A calculation method for the effective flow area of an EGR valve

Abstract

The present invention discloses a method for calculating the effective flow area of an EGR valve. The calculation method includes the following steps: S01: Establish a fluid domain model under the maximum effective opening of the EGR valve; S02: Perform structural processing on the fluid domain model in step S01; S03: Perform preprocessing on the fluid domain model in step S02; S04: Perform fluid analysis on the fluid domain model in step S03 to calculate the flow rate and pressure values; S05: Calculate the effective flow area based on the flow rate and pressure values obtained in step S04; S06: Determine whether the effective flow area obtained in step S05 meets the usage requirements; The technical solution adopts the calculation method of total - total pressure difference, and the calculation result can be more in line with the actual situation. In actual application, the outlet pressure does not expand rapidly. Based on this, the present invention considers the influence of dynamic pressure, and the calculated effective flow area curve of the EGR valve can be better applied to performance evaluation. It can be applied in the initial stage of engine development, effectively saving development time and having higher accuracy.

Description

Technical Field

[0001] The present invention relates to the field of EGR valve calculation and selection for diesel engines, and particularly to a method for calculating the effective flow area of an EGR valve. Background Art

[0002] Currently, diesel engines are facing considerations regarding the upgrading of emission regulations, and the EGR route has been selected to varying degrees in the vehicle National VI stage and the non-vehicle National IV stage. In the development of the EGR system, the reasonable selection of the EGR valve is crucial. To select a suitable EGR valve, it is necessary to calculate the effective flow area of the EGR valve.

[0003] In the development of EGR valves, the experimental method is usually used to evaluate the flow area of the valve. However, this method needs to be carried out after the sample design is completed, usually cannot meet the requirements in the development stage, and requires a lot of time for the layout of the test room and the production of samples.

[0004] With the development of computer simulation technology, accurate simulation and rapid judgment can be achieved through computational fluid dynamics (CFD). And through calculation, the flow characteristics of the EGR valve can be clearly observed. At the same time, it is interactively verified with subsequent tests, making the selection and evaluation of the EGR valve more accurate;

[0005] The existing calculation method using the static-static pressure difference in thermodynamics increases the loss of expansion work, resulting in inaccurate calculation of the effective flow area, and thus affecting subsequent applications.

[0006] In view of the above-mentioned defects, the present invention provides a method for calculating the effective flow area of an EGR valve. Summary of the Invention

[0007] The present invention provides a method for calculating the effective flow area of an EGR valve, which accurately and rapidly simulates the flow characteristics of the EGR valve by establishing a fluid domain model and using a grid division method, and obtains the effective flow area of the EGR valve based on the total-total pressure difference calculation, effectively characterizing the flow characteristics of the EGR valve on the engine, thereby solving the technical problems such as the increase in expansion work loss and inaccurate calculation of the effective flow area caused by the existing static-static pressure difference calculation method.

[0008] The present invention is realized through the following technical solutions:

[0009] A method for calculating the effective flow area of an EGR valve specifically includes the following operating steps:

[0010] S01: Establish a fluid domain model under the maximum effective opening of the EGR valve;

[0011] S02: Perform structural processing on the fluid domain model in step S01;

[0012] S03: Preprocess the fluid domain model in step S02;

[0013] S04: Perform a fluid analysis on the fluid domain model in step S03, and calculate the flow rate and pressure values;

[0014] S05: Calculate the effective flow area based on the flow rate and pressure values obtained in step S04;

[0015] S06: Determine whether the effective flow area obtained in step S05 meets the usage requirements. If it meets the usage requirements, calculate the effective area within the entire lift range; otherwise, return to step S01 to re - establish the fluid domain model.

[0016] Among them, the maximum effective opening of the EGR valve in step S01 refers to the opening at which the EGR valve on the engine can be effectively used, generally 80% of the maximum nominal opening.

[0017] Furthermore, in step S01, set the opening of the EGR valve to 80% of the maximum nominal opening position and establish the fluid domain model.

[0018] Among them, the maximum nominal opening refers to the maximum lift that the valve can reach.

[0019] Furthermore, in step S02, the method for structurally processing the fluid domain model in step S01 includes:

[0020] 1) Remove narrow structures that do not affect the calculation;

[0021] 2) Extend the inlet section of the EGR valve by a length of 2 - 4 times the equivalent diameter of the wet perimeter of the valve inlet;

[0022] 3) Extend the outlet section of the EGR valve by a length of 4 - 6 times the equivalent diameter of the wet perimeter of the valve outlet;

[0023] In this technical solution, the main function of setting the extension length in the inlet section of the EGR valve is to allow the EGR valve to fully develop and reduce the influence of turbulence. The extension length of the inlet section is preferably 2 - 4 times the equivalent diameter of the wet perimeter of the valve inlet. For the specific setting of the length, when the EGR gas enters the EGR valve, it can enter in a laminar flow state. Correspondingly, the extension length of the outlet section of the EGR valve is set to 4 - 6 times the equivalent diameter of the wet perimeter of the valve outlet. Its function is to effectively reduce the influence of backflow at the outlet, and at the same time, it can also simulate the actual measurement state. After the gas comes out of the EGR valve, it will not immediately expand, which can reduce energy loss. In actual EGR measurement, there are long connecting pipes at both the inlet and outlet of the EGR valve, and the setting of the connecting pipes can further reduce the loss of outlet expansion work.

[0024] Furthermore, the preprocessing method for the fluid domain model in step S02 is as follows:

[0025] 1) Set inlet and outlet boundary name identifiers at the inlet and outlet positions of the EGR valve flow passage respectively;

[0026] 2) Divide the fluid domain grid, with the grid size being 3 - 6 mm; the fluid domain grid of the EGR valve body is a hybrid grid with a size of 1 - 2 mm; the size of the first layer of the boundary layer grid is 0.2 - 0.4 mm, the number of layers ≥ 6, and the boundary layer grid growth rate is 1.05 - 1.08; the number of grids between the valve and the valve seat ≥ 6 layers.

[0027] In this technical solution, when dividing the fluid domain grid, for different applications, the combination of the grid division size and the boundary setting is different, and the boundary layer and the hybrid grid size are optimized. By means of a suitable grid density, the accuracy of the eddy current simulation is improved, and the wall grid reduces the wall influence; for applications with a relatively high turbulence intensity such as the EGR valve, incorrect grid size and wall grid division will have a significant impact on the trend of the final effective flow area. Therefore, data such as the fluid domain grid size, hybrid grid size, first layer grid size, and boundary layer grid growth rate involved in the technical solution are empirical settings obtained through a large number of calculations and experimental comparisons.

[0028] Furthermore, the fluid analysis method for the fluid domain model in step S03 is as follows:

[0029] 1) Set the fluid domain boundary to a pressure boundary, where the inlet boundary is the total pressure of 6000 Pa, the outlet boundary is the static pressure of 0 Pa, and the pressures are all relative pressures;

[0030] 2) Set the fluid to a compressible fluid, with an initial temperature of 25 °C, select the Realizable κ - ε turbulence model, and the wall function is Scalable Wall;

[0031] 3) The minimum number of calculation steps is 1000 times, monitor the change in the outlet flow rate, and the flow rate oscillation deviation ≤ 0.5%; if the flow rate oscillation deviation > 0.5%, adjust the relaxation factor and recalculate;

[0032] 4) After the calculation is completed, read the total pressure P in_EGR at the inlet of the EGR valve, the total pressure P out_EGR, at the outlet of the EGR valve, the density ρ_ EGR at the outlet of the EGR valve, and the fluid domain outlet flow rate m_out.

[0033] Among them, the relaxation factor is common knowledge in fluid mechanics calculations. Its introduction can effectively reduce the number of iterations required for fluid analysis in the fluid domain model and reduce the calculation time required.

[0034] Further, the calculation method for the effective flow area based on the flow rate and pressure values obtained in step S04 is as follows: The total-to-total pressure difference calculation method is adopted, and the calculation formula is:

[0035] A eff =m_ out / sqrt(2*ρ_ EGR *Dp)

[0036] Dp=P in_EGR —P out_EGR 。

[0037] Adopting the total-to-total pressure difference calculation method, the result is more in line with the actual situation. Considering that in actual applications, the outlet pressure does not expand rapidly, and combining the influence of dynamic pressure, the curve of the effective flow area of the EGR valve calculated in this way can be better applied to performance evaluation.

[0038] Further, the method for determining whether the effective flow area obtained in step S05 meets the usage requirements is as follows:

[0039] Compare the calculated effective flow area with the overall EGR system. If the effective flow area at the maximum effective opening of the EGR is less than the effective flow area of the overall pipeline, the gas can be controlled by the EGR valve, and the effective flow area within the entire lift range is calculated; otherwise, a new selection needs to be made.

[0040] Further, it also includes step S07: Calculate the effective flow area within the entire lift range. The operation steps are as follows: Set the opening range from 0 to the maximum nominal opening; Calculate the number of positions > 6; Calculate the flow area respectively according to steps S01 - S06 in sequence; Draw a relationship curve of the effective flow area of the EGR valve versus the opening based on the obtained effective flow area data at different openings.

[0041] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0042] 1) In this technical solution, in the processing of step S02 of the fluid domain model, the extended length of the inlet section of the EGR valve is 2 - 4 times the equivalent diameter of the wet perimeter at the valve inlet, which can effectively simulate the full development and stable state of the gas before entering the EGR valve, and reduce the influence of turbulence;

[0043] The extended length of the outlet section of the EGR valve is 4 - 6 times the equivalent diameter of the wet perimeter at the valve outlet, simulating the layout on an actual engine and reducing the loss of outlet expansion work;

[0044] Dividing the fluid domain mesh can improve the mesh accuracy and reduce the continuous trial-and-error stage of mesh adaptability. In the calculation settings, the selection of the turbulence model and wall functions, as well as the division of the boundary layer mesh, reduce the dependence on the wall mesh Y+ and take into account the influence of rotating eddies, increasing the calculation accuracy.

[0045] 2) In this technical solution, the total-to-total pressure difference calculation method is adopted, and the calculation results can be more in line with the actual situation. In actual applications, the outlet pressure does not expand rapidly. Based on this, the present invention considers the influence of dynamic pressure, and the calculated EGR valve effective flow area curve can be better applied to performance evaluation.

[0046] 3) The calculation method described in the present invention can be applied in the initial stage of engine development, which is conducive to quickly understanding the flow characteristics of the valve, selecting a suitable EGR valve for characteristic performance matching, and saving development time. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic block diagram of the process structure of the present invention;

[0048] Figure 2 is a schematic diagram of the fluid domain model processing;

[0049] Figure 3 is a schematic diagram of obtaining the relationship between the effective flow area and the opening degree in Embodiment 1;

[0050] Wherein: 1 - fluid domain of the valve, 2 - inlet extension section, 3 - EGR valve inlet, 4 - outlet extension section, 5 - EGR valve outlet, 6 - inlet boundary, 7 - outlet boundary. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0052] Embodiment 1:

[0053] As Figure 1 — Figure 3 shown, a method for calculating the effective flow area of an EGR valve specifically includes the following operation steps:

[0054] S01: Establish a fluid domain model under the maximum effective opening of the EGR valve, and set the opening of the EGR valve to 80% of the maximum nominal opening;

[0055] S02: Perform structural processing on the fluid domain model in step S01. The specific method is as follows: 1) Remove the narrow structures that do not affect the calculation;

[0056] 2) The extended length L1 of the inlet section of the EGR valve is 2 - 4 times the equivalent diameter of the wet perimeter at the valve inlet;

[0057] 3) The extended length L2 of the outlet section of the EGR valve is 4 - 6 times the equivalent diameter of the wet perimeter at the valve outlet;

[0058] S03: Preprocess the fluid domain model in step S02;

[0059] S04: Perform a fluid analysis on the fluid domain model in step S03 to calculate the flow rate and pressure values;

[0060] S05: Calculate the effective flow area based on the flow rate and pressure values obtained in step S04;

[0061] S06: Determine whether the effective flow area obtained in step S05 meets the usage requirements. If it meets the usage requirements, calculate the effective area within the entire lift range; otherwise, go back to step S01 to re - establish the fluid domain model.

[0062] In this embodiment, as Figure 2 shown, the fluid domain model is established based on the fluid domain 1 of the valve; the extended inlet section of the EGR valve is the extended inlet section 2; the extended outlet section of the EGR valve is the extended outlet section 4.

[0063] Embodiment 2:

[0064] Based on Embodiment 1, the preprocessing method for the fluid domain model in step S02 is as follows:

[0065] 1) Set inlet and outlet boundary name identifiers at the inlet and outlet positions of the EGR valve flow channel respectively;

[0066] 2) Divide the fluid domain grid, with the grid size being 3 - 6 mm; the fluid domain grid of the EGR valve body is a hybrid grid with a size of 1 - 2 mm; the size of the first layer of the boundary layer grid is 0.2 - 0.4 mm, the number of layers ≥ 6, and the boundary layer grid growth rate is 1.05 - 1.08; the number of grids between the air valve and the air valve seat ≥ 6 layers.

[0067] In this embodiment, as Figure 2 shown, the inlet position of the EGR valve flow channel is the EGR valve inlet 3, and the outlet position of the EGR valve flow channel is the EGR valve outlet 5.

[0068] The inlet and outlet boundaries are respectively the inlet boundary 6 and the outlet boundary 7 as Figure 2 shown.

[0069] Embodiment 3:

[0070] Based on the above - mentioned embodiments, the method for performing a fluid analysis on the fluid domain model in step S03 is as follows:

[0071] 1) Set the fluid domain boundary as a pressure boundary. Among them, the inlet boundary is the total pressure with a magnitude of 6000 Pa, and the outlet boundary is the static pressure with a magnitude of 0 Pa. Both pressures are relative pressures.

[0072] 2) Set the fluid as a compressible fluid with an initial temperature of 25 °C. Select the Realizable κ-ε turbulence model, and the wall function is Scalable Wall.

[0073] 3) The minimum number of calculation steps is 1000 times. Monitor the change in the outlet flow rate, and the flow oscillation deviation ≤ 0.5%; if the flow oscillation deviation > 0.5%, adjust the relaxation factor and recalculate.

[0074] 4) After the calculation is completed, read the total pressure P at the inlet of the EGR valve in_EGR , the total pressure P at the outlet of the EGR valve out_EGR, , the density ρ_ at the outlet of the EGR valve EGR , and the fluid domain outlet flow rate m_out.

[0075] Example 4:

[0076] Based on the above example, the calculation method of the effective flow area according to the flow rate and pressure values obtained in step S04 is as follows: Adopt the total - total pressure difference calculation method, and the calculation formula:

[0077] A eff = m_ out / sqrt(2 * ρ_ EGR * Dp)

[0078] Dp = P in_EGR — P out_EGR .

[0079] Among them, the method for judging whether the effective flow area obtained in step S05 meets the usage requirements is as follows:

[0080] Compare the calculated effective flow area with the overall EGR system. If the effective flow area at the maximum effective opening of the EGR is less than the effective flow area of the overall pipeline, the gas can be controlled by the EGR valve, and the effective flow area within the entire lift range is calculated; otherwise, a new model needs to be selected.

[0081] Example 5:

[0082] This embodiment further limits on the basis of the above embodiment. In step S07: calculating the effective flow area within the entire lift range, the operation steps are as follows: setting the opening range from 0 to the maximum nominal opening; calculating that the number of positions > 6; successively calculating the flow area according to steps S01 - S06; and drawing a relationship curve of the effective flow area of the EGR valve and the opening according to the obtained effective flow area data at different openings, as Figure 3 shown.

[0083] In this embodiment, the total - total pressure difference calculation method is adopted, and the calculation result can be more in line with the actual situation. Considering the influence of the outlet pressure in actual application, the calculated effective flow area curve of the EGR valve can be better applied to performance evaluation, and can be applied in the initial stage of engine development, which is conducive to quickly understanding the flow characteristics of the valve, selecting a suitable EGR valve for characteristic performance matching, and saving development time.

[0084] Example 6:

[0085] Taking a specific case as an example, in the development of the B5.9 CS4 engine, calculate the effective flow area of the double - spool EGR valve;

[0086] The inlet diameter of the EGR valve Din = 40mm, and the inlet extension section L1 = 3Din = 120mm; the equivalent diameter of the outlet wetted perimeter Dout = 80mm, and the outlet extension section L2 = 4Dout = 320mm;

[0087] Divide the fluid domain grid, with the grid size of 3mm; the fluid domain grid of the EGR valve body is a hybrid grid, with a size of 1mm; the size of the first layer of the boundary layer grid is 0.3mm, the number of layers = 8, and the boundary layer grid growth rate is 1.05; the number of grids between the valve and the valve seat = 6 layers;

[0088] The fluid is set as a compressible fluid, with an initial temperature of 25°C. Select the Realizable κ - ε turbulence model, and the wall function is Scalable Wall; the number of calculation steps is 1500 times. Monitor the change of the outlet flow rate, with a flow oscillation deviation of 0.5%, and calculate the effective flow area using the total - total pressure difference calculation method.

[0089] Example 7:

[0090] In the prior art, the total - static pressure difference calculation method is adopted. In actual measurement, only the static pressure is measured, and the total pressure needs to be converted and calculated, and the compressibility of the EGR exhaust gas needs to be considered;

[0091] In the total - total pressure difference calculation method adopted in Example 6:

[0092] D p =(P static_in+1 / 2*ρ in *V in ^2)-(P static_in +1 / 2*ρ out *V out ^2)

[0093] Total-static pressure difference calculation method:

[0094] D p =(P static_in +1 / 2*ρ in *V in ^2)-(P static_in )

[0095] Lack of outlet dynamic pressure causes the pressure difference D p to be too large, which will ultimately lead to the calculated A eff being too small;

[0096] Static-static pressure difference calculation method:

[0097] D p =(P static_in )-(P static_in )

[0098] D p Pressure difference; P static Static pressure ρ Density V in Gas velocity

[0099] Without considering the inlet and outlet dynamic pressures,

[0100] If the outlet dynamic pressure is less than the inlet dynamic pressure, then D p will decrease, which will ultimately lead to the calculated A eff being too large;

[0101] If the outlet dynamic pressure is greater than the inlet dynamic pressure, then D p will increase, which will ultimately lead to the calculated A eff being too small;

[0102] When the EGR gas flows inside the EGR valve, due to factors such as the rotation of the internal structure of the valve and the narrow valve port area, there will be a sharp change in the gas pressure. Using the total-total pressure difference can take into account the combined effects of static pressure and dynamic pressure, making the calculation more accurate.

[0103] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the effective flow area of an EGR valve, characterized in that: Its calculation method includes the following steps: S01: Establish a fluid domain model at the maximum effective opening of the EGR valve; S02: Perform structural processing on the fluid domain model in step S01; S03: Perform preprocessing on the fluid domain model in step S02; S04: Perform fluid analysis on the fluid domain model in step S03, and calculate the flow rate and pressure values; S05: Calculate the effective flow area according to the flow rate and pressure values obtained in step S04; S06: Determine whether the effective flow area obtained in step S05 meets the usage requirements. If it meets the usage requirements, calculate the effective area within the entire lift range; otherwise, enter step S01 to re-establish the fluid domain model; In step S01, set the opening of the EGR valve to 80% of the maximum nominal opening, and establish a fluid domain model; In step S02, the method for performing structural processing on the fluid domain model in step S01 includes: 1) Remove narrow structures that do not affect the calculation; 2) Extend the inlet section of the EGR valve by a length that is 2-4 times the equivalent diameter of the valve inlet wetted perimeter; 3) Extend the outlet section by a length that is 4-6 times the equivalent diameter of the valve outlet wetted perimeter; The preprocessing method for the fluid domain model in step S02 is: 1) Set inlet and outlet boundary name identifiers at the inlet and outlet positions of the EGR valve flow channel respectively; 2) Divide the fluid domain grid, with the grid size being 3-6 mm; the fluid domain grid of the EGR valve body is a hybrid grid, with a size of 1-2 mm; the size of the first layer of the boundary layer grid is 0.2-0.4 mm, the number of layers ≥ 6, and the boundary layer grid growth rate is 1.05-1.08; The number of grids between the valve and the valve seat ≥ 6 layers; The fluid analysis method for the fluid domain model in step S03 is: 1) Set the fluid domain boundary as a pressure boundary. Among them, the inlet boundary is the total pressure, with a size of 6000 Pa, and the outlet boundary is the static pressure, with a size of 0 Pa. The pressures are all relative pressures; 2) Set the fluid as a compressible fluid, with an initial temperature of 25 °C. Select the Realizable κ-ε turbulence model, and the wall function is Scalable Wall; 3) The minimum number of calculation steps is 1000 times. Monitor the change in the outlet flow rate, and the flow rate oscillation deviation ≤ 0.5%; if the flow rate oscillation deviation > 0.5%, adjust the relaxation factor and recalculate; 4) After the calculation is completed, read the total pressure at the inlet of the EGR valve , the total pressure at the outlet of the EGR valve , the density at the outlet of the EGR valve , the flow rate at the outlet of the fluid domain ; The calculation method for the effective flow area based on the flow rate and pressure values obtained in step S04 is as follows: The total-total pressure difference calculation method is adopted, and the calculation formula is: ; The method for determining whether the effective flow area obtained in step S05 meets the usage requirements is: Compare the calculated effective flow area with the overall EGR system. If the effective flow area at the maximum effective opening of the EGR is less than the effective flow area of the overall pipeline, the gas can be controlled by the EGR valve, and calculate the effective flow area within the entire lift range; otherwise, a new selection is required; It also includes step S07: Calculate the effective flow area within the entire lift range. The operation steps are: Set the opening range from 0 to the maximum nominal opening; The number of calculated positions > 6; Calculate the flow area respectively according to steps S01-S06 in sequence; Draw a relationship curve of the effective flow area of the EGR valve versus the opening based on the obtained effective flow area data at different openings.

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