068] Step 16: Further, convert the volume average diameter of the droplets into the volume V of the droplets through the relationship between the gravitational acceleration and the surface tension m , where α and β are constants, and γ is the surface tension of the droplet; the surface tension of the droplet can be measured by a surface tensiometer;

[0069] Step 17: Further, calculate the number of grids in the droplet region K; fit the spray contour line of the droplet region to g(x) through a matlab program; the volume of a grid cube is E 3 ; Further, the number of grids in the droplet region is

[0070] Step 18: Further, calculate the liquid phase mass M2 in the droplet region K, M2 = ρ2NηV m ;

[0071] Step 19: The transient evaporation amount M of the liquid fuel e = M0 - M1 - M2;

[0072] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made according to the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A method for discriminating the spray area of liquid fuel and calculating the transient evaporation rate based on ballistic light imaging, characterized in that, The following steps are involved: Step 1: Use a ballistic light imaging device to obtain a spray image of a liquid fuel; Step 2: Use a grayscale function processing method and a curvature optimization method to divide the captured spray image into a liquid column area and a droplet area; Step 3: Calculate the transient evaporation amount based on the spray image after area division; The specific process of step 2 is: Step 2.1: Use the ballistic light imaging device to obtain the spray field imaging picture, denoted as T; Step 2.2: Preprocess the image T; the image T is preprocessed by using the shearing algorithm in the matlab toolbox to remove the invalid black border; the image T is grayed by using the maximum value method, and the maximum value of the three-component brightness in the RGB image is selected as the gray value; the image noise is further removed by using the Gaussian filter method, and the processed image is recorded as T1; Step 2.3: Further set the threshold and perform binarization on the image; pixels with grayscale values ​​greater than the threshold are considered as interference elements and deleted; The area with gray value of 0 is regarded as the atmosphere, which is deleted and the processed image is recorded as T2; Step 2.4: Calculate the grayscale function I=f(x,y) of image T2, where x and y are the horizontal and vertical coordinates of the image, respectively, and I is the grayscale value at the image coordinate (x,y); Step 2.5: Based on step 2.4, the grayscale value of each pixel point of image T2 is obtained to form a grayscale matrix; the contour analysis algorithm is used to screen the contour line of the liquid column area in image T2; the contour analysis algorithm is to distinguish the liquid column contour features from the axis of the liquid column area to the grayscale matrix on both sides, and preliminarily divide the area where the grayscale value drops sharply into the contour line of the liquid column or droplet; Step 2.6: Based on the contour line of the liquid column or liquid droplet preliminarily divided in step 2.5, further precise division is performed using the curvature optimization method; the curvature optimization method is to use a square grid with a side length of E mm to perform optimization on both sides of the preliminarily divided contour line; E = 10d0; d0 is the initial value of the droplet particle size based on empirical assumptions; Step 2.7: further dividing the contour of the liquid column or droplet into J square grids with a side length of E mm, and calculating the radius of curvature of each figure in the J square grids; Step 2.8: When calculating the curvature radius of each figure in the jth grid, where j = 1, 2, 3 ... J; the average curvature radius of the figures near the jth grid must be calculated first; Step 2.9: The calculation steps for the average radius of curvature of the figure near the j-th grid are as follows: Randomly select 10 square cells with a side length of E millimeters within a semi-circle with the j-th grid as the center and a radius of 5E; Calculate the average radius of curvature of the droplets within these 10 cells, and repeat the calculation 12 times to reduce errors; Further calculate the average value of the radius of curvature of these 120 cells and the standard deviation s, then the standard error Set the significance level α to 0.

05. Looking up the standard normal distribution z-value table, we know that the standard score z = 1.96; Then the confidence interval is Step 2.10: Calculate the radius of curvature of each figure within the j-th grid where j = 1, 2, 3…J; Step 2.11: Mark the figures in the J grids in Step 2.10 whose radius of curvature is greater than ; Further connect all the marked figures, which is denoted as the contour line of the liquid column area; Step 2.12: At this point, the contour line of the droplet area is divided. The area inside the contour line is the liquid column area, recorded as L; the area outside the contour line is the droplet area, recorded as K; The specific process of step 3 is as follows: Step 3.1: Calculate the instantaneous fuel mass M0 based on the fuel injection law; Step 3.2: Calculate the liquid-phase mass in the spray column region; Denote the nozzle as a, the demarcation line as b, and the spray end as c; Denote the mass of the liquid-phase fuel in the spray column region as M1; The fuel temperature at the nozzle is close to room temperature, and the fuel temperature in the liquid column region is close to the temperature of the ambient gas. Then, denote the density of the liquid-phase fuel at the nozzle as ρ1 and the density at the end of the liquid column region as ρ2. After weighted processing of the overall density of the liquid column, ρ = 2 / 3ρ1 + ρ2; The fuel density in the droplet region is the density of the fuel at the ambient gas temperature; Fit the spray contour line in the spray column region to f(x) through the matlab program, then Step 3.3: Divide the droplet area into grids, divide the droplet area into m sub-areas with a side length of E millimeters, and use m i to represent the i-th sub-area, and η i to represent the number of droplets in the i-th sub-area, and d i to represent the average diameter of the droplets in the i-th sub-area, where i = 1...m; Average number of droplets in m sub-regions of the droplet region The average droplet volume diameter of the m sub-regions in the droplet region is Step 3.4: Convert the average diameter of the droplet volume into the volume V of the droplet based on the relationship between the acceleration due to gravity and the surface tension m , where α and β are constants, and γ is the surface tension; Step 3.5: Fit the spray contour line in the droplet region to g(x) through a Matlab program; the volume of a grid cube is E 3 ; further, the number of grid cells in the droplet region is Step 3.6: The liquid phase mass in the droplet region is M2 = ρNηV m ; Step 3.7: Transient evaporation amount M of liquid fuel e = M0 - M1 - M2; The ballistic optical imaging device includes: a femtosecond laser, a beam splitter, a frequency multiplier, a bandpass filter 1, a reflector 1, a constant volume bullet, a reflector 2, a lens 1, a polarizer 1, a dichroic mirror, an optical Kerr medium, a bandpass filter 2, a polarizer 2, a lens 2, and a high-speed camera; The optical path propagation of the ballistic light imaging device is a femtosecond laser that outputs laser pulses. After passing through a frequency amplifier, the beam splitter divides the laser pulses into a switching beam and an imaging beam; the ratio of the two beams is 7:3; the imaging beam is converted to 400 nm after passing through a frequency doubler; the frequency doubler is a barium metaborate crystal; the imaging beam passes through band-pass filter 1 and then passes through mirror 1 to pass through a constant-volume combustion bomb to obtain spray field information; there is an elliptical quartz glass window on each side of the cavity of the constant-volume bomb; after the imaging beam obtains the spray field information, it passes through mirror 2, lens 1, polarizer 1 and dichroic mirror and then converges with the switching beam in the optical Kerr medium; lens 1 plays a role in spatial filtering; polarizer 1 plays a role in polarization filtering; the optical Kerr medium is filled with CS2 liquid; the CS2 liquid is an isotropic transparent liquid when no switching beam passes through; when a switching beam passes through the CS2 liquid, the dipole moment of CS2 molecules is arranged along the polarization direction of the switching beam under the strong electromagnetic field of the laser pulse, causing the CS2 liquid to generate the Kerr effect and twist the polarization of the imaging beam; using the optical Kerr effect, ballistic photons can be separated from the imaging beam; the imaging beam passes through band-pass filter 2, polarizer 2 and lens 2 and then irradiates onto a high-speed camera.

2. The discriminant method for the liquid fuel spray area and the calculation method for the transient evaporation rate based on the ballistic light imaging according to claim 1, wherein In step 2.10: When the radius of curvature of each figure in the grid is less than , it is considered that the position where the grid is located at this time is the droplet area; When the radius of curvature of the figure in the grid is greater than , it is considered that the position where the grid is located at this time is the liquid column area.

3. A method for discriminating a liquid fuel spray region and calculating a transient evaporation rate based on ballistic light imaging according to claim 1, characterized in that, The femtosecond laser outputs laser pulses with a wavelength of 800 nm, a pulse width of 100 fs, a single-pulse energy of 4 mJ, and a frequency of 1000 Hz.

4. A method for discriminating a liquid fuel spray area and calculating a transient evaporation amount based on ballistic light imaging according to claim 1, characterized in that, The effective pixels of the high-speed camera are 1024×1024, the camera shutter time is 100 us, and the acquisition time is 1 ms ASOI.

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