A forward design and evaluation method for the combustion chamber of a China VI two-valve diesel engine

Abstract

This invention provides a forward design and evaluation method for the combustion chamber of a China VI two-valve diesel engine. The method includes 1) confirming the critical combustion chamber dimensional range; 2) designing the combustion chamber solution; 3) screening combustion chamber solutions based on the oil beam drop point; 4) screening combustion chamber solutions based on the compression ratio; 5) evaluating combustion simulations using CFD; 6) recommending combustion chamber solutions; and 7) experimental verification of the combustion chamber solutions. This method not only forward-designs the combustion chamber shape and dimensions but also evaluates the performance and emissions of the combustion chamber under the current combustion system. This method can be used for both the design and selection of combustion chambers for new diesel engines and for improving combustion performance when upgrading existing diesel engines.

Description

Technical Field

[0001] The present invention relates to the technical field of forward design of a combustion chamber of a National VI two-valve diesel engine, and in particular to a forward design and evaluation method for a combustion chamber of a National VI two-valve diesel engine. Background Art

[0002] Although the vast majority of newly developed diesel engines are four-valve engines, two-valve engines are still active in the market due to their low cost, simple structure and good reliability.

[0003] Compared to a four-valve engine, the intake area of ​​a two-valve engine is approximately 30% lower, and the exhaust area is approximately 50% lower, which is detrimental to engine charging efficiency and pumping losses. Furthermore, the eccentric design of the combustion chamber and the tilted placement of the injectors make engine oil-gas mixing relatively more difficult. Compared to the previous generation National V emission standard, the current National VI standard reduces the NOx limit for heavy-duty diesel engines by 77% and the PM limit by 67%. Therefore, the requirements for the combustion system are becoming increasingly stringent. The shape of the combustion chamber is one of the most important components of the combustion system, but there is currently no forward design method for the combustion chamber of a two-valve diesel engine in the industry. Summary of the Invention

[0004] The purpose of the present invention is to address the shortcomings of the existing technology and provide a forward design and evaluation method for the combustion chamber of a National VI two-valve diesel engine. The method can not only forward design the shape and size of the combustion chamber, but also evaluate the performance and emissions of the combustion chamber under the current combustion system. It can be used for the design and selection of combustion chambers for new diesel engines, and can also improve the engine combustion level when upgrading existing diesel engines.

[0005] To achieve the above objectives, the present invention proposes a forward design and evaluation method for the combustion chamber of a China VI two-valve diesel engine, comprising the following steps:

[0006] Step 1: Confirm the critical size range of the combustion chamber: Calculate the optional range of the key parameters of the combustion chamber based on the size of the engine cylinder bore;

[0007] Step 2: Combustion chamber scheme design: Based on the range of key combustion chamber parameters calculated in step 1, set the allocation level of each parameter and use the DOE method to design the combustion chamber scheme;

[0008] Step 3: Select combustion chamber solutions based on fuel beam landing points: Draw the fuel beam landing points on the combustion chamber based on the nozzle injection cone angle. Due to the eccentricity of the combustion chamber and the tilted placement of the injector, the fuel beam landing point heights of each nozzle hole are different. Calculate the height z of each fuel beam landing point and retain all combustion chamber solutions with landing point heights z within the range of 0.5-0.7H.

[0009] Step 4: Combustion chamber solution screening based on compression ratio: Eliminate combustion chamber solutions that do not meet the compression ratio requirements within the range of ±0.5 of the target compression ratio;

[0010] Step 5: CFD combustion simulation evaluation: Build an engine in-cylinder fluid dynamics model, calculate the intake combustion process from the intake valve opening to the exhaust valve opening, calculate all remaining combustion chamber options, and output results for specific fuel consumption, nitrogen oxide emissions, and soot emissions. These results are normalized and then weighted average scores for specific fuel consumption, nitrogen oxide emissions, and soot emissions are calculated using 0.4, 0.3, and 0.3 as weights.

[0011] Step 6: Combustion chamber scheme recommendation: Select the two combustion chambers with the lowest scores in step 5 as the schemes for the combustion chamber comparison experiment;

[0012] Step 7. Experimental verification of the combustion chamber scheme: Verify the performance and emission levels of the two sets of combustion chamber schemes on the engine test bench. Repeat Step 5 to normalize the test results of specific fuel consumption, nitrogen oxide emissions, and soot emissions. Then, using 0.4, 0.3, and 0.3 as weights, calculate the weighted average scores of specific fuel consumption, nitrogen oxide emissions, and soot emissions. The scheme with the lowest score is the optimal combustion chamber scheme.

[0013] Specifically, the key parameters of the combustion chamber in step one include the combustion chamber diameter D, the combustion chamber depth H, the throat diameter B, the throat depth C and the pit center angle.

[0014] The beneficial effects of the present invention compared to the prior art are as follows:

[0015] The present invention provides a forward design and evaluation method for the combustion chamber of a National VI two-valve diesel engine. The method can not only forward design the shape and size of the combustion chamber, but also evaluate the performance and emissions of the combustion chamber under the current combustion system. It can be used for the design and selection of combustion chambers for new diesel engines, and can also improve the engine combustion level when upgrading existing diesel engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of key parameters of the combustion chamber in an embodiment of the present invention;

[0017] Figure 2 This is an example of a combustion chamber solution that is eliminated in the embodiment of the present invention;

[0018] Figure 3 Schematic diagram of the optimal combustion chamber solution of an embodiment of the present invention. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0020] Example: See Figure 1-Figure 3 .

[0021] The present invention proposes a forward design and evaluation method for the combustion chamber of a China VI two-valve diesel engine, comprising the following steps:

[0022] Step 1: Confirmation of the critical size range of the combustion chamber

[0023] like Figure 1 As shown, the key parameters of the combustion chamber include the combustion chamber diameter D, the combustion chamber depth H, the throat diameter B, the throat depth C and the pit center angle;

[0024] In this embodiment, the engine cylinder bore Bore is 93 mm, and the optional ranges of the key parameters of the combustion chamber are calculated as shown in Table 1 below.

[0025] Table 1 Optional ranges of key parameters of combustion chamber

[0026]

[0027]

[0028] Step 2: Combustion chamber design

[0029] Based on the key combustion chamber parameter ranges calculated in step 1, a full factorial DOE approach was used to design 243 combustion chamber solutions, with each parameter at three levels. The ranges of non-critical combustion chamber parameters were modified as appropriate based on the smoothness of the combustion chamber. Due to some dimensional interference, invalid solutions were eliminated, and 200 combustion chamber solutions were selected.

[0030] Step 3: Combustion chamber solution screening based on oil beam landing point

[0031] Draw the landing point of the fuel beam on the combustion chamber according to the nozzle injection cone angle; due to the eccentricity of the combustion chamber and the tilt of the injector, the landing point height of the fuel beam of each nozzle hole is different. Count the height z of each fuel beam landing point and retain all combustion chamber solutions with landing point height z within the range of 0.5-0.7H. Figure 2As shown, H is 16.5mm, and the recommended range for Z is 8.25-11.55mm. In the 8-hole injector, the oil beam landing point on the left exceeds 11.55mm, while the oil beam landing point on the right is within the recommended range, so it should be eliminated. After this round of screening, 83 solutions remain;

[0032] Step 4: Combustion chamber solution screening based on compression ratio

[0033] According to the target compression ratio range of 16.8±0.5, the schemes that do not meet the compression ratio requirements are eliminated, and 32 schemes remain;

[0034] Step 5: CFD combustion simulation evaluation

[0035] A fluid dynamics model was established for the engine cylinder, calculating the intake and combustion process from the start of the intake valve opening to the exhaust valve opening. All remaining combustion chamber solutions were calculated, and the results for specific fuel consumption, nitrogen oxide emissions, and soot emissions were output. The results were normalized and then weighted average scores for specific fuel consumption, nitrogen oxide emissions, and soot emissions were calculated using weights of 0.4, 0.3, and 0.3, respectively. The results for the top four solutions are listed in Table 2 below.

[0036] Table 2 The top four combustion chamber schemes ranked by weighted average score

[0037]

[0038] Step 6: Combustion chamber solution recommendation

[0039] Select Scheme 1 and Scheme 2 with the lowest scores in Step 5 as the schemes for the combustion chamber comparison test;

[0040] Step 7: Experimental verification of the combustion chamber scheme

[0041] Verify the performance and emission levels of the two combustion chamber solutions on the engine bench. Refer to the method in step 5 to normalize the test results of specific fuel consumption, nitrogen oxide emissions and soot emissions, and then calculate the weighted average scores of specific fuel consumption, nitrogen oxide emissions and soot emissions with weights of 0.4, 0.3 and 0.3 respectively. The solution with the lowest score is the best combustion chamber solution. Figure 3 shown.

[0042] The above description is only a preferred embodiment of the present invention and does not limit the structure of the present invention in any form. Any simple modification, equivalent change and modification of the above embodiment based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A forward design and evaluation method for the combustion chamber of a China VI two-valve diesel engine, characterized in that: The following steps are involved: Step 1: Confirm the critical size range of the combustion chamber: Calculate the optional range of the key parameters of the combustion chamber based on the size of the engine cylinder bore; Step 2: Combustion chamber scheme design: Based on the range of key combustion chamber parameters calculated in step 1, set the allocation level of each parameter and use the DOE method to design the combustion chamber scheme; Step 3: Select combustion chamber solutions based on fuel beam landing points: Draw the fuel beam landing points on the combustion chamber based on the nozzle injection cone angle. Due to the eccentricity of the combustion chamber and the tilted placement of the injector, the fuel beam landing point heights of each nozzle hole are different. Calculate the height z of each fuel beam landing point and retain all combustion chamber solutions with landing point heights z within the range of 0.5-0.7H. Step 4: Combustion chamber solution screening based on compression ratio: Eliminate combustion chamber solutions that do not meet the compression ratio requirements within the range of ±0.5 of the target compression ratio; Step 5: CFD combustion simulation evaluation: Build an engine in-cylinder fluid dynamics model, calculate the intake combustion process from the intake valve opening to the exhaust valve opening, calculate all remaining combustion chamber options, and output results for specific fuel consumption, nitrogen oxide emissions, and soot emissions. These results are normalized and then weighted average scores for specific fuel consumption, nitrogen oxide emissions, and soot emissions are calculated using 0.4, 0.3, and 0.3 as weights. Step 6: Combustion chamber scheme recommendation: Select the two combustion chambers with the lowest scores in step 5 as the schemes for the combustion chamber comparison experiment; Step 7. Experimental verification of the combustion chamber scheme: Verify the performance and emission levels of the two sets of combustion chamber schemes on the engine test bench. Repeat Step 5 to normalize the test results of specific fuel consumption, nitrogen oxide emissions, and soot emissions. Then, using 0.4, 0.3, and 0.3 as weights, calculate the weighted average scores of specific fuel consumption, nitrogen oxide emissions, and soot emissions. The scheme with the lowest score is the optimal combustion chamber scheme.

2. The method for forward design and evaluation of a combustion chamber of a China VI two-valve diesel engine according to claim 1, characterized in that: The key parameters of the combustion chamber described in step 1 include the combustion chamber diameter D, the combustion chamber depth H, the throat diameter B, the throat depth C and the pit center angle.

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