Design method of narrow domain combustion system with high expansion ratio

Abstract

The present invention discloses a design method for a narrow-domain combustion system with a high expansion ratio. The combustion system includes a cylinder, a piston, and a cylinder head. The piston is disposed inside the cylinder, and the cylinder head is horizontally mounted on the top of the cylinder. The bottom surface of the cylinder head, the inner wall of the cylinder, and the top of the piston jointly enclose a combustion chamber. An intake pipe communicating with the combustion chamber is provided on the cylinder head, and an intake cam for controlling the opening and closing of the intake valve is provided on the intake pipe. The design method includes: adjusting the phase of the intake cam to adjust the closing phase of the intake valve, so that during the upward movement of the piston in the vertical direction, the amount of gas compressed by the piston is reduced; adjusting the geometric dimensions of the top of the piston to reduce the first volume of the combustion chamber, and the first volume and the amount of gas compressed by the piston are reduced in equal proportion, so that the pressure in the combustion system at the end of the compression stroke remains substantially unchanged, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system; the first volume is the volume of the combustion chamber when the piston is at the top dead center.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to the technical field of engines, and particularly to a design method of a narrow-domain combustion system with a high expansion ratio. Background Art

[0002] Currently, commercial vehicles mainly powered by diesel engines consume a large amount of petroleum resources. Energy conservation and emission reduction are of great significance for reducing petroleum consumption, greenhouse gas emissions, reducing dependence on foreign petroleum, and protecting the environment. Compared with traditional engines, hybrid power systems can flexibly adjust the power output of internal combustion engines and motors according to the power demand of the whole vehicle, reducing the probability of internal combustion engines operating in low-load, transient, and other poor-economy intervals. The operating conditions of the engine can be concentrated in a smaller range, thereby improving the economic level of the whole vehicle. Therefore, it is necessary to reasonably design and match the intake system, combustion chamber, and fuel injection system according to the operating conditions of hybrid-specific engines to achieve efficient and clean combustion of the engine.

[0003] In the engine thermodynamic cycle, by increasing the expansion stroke to fully improve the expansion degree of the expansion process, the heat released by fuel combustion can be further fully converted into mechanical work, improving the engine thermal efficiency. In the prior art, the design method of the combustion system usually adopts the traditional Otto thermodynamic cycle. Based on the fact that the expansion ratio of the engine is the same as the compression ratio in the traditional Otto thermodynamic cycle, the existing design method of the combustion system has the problems that the increase in the expansion ratio is limited by the mechanical load or knocking of the engine, and if the separation of the compression ratio and the expansion ratio is to be achieved, a complex mechanical structure needs to be adopted, resulting in poor reliability and high manufacturing cost. Summary of the Invention

[0004] In view of this, the embodiments of the present invention provide a design method of a narrow-domain combustion system with a high expansion ratio. By adjusting the phase of the intake cam and the geometric size of the top of the piston, the first volume and the amount of gas compressed by the piston are reduced in equal proportion to increase the expansion stroke of the combustion system.

[0005] According to an embodiment of the present invention, a design method for a narrow-domain combustion system with a high expansion ratio is provided. The combustion system includes a cylinder, a piston, and a cylinder head. The piston is disposed inside the cylinder, and the cylinder head is horizontally mounted on the top of the cylinder. The bottom surface of the cylinder head, the inner wall of the cylinder, and the top of the piston together enclose a combustion chamber. An intake pipe communicating with the combustion chamber is further provided on the cylinder head, and an intake cam for controlling the opening and closing of an intake valve is provided on the intake pipe. The design method includes: adjusting the phase of the intake cam to adjust the closing phase of the intake valve, so that during the upward movement of the piston in the vertical direction, the amount of gas compressed by the piston is reduced; and adjusting the geometric size of the top of the piston to reduce a first volume of the combustion chamber, the first volume being reduced in proportion to the amount of gas compressed by the piston, so that the pressure in the combustion system at the end of the compression stroke remains substantially unchanged, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system; wherein the first volume is the volume of the combustion chamber when the piston is at the top dead center.

[0006] According to an embodiment of the present invention, the design method further includes: setting a plurality of preset geometric compression ratios and a plurality of preset phases of the intake cam; determining a first phase of the intake cam and a first geometric compression ratio of the combustion system from the plurality of preset geometric compression ratios and the plurality of preset phases based on the minimum value of the fuel consumption of the combustion system; and determining the first volume of the combustion chamber based on the first geometric compression ratio.

[0007] According to an embodiment of the present invention, determining the first phase of the intake cam and the first geometric compression ratio of the combustion system from the plurality of preset geometric compression ratios and the plurality of preset phases based on the minimum value of the fuel consumption of the combustion system includes: respectively obtaining a plurality of first fuel consumption values corresponding to the plurality of preset phases under the conditions of the plurality of preset geometric compression ratios; obtaining a plurality of first curves respectively representing the corresponding relationships between the preset phases and the first fuel consumption values corresponding to the plurality of preset geometric compression ratios; determining the preset geometric compression ratio corresponding to the minimum value among all the first fuel consumption values from the plurality of first curves, and determining the preset geometric compression ratio corresponding to the minimum value as the first geometric compression ratio; and determining the preset phase corresponding to the minimum value in the first curve corresponding to the first geometric compression ratio, and determining the preset phase corresponding to the minimum value as the first phase.

[0008] According to an embodiment of the present invention, a recessed portion is provided on the top of the piston. The recessed portion includes: a throat area connected to the top surface of the piston, which is configured as a stepped curved surface recessed in the axial direction; two pit areas respectively connected to the lower side of the throat area, and the pit area is configured as an arc surface with the center of the circle located inside the recessed portion; and a raised area, the periphery of the raised area is connected to the inner sides in the radial direction of the two pit areas. The design method further includes: based on the first volume of the combustion chamber, determining the minimum diameter d in the radial direction of the throat area, the distance h in the axial direction from the bottom of the cylinder head to the lower end of the throat area, the distance H in the axial direction from the bottom of the cylinder head to the bottom of the pit area, and the radius R of the arc surface of the pit area.

[0009] According to an embodiment of the present invention, the value range of the preset phase is -80° to 120°, preferably -60°, -40°, -20°, 0°, 20°, 40°, 60°, 80°.

[0010] According to an embodiment of the present invention, the value range of the preset geometric compression ratio is 18 to 23, preferably 19, 20, 21, 22.

[0011] According to an embodiment of the present invention, the combustion system further includes an injector with one end extending into the combustion chamber. The design method further includes: based on the minimum value of the fuel consumption of the combustion system, determining the number of holes of the injection holes of the injector, the diameter of the injector, and the flow rate of the injector.

[0012] According to an embodiment of the present invention, another design method of a narrow-domain combustion system with a high expansion ratio is provided. The combustion system includes a cylinder, a piston, and a cylinder head. The piston is disposed inside the cylinder, the cylinder head is horizontally installed on the top of the cylinder, and the bottom surface of the cylinder head, the inner wall of the cylinder, and the top of the piston jointly enclose a combustion chamber. An intake pipe communicating with the combustion chamber is further provided on the cylinder head, and a supercharger is provided on the intake pipe. The design method includes: reducing the intake air volume in the combustion system through the supercharger; and reducing the first volume of the combustion chamber, and the first volume is reduced in equal proportion to the intake air volume, so that the pressure in the combustion system at the end of the compression stroke is substantially unchanged, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system; wherein the first volume is the volume of the combustion chamber when the piston is at the top dead center.

[0013] According to an embodiment of the present invention, the supercharger is a turbocharger, and the value range of the maximum efficiency η of the supercharger is 80% < η < 100%.

[0014] According to an embodiment of the present invention, a recessed portion is provided at the top of the piston. The recessed portion includes: a throat area connected to the top surface of the piston and configured as a stepped curved surface recessed in the axial direction; two pit areas respectively connected to the lower side of the throat area, and the pit area is configured as an arc surface with the center of the circle located inside the recessed portion; and a raised area, with the periphery of the raised area connected to the inner sides in the radial direction of the two pit areas. The design method further includes: based on the first volume of the combustion chamber, determining the minimum diameter d in the radial direction of the throat area, the distance h in the axial direction from the bottom of the cylinder head to the lower end of the throat area, the distance H in the axial direction from the bottom of the cylinder head to the bottom of the pit area, and the radius R of the arc surface of the pit area.

[0015] According to the design method of the narrow-domain combustion system with a high expansion ratio according to the above embodiment of the present invention, by adjusting the phase of the intake cam and the geometric dimensions of the top of the piston, the first volume and the amount of gas compressed by the piston are reduced in equal proportion, so as to increase the expansion ratio of the combustion system and further increase the expansion stroke of the combustion system. Description of the Drawings

[0016] Figure 1 is a schematic diagram of the principle of the narrow-domain combustion system with a high expansion ratio of the present invention;

[0017] Figure 2 is a schematic diagram of the geometry and dimensions of the top of the piston;

[0018] Figure 3 is an assembly schematic diagram between the piston, the cylinder and the cylinder head; and

[0019] Figure 4 is a change curve graph between the preset phase of the intake cam and the first fuel consumption value under different preset geometric compression ratios.

[0020] In the figure:

[0021] 1 - cylinder;

[0022] 2 - piston; 21 - recessed portion; 211 - throat area; 212 - pit area; 213 - raised area;

[0023] 3 - cylinder head;

[0024] 4 - combustion chamber;

[0025] 5 - intake pipe; 51 - intake cam; 52 - supercharger; 53 - turbine; 54 - intercooler; 55 - throttle valve;

[0026] 6 - intake valve;

[0027] 7 - injector;

[0028] 8 - Exhaust pipe;

[0029] 9 - Exhaust valve. Detailed implementation manners

[0030] 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 specific embodiments and the accompanying drawings.

[0031] According to the inventive concept of one aspect of the present invention, a design method for a narrow - domain combustion system with a high expansion ratio is provided. The combustion system includes a cylinder, a piston and a cylinder head. The piston is disposed inside the cylinder, the cylinder head is horizontally installed on the top of the cylinder, and the bottom surface of the cylinder head, the inner wall of the cylinder and the top of the piston jointly enclose a combustion chamber. An intake pipe communicating with the combustion chamber is further provided on the cylinder head, and an intake cam for controlling the opening and closing of an intake valve is provided on the intake pipe. The design method includes: adjusting the phase of the intake cam to adjust the closing phase of the intake valve, so that during the process of the piston moving upward in the vertical direction, the amount of gas compressed by the piston is reduced; and adjusting the geometric dimension of the top of the piston to reduce the first volume of the combustion chamber. The first volume is reduced in proportion to the amount of gas compressed by the piston, so that the pressure in the combustion system at the end of the compression stroke remains substantially unchanged, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system. Wherein, the first volume is the volume of the combustion chamber when the piston is at the top dead center.

[0032] Figure 1 It is a schematic diagram of the principle of the narrow - domain combustion system with a high expansion ratio of the present invention.

[0033] According to an exemplary embodiment of the present invention, please refer to Figure 1 , a design method for a narrow - domain combustion system with a high expansion ratio is provided. The combustion system includes a cylinder 1, a piston 2 and a cylinder head 3. The piston 2 is disposed inside the cylinder 1, the cylinder head 3 is horizontally installed on the top of the cylinder 1, and the bottom surface of the cylinder head 3, the inner wall of the cylinder 1 and the top of the piston 2 jointly enclose a combustion chamber 4. An intake pipe 5 communicating with the combustion chamber 4 is further provided on the cylinder head 3, and an intake cam 51 for controlling the opening and closing of an intake valve 6 is provided on the intake pipe 5. The design method includes: adjusting the phase of the intake cam 51 to adjust the closing phase of the intake valve 6, so that during the process of the piston 2 moving upward in the vertical direction, the amount of gas compressed by the piston 2 is reduced. Adjusting the geometric dimension of the top of the piston 2 to reduce the first volume of the combustion chamber 4. The first volume is reduced in proportion to the amount of gas compressed by the piston 2, so that the pressure in the combustion system at the end of the compression stroke remains substantially unchanged, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system. Wherein, the first volume is the volume of the combustion chamber 4 when the piston 2 is at the top dead center.

[0034] In this embodiment, by adjusting the phase of the intake cam 51 and the geometric dimensions of the top of the piston 2, the closing phase of the intake valve 6 is adjusted and the first volume of the combustion chamber 4 is reduced, so that the first volume and the amount of gas compressed by the piston 2 are reduced in equal proportion, and the pressure in the combustion system at the end of the compression stroke remains substantially unchanged, so as to increase the expansion ratio of the combustion system and further increase the expansion stroke of the combustion system. Further, by adjusting the phase of the intake cam 51 and combining with adjusting the geometric dimensions of the top of the piston 2, the separation of the compression ratio and the expansion ratio can be achieved, and the problem that the increase in the expansion ratio in the existing design method of the combustion system is limited by the mechanical load or knock of the engine is solved.

[0035] In addition, on the one hand, the design method of the present invention can quickly and reasonably match the combustion chamber and the intake system according to the relatively narrow optimized operating condition range of the hybrid special engine, so as to achieve efficient and clean combustion of the internal combustion engine; on the other hand, under the condition of maintaining the maximum combustion pressure unchanged under the optimized operating condition of the hybrid special engine, a high expansion ratio of the combustion system is achieved, and the efficiency of the thermal work conversion of the combustion system is improved.

[0036] It should be noted that in this embodiment, the phase of the intake cam 51 refers to the angle of cam rotation from the opening of the intake valve 6 to the closing of the intake valve 6, and the closing phase of the intake valve 6 refers to the duration of the intake valve 6 closing in advance or delaying.

[0037] In some exemplary embodiments, the design method further includes: setting a plurality of preset geometric compression ratios and a plurality of preset phases of the intake cam 51. Based on the minimum value of the fuel consumption of the combustion system, the first phase of the intake cam 51 and the first geometric compression ratio of the combustion system are determined from the plurality of preset geometric compression ratios and the plurality of preset phases. The first volume of the combustion chamber 4 is determined based on the first geometric compression ratio.

[0038] In this embodiment, through the above setting method, the first geometric compression ratio of the combustion system and the first phase of the intake cam 51 can be selected when the fuel consumption value of the combustion system is minimized. And the first volume of the combustion chamber 4 is determined according to the first geometric compression ratio. Thereby increasing the expansion ratio of the combustion system to increase the expansion stroke of the combustion system, and further increasing the efficiency of the thermal work conversion of the combustion system.

[0039] In some exemplary embodiments, based on the minimum value of the fuel consumption of the combustion system, determining the first phase of the intake cam 51 and the first geometric compression ratio of the combustion system from a plurality of preset geometric compression ratios and a plurality of preset phases includes: respectively obtaining a plurality of first fuel consumption values corresponding to the plurality of preset phases under the conditions of the plurality of preset geometric compression ratios. Obtaining a plurality of first curves representing the corresponding relationships between the preset phases and the first fuel consumption values respectively corresponding to the plurality of preset geometric compression ratios. Determining the preset geometric compression ratio corresponding to the minimum value among all the first fuel consumption values from the plurality of first curves, and determining the preset geometric compression ratio corresponding to the minimum value as the first geometric compression ratio. Determining the preset phase corresponding to the minimum value in the first curve corresponding to the first geometric compression ratio, and determining the preset phase corresponding to the minimum value as the first phase.

[0040] It should be noted that in this embodiment, the above-mentioned first curve, first geometric compression ratio and first phase can be obtained through the DOE full factor experiment in combination with the one-dimensional thermodynamic model of the engine.

[0041] Among them, the DOE full factor experiment means that all combinations of all levels of all factors are at least experimented once, and all main effects and all interaction effects of all orders can be estimated.

[0042] Figure 2 is a schematic diagram of the geometry and dimensions of the top of the piston; Figure 3 is an assembly schematic diagram of the piston, cylinder and cylinder head.

[0043] In some exemplary embodiments, referring to Figures 2 - 3 , a recess 21 is provided on the top of the piston 2. The recess 21 includes a throat area 211, two pit areas 212 and a raised area 213. The throat area 211 is connected to the top surface of the piston 2 and is configured as a stepped curved surface recessed in the axial direction. The two pit areas 212 are respectively connected to the lower side of the throat area 211, and the pit area 212 is configured as an arc surface with the center of the circle located inside the recess 21. The periphery of the raised area 213 is connected to the inner side in the radial direction of the two pit areas 212. This design method further includes: based on the first volume of the combustion chamber 4, determining the minimum diameter d in the radial direction of the throat area 211, the distance h from the bottom of the cylinder head 3 to the lower end of the throat area 211 in the axial direction, the distance H from the bottom of the cylinder head 3 to the bottom of the pit area 212 in the axial direction, and the radius R of the arc surface of the pit area 212.

[0044] It should be noted that in this embodiment, the minimum diameter d of the throat area 211 in the radial direction, the distance h from the bottom of the cylinder head 3 to the lower end of the throat area 211 in the axial direction, the distance H from the bottom of the cylinder head 3 to the bottom of the pit area 212 in the axial direction, and the radius R of the arc surface of the pit area 212 can be obtained through a three-dimensional fluid simulation model combined with a fractional factorial DOE experiment.

[0045] Among them, the fractional factorial DOE experiment refers to the possible effects of a subset (or part) of the combinations of all experimental factor levels on the response.

[0046] In some exemplary embodiments, the value range of the preset phase is -80° to 120°, preferably -60°, -40°, -20°, 0°, 20°, 40°, 60°, 80°.

[0047] In some exemplary embodiments, the value range of the preset geometric compression ratio is 18 to 23, preferably 19, 20, 21, 22.

[0048] Figure 4 It is a change curve graph between the preset phase of the intake cam and the first fuel consumption value under different preset geometric compression ratios.

[0049] It should be noted that in this embodiment, the value range of the preset phase is -80° to 120°, the value interval between adjacent two preset phases is 20°, the value range of the preset geometric compression ratio is 18 - 23, and the value interval between adjacent two preset geometric compression ratios can be 0.5.

[0050] Furthermore, in the specific calculation process, the actual engine operating conditions need to be considered and some constraint conditions are imposed. First, the intake air temperature after turbocharging and intercooling, the ratio of the recirculated exhaust gas volume to the total intake air volume inhaled into the cylinder 1 (EGR rate), and the fuel injection amount need to be kept consistent with the basic test engine. Secondly, the throttle valve 55 is fully open, and the speed of the supercharger 52 is limited within the maximum speed (wherein, if there is no supercharger 52 in the combustion system, no adjustment is required). Finally, the fuel injection timing of the fuel injector 7 in the combustion system and the opening degree of the turbine waste valve (not shown in the figure) are adjusted to control the maximum combustion pressure to be consistent. Using the one-dimensional thermodynamic model of the engine, the change curve graph between the preset phase of the intake cam 51 and the first fuel consumption value under different preset geometric compression ratios is calculated, as Figure 4 shown. For example, a preset phase of 20° means that the closing phase of the intake valve 6 is delayed by 20°, and a preset phase of -20° means that the closing phase of the intake valve 6 is advanced by 20°. From Figure 4It can be seen that at the same preset geometric compression ratio, the first fuel consumption value presents a "W" shape with the change of the closing phase of the intake valve 6. That is to say, with the advance or delay of the closing phase of the intake valve 6, the first fuel consumption value shows a trend of first decreasing and then increasing. Therefore, based on the minimum value among all the first fuel consumption values, the first geometric compression ratio and the first phase of the intake cam 51 can be determined. Among them, in this embodiment, the intercooler 54 is arranged on the intake pipe 5 to reduce the intake air temperature of the combustion system by using the intercooler 54. The intercooler 54 and the throttle valve 55 are arranged on the intake pipe 5 in sequence along the intake direction. An exhaust pipe 8 communicating with the combustion chamber 4 is also arranged on the cylinder head 3, and an exhaust valve 9 for controlling the communication or disconnection between the combustion chamber 4 and the exhaust pipe 8 is also arranged on the exhaust pipe 8.

[0051] In some exemplary embodiments, referring to Figure 1 , the combustion system further includes an injector 7 with one end extending into the interior of the combustion chamber 4. This design method further includes: determining the number of injection holes of the injector 7, the diameter of the injector 7, and the flow rate of the injector 7 based on the minimum value of the fuel consumption of the combustion system.

[0052] It should be noted that in this embodiment, the number of injection holes of the injector 7, the diameter of the injector 7, and the flow rate of the injector 7 can be calculated by using a three-dimensional fluid simulation model to improve the formation of the air-fuel mixture in the cylinder 1 and achieve a reasonable matching of the fuel injection system with the intake system and the combustion chamber.

[0053] According to an exemplary embodiment of the present invention, please refer to Figure 1 , another design method for a narrow-domain combustion system with a high expansion ratio is also provided. The combustion system includes a cylinder 1, a piston 2, and a cylinder head 3. The piston 2 is arranged inside the cylinder 1, the cylinder head 3 is horizontally installed on the top of the cylinder 1, and the bottom surface of the cylinder head 3, the inner wall of the cylinder 1, and the top of the piston 2 jointly enclose a combustion chamber 4. An intake pipe 5 communicating with the combustion chamber 4 is also arranged on the cylinder head 3, and a supercharger 52 is arranged on the intake pipe 5. This design method includes: reducing the intake air volume in the combustion system through the supercharger 52. Reducing the first volume of the combustion chamber 4, and the first volume is reduced in proportion to the intake air volume, so that the pressure in the combustion system at the end of the compression stroke remains substantially unchanged, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system. Wherein, the first volume is the volume of the combustion chamber 4 when the piston 2 is at the top dead center.

[0054] In some exemplary embodiments, the supercharger 52 is a turbocharger, and the value range of the maximum efficiency η of the supercharger 52 is 80% < η < 100%.

[0055] It should be noted that in this embodiment, the intake air volume in the combustion system is reduced by the supercharger 52, and the first volume of the combustion chamber 4 is reduced, and the first volume is reduced in proportion to the intake air volume, so that the pressure in the combustion system at the end of the compression stroke remains substantially unchanged, so as to increase the expansion ratio of the combustion system, thereby increasing the expansion stroke of the combustion system and improving the efficiency of the thermal work conversion of the combustion system. However, when adopting this design method, a suitable turbocharger needs to be matched, and the position of the operating point in the combined characteristic diagram cannot be close to the surge line of the supercharger 52 and the choke line of the turbine 53, but should always be located in the high-efficiency area, and the maximum efficiency of the supercharger 52 needs to reach more than 80%. Among them, the combined characteristic diagram refers to the ignition control curve required by the engine combustion system under various operating conditions. The turbine 53 is arranged on the exhaust pipe 8 and is connected to the supercharger 52.

[0056] In some exemplary embodiments, referring to Figures 2 - 3 , a recessed portion 21 is provided on the top of the piston 2. The recessed portion 21 includes a throat area 211, two pit areas 212, and a raised area 213. The throat area 211 is connected to the top surface of the piston 2 and is configured as a stepped curved surface recessed in the axial direction. The two pit areas 212 are respectively connected to the lower side of the throat area 211, and the pit area 212 is configured as an arc surface with the center of the circle located inside the recessed portion 21. The periphery of the raised area 213 is connected to the inner side in the radial direction of the two pit areas 212. This design method further includes: based on the first volume of the combustion chamber 4, determining the minimum diameter d in the radial direction of the throat area 211, the distance h in the axial direction from the bottom of the cylinder head 3 to the lower end of the throat area 211, the distance H in the axial direction from the bottom of the cylinder head 3 to the bottom of the pit area 212, and the radius R of the arc surface of the pit area 212.

[0057] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A design method for a narrow-domain combustion system with a high expansion ratio, the combustion system comprising a cylinder (1), a piston (2) and a cylinder head (3), the piston (2) being disposed inside the cylinder (1), and a recessed portion (21) being provided at the top of the piston (2), the recessed portion (21) comprising: The throat area (211), which is connected to the top surface of the piston (2), is configured as a stepped curved surface that is recessed in the axial direction; two pit areas (212), which are respectively connected to the lower side of the throat area (211), and the pit area (212) is configured as an arc surface with the center of the circle located inside the recessed portion (21); and a raised area (213), the periphery of the raised area (213) is connected to the inner sides in the radial direction of the two pit areas (212); the cylinder head (3) is horizontally installed on the top of the cylinder (1), the bottom surface of the cylinder head (3), the inner wall of the cylinder (1), and the top of the piston (2) jointly enclose a combustion chamber (4), and an intake pipe (5) communicating with the combustion chamber (4) is further provided on the cylinder head (3), and an intake cam (51) for controlling the opening and closing of the intake valve (6) is provided on the intake pipe (5); the design method includes: Adjusting the phase of the intake cam (51) to adjust the closing phase of the intake valve (6), so that during the process of the piston (2) moving upward in the vertical direction, the amount of gas compressed by the piston (2) is reduced; and Adjusting the geometric dimensions of the top of the piston (2) to reduce the first volume of the combustion chamber (4), and the first volume is reduced in proportion to the amount of gas compressed by the piston (2), so that the pressure in the combustion system remains unchanged at the end of the compression stroke, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system and improve the thermal efficiency of the combustion system; The design method further includes: Setting a plurality of preset geometric compression ratios and a plurality of preset phases of the intake cam (51); Based on the minimum value of the fuel consumption of the combustion system, determining the first phase of the intake cam (51) and the first geometric compression ratio of the combustion system from the plurality of preset geometric compression ratios and the plurality of preset phases; and Determining the first volume of the combustion chamber (4) based on the first geometric compression ratio; Based on the first volume of the combustion chamber (4), determining the minimum diameter d in the radial direction of the throat area (211), the distance h in the axial direction from the bottom of the cylinder head (3) to the lower end of the throat area (211), the distance H in the axial direction from the bottom of the cylinder head (3) to the bottom of the pit area (212), and the radius R of the arc surface of the pit area (212); Wherein, the first volume is the volume of the combustion chamber (4) when the piston (2) is at the top dead center.

2. The design method of the narrow-domain combustion system with a high expansion ratio according to claim 1, wherein, Based on the minimum value of the fuel consumption of the combustion system, determining the first phase of the intake cam (51) and the first geometric compression ratio of the combustion system from the plurality of preset geometric compression ratios and the plurality of preset phases includes: Respectively under the conditions of the plurality of preset geometric compression ratios, obtaining a plurality of first fuel consumption values corresponding to the plurality of preset phases; Obtaining a plurality of first curves respectively corresponding to the plurality of preset geometric compression ratios and representing the corresponding relationship between the preset phase and the first fuel consumption value; Determine the preset geometric compression ratio corresponding to the minimum value among all the first fuel consumption values from the multiple first curves, and determine the preset geometric compression ratio corresponding to the minimum value as the first geometric compression ratio; and Determine the preset phase corresponding to the minimum value in the first curve corresponding to the first geometric compression ratio, and determine the preset phase corresponding to the minimum value as the first phase.

3. The design method of the narrow-domain combustion system with a high expansion ratio according to claim 2, wherein, The value range of the preset phase is -80° to 120°.

4. The design method of the narrow-domain combustion system with a high expansion ratio according to claim 3, wherein, The value of the preset phase is any one of -60°, -40°, -20°, 0°, 20°, 40°, 60°, 80°.

5. The design method of the narrow-domain combustion system with a high expansion ratio according to claim 2, wherein, The value range of the preset geometric compression ratio is 18 to 23.

6. The design method of the narrow-domain combustion system with a high expansion ratio according to claim 5, wherein, The value of the preset geometric compression ratio is any one of 19, 20, 21, 22.

7. The design method of the narrow-domain combustion system with a high expansion ratio according to claim 1, wherein, The combustion system further includes an injector (7) with one end extending into the interior of the combustion chamber (4), and the design method further includes: Based on the minimum value of the fuel consumption of the combustion system, determine the number of holes of the injection holes of the injector (7), the diameter of the injector (7), and the flow rate of the injector (7).

8. A design method for a narrow-domain combustion system with a high expansion ratio, the combustion system comprising a cylinder (1), a piston (2) and a cylinder head (3), the piston (2) being disposed inside the cylinder (1), a recessed portion (21) being provided at the top of the piston (2), the recessed portion (21) comprising: The throat area (211), connected to the top surface of the piston (2), is configured as a stepped curved surface recessed in the axial direction; two pit areas (212), respectively connected to the lower side of the throat area (211), and the pit area (212) is configured as an arc surface with the center of the circle located inside the recessed part (21); and a raised area (213), the periphery of the raised area (213) is connected to the inner sides in the radial direction of the two pit areas (212); the cylinder head (3) is horizontally installed on the top of the cylinder (1), the bottom surface of the cylinder head (3), the inner wall of the cylinder (1), and the top of the piston (2) together enclose the combustion chamber (4), and an intake pipe (5) communicating with the combustion chamber (4) is further provided on the cylinder head (3), and a supercharger (52) is provided on the intake pipe (5); the design method includes: Reduce the intake air volume in the combustion system through the supercharger (52); and Reduce the first volume of the combustion chamber (4), and the first volume is reduced in equal proportion to the intake air volume, so that the pressure in the combustion system at the end of the compression stroke remains unchanged, and the expansion ratio of the combustion system is increased to increase the expansion stroke of the combustion system and improve the thermal efficiency of the combustion system; Wherein, the first volume is the volume of the combustion chamber (4) when the piston (2) is at the top dead center; The design method further includes: Based on the first volume of the combustion chamber (4), determine the minimum diameter d in the radial direction of the throat area (211), the distance h in the axial direction from the bottom of the cylinder head (3) to the lower end of the throat area (211), the distance H in the axial direction from the bottom of the cylinder head (3) to the bottom of the pit area (212), and the radius R of the arc surface of the pit area (212).

9. The design method of the narrow-domain combustion system with a high expansion ratio according to claim 8, wherein, The supercharger (52) is a turbocharger, and the value range of the maximum efficiency η of the supercharger (52) is 80% < η < 100%.

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