Gas machine compound combustion system and control method thereof

Abstract

The invention discloses a compound combustion system of a gas engine. The compound combustion system is suitable for medium and heavy-duty engines with fuels such as natural gas and ammonia gas. According to the system, the arrangement form of three intake valves and two exhaust valves is adopted, the intake valves on the two sides are configured to be spiral vortex intake ducts, the tumble intake duct is configured in the middle, and a novel composite combustion mode with the vortex and tumble synergistic effect is jointly constructed by combining a ceiling type air cylinder cover and an eccentric flow guide piston. According to the system, tumble flow can be formed near a spark plug, small-scale turbulence energy is improved, and initial fire nucleus development is promoted; and meanwhile, a dominant large-scale vortex is formed in a peripheral flow field of the combustion chamber, so that later-stage flame rapid propagation is maintained, and detonation generated by tail end gas is effectively inhibited. According to control over the full-working-condition variable valve of the compound combustion system, the opening and closing time of the inlet valve and the valve lift can be dynamically adjusted according to the load and the rotating speed of the engine, supercharged deep Miller cycle is achieved, and therefore the heat efficiency of medium and heavy gas machines such as heavy trucks and ships is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to engine control, in particular to a gas engine compound combustion system and control strategy. BACKGROUND

[0002] Under the background of the "double carbon" strategy, low-carbon or zero-carbon fuels such as natural gas and ammonia are widely used in heavy vehicle and ship engines due to their low carbon dioxide emissions, no particulate matter emissions, and wide sources. However, such fuels have low reactivity, and the flame burning speed is significantly lower than that of gasoline and diesel, which is particularly prominent in medium and heavy engines with large cylinder diameter and low speed. Currently, most medium and heavy engines are modified from diesel engines, and the vortex motion formed by the swirl intake port dominates in the combustion chamber, but spark ignition and flame propagation are still used to organize the engine combustion process. Due to the weak turbulent kinetic energy in the core area around the spark plug in the combustion chamber, the initial kernel development is slow, the combustion duration is prolonged, and the afterburning is severe, resulting in low thermal efficiency and frequent knocking.

[0003] Most of the existing improvement schemes are based on four-valve structure, mainly including two ways: one is to adjust the flow difference of the double intake manifold to enhance the in-cylinder turbulence; the other is to use a combination of tumble and swirl airways to form a skew-axis vortex in the cylinder. Although these methods can accelerate combustion to some extent, there are two key defects: first, there is a restrictive relationship between turbulence enhancement and intake flow coefficient, and it is difficult to balance the increase of charge efficiency and turbulence intensity; second, simply increasing the strength of tumble or swirl cannot meet the needs of accelerating the formation of initial kernel and high-speed combustion of flame in the later stage, and the effect is limited in improving engine thermal efficiency and suppressing knocking. In addition, although the Miller cycle can effectively improve the thermal efficiency and suppress knocking, there is currently a lack of systematic methods for coordinated regulation of tumble and swirl, making it difficult to dynamically optimize and match the flow field in the combustion chamber in the full working condition range. SUMMARY

[0004] In view of the above prior art, the present application provides a gas engine compound combustion system, which adopts a "three intake valves + two exhaust valves" arrangement, in which the two side intake valves adopt a swirl intake port for forming a dominant large-scale vortex in the periphery of the combustion chamber; the middle intake valve adopts a tumble intake port for forming a tumble flow near the spark plug; the airway of the three intake valves is matched with the shed roof type combustion chamber and the eccentric guide piston structure to form a new compound combustion system with synergistic effect of swirl and tumble. This system can form a tumble flow near the spark plug, effectively improve the small-scale turbulent kinetic energy, accelerate the development of the initial kernel, and at the same time form a flow field dominated by large-scale vortex in the peripheral flow field to maintain the rapid propagation of the flame in the later stage and suppress the self-ignition and knocking of the end gas.

[0005] In order to solve the above technical problems, the application provides a gas engine compound combustion system, which comprises a combustion chamber and an air intake and exhaust system, wherein the combustion chamber comprises a cylinder wall, a cylinder head and a piston, the cylinder head is provided with three air intake valves and two exhaust valves, the three air intake valves are located on one side of the cylinder head, the three air intake valves are sequentially recorded as a first side air intake valve, a middle air intake valve and a second side air intake valve according to the arrangement position, and the two exhaust valves are located on the other side of the cylinder head; the air intake and exhaust system comprises an air intake passage and an exhaust passage, the air intake passage comprises a main channel and three branch channels which are connected to the main channel and correspondingly connected to the three air intake valves, among the three branch channels, the branch channel connected to the first side air intake valve is recorded as a first side branch channel, the branch channel connected to the middle air intake valve is recorded as a middle branch channel, and the branch channel connected to the second side air intake valve is recorded as a second side branch channel; the first side branch channel and the second side branch channel are spiral vortex air intake passages with the same rotation direction on the side of the air intake valve; the middle branch channel is a tumble flow air intake passage with a downward arc flow guiding characteristic on the side of the air intake valve; the piston is a shallow basin type eccentric flow guiding piston, and the cylinder head is a shed top type structure matched with the shallow basin type eccentric flow guiding piston; the air intake flow from the air intake passage through the three branch channels enters the combustion chamber, moves towards the spark plug area under the guidance of the shallow basin type eccentric flow guiding piston, and forms a tumble flow which strengthens the development of the spark core and a vortex flow which promotes the flame propagation around the combustion chamber under the joint action of the shed top type cylinder head; and the air intake kinetic energy is converted into the compound turbulent flow field of the core tumble flow and the peripheral vortex flow.

[0006] Further, the gas engine compound combustion system provided by the application has the following beneficial effects.

[0007] The included angle α between the side surface of the cylinder head and the horizontal plane is 20°-23°, preferably, the included angle α is 22°.

[0008] The radius of the shallow basin type eccentric flow guiding piston is R1, the depth of the shallow basin of the shallow basin type eccentric flow guiding piston is h, h=0.1R1-0.3R1; the upper edge radius of the shallow basin of the shallow basin type eccentric flow guiding piston is R2, R2=0.85R1-0.9R1; the lower edge radius of the shallow basin of the shallow basin type eccentric flow guiding piston is R3, R3=0.7R1-0.75R1; the lower edge of the shallow basin of the shallow basin type eccentric flow guiding piston is deviated to the air intake side of the combustion chamber, and the eccentricity between the central axis of the lower edge of the shallow basin of the shallow basin type eccentric flow guiding piston and the piston central axis is e, e=0.03R1-0.08R1.

[0009] Preferably, h=0.2R1, R2=0.88R1, R3=0.72R1, and e=0.05R1.

[0010] Meanwhile, the application also provides a control method of the gas engine compound combustion system, which is used for variable valve timing and lift control, and the control strategy of the gas engine under all working conditions comprises the following steps of: under cold start or low load working condition, the intake valve is closed 30-50°CA in advance, and small valve lift is adopted; under medium load working condition, the intake valve is closed 15-30°CA in delay, and medium valve lift is adopted; under medium-high load working condition, the intake valve is closed 20-40°CA in delay, and medium-low valve lift is adopted; and under high load or super-high load working condition, the intake valve is closed 40-60°CA in delay, and large valve lift is adopted.

[0011] Further, the control strategy is as follows:

[0012] under cold start or low load working condition, the intake valve is closed 30-50°CA in advance, and small valve lift is adopted; under medium load working condition, the intake valve is closed 15-30°CA in delay, and medium valve lift is adopted; under medium-high load working condition, the intake valve is closed 20-40°CA in delay, and medium-low valve lift is adopted; and under high load or super-high load working condition, the intake valve is closed 40-60°CA in delay, and large valve lift is adopted.

[0013] under cold start or low load working condition, the intake valve is closed 30-50°CA in advance, and small valve lift is adopted; under medium load working condition, the intake valve is closed 15-30°CA in delay, and medium valve lift is adopted; under medium-high load working condition, the intake valve is closed 20-40°CA in delay, and medium-low valve lift is adopted; and under high load or super-high load working condition, the intake valve is closed 40-60°CA in delay, and large valve lift is adopted.

[0014] under cold start or low load working condition, the intake valve is closed 30-50°CA in advance, and small valve lift is adopted; under medium load working condition, the intake valve is closed 15-30°CA in delay, and medium valve lift is adopted; under medium-high load working condition, the intake valve is closed 20-40°CA in delay, and medium-low valve lift is adopted; and under high load or super-high load working condition, the intake valve is closed 40-60°CA in delay, and large valve lift is adopted.

[0015] under cold start or low load working condition, the intake valve is closed 30-50°CA in advance, and small valve lift is adopted; under medium load working condition, the intake valve is closed 15-30°CA in delay, and medium valve lift is adopted; under medium-high load working condition, the intake valve is closed 20-40°CA in delay, and medium-low valve lift is adopted; and under high load or super-high load working condition, the intake valve is closed 40-60°CA in delay, and large valve lift is adopted.

[0016] Compared with the prior art, the application has the beneficial effects that:

[0017] (1) Significantly optimize the in-cylinder airflow organization. The gas engine compound combustion system of the present application forms a compound turbulent flow field in the cylinder through the arrangement of "three intake valves + two exhaust valves", combined with the collaborative design of the two-side vortex intake port and the middle rolling flow intake port, in cooperation with the shed-top combustion chamber and the eccentric guide piston structure. Specifically, the middle rolling flow intake port forms a rolling flow near the spark plug, effectively enhancing the turbulent kinetic energy of the ignition area, shortening the initial kernel formation and development time, and significantly improving the ignition stability; the two-side vortex intake port forms a flow field dominated by large-scale vortex flow in the periphery of the combustion chamber, continuously promoting the rapid propagation of the flame.

[0018] (2) Effectively suppress the engine knock tendency and expand the high-efficiency operating range. The compound turbulent flow field formed by the combustion system of the present application improves the uniformity of the in-cylinder mixture, reduces the formation of local high-temperature zones, and simultaneously realizes the continuous acceleration of the spark ignition flame propagation in the cylinder, effectively shortening the residence time of the end gas, thereby reducing the probability of engine knock. The multi-valve mechanism provides greater flexibility for combustion organization and engine performance regulation. According to the engine load and speed, the variable valve timing and valve lift are dynamically adjusted to meet the requirements of engine power, economy and reliability under different operating conditions.

[0019] (3) Break through the constraints between turbulent flow strengthening and intake flow coefficient. Through the collaborative innovation of valve number and airflow organization, the constraint relationship between turbulent intensity and intake flow coefficient is effectively overcome. Specifically, the use of three intake valves significantly increases the total valve flow area; at the same time, through the functional design of the air port, the middle rolling flow intake port is specially designed to strengthen the turbulence near the spark plug, and the two-side vortex intake port is specially designed to generate vortex flow to promote flame propagation, realizing the decoupling of turbulent flow generation and intake function. With the dynamic regulation of the variable valve timing system on airflow organization, high charging efficiency and strong turbulent intensity are simultaneously achieved in the full operating range, realizing the simultaneous improvement of charging efficiency and turbulent intensity.

[0020] (4) Adapt to multiple low-carbon fuels, with good scalability and expandability. The present application is not only suitable for natural gas and ammonia, but also can be extended to partial dual-fuel systems of composite hydrogen, bio-gas and other low-carbon or zero-carbon fuels, focusing on solving the common needs of accelerating the initial kernel formation and the sustained high-speed combustion of the later flame, especially suitable for large-bore, low-speed heavy-duty engine application scenarios such as heavy-duty trucks and marine power systems. The system structure is highly compatible with the traditional four-valve system, with low modification cost and good industrialization application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic diagram of the structure and mechanism of the gas engine compound combustion system;

[0022] Figure 2 is Figure 1An enlarged schematic view of the structure of the middle piston;

[0023] Figure 3 is a schematic view of the arrangement of three intake valves and two exhaust valves on the cylinder head in the present application;

[0024] Figure 4 is a schematic view of the variable valve timing and lift control of the gas engine compound combustion system in the present application, wherein the red curve is the valve lift curve of the exhaust valve, and BDC represents the bottom dead center of the piston.

[0025] In the figure:

[0026] 1 - helical vortex intake port, 2 - tumble intake port, 3 - piston, 4 - cylinder head, 5 - exhaust port, 6 - tumble near the spark plug to strengthen the development of the kernel, 7 - vortex outside the combustion chamber to promote flame propagation. DETAILED DESCRIPTION

[0027] The design concept of the gas engine compound combustion system proposed in the present application is as follows: the system adopts a three-intake-valve and two-exhaust-valve arrangement, the two side intake valves are configured as helical vortex intake ports for forming a dominant large-scale vortex outside the combustion chamber, and the middle is configured as a tumble intake port for forming a tumble near the spark plug; the combustion chamber in the present application is combined with a shed roof type cylinder head and an eccentric guide piston to jointly construct a new compound combustion mode with the synergistic effect of vortex and tumble. The system can form a tumble near the spark plug, effectively improve the small-scale turbulent kinetic energy, and promote the development of the initial kernel; at the same time, a dominant large-scale vortex is formed in the flow field outside the combustion chamber to maintain the rapid propagation of the flame in the later stage and effectively suppress the natural and detonation of the end gas. The gas engine compound combustion system in the present application is suitable for medium and heavy duty engines of natural gas, ammonia and other fuels.

[0028] The application also proposes a control of the full working condition variable valve of the gas machine with the composite combustion system, which is used for variable valve timing and lift control, and can dynamically adjust the opening and closing time of the intake valve and the valve lift according to the engine load and speed, so as to realize the supercharged deep Miller cycle, thereby significantly improving the thermal efficiency of the heavy truck, ship and other medium and heavy gas machines. The control system mainly consists of an ECU, a variable valve timing actuator, a variable valve lift actuator, an engine speed sensor, a knock sensor, an intake pressure / temperature sensor and the like. The control system realizes the performance optimization of the engine in the full working condition range through the closed loop control of real-time monitoring, decision-making and execution, and cooperates with the supercharging system. The core process is that the ECU queries the pre-set control pulse spectrum in real time according to the sensor information, dynamically adjusts the opening / closing time and lift height of the intake and exhaust valves according to the working condition parameters such as the speed and load of the engine, and finally realizes the target in-cylinder flow field organization and combustion process control. The control strategy of the full working condition of the gas machine comprises that in the cold start or low load working condition, the intake valve is closed 30-50°CA in advance, and small valve lift is adopted, so as to reduce the intake amount, ensure the fresh mixture concentration and reduce the pumping loss; in the medium load working condition, the intake valve is closed 15-30°CA in delay, and medium valve lift is adopted, so that part of the air backflows into the intake port, and the exhaust turbocharging or mechanical supercharging is combined to improve the engine thermal efficiency on the premise of ensuring the torque output; in the medium and high load working condition, the intake valve is closed 20-40°CA in delay, and medium and low valve lift is adopted, so as to further enhance the intake flow speed, and the exhaust turbocharging and intercooling system are combined to ensure the power and economy of the engine while suppressing the engine knock; in the high load or super high load working condition, the intake valve is closed 40-60°CA in delay, and large valve lift is adopted, so as to promote more air backflow, and the exhaust turbocharging, exhaust gas recirculation and intercooling system are combined to improve the engine thermal efficiency and suppress the knock and control the exhaust temperature.

[0029] The application will be further described below in combination with the drawings and specific embodiments, but the following embodiments are by no means any limitation on the application.

[0030] As shown in the drawings, Figures 1 to 3 The application proposes a composite combustion system of a gas machine, which comprises a combustion chamber and an intake and exhaust system thereof.

[0031] The combustion chamber comprises a cylinder wall, a cylinder head 4 and a piston 3. The cylinder head 4 is provided with three intake valves and two exhaust valves. The three intake valves are located on one side of the cylinder head 4, and are sequentially recorded as a first side intake valve, a middle intake valve and a second side intake valve according to the arrangement position. The two exhaust valves are located on the other side of the cylinder head 4. Figure 3The piston 3 is a shallow-pot eccentric guide piston, and the cylinder head 4 is a shed roof type structure matched with the shallow-pot eccentric guide piston. The angle α between the side surface of the cylinder head 4 and the horizontal plane is 20°-23°, preferably α=22° as shown in Figure 1 and Figure 2 The structure of the cylinder head 4 matched with the shallow-pot eccentric guide piston is shown in the figure. The structural dimensions of the piston are as follows: the radius of the piston is R1, the depth h of the shallow pot of the piston is 0.1-0.3 times the radius R1 of the piston, preferably h=0.2R1; the radius R2 of the upper edge of the shallow pot of the piston is 0.85-0.9 times the radius R1 of the piston, preferably R2=0.88R1; the radius R3 of the lower edge of the shallow pot of the piston is 0.7-0.75 times the radius R1 of the piston, preferably R3=0.72R1; the key design is that the lower edge of the shallow pot of the shallow-pot eccentric guide piston is deviated to the intake side of the combustion chamber, that is, the central axis of the lower edge of the shallow pot is deviated from the central axis of the piston by an eccentricity e, and the value of the eccentricity e is 0.03-0.08 times the radius R1 of the piston, and the lower edge is deviated to the tumble intake side, preferably e=0.05R1. The eccentric structure can effectively guide the intake air flow to move towards the spark plug area, and together with the shed roof type combustion chamber, the kinetic energy of the intake air is converted into a composite turbulent flow field of "core tumble flow 6+peripheral vortex flow 7", which provides a structural basis for rapid and stable combustion.

[0032] The intake and exhaust system includes an intake passage and an exhaust passage 5. The intake passage includes a main passage and three branch passages which are respectively connected to three intake valves. Among the three branch passages, the branch passage connected to the first side intake valve is referred to as the first side branch passage, the branch passage connected to the middle intake valve is referred to as the middle branch passage, and the branch passage connected to the second side intake valve is referred to as the second side branch passage. The first side branch passage and the second side branch passage are both helical vortex intake passages 1 of the same rotation direction on one side of the intake valve, and the design target is to generate a flow field dominated by large-scale vortex flow in the periphery of the cylinder. The middle branch passage is a tumble intake passage 2 with a downward arc-shaped guide feature on one side of the intake valve, and the design target is to generate tumble flow near the spark plug. The intake air flow entering the combustion chamber from the intake passage through the three branch passages moves towards the spark plug area under the guidance of the shallow-pot eccentric guide piston 3, and under the joint action of the shed roof type cylinder head 4, the intake air flow forms tumble flow which strengthens the development of the ignition kernel near the spark plug and forms vortex flow which promotes flame propagation in the periphery of the combustion chamber; thereby realizing the conversion of the kinetic energy of the intake air into a composite turbulent flow field of core tumble flow and peripheral vortex flow as shown in Figure 1 and Figure 3 .

[0033] The full working condition control of the gas machine with the composite combustion system of the application includes:

[0034] (1) Cold start and low speed and low load condition (speed < 1000 rpm, load < 20%)

[0035] Under this condition, the control system makes decisions according to the speed signal provided by the speed sensor and the low load state signal measured by the sensor. The ECU accordingly issues an instruction to the variable valve lift actuator to set it in the low lift mode, with a lift range of 30% to 50% of the maximum lift. At the same time, the ECU drives the variable valve timing actuator to implement the early closing strategy of the intake valve, with the closing angle set in the interval of 30-50° CA before the bottom dead center of compression. The control strategy curve is shown as the a-type line in Figure 4 The knock sensor continuously monitors the combustion process. This strategy effectively locks the in-cylinder charge through early closing of the intake valve, enhances the stability of ignition, reduces the combustion cycle fluctuation by more than 5%, and effectively reduces the pumping loss.

[0036] (2) Medium load condition (speed between 1500-2200 rpm, load 20%-50%)

[0037] When the ECU determines that the engine enters the medium load interval through the speed signal and the intake pressure / flow signal, it immediately instructs the intake valve variable valve lift actuator to switch to medium lift, with a lift height of about 60%-80% of the maximum lift. At the same time, the ECU drives the variable valve timing actuator to implement delayed closing of the intake valve, with the closing angle set at 15-30° CA after the bottom dead center of compression. The control strategy curve is shown as the b-type line in Figure 4 Based on the change in intake air caused by this variable valve timing strategy, the ECU establishes medium boost pressure through the exhaust turbocharger according to the signals of the intake pressure sensor and the air mass flow meter. While ensuring linear response of torque, the in-cylinder tumble flow intensity is maintained, the compression end temperature is reduced, and the engine thermal efficiency is continuously optimized.

[0038] (3) Medium-high load and knock-sensitive condition (speed 1000-1800 rpm, load 50%-80%)

[0039] Under this condition, the ECU focuses on monitoring the knock signal. After the ECU determines that it enters the knock-sensitive zone through the speed and load signals, it instructs the intake valve variable valve lift actuator to maintain medium-low lift, with a lift height of about 40%-60% of the maximum lift; at the same time, it instructs the intake valve variable valve timing actuator to implement severe Miller cycle, with the closing angle of the intake valve significantly delayed to 20-40° CA after the bottom dead center of compression. The control strategy curve is shown as the c-type line in Figure 4The ECU maintains high boost levels through the exhaust turbocharger and compensates for the intake air loss due to deep Miller cycle through boost pressure. This synergistic control allows for a significant reduction in the effective compression ratio in the cylinder and a reduction in knock intensity, thus effectively protecting the engine and maintaining power output in high demand operating conditions.

[0040] (4) High and ultra-high load conditions (1000-1500 rpm, >80% load)

[0041] In extreme conditions, the ECU instructs the intake valve variable lift actuator to use maximum valve lift based on sensor signals. The variable valve timing actuator is synergistically controlled to implement deep Miller cycle, setting the intake valve closing angle at 40-60° CA after the bottom dead center of compression. The control strategy curve is shown in FIG. 4. Figure 4 The ECU adjusts the boost system to work at maximum pressure to provide the maximum possible intake air. The ECU activates the exhaust gas recirculation valve in time according to the thermal load feedback of the temperature sensor to introduce part of the exhaust gas into the cylinder to inhibit the generation of nitrogen oxides and control the combustion temperature, ultimately ensuring the engine's operating durability and emission compliance under extreme load.

[0042] Although the present application has been described in connection with the preferred embodiments thereof with reference to the drawings, it is not to be limited to the preferred embodiments but on the contrary, it is to be reasonably construed to cover all modifications and variations as they come within the scope of the application.

Claims

1. A gas engine combined combustion system comprising a combustion chamber and its intake and exhaust system, said combustion chamber comprising a cylinder wall, a cylinder head (4) and a piston (3), characterized in that, The cylinder cover (4) is provided with three intake valves and two exhaust valves, the three intake valves are located on one side of the cylinder cover (4), and are sequentially recorded as a first side intake valve, a middle intake valve and a second side intake valve according to the arrangement position, and the two exhaust valves are located on the other side of the cylinder cover (4); the intake and exhaust system comprises an intake passage and an exhaust passage (5); The intake passage comprises a main passage and three branch passages which are respectively connected to the main passage and correspondingly connected to the three intake valves, among the three branch passages, the branch passage connected to the first side intake valve is recorded as a first side branch passage, the branch passage connected to the middle intake valve is recorded as a middle branch passage, and the branch passage connected to the second side intake valve is recorded as a second side branch passage; the first side branch passage and the second side branch passage are both spiral vortex intake passages (1) with the same rotation direction on the side of the intake valve, and the middle branch passage is a rolling flow intake passage (2) with a downward arc flow guiding characteristic on the side of the intake valve; The piston (3) is a shallow basin type eccentric flow guiding piston, and the cylinder cover (4) is a shed top type structure matched with the shallow basin type eccentric flow guiding piston; The intake air flow entering the combustion chamber from the intake passage through the three branch passages moves towards the spark plug area under the guidance of the shallow basin type eccentric flow guiding piston (3), and under the joint action of the shed top type cylinder cover (4), the intake air flow forms a rolling flow for strengthening the development of the core fire kernel and a vortex flow for promoting the flame propagation around the combustion chamber; so as to realize the conversion of the intake kinetic energy into a composite turbulent flow field of the core rolling flow and the peripheral vortex flow.

2. The gas engine combined combustion system of claim 1, wherein, The included angle α between the side surface of the cylinder cover (4) and the horizontal plane is 20°-23°.

3. The gas engine combined combustion system of claim 2, wherein, α=22°。 4. The gas engine combined combustion system of claim 1, wherein, The radius of the shallow basin type eccentric flow guiding piston is R1, The shallow basin depth of the shallow basin type eccentric flow guiding piston is h, h=0.1R1-0.3R1; The upper edge radius of the shallow basin of the shallow basin type eccentric flow guiding piston is R2, R2=0.85R1-0.9R1; The lower edge radius of the shallow basin of the shallow basin type eccentric flow guiding piston is R3, R3=0.7R1-0.75R1; The lower edge of the shallow basin of the shallow basin type eccentric flow guiding piston is deviated to the intake side of the combustion chamber, and the eccentricity between the center axis of the lower edge of the shallow basin and the piston center axis is e, e=0.03R1-0.08R1.

5. The gas engine combined combustion system of claim 4, wherein, h=0.2R1, R2=0.88R1, R3=0.72R1, and e=0.05R1.

6. A control method of a gas engine compound combustion system for variable valve timing and lift control of a gas engine, characterized by, The control strategy of the gas machine under full working conditions of the gas machine composite combustion system as claimed in any one of claims 1 to 5 comprises: In the cold start or low load working condition, the intake valve is closed 30-50°CA in advance, and a small valve lift is adopted; in the medium load working condition, the intake valve is closed 15-30°CA in delay, and a medium valve lift is adopted; in the medium-high load working condition, the intake valve is closed 20-40°CA in delay, and a medium-low valve lift is adopted; and in the high load or super-high load working condition, the intake valve is closed 40-60°CA in delay, and a large valve lift is adopted.

7. The control method of the gas engine combined combustion system according to claim 6, characterized by, The specific content of the control strategy of the gas machine under full working conditions is as follows: Cold start or low load condition, gas engine speed <1000 rpm, load <20%, ECU sends instructions to variable valve lift actuator, control lift range is 30%~50% of maximum valve lift; at the same time, ECU drives variable valve timing actuator, set closing angle in 30~50° CA interval before compression bottom dead center; Medium load condition, gas engine speed between 1500~2200 rpm, load 20%~50%, ECU sends instructions to variable valve lift actuator, control lift range is 60%~80% of maximum valve lift; at the same time, ECU drives variable valve timing actuator, set closing angle in 15~30° CA interval after compression bottom dead center; Medium-high load and knock-sensitive condition, gas engine speed between 1000~1800 rpm, load 50%~80%, ECU sends instructions to variable valve lift actuator, control lift range is 40%~60% of maximum valve lift; at the same time, ECU drives variable valve timing actuator, set closing angle in 20~40° CA interval after compression bottom dead center; High load and super-high load condition, gas engine speed between 1000~1500 rpm, load >80%, ECU sends instructions to variable valve lift actuator, control lift range is 40%~60% of maximum valve lift; at the same time, ECU drives variable valve timing actuator, set closing angle in 20~40° CA interval after compression bottom dead center.

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