A diesel engine combustion system and optimization method

Abstract

The application discloses a diesel engine combustion system and an optimization method, and belongs to the technical field of diesel engines. The diesel engine combustion system comprises a piston, a first recess and a second recess connected to each other, and the first recess is arranged around the second recess; and an oil injector is arranged at one side of the piston along a height direction and located on a central axis of the second recess. The fuel injected by a first group of injection holes impacts on the first recess, and the fuel injected by a second group of injection holes impacts on the second recess, so that the fuel can be uniformly dispersed and has a large contact area with air, the fuel combustion is ensured to be more sufficient, the combustion efficiency is improved, and a throat part is arranged at the connection position of the first recess and the second recess, which is used for spacing the fuel in the first recess and the second recess, so that the fuel is prevented from gathering at the throat part and increasing the amount and concentration of the fuel, the fuel combustion is insufficient, the combustion efficiency is reduced, and therefore the combustion efficiency can be further improved through the arranged throat part.

Description

Technical Field

[0001] This application relates to the field of diesel engine technology, and in particular to a diesel engine combustion system and optimization method. Background Technology

[0002] Marine diesel engines are characterized by high power and large space size. To achieve higher power output, a large fuel supply and high-pressure fuel injection are required to ensure that a large amount of fuel is fully combusted in a large space. High boost is also required to ensure that the intake air volume meets the excess air coefficient requirements for the combustion of a large amount of fuel. The large fuel spray cone angle and high flow rate high-pressure fuel injection form a long-penetrating high-concentration spray, which results in a slow fuel-air mixing rate and low combustion efficiency. Summary of the Invention

[0003] This application provides a diesel engine combustion system to solve the technical problem of low fuel combustion efficiency.

[0004] To achieve the above objectives, according to a first aspect of this application, a diesel engine combustion system is provided, comprising: A piston includes a first recess and a second recess connected to each other, the first recess being disposed around the second recess; The injector is spaced apart on one side of the piston along the height direction and located on the central axis of the second recess. The injector includes a first group of nozzles and a second group of nozzles spaced apart. The first group of nozzles is disposed toward the first recess and is used to inject fuel into the first recess. The second group of nozzles is disposed toward the second recess and is used to inject fuel into the second recess. The first recess and the second recess are connected by a throat portion that protrudes toward the injector, and the throat portion is used to separate the fuel in the first recess and the second recess.

[0005] Optionally, the first recess has a first arc surface, and when the first nozzle group injects fuel into the first recess, the first arc surface is used to extend the fuel in multiple directions. The second recess has a second arc surface, the first arc surface and the second arc surface are connected, and the first arc surface is arranged around the second arc surface. When the second nozzle group injects fuel into the second recess, the second arc surface is used to extend the fuel in multiple directions.

[0006] Optionally, the piston has a first chamfered surface, and the top surface of the piston is connected to the first arc surface through the first chamfered surface; The throat portion has a second chamfered surface, and the first arc surface is connected to the second arc surface through the second chamfered surface.

[0007] Optionally, the first nozzle group includes a plurality of first holes spaced apart circumferentially along the injector, each first hole being disposed toward the first recess for injecting fuel into the first recess; The second nozzle group includes a plurality of second holes spaced apart circumferentially along the injector, each second hole being disposed toward the second recess for injecting fuel into the second recess.

[0008] Optionally, the first recess has a first radius r, and the second recess has a second radius R, wherein the first radius r is smaller than the second radius R; The diameter of the first hole is smaller than the diameter of the second hole.

[0009] Optionally, the first hole and the second hole are offset along the height direction of the piston.

[0010] According to a second aspect of this application, a method for optimizing a diesel engine combustion system is provided, comprising: Based on the three-dimensional simulation analysis of the diesel engine combustion process, and with the goals of improving thermal efficiency and reducing heat load, the optimization direction of combustion characteristics is obtained, including the spray flame distribution and combustion phase interval. Based on any one of the above-mentioned diesel engine combustion systems and the optimization direction of the combustion characteristics, the spray flame distribution optimization design and combustion phase interval optimization design of the diesel engine combustion system are obtained. Based on the optimized diesel engine combustion system with spray flame distribution and combustion phase range, it is determined whether the goals of improving thermal efficiency and reducing heat load have been achieved.

[0011] Optionally, the piston of the diesel engine combustion system includes a first recess and a second recess, and the injector of the diesel engine combustion system includes a first nozzle group and a second nozzle group, wherein the first nozzle group includes a plurality of first nozzles and the second nozzle group includes a plurality of second nozzles. The process of obtaining the optimized design of the spray flame distribution of the diesel engine combustion system includes: Based on the three-dimensional simulation analysis of the diesel engine combustion process, the fuel injection ratio of the first recess and the second recess of the piston is obtained, and the orifice diameter of the first orifice and the orifice diameter of the second orifice are obtained according to the fuel injection ratio. Based on the structure of the piston and the structure of the injector, the shape of the first recess and the shape of the second recess, as well as the included angle between the first hole and the corresponding second hole, are obtained; Based on the shapes of the first and second recesses, the diameters of the first and second holes, and the included angle between the first and second holes, a three-dimensional simulation analysis is performed to obtain the oil-gas mixing condition, thermal efficiency, and heat transfer of the heated component wall. A scheme selection is then made to obtain the optimized design of the spray flame distribution of the diesel engine combustion system.

[0012] Optionally, the distribution of the spray flame includes the distribution of the free jet of fuel, the impact position of the spray jet on the wall, and the development of the spray flame along the wall surface after impact. Based on the shapes of the first and second recesses, the apertures of the first and second holes, and the included angle between the first and second holes, the distribution of the free fuel jet, the impact position of the spray jet on the wall, and the development of the spray flame along the wall after impact are optimized.

[0013] Optionally, the step of obtaining the aperture of the first hole and the aperture of the second hole includes: Based on the three-dimensional simulation analysis of the diesel engine combustion process, the ratio of the amount of oil extending along the top surface of the piston after the spray flame hits the wall to the total amount of oil is obtained. After the spray flame hits the wall, the ratio of the amount of oil extending along the top surface to the total amount of oil is determined as the initial value of the oil spray ratio of the first nozzle group. Based on the initial value of the oil spray ratio of the first nozzle group, as well as the number of the first nozzle and the number of the second nozzle, the aperture of the first nozzle and the aperture of the second nozzle are obtained.

[0014] Optionally, the step of obtaining the shapes of the first recess and the second recess includes: The first recess has a first radius r and a first slope K1, and the second recess has a second radius R and a second slope K2; Based on the orthogonal design method, multiple horizontal values ​​are set for the first radius r, the first slope K1, the second radius R, and the second slope K2, respectively, to obtain different shapes of the first concave part and the second concave part, and to select a scheme to improve the thermal efficiency of the diesel engine combustion system and reduce the heat load.

[0015] Optionally, the step of obtaining the included angle between the first hole and the second hole includes: Based on the apertures of the first hole and the second hole, and the shapes of the different first and second recesses, different included angles between the first hole and the corresponding second hole are obtained, and a scheme is selected so that the fuel sprayed from the first hole is located in the first recess and the fuel sprayed from the second hole is located in the second recess.

[0016] Optionally, the optimization design for obtaining the combustion phase range includes: The combustion phase interval includes the combustion start point and the combustion duration. Based on the combustion start point and the combustion duration, the injection timing and the injection duration are obtained. Based on the orthogonal design method, multiple horizontal values ​​are set for the injection timing and the injection duration, and three-dimensional simulation calculations are performed and selected so that the piston is near top dead center at the injection timing and the thermal load is within a preset range during the injection duration.

[0017] The diesel engine combustion system of this application embodiment includes: a piston, including a first recess and a second recess connected to each other, the first recess surrounding the second recess; and a fuel injector, spaced apart on one side of the piston along the height direction and located on the central axis of the second recess. The fuel injector includes a first nozzle group and a second nozzle group spaced apart, the first nozzle group facing the first recess for injecting fuel into the first recess, and the second nozzle group facing the second recess for injecting fuel into the second recess. A throat portion is formed at the connection between the first recess and the second recess, protruding towards the fuel injector, and the throat portion is used to separate the fuel within the first recess and the second recess. The fuel injected by the first nozzle group impacts the first recess, and the fuel injected by the second nozzle group impacts the second recess. This allows the fuel to be dispersed more evenly, with a larger contact area with air, ensuring more complete combustion and improving combustion efficiency. Furthermore, a throat is provided at the connection between the first and second recesses to separate the fuel within the two recesses, preventing fuel from accumulating at the throat and increasing its quantity and concentration, leading to incomplete combustion and decreased combustion efficiency. Therefore, the throat further improves combustion efficiency. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0020] Figure 1 This is a schematic diagram of the piston and injector provided in an exemplary embodiment of this disclosure; Figure 2 This is a schematic diagram of the piston structure provided in an exemplary embodiment of this disclosure; Figure 3This is a schematic diagram of the structure of the injector provided in an exemplary embodiment of this disclosure; Figure 4 This is a schematic diagram of the structure of the first hole and the second hole on the injector provided in an exemplary embodiment of this disclosure; Figure 5 This is provided in the exemplary embodiments of this disclosure. Figure 2 Enlarged view of a portion of area A in the middle; Figure 6 This is provided in the exemplary embodiments of this disclosure. Figure 2 Enlarged view of a section in area B; Figure 7 This is a schematic diagram showing the position of the oil jets injected through the first and second holes within the first and second recesses, as provided in an exemplary embodiment of this disclosure. Figure 8 This is a flowchart of an optimization method for a diesel engine combustion system provided in an exemplary embodiment of this disclosure.

[0021] Explanation of reference numerals in the attached figures: 10-Piston; 11-First recess; 111-First arc surface; 12-Second recess; 121-Blocking structure; 122-Second arc surface; 13-Central axis; 14-Throat; 141-Second chamfered surface; 15-First chamfered surface; 16-Top surface; 20-Injector; 21-First nozzle group; 211-First hole; 22-Second nozzle group; 221-Second hole; 30-Fuel; 40-First position; 50-Second position; X-Height direction. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0023] Marine diesel engines are characterized by high power and large space size. To achieve higher power output, a large fuel supply and high-pressure fuel injection are required to ensure that a large amount of fuel is fully combusted in a large space. High boost is also required to ensure that the intake air volume meets the excess air coefficient requirements for the combustion of a large amount of fuel. The large fuel spray cone angle and high flow rate high-pressure fuel injection form a long-penetrating high-concentration spray, which results in a slow fuel-air mixing rate and low combustion efficiency.

[0024] Please see Figure 1 and Figure 3This application provides a diesel engine combustion system, including a piston 10 and a fuel injector 20. The piston 10 includes a first recess 11 and a second recess 12 connected to each other, with the first recess 11 surrounding the second recess 12. Figure 1 The piston 10 shown represents its top structure; other parts are not depicted. Injectors 20 are spaced apart on one side of the piston 10 along the height direction X and located on the central axis 13 of the second recess 12. Injectors 20 include a first nozzle group 21 and a second nozzle group 22 spaced apart along the height direction X. The first nozzle group 21 faces the first recess 11 and is used to inject fuel 30 into the first recess 11. The second nozzle group 22 faces the second recess 12 and is used to inject fuel 30 into the second recess 12. A throat portion 14 is formed at the connection between the first recess 11 and the second recess 12, protruding towards the injector 20. The throat portion 14 serves to separate the fuel 30 within the first recess 11 and the second recess 12.

[0025] Understandably, the combustion chamber is formed by the cylinder head, cylinder liner, and piston 10, with the fuel injector 20 mounted on the cylinder head. The fuel injector 20 injects fuel 30 into the combustion chamber, allowing the fuel 30 to burn inside. The piston 10 has upper and lower recesses, namely a first recess 11 and a second recess 12. The second recess 12 is located at the center of the piston 10 and has a larger accommodating space. The first recess 11 surrounds the second recess 12, and the internal space of the first recess 11 is smaller than that of the second recess 12. This allows the main combustion process in the piston 10 to take place within the second recess 12, enabling more thorough mixing of fuel 30 and air and improving combustion efficiency.

[0026] Two sets of nozzles are provided on the injector 20, namely a first nozzle group 21 and a second nozzle group 22. The first nozzle group 21 sprays fuel 30 towards the first recess 11. The fuel 30 sprayed by the first nozzle group 21 impacts the first recess 11, causing the fuel 30 to be more evenly dispersed within the first recess 11, increasing the contact area with air and making it mix more thoroughly. This improves the combustion efficiency and thermal efficiency of the fuel 30 within the first recess 11. The second nozzle group 22 sprays fuel 30 towards the second recess 12. Similarly, the fuel 30 sprayed by the second nozzle group 22 impacts the second recess 12, causing the fuel 30 to be more evenly dispersed within the second recess 12, increasing the contact area with air and making it mix more thoroughly. This also improves the combustion efficiency and thermal efficiency of the fuel 30 within the second recess 12.

[0027] A throat 14 is provided at the connection position of the first recess 11 and the second recess 12. The throat 14 surrounds the second recess 12, and the first recess 11 surrounds the throat 14. Both the first recess 11 and the second recess 12 are recessed structures. When the injector 20 injects fuel 30 into the first recess 11 and the second recess 12 respectively, the fuel 30 will spread outwards under the impact force. Some of the fuel 30 will flow towards the throat 14. Since the throat 14 protrudes from the first recess 11 and the second recess 12, this part of the fuel 30 will impact the throat 14, thereby preventing some of the fuel 30 in the first recess 11 and the second recess 12 from accumulating at the throat 14, which would result in excessive amount and concentration of fuel 30, incomplete combustion, and reduced combustion efficiency. Therefore, by separating the fuel 30 in the first recess 11 and the second recess 12 through the throat 14, the fuel 30 can be fully burned at the corresponding positions, which can further improve its combustion efficiency.

[0028] Please see Figure 1 In conjunction with the above embodiments, in some embodiments, the second recess 12 includes a blocking structure 121 that protrudes toward the injector 20. The blocking structure 121 is located on the central axis 13 of the second recess 12 and is used to block a portion of the fuel 30 in the second recess 12.

[0029] It is understood that a blocking structure 121 is provided at the center of the second recess 12, and the blocking structure 121 protrudes from the second recess 12. When the second nozzle group 22 on the injector 20 injects fuel 30 into the second recess 12, the point where the fuel 30 impacts the second recess 12 surrounds the blocking structure 121. After the impact, the fuel 30 spreads in all directions, and some of the fuel 30 tends to converge towards the center of the second recess 12. Due to the obstruction of the blocking structure 121, this part of the fuel 30 cannot converge, thereby avoiding the situation where the volume and concentration of the fuel 30 increases after convergence, resulting in incomplete combustion. To a certain extent, this improves the combustion efficiency of the fuel 30 in the second recess 12.

[0030] Please see Figure 2 In conjunction with the above embodiments, in some embodiments, the first recess 11 has a first arc surface 111. When the first nozzle group 21 injects fuel 30 into the first recess 11, the first arc surface 111 is used to extend the fuel 30 in multiple directions. The second recess 12 has a second arc surface 122. The first arc surface 111 and the second arc surface 122 are connected, and the first arc surface 111 is arranged around the second arc surface 122. When the second nozzle group 22 injects fuel 30 into the second recess 12, the second arc surface 122 is used to extend the fuel 30 in multiple directions.

[0031] It is understandable that the inner wall surface of the first recess 11 is a first arc surface 111, and the surface of the first arc surface 111 is relatively smooth. When the fuel 30 impacts the first arc surface 111, it spreads outwards and is evenly distributed on the surface of the first arc surface 111. Similarly, the inner wall surface of the second recess 12 is a second arc surface 122. When the fuel 30 impacts the second arc surface 122, it spreads outwards and is evenly distributed on the surface of the second arc surface 122. By setting the first arc surface 111 and the second arc surface 122, the fuel 30 has a larger spreading area, and no accumulation occurs during the spreading process, avoiding excessively high concentrations in local areas and incomplete combustion. Preferably, as... Figure 1 As shown, the fuel 30 injected by the first nozzle group 21 impacts the middle position of the first arc surface 111, and the fuel 30 injected by the second nozzle group 22 impacts the middle position of the second arc surface 122, so that the fuel 30 has enough space to extend to both sides and is not easy to accumulate.

[0032] Please see Figure 2 , Figure 5 and Figure 6 In conjunction with the above embodiments, in some embodiments, the piston 10 has a first chamfered surface 15, and the top surface 16 of the piston 10 is connected to the first arc surface 111 through the first chamfered surface 15. The throat portion 14 has a second chamfered surface 141, and the first arc surface 111 is connected to the second arc surface 122 through the second chamfered surface 141.

[0033] It is understandable that the top surface 16 of the piston 10 is a plane, such as... Figure 5 As shown, a first chamfered surface 15 is provided at the position where the top surface 16 connects to the first arc surface 111. Originally, the top surface 16 and the first arc surface 111 were directly connected, and the connection point was relatively sharp. During the operation of the combustion system, there was a large stress concentration at the connection point. By providing the first chamfered surface 15 between the two for transition, the stress at the connection point can be dispersed, making the stress distribution uniform, reducing the stress concentration at the connection point, and protecting the piston 10.

[0034] Similarly, the first arc surface 111 and the second arc surface 122 are directly connected, and the connection point is relatively sharp, which will generate a large stress concentration. By setting the second chamfered surface 141 between the two for transition, the stress distribution at the connection point can be made uniform, reducing the stress concentration at the connection point and protecting the piston 10.

[0035] Please see Figure 3 and Figure 4In conjunction with the above embodiments, in some embodiments, the first nozzle group 21 includes a plurality of first nozzles 211 spaced apart circumferentially along the injector 20, each first nozzle 211 being disposed toward the first recess 11 for injecting fuel 30 into the first recess 11. The second nozzle group 22 includes a plurality of second nozzles 221 spaced apart circumferentially along the injector 20, each second nozzle 221 being disposed toward the second recess 12 for injecting fuel 30 into the second recess 12.

[0036] Understandably, the multiple first holes 211 in the first nozzle group 21 are spaced circumferentially along the bottom end of the injector 20 and spray fuel 30 toward the first recess 11. Similarly, the multiple second holes 221 in the second nozzle group 22 are spaced circumferentially along the bottom end of the injector 20 and spray fuel 30 toward the second recess 12. Based on the relative positions of the first recess 11 and the second recess 12, the multiple first holes 211 are positioned above the multiple second holes 221, ensuring that the fuel 30 sprayed from the first holes 211 does not interfere with the fuel 30 sprayed from the second holes 221. The multiple first holes 211 and the multiple second holes 221 are arranged in a ring, allowing the multiple first holes 211 to spray fuel 30 toward different positions in the first recess 11, and the multiple second holes 221 to spray fuel 30 toward different positions in the second recess 12. This facilitates even distribution of the fuel 30, reduces the risk of accumulation, ensures complete combustion, and improves combustion efficiency.

[0037] Please see Figure 2 In conjunction with the above embodiments, in some embodiments, the first recess 11 has a first radius r, and the second recess 12 has a second radius R, wherein the first radius r is smaller than the second radius R. The diameter of the first hole 211 is smaller than the diameter of the second hole 221.

[0038] It is understandable that since the diameter of the first hole 211 is smaller than that of the second hole 221, the amount of fuel 30 injected through the first hole 211 is less than that injected through the second hole 221 within the same time period. Since the first radius r of the first recess 11 is smaller than the second radius R of the second recess 12, the opening of the first recess 11 is smaller than the opening of the second recess 12, and the internal space of the first recess 11 is smaller than that of the second recess 12. A larger amount of fuel 30 is injected into the interior of the second recess 12 through multiple second holes 221, causing the combustion process to mainly occur within the second recess 12. A smaller amount of fuel 30 is injected into the interior of the first recess 11 through multiple first holes 211, reducing the risk of fuel 30 slipping out of the piston 10 and avoiding fuel waste. This also avoids the waste of heat caused by fuel 30 burning outside the piston 10, thus improving the thermal efficiency of the combustion system.

[0039] Please see Figure 7In conjunction with the above embodiments, in some embodiments, the first hole 211 and the second hole 221 are misaligned along the height direction X of the piston 10.

[0040] It is understandable that multiple first holes 211 spray fuel 30 toward the first recess 11, and the position of the fuel 30 sprayed by each first hole 211 on the first recess 11 is as follows: Figure 7 At the first position 40, multiple second holes 221 spray fuel 30 toward the second recess 12, and the position of the fuel 30 sprayed by each second hole 221 on the second recess 12 is as follows. Figure 7 The second position 50 is located in the first recess 11. Multiple first holes 211 correspond one-to-one with multiple first positions 40, and multiple second holes 221 correspond one-to-one with multiple second positions 50. Specifically, in the radial direction of the first recess 11, the first positions 40 and second positions 50 are offset from each other. When the fuel 30 at the first position 40 diffuses, it is less likely to converge with the fuel 30 diffused at the second position 50 at the throat 14. This further prevents the fuel 30 in the first recess 11 and the second recess 12 from converging, thus avoiding incomplete combustion.

[0041] Meanwhile, the fuel 30 at the first position 40 and the second position 50 generally diffuses in a shape similar to a circle or an ellipse. The diffusion positions can be staggered. If the fuel 30 diffuses to the throat 14, the combustion positions can also be staggered. For example, if fuel 30 diffuses on one side of the throat 14 facing the first recess 11, but not on the other side, then fuel 30 will burn on one side of the throat 14, but not on the other side, thereby reducing the heat load at that position on the throat 14.

[0042] Please see Figure 8 In conjunction with the above embodiments, this application also provides an optimization method for a diesel engine combustion system, including: S11: Based on the three-dimensional simulation analysis of the diesel engine combustion process, and with the goals of improving thermal efficiency and reducing heat load, the optimization direction of combustion characteristics is obtained, including the spray flame distribution and combustion phase interval. S12: Based on the diesel engine combustion system described above and the optimization direction of combustion characteristics, obtain the spray flame distribution optimization design and combustion phase interval optimization design of the diesel engine combustion system; S13: Based on the optimized diesel engine combustion system with spray flame distribution and combustion phase range, determine whether the goals of improving thermal efficiency and reducing heat load have been achieved.

[0043] Understandably, performing three-dimensional CFD (Computational Fluid Dynamics) simulation analysis on the combustion process of the existing diesel engine combustion system requires attention to combustion characteristics such as the air-fuel mixture velocity, stoichiometric ratio spatial distribution, spray flame spatial distribution, and combustion phase interval. The optimization method aims to improve the thermal efficiency and reduce the thermal load of the combustion system. During the simulation, a significant correlation was found between the thermal efficiency and thermal load of the corresponding structure and the spray flame spatial distribution and combustion phase interval. Therefore, the optimization direction determined through simulation analysis is to optimize the spray flame spatial distribution and combustion phase interval.

[0044] The structure of the diesel engine combustion system described above includes a piston 10 and an injector 20. The piston 10 includes a first recess 11 and a second recess 12. The injector 20 includes a first nozzle group 21 and a second nozzle group 22. By adjusting the structural parameters of the first recess 11, the second recess 12, the first nozzle group 21, and the second nozzle group 22, the spatial distribution of the spray flame and the combustion phase interval are optimized. This results in the corresponding optimized design of the spray flame spatial distribution and the optimized design of the combustion phase interval, which reduces the penetration distance of the spray jet of the injector 20 and distributes it as much as possible within the internal space of the piston 10. This promotes fuel-air mixing, improves the in-cylinder air utilization rate, and reduces the heat transfer of the spray flame to the cylinder liner.

[0045] Since the optimized spray flame spatial distribution and combustion phase range are obtained by adjusting the parameters of structures such as the first recess 11, the second recess 12, the first nozzle group 21, and the second nozzle group 22, the adjusted parameters of these structures are input into the simulation software to perform a three-dimensional simulation analysis of the combustion process again. This yields the optimized thermal efficiency and heat load of the corresponding structure, which are then compared with the thermal efficiency and heat load of the structure before optimization to determine whether the thermal efficiency has been improved and the heat load reduced. If the optimization objective is achieved, the optimized structural parameters can be used to design the diesel engine. If the optimization objective is not achieved, the above steps are repeated to continue adjusting the corresponding structural parameters to optimize the spray flame spatial distribution and combustion phase range until the goal of improving combustion thermal efficiency and reducing structural heat load is ultimately achieved.

[0046] In conjunction with the above embodiments, in some embodiments, the piston 10 of the diesel engine combustion system includes a first recess 11 and a second recess 12, and the injector 20 of the diesel engine combustion system includes a first nozzle group 21 and a second nozzle group 22. The first nozzle group 21 includes a plurality of first holes 211, and the second nozzle group 22 includes a plurality of second holes 221.

[0047] The steps for obtaining the optimal design of the spray flame distribution of a diesel engine combustion system include: Based on the three-dimensional simulation analysis of the diesel engine combustion process, the fuel injection ratio of the first recess 11 and the second recess 12 of the piston 10 is obtained, and the aperture of the first hole 211 and the aperture of the second hole 221 are obtained according to the fuel injection ratio. Based on the structure of piston 10 and injector 20, such as the diameter of the first hole 211 and the diameter of the second hole 221 on injector 20, the shape of the first recess 11 and the shape of the second recess 12, the diameter of the first hole 211 and the diameter of the second hole 221, and the included angle between the first hole 211 and the corresponding second hole 221 are obtained. Based on the shape of the first recess 11 and the shape of the second recess 12, the aperture of the first hole 211 and the aperture of the second hole 221, and the included angle between the first hole 211 and the second hole 221, a three-dimensional simulation analysis is performed to obtain the oil-gas mixing situation, thermal efficiency and heat transfer of the wall surface of the heated components, and the scheme is optimized to obtain the spray flame distribution optimization design of the diesel engine combustion system.

[0048] Understandably, when optimizing the spray flame distribution of the diesel engine combustion system, it is necessary to determine the orifice diameters of the first hole 211 and the second hole 221, so that the amount of fuel 30 injected by the first hole 211 is less than the amount of fuel 30 injected by the second hole 221, and the first hole 211 sprays towards the first recess 11, while the second hole 221 sprays towards the second recess 12. The purpose is to minimize the amount of fuel 30 sprayed onto the top surface 16 of the piston 10, thereby preventing the fuel 30 from burning on the top surface 16, thus reducing the flame distribution near the cylinder liner wall and lowering the cylinder liner thermal load.

[0049] Understandably, the combustion chamber is composed of the cylinder head above, the piston below, and the cylinder liner surrounding it. The injector 20 is fixed to the center of the cylinder head. Ideally, high-thermal-efficiency, low-heat-load combustion should occur at the center, with less flame extending towards the cylinder liner, thus reducing heat dissipation to the cylinder liner and lowering its thermal load. This is why the injector 20 in this application is designed with a small upper nozzle, a low injection volume, and a corresponding small space in the first recess 11—to reduce the extension of the flame towards the cylinder liner.

[0050] The shapes of the first recess 11 and the second recess 12 also need to be determined. Their shapes can be adjusted, for example, to be "narrowed," "open," or "straight." The smoothness of the connection between the first and second recesses 11 and 12, as well as the smoothness of the second recess 12 towards the center of the piston 10, can also be changed. Specifically, the first radius r of the first recess 11 is smaller than the second radius R of the second recess 12, allowing most of the fuel 30 to burn and develop within the second recess 12, reducing the amount of fuel 30 in the first recess 11. While maintaining a constant diesel engine compression ratio, the smaller volume of the first recess 11 provides ample space for the development of most of the fuel 30 within the second recess 12, which is beneficial for the overall spray flame distribution within the combustion chamber. Since the shapes of the first and second recesses 11 and 12 guide the spray flame after impact, determining its development and thus affecting air utilization and heat load distribution, a recess shape scheme including "narrowed," "open," and "straight" types with varying degrees of smoothness is selected for subsequent optimal selection.

[0051] Then, based on the apertures of the first hole 211 and the second hole 221, as well as the shapes of the first recess 11 and the second recess 12, the included angle between the first hole 211 and the second hole 221 is determined to ensure that the fuel 30 injected from the first hole 211 is located in the first recess 11 and the fuel 30 injected from the second hole 221 is located in the second recess 12. This avoids the fuel 30 injected from the first hole 211 and the second hole 221 from interfering with each other after hitting the wall and splitting, resulting in local over-richness and reduced combustion efficiency.

[0052] By determining the aperture of the first hole 211 and the second hole 221, the shape of the first recess 11 and the second recess 12, and the included angle between the first hole 211 and the second hole 221, a three-dimensional simulation analysis is performed to obtain the oil-gas mixing condition, thermal efficiency, and heat transfer (heat load) of the heated component wall corresponding to these parameters. Since the above parameters can be tested and adjusted, multiple parameter schemes can be selected, and the better scheme can be selected from these schemes to complete the optimized design of the spray flame distribution.

[0053] In conjunction with the above embodiments, in some embodiments, the distribution of the spray flame includes the distribution of the free jet of fuel 30, the impact position of the spray jet on the wall, and the development of the spray flame along the wall after impact. Based on the shape of the first recess 11 and the shape of the second recess 12, the aperture of the first hole 211 and the aperture of the second hole 221, and the included angle between the first hole 211 and the second hole 221, the distribution of the free jet of fuel 30, the impact position of the spray jet on the wall, and the development of the spray flame along the wall after impact are optimized.

[0054] It is understandable that the distribution of the spray flame includes the distribution of the free jet of fuel 30, the impact position of the spray jet on the wall, and the development of the spray flame along the wall after impact. These features are all related to the shape of the first recess 11 and the shape of the second recess 12, the aperture of the first hole 211 and the aperture of the second hole 221, and the included angle between the first hole 211 and the second hole 221. By designing these parameters, the distribution of the free jet of fuel 30, the impact position of the spray jet on the wall, and the development of the spray flame along the wall after impact can be achieved, thereby optimizing the distribution of the spray flame.

[0055] In conjunction with the above embodiments, in some embodiments, the steps of obtaining the aperture of the first hole 211 and the aperture of the second hole 221 include: Based on the three-dimensional simulation analysis of the diesel engine combustion process, the ratio of the amount of oil extending along the top surface 16 of the piston 10 to the total amount of oil after the spray flame hits the wall is obtained. After the spray flame hits the wall, the ratio of the amount of oil extending along the top surface 16 to the total amount of oil is determined as the initial value of the oil spray ratio of the first nozzle group 21. Based on the initial value of the oil spray ratio of the first nozzle group 21, as well as the number of the first hole 211 and the number of the second hole 221, the aperture of the first hole 211 and the aperture of the second hole 221 are obtained.

[0056] Understandably, during the three-dimensional simulation analysis of the combustion process of the original diesel engine, after the spray flame impacts the wall, some fuel 30 will slide or splash onto the top surface 16 of the piston 10. The heat generated by this portion of fuel 30 increases the thermal load on the cylinder liner, so it is necessary to reduce the flame distribution near the cylinder liner wall. Through calculation and analysis, the proportion of this portion of fuel 30 to the total fuel 30 injected by the injector 20 is obtained. This proportion is set as the proportion of fuel 30 injected into the first recess 11 by the first nozzle group 21 to the total amount of fuel injected by the injector 20. Through design adjustments, the fuel 30 that originally slid or splashed onto the top surface 16 of the piston 10 is injected into the first recess 11, minimizing the amount of fuel 30 on the top surface 16. Based on the proportion of fuel injected by the first nozzle group 21, and the number of first holes 211 and second holes 221, the orifice diameters of the first holes 211 and second holes 221 are calculated using corresponding formulas.

[0057] For example: the fuel injection quantities of the first and second nozzle groups are respectively and The number of nozzles in the first nozzle group and the second nozzle group are respectively and The nozzle radii of the first and second nozzle groups are respectively and Since the first and second nozzle groups have the same injection pressure, their injection speed... Same. During the spray duration... Then: , ; Therefore, we can conclude that .

[0058] In conjunction with the above embodiments, in some embodiments, the step of obtaining the shape of the first recess 11 and the second recess 12 includes: like Figure 2 As shown, the first recess 11 has a first radius r and a first slope K1, and the second recess 12 has a second radius R and a second slope K2; Based on the orthogonal design method, multiple horizontal values ​​are set for the first radius r, the first slope K1, the second radius R, and the second slope K2, respectively, to obtain different shapes of the first concave part 11 and the second concave part 12, and to optimize the scheme, so as to improve the thermal efficiency of the diesel engine combustion system and reduce the heat load.

[0059] It is understandable that adjusting the shapes of the first recess 11 and the second recess 12 can be achieved by setting the first radius r and the first slope K1 of the first recess 11, and the second radius R and the second slope K2 of the second recess 12. Through orthogonal design, multiple horizontal values ​​can be selected for the first radius r, the first slope K1, the second radius R, and the second slope K2, for example, three to five horizontal values. By changing the first radius r and the second radius R, the first recess 11 and the second recess 12 can be adjusted to shapes such as "narrowed," "open," or "straight." By changing the first slope K1, the smoothness of the connection between the first recess 11 and the second recess 12 can be adjusted, and by changing the second slope K2, the smoothness of the second recess 12 towards the center of the piston 10 can be adjusted. By selecting appropriate design parameters, most of the fuel 30 can burn and develop within the second recess 12, which is beneficial to the overall spray flame distribution inside the combustion chamber, thereby improving air utilization and reducing heat load.

[0060] In conjunction with the above embodiments, in some embodiments, the step of obtaining the included angle between the first hole 211 and the second hole 221 includes: Based on the aperture of the first hole 211 and the aperture of the second hole 221, as well as the shapes of the different first recesses 11 and the second recesses 12, different included angles between the first hole 211 and the corresponding second hole 221 are obtained, and the scheme is optimized so that the fuel 30 sprayed from the first hole 211 is located in the first recess 11, and the fuel 30 sprayed from the second hole 221 is located in the second recess 12.

[0061] Understandably, after determining the diameters of the first hole 211 and the second hole 221, different included angles between the first hole 211 and the corresponding second hole 221 are designed using 3D simulation software based on the different shapes of the first recess 11 and the second recess 12. Each included angle corresponds to a specific shape of the first recess 11 and the second recess 12. When designing this included angle, it is necessary to ensure that during the injection duration, the fuel 30 injected by the first hole 211 is within the first recess 11, and the fuel 30 injected by the second hole 221 is within the second recess 12. This avoids interference between the injected fuel 30, preventing localized over-rich fuel 30 and resulting in lower combustion efficiency, thus ensuring high thermal efficiency of the combustion system. The injection duration refers to the time interval from the start of fuel injection 30 into the combustion chamber by the diesel engine's injector 20 to the cessation of fuel injection 30.

[0062] In conjunction with the above embodiments, in some embodiments, obtaining the optimized design of the combustion phase range includes: The combustion phase range includes the combustion start-up and combustion duration. Based on the combustion start-up and combustion duration, the injection timing and injection duration are obtained. Based on the orthogonal design method, multiple horizontal values ​​are set for the injection timing and injection duration, and three-dimensional simulation calculations are performed. The optimal value is selected to ensure that the piston is near top dead center at the injection timing and the thermal load is within the preset range during the injection duration.

[0063] It is understandable that the combustion phase range of a diesel engine includes the combustion start-up and combustion duration, which depend on the injection timing and injection duration. Therefore, optimizing the diesel engine combustion phase range is equivalent to optimizing the injection timing and injection duration. Specifically, the combustion start-up refers to the instant when the compressed fuel 30 and air mixture in the diesel engine combustion chamber begins a stable combustion reaction; the combustion duration refers to the time interval from the combustion start-up to the completion of the combustion reaction at a specified ratio; and the injection timing refers to the moment when the diesel engine injector 20 begins to inject fuel 30 into the combustion chamber, usually expressed as the crankshaft angle relative to the piston reaching top dead center (e.g., compression top dead center), used to precisely control the matching relationship between fuel injection and the engine's working cycle (e.g., compression and power processes).

[0064] Using orthogonal design methods, multiple horizontal values ​​(e.g., 3 to 5) are selected for injection timing and injection duration, and three-dimensional simulation calculations are performed. The matching of injection timing and injection duration must correspond to the diesel engine's operating characteristics, ensuring concentrated heat release near top dead center (TDC) to reduce negative work, minimize heat loss, and improve thermal efficiency. Therefore, when the piston moves to near TDC, this moment is preferentially used as the corresponding injection timing. For a given injection quantity, there is a one-to-one correspondence between injection duration and injection pressure; changing the injection duration requires corresponding adjustments to the injection pressure. Multiple horizontal values ​​for injection duration are selected as needed and input into the simulation software for analysis and calculation. While ensuring the structural thermal load remains within a preset range, the value with higher thermal efficiency is selected as the parameter for the optimized injection duration. The preset range refers to the range of thermal loads the structure can withstand.

[0065] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0066] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0067] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0068] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A method for optimizing a diesel engine combustion system, characterized in that, include: A diesel engine combustion system is provided, the diesel engine combustion system comprising: The piston (10) includes a first recess (11) and a second recess (12) connected to each other, wherein the first recess (11) is disposed around the second recess (12); The injector (20) is spaced apart on one side of the piston (10) along the height direction (X) and located on the central axis (13) of the second recess (12). The injector (20) includes a first nozzle group (21) and a second nozzle group (22) spaced apart. The first nozzle group (21) is disposed toward the first recess (11) and is used to inject fuel (30) into the first recess (11). The second nozzle group (22) is disposed toward the second recess (12) and is used to inject the fuel (30) into the second recess (12). The first nozzle group (21) includes a plurality of first holes (211), and the second nozzle group (22) includes a plurality of second holes (221). The optimization method includes: based on three-dimensional simulation analysis of the diesel engine combustion process and the objectives of improving thermal efficiency and reducing heat load, obtaining optimization directions for combustion characteristics, including spray flame distribution and combustion phase interval; based on the diesel engine combustion system and the optimization directions of the combustion characteristics, obtaining optimized designs for the spray flame distribution and combustion phase interval of the diesel engine combustion system; and based on the optimized diesel engine combustion system with optimized spray flame distribution and combustion phase interval, determining whether the objectives of improving thermal efficiency and reducing heat load have been achieved. The process of obtaining the optimized design of the spray flame distribution of the diesel engine combustion system includes: obtaining the fuel injection ratio of the first recess (11) and the second recess (12) of the piston (10) based on the three-dimensional simulation analysis of the diesel engine combustion process, and obtaining the aperture of the first hole (211) and the aperture of the second hole (221) according to the fuel injection ratio; obtaining the shape of the first recess (11) and the shape of the second recess (12), as well as the included angle between the first hole (211) and the corresponding second hole (221), based on the structure of the piston (10) and the structure of the injector (20); performing three-dimensional simulation analysis based on the shape of the first recess (11) and the shape of the second recess (12), the aperture of the first hole (211) and the aperture of the second hole (221), and the included angle between the first hole (211) and the second hole (221), obtaining the oil-gas mixing situation, thermal efficiency and heat transfer of the wall of the heated component, and selecting a scheme to obtain the optimized design of the spray flame distribution of the diesel engine combustion system.

2. The optimization method for a diesel engine combustion system according to claim 1, characterized in that, A throat (14) is formed at the connection between the first recess (11) and the second recess (12) and protrudes toward the injector (20). The throat (14) is used to separate the fuel (30) in the first recess (11) and the second recess (12).

3. The method for optimizing a diesel engine combustion system according to claim 2, characterized in that, The first recess (11) has a first arc surface (111), and when the first nozzle group (21) injects fuel (30) into the first recess (11), the first arc surface (111) is used to extend the fuel (30) in multiple directions; The second recess (12) has a second arc surface (122), the first arc surface (111) and the second arc surface (122) are connected, and the first arc surface (111) is arranged around the second arc surface (122). When the second nozzle group (22) injects fuel (30) into the second recess (12), the second arc surface (122) is used to extend the fuel (30) in multiple directions.

4. The method for optimizing a diesel engine combustion system according to claim 3, characterized in that, The piston (10) has a first chamfered surface (15), and the top surface (16) of the piston (10) is connected to the first arc surface (111) through the first chamfered surface (15); The throat portion (14) has a second chamfered surface (141), and the first arc surface (111) is connected to the second arc surface (122) through the second chamfered surface (141).

5. The method for optimizing a diesel engine combustion system according to claim 1, characterized in that, The first nozzle group (21) includes a plurality of first holes (211) arranged circumferentially along the injector (20), each first hole (211) being disposed toward the first recess (11) for injecting fuel (30) into the first recess (11); The second nozzle group (22) includes a plurality of second holes (221) spaced apart circumferentially along the injector (20), each second hole (221) being disposed toward the second recess (12) for injecting fuel (30) into the second recess (12).

6. The method for optimizing a diesel engine combustion system according to claim 5, characterized in that, The first recess (11) has a first radius r, and the second recess (12) has a second radius R, wherein the first radius r is smaller than the second radius R; The diameter of the first hole (211) is smaller than the diameter of the second hole (221).

7. The method for optimizing a diesel engine combustion system according to claim 5, characterized in that, Along the height direction (X) of the piston (10), the first hole (211) and the second hole (221) are misaligned.

8. The method for optimizing a diesel engine combustion system according to claim 1, characterized in that, The distribution of the spray flame includes the distribution of the free jet of fuel (30), the impact position of the spray oil jet on the wall, and the development of the spray flame along the wall after impact. Based on the shape of the first recess (11) and the shape of the second recess (12), the aperture of the first hole (211) and the aperture of the second hole (221), and the included angle between the first hole (211) and the second hole (221), the distribution of the free jet of fuel (30), the impact position of the spray jet on the wall and the development of the spray flame along the wall after impact are optimized.

9. The method for optimizing a diesel engine combustion system according to claim 1, characterized in that, The steps of obtaining the aperture of the first hole (211) and the aperture of the second hole (221) include: Based on the three-dimensional simulation analysis of the diesel engine combustion process, the ratio of the amount of oil extending along the top surface (16) of the piston (10) after the spray flame hits the wall to the total amount of oil is obtained. After the spray flame hits the wall, the ratio of the amount of oil extending along the top surface (16) to the total amount of oil is determined as the initial value of the oil spray ratio of the first nozzle group (21). Based on the initial value of the oil spray ratio of the first nozzle group (21), the number of the first hole (211) and the number of the second hole (221), the aperture of the first hole (211) and the aperture of the second hole (221) are obtained.

10. The method for optimizing a diesel engine combustion system according to claim 1, characterized in that, The step of obtaining the shapes of the first recess (11) and the second recess (12) includes: The first recess (11) has a first radius r and a first slope K1, and the second recess (12) has a second radius R and a second slope K2; Based on the orthogonal design method, multiple horizontal values ​​are set for the first radius r, the first slope K1, the second radius R and the second slope K2 respectively, to obtain different shapes of the first concave part (11) and the second concave part (12), and to select a scheme to improve the thermal efficiency of the diesel engine combustion system and reduce the heat load.

11. The method for optimizing a diesel engine combustion system according to claim 1, characterized in that, The step of obtaining the included angle between the first hole (211) and the second hole (221) includes: Based on the aperture of the first hole (211) and the aperture of the second hole (221), and the shapes of the different first recesses (11) and the second recesses (12), different included angles between the first hole (211) and the corresponding second hole (221) are obtained, and a scheme is selected so that the fuel (30) sprayed from the first hole (211) is located in the first recess (11), and the fuel (30) sprayed from the second hole (221) is located in the second recess (12).

12. The method for optimizing a diesel engine combustion system according to claim 1, characterized in that, The optimization design for obtaining the combustion phase range includes: The combustion phase interval includes the combustion start point and the combustion duration. Based on the combustion start point and the combustion duration, the injection timing and the injection duration are obtained. Based on the orthogonal design method, multiple horizontal values ​​are set for the injection timing and the injection duration, and three-dimensional simulation calculations are performed and selected so that the piston is near top dead center at the injection timing and the thermal load is within a preset range during the injection duration.

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