Optimization method for calibrating wall-adhered oil film by refractive index matching method

Abstract

The application discloses an optimization method for calibrating wall-attached oil film by refractive index matching method, and belongs to the technical field of diesel engines. In the application, the order of magnitude of the wall-attached oil film thickness is micron, the calibration solution consistent with the refractive index of the test fuel is obtained by matching dodecane and tetrahydro naphthalene calibration solution, and the calibration precision is improved. In view of the non-uniformity of the oil film thickness during the calibration of the wall-attached oil film, the application judges the relationship between the gray value uniformity of the image and the preset uniformity threshold value, and removes the test working condition points with non-uniform thickness, so that the success rate of the calibration test is increased, and the calibration precision is improved. In view of the problem that the heavy components in the calibration solution evaporate in advance, the application compares the error between the test volume of the heavy components in the calibration solution and the known volume, removes the test working condition points affecting the precision, and improves the calibration precision. The application measures the oil film thickness of the oil spray impinging on the wall surface of the piston in the engine by the expression of the change relationship between the wall-attached oil film thickness and the scattered light intensity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diesel engines, and relates to an optimization method for calibrating an oil film adhering to a wall through refractive index matching. BACKGROUND

[0002] Diesel engines have become the main land-based power device platform in China due to their excellent thermal efficiency, power performance and durability. Diesel engines are developing towards small size and high power density. High-strength diesel engines usually use high injection pressure, which will lead to an increase in injection penetration distance, and a large amount of fuel is injected onto the piston surface and the cylinder liner wall to form an oil film adhering to the wall. The evaporation rate of the oil film adhering to the wall is much lower than the gasification rate of the liquid drop in the air, and the fuel under the flame on the surface of the oil film cannot be fully mixed with the air in the cylinder, which will cause the ablation of the piston surface and the generation of a large amount of soot. It has been found that the number of emission particles is related to the oil film adhering to the wall, especially the thickness of the oil film adhering to the wall. Therefore, the study on the oil film adhering to the wall has important guiding significance for reducing soot emission.

[0003] At present, the measurement methods of the oil film adhering to the wall include total reflection method, interference method, laser-induced fluorescence method and refractive index matching method. The refractive index matching method is widely used because the test system is simple, the two-dimensional distribution law of the oil film adhering to the wall can be quantitatively obtained, and the method has high time resolution and test accuracy. The refractive index matching method is based on the fact that the refractive index of fuel is close to that of quartz glass, and the relationship between the thickness of the oil film and the change of transmittance needs to be established. However, the calibration test of the oil film adhering to the wall through the refractive index matching method is relatively rough at present, the test error is great, the accuracy cannot be guaranteed, and there is a lack of relevant verification.

[0004] In view of the above, in order to more accurately and rigorously explore the oil film adhering to the wall formed by the diesel engine spray impinging on the wall, an optimization method for calibrating the oil film adhering to the wall through the refractive index matching method is urgently needed. SUMMARY

[0005] The technical problem of the optimization method for calibrating the oil film adhering to the wall through the refractive index matching method disclosed by the application is that: (1) the precision problem caused by the difference in refractive index between the test fuel and the calibration solution in the calibration of the oil film adhering to the wall through the refractive index matching method is solved; (2) the precision problem caused by the non-uniform thickness of the calibration solution in the calibration process is solved; (3) the error problem caused by the early evaporation of the heavy component of the calibration solution in the calibration process is solved; and (4) the problem that the calibration formula for the oil film adhering to the wall through the refractive index matching method lacks relevant verification is solved.

[0006] To achieve the above-mentioned purpose, the application adopts the following technical solution:

[0007] The optimization method for calibrating the oil film adhering to the wall through the refractive index matching method disclosed by the application comprises the following steps:

[0008] Step 1: The refractive index of the test fuel to be tested is measured by using the critical angle method.

[0009] Step two, according to the same refractive index of the test fuel calibration solution, the calibration solution is a mixture of dodecane and tetrahydronaphthalene; the expression of the relationship between the refractive index of the calibration solution and the concentration of tetrahydronaphthalene is obtained; the refractive index of the test fuel measured in step one is brought into the expression of the relationship between the refractive index of the calibration solution and the concentration of tetrahydronaphthalene to determine the concentration of tetrahydronaphthalene.

[0010] The expression of the relationship between the refractive index of the calibration solution and the concentration of tetrahydronaphthalene is as follows:

[0011] n = 0.119c + 1.422

[0012] In the formula, n is the refractive index of the solution, and c is the concentration of tetrahydronaphthalene in the calibration solution.

[0013] Step three, according to the calibration solution with the same refractive index as the test fuel obtained in step two, mix it with the volatile light component isooctane solution according to different volume ratios. The role of isooctane is to promote the flow of the calibration solution, so that the calibration solution after adding isooctane is uniformly distributed.

[0014] Step four, use a microliter syringe to inject the calibration solution in step three onto the surface of the quartz glass, and use a high-speed camera to shoot the relevant images and record the light intensity I dry under the dry glass wet ;

[0015] Step five, according to the I wet image obtained by shooting in step four, judge the uniformity of the titration thickness of the calibration solution. If the uniformity of the gray value of the image is above the preset uniformity threshold, proceed to the next step. If the uniformity of the gray value does not meet the requirements, re-perform step four. Since isooctane evaporates first in the calibration process, it does not participate in the oil film thickness calculation.

[0016] Step six, according to the solution determined in step five, obtain the oil film area of the solution under the I wet image through image processing, and calculate the wall-adherent oil film thickness h at this time according to the volume of the unevaporated dodecane and tetrahydronaphthalene in the titration solution.

[0017] Step seven, according to the wall-adherent oil film thickness calculated in step six, obtain the relationship between the wall-adherent oil film thickness and the scattered light intensity through the expression of the relationship between the wall-adherent oil film thickness and the scattered light intensity at different proportions of isooctane solution.

[0018] The expression of the relationship between the wall-adherent oil film thickness and the scattered light intensity is as follows:

[0019] h = 2.497 Δi 2 + 0.5406 Δi

[0020] In the formula, h is the wall-attached oil film thickness,

[0021] Step eight, judging the influence of the evaporation of the heavy components dodecane and tetrahydronaphthalene in the calibration solution in the calibration process, according to the change relationship between the wall-attached oil film thickness and the scattered light intensity in step seven, calculating the test volume of dodecane and tetrahydronaphthalene in the calibration solution, comparing the test volume with the known volume, if greater than the preset volume error threshold, discarding the calibration test point, returning to step five; if the error is less than the preset volume error threshold, the selected change relationship between the wall-attached oil film thickness and the scattered light intensity is taken as the wall-attached oil film calibration result of the refractive index matching method, that is, the optimization of the wall-attached oil film calibration of the refractive index matching method is realized.

[0022] It also includes step nine: according to the wall-attached oil film calibration result of the refractive index matching method obtained from steps one to eight, measuring the oil film thickness of the fuel spray impinging on the wall surface of the piston in the engine through the expression of the change relationship between the wall-attached oil film thickness and the scattered light intensity, and analyzing that the wall-attached oil film can support the reduction of soot emission.

[0023] As a preferred, step two selects dodecane with a refractive index of 1.422, and tetrahydronaphthalene with a refractive index of 1.541.

[0024] As a preferred, in step three, the proportion of the calibration solution in the total solution is 1%, 2%, 3%, 4%, 5% or 10%; the total solution is the sum of the calibration solution and the isooctane solution.

[0025] As a preferred, in step four, the volume of the microliter syringe titration solution is 0.6 μL.

[0026] As a preferred, in step five, the preset uniformity threshold is selected as 95%.

[0027] As a preferred, in step eight, the preset volume error threshold is 5%.

[0028] Beneficial effects:

[0029] 1. The optimization method for the wall-attached oil film calibration of the refractive index matching method disclosed in the application, the order of magnitude of the wall-attached oil film thickness is microns, and the different refractive indexes of the test fuel and the calibration solution will lead to the inability to guarantee the calibration accuracy, by matching the dodecane and tetrahydronaphthalene calibration solution, the calibration solution with the same refractive index as the test fuel is obtained, and the calibration accuracy is improved.

[0030] 2. The optimization method for calibrating the wall-adhered oil film by the refractive index matching method, which is used for the case that the oil film thickness is uneven during the calibration of the wall-adhered oil film, and the test working condition points with uneven thickness are removed by judging the relationship between the gray value uniformity of the image and the preset uniformity threshold, so as to increase the success rate of the calibration test and improve the calibration accuracy.

[0031] 3. The optimization method for calibrating the wall-adhered oil film by the refractive index matching method, which is used for the problem that the heavy component in the calibration solution evaporates in advance, and the test working condition points affecting the accuracy are removed by comparing the error between the test volume and the known volume of the heavy component in the calibration solution, so as to reduce the test error and improve the calibration accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments illustrated in the drawings are provided to explain the present application and are not meant to limit the present application.

[0033] Figure 1 It is a working principle diagram of the present application.

[0034] Figure 2 It is a principle diagram of the refractive index matching method.

[0035] Figure 3 It is a light intensity change diagram of the calibration solution in the evaporation process of the refractive index matching method.

[0036] Figure 4 It is a schematic diagram of the change relationship between the wall-adhered oil film thickness and the scattered light intensity.

[0037] Figure 5 It is a comparison diagram of the test volume and the known volume of the heavy component in the calibration solution. DETAILED DESCRIPTION

[0038] In order to better illustrate the purpose and advantages of the present application, the content of the application will be further described in combination with the drawings and examples.

[0039] The present embodiment provides an optimization method for calibrating the wall-adhered oil film by the refractive index matching method, referring to Figure 1 , and the specific steps are as follows:

[0040] Step one, the refractive index of the test fuel is measured by using the critical angle method;

[0041] Step 2: Based on the standard solution with the same refractive index used in the test, dodecane and tetrahydronaphthalene organic solutions are selected as the mixing solutions; the expression for the relationship between the refractive index of the standard solution and the concentration of tetrahydronaphthalene is used to obtain the relationship between the refractive index of the standard solution and the concentration of tetrahydronaphthalene; the refractive index of the fuel to be tested measured in Step 1 is substituted into the expression for the relationship between the refractive index of the calibrated solution and the concentration of tetrahydronaphthalene to determine the concentration of tetrahydronaphthalene.

[0042] The expression for the relationship between the refractive index of the calibration solution and the concentration of tetrahydronaphthalene is as follows:

[0043] n = 0.119c + 1.422

[0044] In the formula, n is the refractive index of the solution, and c is the concentration of tetrahydronaphthalene in the calibration solution.

[0045] Step three: Based on the proportions in step two, obtain a calibration solution with the same refractive index as the test fuel. Then, mix this solution with a volatile light component, isooctane, in different volume ratios, with the calibration solution accounting for 3% of the total solution volume. The total solution is the sum of the calibration solution and the isooctane solution. The role of isooctane is to promote the flow of the calibration solution and ensure its uniform distribution after addition.

[0046] Figure 2 The changes in incident light with and without oil film adhering to the glass were compared. When the quartz glass surface is dry, the light incident on the rough surface undergoes diffuse reflection, and more scattered light enters the camera lens, resulting in a bright image of the glass surface in the camera. When an oil film adheres to the rough glass surface, most of the incident light at the oil film location is transmitted, and this portion of the light cannot enter the camera lens, thus darkening the oil film area on the quartz glass.

[0047] Step four: Using a micro-syringe, the standard solution from step three is dripped onto the quartz glass surface. The volume of solution dripped using the micro-syringe is 0.6 μL. A high-speed camera captures relevant images, such as... Figure 3 As shown, the light intensity I under the dry glass was recorded. dry The light intensity I under conditions where isooctane is completely evaporated but dodecane and tetrahydronaphthalene are not evaporated wet ;

[0048] Step 5, based on the image obtained in Step 4 showing that isooctane was completely evaporated but dodecane and tetrahydronaphthalene were not evaporated, I... wet The image is used to determine the uniformity of the titration thickness of the calibration solution. If the uniformity of the grayscale values ​​in the image is above the preset uniformity threshold, proceed to the next step. The preset uniformity threshold is set to 95%. If the uniformity of the grayscale values ​​does not meet the requirements, repeat step four. Since isooctane evaporates first during the calibration process, it is not included in the oil film thickness calculation.

[0049] Step six, according to the solution determined in step five, the I is obtained by image processing wet The oil film area of the solution under the image is calculated according to the volume of the un-evaporated dodecane and tetrahydronaphthalene in the titration solution, and the wall-adhesion oil film thickness h at this time is calculated;

[0050] Step seven, according to the wall-adhesion oil film thickness calculated in step six, the change relationship between the wall-adhesion oil film thickness and the scattering light intensity is obtained by calibrating the expression of the change relationship between the wall-adhesion oil film thickness and the scattering light intensity under different proportions of isooctane solution, and the final relationship diagram is shown in Figure 4 The fitting coefficient R 2 It can reach 99.55%,;

[0051] The expression of the change relationship between the wall-adhesion oil film thickness and the scattering light intensity is as follows:

[0052] h = 2.497Δi 2 + 0.5406Δi

[0053] In the formula, h is the wall-adhesion oil film thickness,

[0054] Step eight, judging the influence of the evaporation of the heavy components dodecane and tetrahydronaphthalene in the calibration solution in the calibration process, according to the change relationship between the wall-adhesion oil film thickness and the scattering light intensity in step seven, calculating the test volume of dodecane and tetrahydronaphthalene in the calibration solution, and comparing the test volume with the known volume, as shown in Figure 5 If it is greater than the preset volume error threshold, the calibration test point is discarded, and step five is returned again, and the preset volume error threshold is set to 5%. If the error is less than the preset volume error threshold, the selected change relationship between the wall-adhesion oil film thickness and the scattering light intensity is taken as the wall-adhesion oil film calibration result of the refractive index matching method, that is, the optimization of the wall-adhesion oil film calibration of the refractive index matching method is realized.

[0055] It also includes step nine: according to the wall-adhesion oil film calibration result of the refractive index matching method obtained from steps one to eight, the wall-adhesion oil film thickness of the oil film adhered to the wall surface by the fuel spray impinging on the piston in the engine is measured through the expression of the change relationship between the wall-adhesion oil film thickness and the scattering light intensity, and the soot emission is reduced according to the wall-adhesion oil film thickness.

[0056] The above specific description further details the purpose, technical scheme and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. An optimization method for wall-adhered oil film calibration by refractive index matching method, characterized in that: It comprises the following steps, Step one, the critical angle method is used to measure the refractive index of the test fuel; Step two, the same refractive index of the test fuel is used to select the calibration solution, and the organic solution of dodecane and tetrahydronaphthalene is selected as the calibration solution; the expression of the relationship between the refractive index of the calibration solution and the concentration of tetrahydronaphthalene is obtained; the refractive index of the test fuel measured in step one is brought into the expression of the relationship between the refractive index of the calibration solution and the concentration of tetrahydronaphthalene to determine the concentration of tetrahydronaphthalene; The expression of the relationship between the refractive index of the calibration solution and the concentration of tetrahydronaphthalene is as follows: n = 0.119c + 1.422 In the formula, n is the refractive index of the solution, and c is the concentration of tetrahydronaphthalene in the calibration solution; Step three, the calibration solution with the same refractive index as the test fuel is obtained according to the solution ratio in step two, and then mixed with the light component isooctane solution according to different volume ratios, and the isooctane solution is used to promote the flow of the calibration solution and make the calibration solution after adding the isooctane solution be uniformly distributed; Step four, the calibration solution in step three is dropped onto the quartz glass surface using a microliter syringe injection, the high-speed camera takes the relevant image, and the light intensity I under the drying glass is recorded dry , the light intensity I under the complete evaporation of isooctane but the evaporation of dodecane and tetrahydro naphthalene wet ; Step five, according to the image taken in step four, the uniformity of the thickness of the calibration solution is judged. If the uniformity of the gray value of the image is above the preset uniformity threshold, step six is entered. If the uniformity of the gray value does not meet the requirement, step four is performed again. Since isooctane evaporates first in the calibration process, it does not participate in the calculation of the oil film thickness. wet Step five, according to the image taken in step four, the uniformity of the thickness of the calibration solution is judged. If the uniformity of the gray value of the image is above the preset uniformity threshold, step six is entered. If the uniformity of the gray value does not meet the requirement, step four is performed again. Since isooctane evaporates first in the calibration process, it does not participate in the calculation of the oil film thickness. Step six, according to the solution determined by step five, through image processing to get I wet The oil film area of the solution under the image is calculated according to the volume of the un-evaporated dodecane and tetrahydronaphthalene in the titration solution, and the wall-adhesion oil film thickness h at this time is calculated. Step seven, according to the wall oil film thickness calculated in step six, the expression of the relationship between the wall oil film thickness and the scattering light intensity is obtained through the calibration of the relationship between the wall oil film thickness and the scattering light intensity under different proportions of the isooctane solution; Step eight, the influence of the evaporation of the heavy components dodecane and tetrahydronaphthalene in the calibration solution is judged, the test volume of dodecane and tetrahydronaphthalene in the calibration solution is calculated according to the relationship between the wall oil film thickness and the scattering light intensity in step seven, and the test volume is compared with the known volume; if the error is greater than the preset volume error threshold, the calibration test point is discarded and step five is returned; if the error is less than the preset volume error threshold, the relationship between the wall oil film thickness and the scattering light intensity is selected as the wall oil film calibration result of the refractive index matching method, that is, the optimization of the wall oil film calibration of the refractive index matching method is realized.

2. The optimization method for calibrating the wall-adherent oil film by the refractive index matching method according to claim 1, characterized in that: In step seven, The expression of the relationship between the wall oil film thickness and the scattering light intensity is as follows: h = 2.497 Δi 2 + 0.5406 Δi where h is the wall-adherent film thickness, 3. The optimization method for calibrating the wall-adherent oil film by the refractive index matching method according to claim 2, characterized in that: It further comprises step nine: according to the wall oil film calibration result of the refractive index matching method obtained in steps one to eight, the wall oil film thickness of the oil film adhered to the wall surface by the fuel spray impinging on the piston in the engine is measured through the expression of the relationship between the wall oil film thickness and the scattering light intensity.

4. The optimization method for calibrating the wall-adherent oil film by the refractive index matching method according to claim 1 or 2, characterized in that: In step two, dodecane with a refractive index of 1.422 is selected, and tetrahydronaphthalene with a refractive index of 1.541 is selected.

5. The optimization method for calibrating the wall-adherent oil film by the refractive index matching method according to claim 1 or 2, characterized in that: The proportion of the calibration solution in the total solution is 1%, 2%, 3%, 4%, 5% or 10%; the total solution is the sum of the calibration solution and the isooctane solution.

6. The optimization method for calibrating the wall-adherent oil film by the refractive index matching method according to claim 1 or 2, characterized in that: In step four, the volume of the microliter syringe titration solution is 0.6 μL.

7. The optimization method for calibrating the wall-adherent oil film by the refractive index matching method according to claim 1 or 2, characterized in that: In step five, the preset uniformity threshold is 95%.

8. The optimization method for calibrating the wall-adherent oil film by the refractive index matching method according to claim 1 or 2, characterized in that: In step eight, the preset volume error threshold is 5%.

Images