Injection control method of dual fuel injection system for natural gas engine

Abstract

The invention discloses a dual fuel injection system for a natural gas engine, comprising an air filter, a supercharger, an intercooler, an electronic throttle and a gas mixer which are sequentially arranged in series on an intake pipeline, the intake pipeline is connected to an intake manifold, a plurality of cylinder intake passages are arranged on the intake manifold, and a gas storage device is also included, a gas delivery pipe and a first gas injection valve are connected between the gas storage device and the gas mixer, the gas storage device is also connected to the intake passages of each cylinder through pipelines, a second gas injection valve is installed between the intake passages of each cylinder and the gas storage device, the electronic throttle, the first gas injection valve and each second gas injection valve are respectively connected to an electronic control unit ECU, and also relates to a control method of the system; the invention has better responsiveness, is conducive to lambda control, the temperature of the fuel which is not heated by the intake pipeline is low, can effectively reduce the temperature in the cylinder, achieve the purpose of reducing the knock tendency, and thus optimize the comprehensive operating performance of the natural gas engine.

Description

Technical Field

[0001] The invention relates to a fuel dual injection system for a natural gas engine and also relates to an injection control method used by the dual injection system. Background Art

[0002] The fuel injection system of a natural gas engine can be divided into a multi-point injection system and a single-point injection system. The multi-point injection system is to install an injection nozzle at the air intake of each cylinder of the natural gas engine, and the engine's electronic control unit (ECU) controls the cylinder-by-cylinder injection or group injection. The fuel is directly injected in front of the air intake of each cylinder, and then enters the cylinder together with the air to form a mixture. This is prone to poor engine intake uniformity, affecting the engine's economy and emission performance. The single-point injection system corresponds to the multi-point injection system, which means that multiple cylinders share one injection nozzle to generate a mixture. This fuel injection method makes the engine's responsiveness poor, making it difficult to achieve the rapid fuel stop and fuel supply function, and increases the tendency to knock.

[0003] Therefore, how to solve the problem of poor uniformity of the multi-point injection system while taking into account the problem of poor responsiveness of the single-point injection system is one of the technical difficulties in improving engine performance, and it has also become one of the technical problems that need to be solved urgently in this field. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a dual fuel injection system for a natural gas engine that can take into account the uniformity, responsiveness and consistency of each cylinder of the engine, reduce the tendency of engine knock, and enable rapid start and stop control of fuel supply.

[0005] In order to solve the above technical problems, the technical solution of the present invention is: a fuel dual injection system for a natural gas engine, used in conjunction with an electronic control unit ECU of the natural gas engine, including an air filter, a supercharger, an intercooler, an electronic throttle and a gas mixer which are sequentially arranged in series on the intake pipeline of the natural gas engine along the direction of gas travel in the pipe, the intake pipeline at the outlet end of the gas mixer is connected to the intake manifold on the natural gas engine, the intake manifold is provided with a cylinder intake passage correspondingly connected to each cylinder in the natural gas engine, and also includes a gas storage device, a gas delivery pipe is connected between the gas storage device and the gas mixer, a first gas injection valve is connected in series on the gas delivery pipe, the gas storage device is also connected to each cylinder intake passage respectively through a pipeline, a second gas injection valve is correspondingly installed on the pipeline between each cylinder intake passage and the gas storage device, the electronic throttle, the first gas injection valve and each second gas injection valve are respectively connected to the electronic control unit ECU.

[0006] As a preferred technical solution, the upper limit of the injection amount of the first gas injection valve is greater than the upper limit of the injection amount of the second gas injection valve.

[0007] As a preferred technical solution, the natural gas engine is further provided with an exhaust device, which is respectively connected to the supercharger, the gas mixer and the electronic control unit ECU.

[0008] As a preferred technical solution, the exhaust device includes an exhaust pipe connected to the exhaust gas discharge end of each cylinder in the natural gas engine, the tail end of the exhaust pipe is connected to the catalyst, the supercharger is connected in series to the exhaust pipe, an oxygen sensor is provided in the exhaust pipe between the supercharger and the catalyst, and the oxygen sensor is connected to the electronic control unit ECU; an exhaust gas recirculation pipe is also connected to the exhaust pipe between the supercharger and the natural gas engine, the exhaust gas recirculation pipe is connected to the gas mixer, and an EGR cooler and an EGR valve are connected in series in sequence on the exhaust gas recirculation pipe along the direction of exhaust gas travel in the pipe, and the EGR valve is connected to the electronic control unit ECU.

[0009] As a preferred technical solution, the gas storage device includes a gas storage tank or a gas storage bottle.

[0010] The present invention also discloses an injection control method for a fuel dual injection system for a natural gas engine, comprising the following steps:

[0011] Step 1: Bench test

[0012] When the natural gas engine is running, the first gas injection valve and the second gas injection valve inject fuel simultaneously, the amount of fuel injected by the first gas injection valve is a single-point injection amount, the sum of the injection amounts of each of the second gas injection valves is a multi-point injection amount, and the multi-point injection amount is obtained by uniform injection of each of the second gas injection valves;

[0013] Adjusting the operating condition of the natural gas engine, determining the speed and torque corresponding to the current operating condition, and, with the cooperation of the electronic control unit ECU, calibrating the fuel injection amount ratio of the single-point injection amount to the multi-point injection amount that can ensure the stable operation of the natural gas engine under the speed and torque, and recording;

[0014] Changing the operating conditions of the natural gas engine, repeating the above test, and recording the fuel injection amount ratio of the single-point injection amount to the multi-point injection amount under the corresponding operating conditions;

[0015] The fuel injection amount ratio of the single-point injection amount and the multi-point injection amount corresponding to each operating condition of the natural gas engine is formed into an injection amount ratio table, and stored in the electronic control unit ECU for standby use;

[0016] Step 2: Actual operation judgment

[0017] The speed sensor provided on the natural gas engine is used to detect the speed of the natural gas engine in real time, and the speed signal is transmitted to the electronic control unit ECU, and the electronic control unit ECU determines the current operating condition of the natural gas engine according to the speed signal;

[0018] When the electronic control unit ECU determines that the speed of the natural gas engine is stable according to the speed signal, the current operating condition of the natural gas engine is determined to be a stable operating condition, the electronic control unit ECU obtains the corresponding speed and torque according to the current stable operating condition, and queries the pre-stored injection amount ratio table according to the current speed and torque, obtains the fuel injection amount ratio of the single-point injection amount and the multi-point injection amount corresponding to the current speed and torque recorded in the injection amount ratio table, and controls the corresponding openings of the first gas injection valve and the second gas injection valve according to the fuel injection amount ratio;

[0019] When the electronic control unit ECU learns through the speed signal that the speed of the natural gas engine is increasing, that is, it determines that the current operating condition of the natural gas engine is an acceleration operating condition, then the acceleration control strategy of step three is entered;

[0020] When the electronic control unit ECU learns through the speed signal that the speed of the natural gas engine is getting smaller and smaller, that is, it determines that the current operating condition of the natural gas engine is a deceleration operating condition, then the deceleration control strategy of step 4 is entered;

[0021] Step 3: Acceleration control strategy

[0022] The electronic control unit ECU first controls the fuel injection amount ratio of the multi-point injection amount to increase, and makes the fuel injection amount ratio of each of the second gas injection valves increase synchronously, that is, the fuel injection amount ratio of the second gas injection valve corresponding to the stable operating condition before the acceleration operation is increased to N times, thereby increasing the amount of fuel entering the intake passage of each of the cylinders;

[0023] The electronic control unit ECU then adjusts the precise opening ratio of each of the second gas injection valves through Lambda closed-loop control according to the detection signal of the oxygen sensor;

[0024] Step 4: Deceleration control strategy

[0025] The electronic control unit ECU first controls the fuel injection amount ratio of the multi-point injection amount to be reduced, and makes the fuel injection amount ratio of each of the second gas injection valves to be reduced synchronously, that is, the fuel injection amount ratio of the second gas injection valve corresponding to the stable operating condition before deceleration operation is reduced to M times, thereby reducing the amount of fuel entering the intake passage of each of the cylinders;

[0026] The electronic control unit ECU then adjusts the precise opening ratio of each of the second gas injection valves through Lambda closed-loop control according to the detection signal of the oxygen sensor.

[0027] As an improvement to the above technical solution, in the acceleration control strategy of step 3, the fuel injection amount ratio of each of the second gas injection valves is controlled to increase by 1 to 1.5 times;

[0028] In the deceleration control strategy of step 4, the fuel injection amount ratio of the second gas injection valve is controlled to be reduced by a multiple of 0.3 to 0.8.

[0029] Due to the adoption of the above technical scheme, the present invention has the following beneficial effects: the first gas injection valve forms a single-point injection of the fuel, and each second gas injection valve forms a multi-point injection of the fuel, so that the present invention forms a dual-injection mode of the fuel, and the fuel delivered by the first gas injection valve is first mixed with the air by the gas mixer, and then delivered to the cylinder, which can effectively reduce the problem of poor mixing caused by only using the intake manifold injection, and another part of the fuel is injected into the corresponding cylinder at the cylinder intake passage through the second gas injection valve. This part of the fuel is closer to the combustion point, so it has better responsiveness, which is beneficial to the lambda control of the engine electronic control unit ECU, and this part of the fuel is not heated by the intake pipe, and the lower temperature can effectively reduce the temperature in the cylinder, so as to achieve the purpose of reducing the tendency of knock, thereby making the comprehensive operating performance of the natural gas engine reach the best. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following drawings are intended only to illustrate and explain the present invention, and are not intended to limit the scope of the present invention.

[0031] Figure 1 is a simplified structural diagram of an embodiment of the present invention;

[0032] In the figure: 1-natural gas engine; 2-electronic control unit ECU; 3-intake pipe; 4-air filter; 5-supercharger; 6-intercooler; 7-electronic throttle; 8-gas mixer; 9-intake manifold; 10-cylinder intake duct; 11-gas storage device; 12-gas delivery pipe; 13-first gas injection valve; 14-second gas injection valve; 15-exhaust pipe; 16-catalyst; 17-oxygen sensor; 18-exhaust gas recirculation pipe; 19-EGR cooler; 20-EGR valve. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and examples. In the following detailed description, certain exemplary embodiments of the present invention are described only by way of illustration. Needless to say, those of ordinary skill in the art will recognize that the described embodiments may be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the drawings and description are illustrative in nature and are not intended to limit the scope of protection of the claims.

[0034] like Figure 1 As shown, the dual fuel injection system for natural gas engine is used in conjunction with the electronic control unit ECU2 of the natural gas engine 1, including an air filter 4, a supercharger 5, an intercooler 6, an electronic throttle 7 and a gas mixer 8 arranged in series on the intake pipe 3 of the natural gas engine 1 along the direction of gas flow in the pipe, and the intake pipe 3 at the outlet end of the gas mixer 8 is connected to the intake manifold 9 on the natural gas engine 1, and the intake manifold 9 is provided with a cylinder intake passage 10 corresponding to each cylinder in the natural gas engine 1, and also includes a gas storage device 11. The gas storage device 11 in this embodiment includes a gas storage tank or a gas storage bottle, which is used to temporarily store compressed natural gas to provide fuel for the operation of the engine. Of course, it can also be set as a high-pressure natural gas storage container in other structural forms.

[0035] A gas delivery pipe 12 is connected between the gas storage device 11 and the gas mixer 8, and a first gas injection valve 13 is connected in series on the gas delivery pipe 12. The gas storage device 11 is also connected to each of the cylinder intake passages 10 through pipelines, and a second gas injection valve 14 is correspondingly installed on the pipeline between each of the cylinder intake passages 10 and the gas storage device 11. The electronic throttle 7, the first gas injection valve 13 and each of the second gas injection valves 14 are respectively connected to the electronic control unit ECU2. Fuel is provided to the cylinders in the natural gas engine 1 through the first gas injection valve 13 and the second gas injection valve 14, respectively, for ignition power conversion in the cylinder. The pipeline between the cylinder intake passage 10 and the gas storage device 11 can be set as a gas supply structure of a main pipe and a branch pipe, even if the gas outlet end of the second gas injection valve 14 is arranged in the corresponding cylinder intake passage 10, the gas inlet end of the second gas injection valve 14 is connected to the gas supply main pipe of the gas storage device 11 through a branch pipe or a branch pipe.

[0036] The upper limit of the injection amount of the first gas injection valve 13 is greater than the upper limit of the injection amount of the second gas injection valve 14. When in use, the injection amount of the first gas injection valve 13 is a main fuel supply valve, which provides a large amount of fuel to the cylinder in the natural gas engine 1 and delivers the fuel to the single-point injection system of the natural gas engine 1; the second gas injection valve 14 is an auxiliary fuel supply valve, which provides a small amount of fuel to the cylinder in the natural gas engine 1 and delivers the fuel to the multi-point injection system of the natural gas engine 1. The fuel fed by the first gas injection valve 13 is fully mixed with the air in the gas mixer 8 to ensure the uniformity of gas mixing, so as to reduce the problem of poor mixing caused by only using the intake manifold 9 for injection. The fuel fed by the second gas injection valve 14 is secondary mixed with the mixed gas at the cylinder intake duct 10 to further improve the uniformity of the mixed gas mixing. At the same time, this part of the fuel is closer to the combustion point, so it has better responsiveness, and this part of the fuel is not heated by the intake pipe 3, and the lower temperature can effectively reduce the temperature in the cylinder, so as to achieve the purpose of reducing the tendency of knocking.

[0037] The natural gas engine 1 is also provided with an exhaust device, which is respectively connected to the supercharger 5, the gas mixer 8 and the electronic control unit ECU2 for exhaust gas recirculation and exhaust control. Specifically, the exhaust device includes an exhaust pipe 15 connected to the exhaust gas discharge end of each cylinder in the natural gas engine 1, the tail end of the exhaust pipe 15 is connected to the catalyst 16, the supercharger 5 is connected in series to the exhaust pipe 15, and an oxygen sensor 17 is provided in the exhaust pipe 15 between the supercharger 5 and the catalyst 16, and the oxygen sensor 17 is connected to the electronic control unit ECU2; the exhaust pipe 15 between the supercharger 5 and the natural gas engine 1 is also connected to an exhaust gas recirculation pipe 18, the exhaust gas recirculation pipe 18 is connected to the gas mixer 8, and the exhaust gas recirculation pipe 18 is sequentially connected in series with an EGR cooler 19 and an EGR valve 20 along the direction of exhaust gas in the pipe, and the EGR valve 20 is connected to the electronic control unit ECU2.

[0038] In this embodiment, the oxygen content in the exhaust gas of the natural gas engine 1 is monitored in real time by the oxygen sensor 17, and is transmitted to the electronic control unit ECU2. After analysis by the electronic control unit ECU2, the coordination relationship between the electronic throttle 7, the first gas injection valve 13 and each of the second gas injection valves 14 is timely controlled according to the data results, so as to ensure that the exhaust gas meets the relevant standards. In addition, the electronic control unit ECU2 can also adjust the amount of exhaust gas recirculation by controlling the opening of the EGR valve 20 in conjunction with the relevant temperature sensor to achieve the control of the intake temperature of the natural gas engine 1. The electronic control unit ECU2 controls the electronic throttle 7 and the first gas injection valve 13 through the oxygen sensor 17, and controls the intake temperature of the natural gas engine 1 through the relevant temperature sensor, which is well known to ordinary technicians in the technical field and will not be described in detail here.

[0039] This embodiment also discloses an injection control method for a dual fuel injection system for a natural gas engine, comprising the following steps:

[0040] Step 1: Bench test

[0041] When the natural gas engine 1 is running, the first gas injection valve 13 and the second gas injection valve 14 inject fuel simultaneously, the amount of fuel injected by the first gas injection valve 13 is a single-point injection amount, the sum of the injection amounts of each of the second gas injection valves 14 is a multi-point injection amount, and the multi-point injection amount is obtained by uniform injection of each of the second gas injection valves 14.

[0042] Adjust the operating conditions of the natural gas engine 1, determine the corresponding speed and torque under the current operating conditions, and with the cooperation of the electronic control unit ECU2, calibrate the fuel injection amount ratio of the single-point injection amount to the multi-point injection amount that can ensure the stable operation of the natural gas engine 1 under the speed and torque, and record it.

[0043] For example, when the speed corresponding to a certain operating condition of the natural gas engine 1 is 1200rpm and the torque is 600Nm, the fuel injection amount ratio of the single-point injection amount and the multi-point injection amount that can ensure the steady operation of the natural gas engine 1 under this operating condition is 95%:5%, that is, the single-point injection amount accounts for 95% of the total fuel injection amount, and the multi-point injection amount accounts for 5% of the total fuel injection amount. It can be seen that when the natural gas engine 1 is running stably, the fuel is injected simultaneously through the first gas injection valve 13 and the second gas injection valve 14.

[0044] In the bench test, the operating conditions of the natural gas engine 1 are changed, the above test is repeated, and the fuel injection amount ratio of the single-point injection amount to the multi-point injection amount under the corresponding operating conditions is recorded.

[0045] The fuel injection amount ratio of the single-point injection amount and the multi-point injection amount corresponding to each operating condition of the natural gas engine 1 is formed into an injection amount ratio table, which is stored in the electronic control unit ECU2 so that the natural gas engine 1 can retrieve data for use during normal operation to control the stable operation of the natural gas engine 1.

[0046] Step 2: Actual operation judgment

[0047] When the natural gas engine 1 is actually running, there are generally two operating conditions, namely, a stable operating condition and a transitional operating condition, wherein the transitional operating condition is further divided into an acceleration operating condition and a deceleration operating condition. Therefore, according to the different operating conditions of the natural gas engine 1, it is necessary to set the corresponding operating condition strategy in the electronic control unit ECU2 in advance, so that the electronic control unit ECU2 can switch and adjust in time, realize the fuel injection adjusted according to the actual operating condition, so as to ensure the stable operation of the natural gas engine 1, and at the same time ensure that the exhaust gas discharged complies with the corresponding regulations.

[0048] The specific operating condition judgment is achieved with the help of a speed sensor provided on the natural gas engine 1, that is, the speed sensor detects the speed of the natural gas engine 1 in real time and transmits the speed signal to the electronic control unit ECU2, and the electronic control unit ECU2 judges the current operating condition of the natural gas engine 1 according to the speed signal.

[0049] When the electronic control unit ECU2 determines that the speed of the natural gas engine 1 is stable according to the speed signal, the so-called stability does not mean that the speed is fixed, but that there may be speed fluctuations, but the fluctuation is within the allowable range, then the current operating condition of the natural gas engine 1 is determined to be a stable operating condition, and the electronic control unit ECU2 obtains the corresponding speed and torque according to the current stable operating condition, and queries the pre-stored injection amount ratio table according to the current speed and torque, and obtains the fuel injection amount ratio of the single-point injection amount and the multi-point injection amount corresponding to the current speed and torque recorded in the injection amount ratio table, and controls the corresponding openings of the first gas injection valve 13 and the second gas injection valve 14 according to the fuel injection amount ratio. The specific control of the first gas injection valve 13 and the second gas injection valve 14 is achieved by the closed-loop control of the electronic control unit ECU2 and the oxygen sensor 17, which is a content well known to ordinary technicians in this technical field.

[0050] When the electronic control unit ECU2 learns through the speed signal that the speed of the natural gas engine 1 is getting higher and higher, that is, it is judged that the current operating condition of the natural gas engine 1 is an acceleration operating condition, then the acceleration control strategy of step 3 is entered. When the electronic control unit ECU2 learns through the speed signal that the speed of the natural gas engine 1 is getting lower and lower, that is, it is judged that the current operating condition of the natural gas engine 1 is a deceleration operating condition, then the deceleration control strategy of step 4 is entered. Corresponding control strategies are specially set for different transition operating conditions, and the fuel injection amount of the first gas injection valve 13 and each of the second gas injection valves 14 is adjusted in time to ensure the stable operation of the natural gas engine 1.

[0051] Step 3: Acceleration control strategy

[0052] The electronic control unit ECU2 first controls the fuel injection amount ratio of the multi-point injection amount to increase, and makes the fuel injection amount ratio of each second gas injection valve 14 increase synchronously, that is, the fuel injection amount ratio of the second gas injection valve 14 corresponding to the stable operating condition before acceleration operation is increased to N times, and the amount of fuel entering each cylinder intake passage 10 is increased. The electronic control unit ECU2 then adjusts the precise opening ratio of each second gas injection valve 14 through Lambda control according to the detection signal of the oxygen sensor 17. In this step, the fuel injection amount ratio of each second gas injection valve 14 is controlled to increase by 1 to 1.5 times.

[0053] During the acceleration operation, the fuel injection of the natural gas engine 1 needs to be accelerated and enriched. Therefore, during the acceleration, each of the second gas injection valves 14 can increase the multi-point injection amount to compensate for the over-lean phenomenon of the mixed gas during the acceleration operation, thereby avoiding the reduction of the power performance of the natural gas engine 1 and the emission of NO in the exhaust gas. x A sudden increase in value.

[0054] Step 4: Deceleration control strategy

[0055] The electronic control unit ECU2 first controls the fuel injection amount ratio of the multi-point injection amount to be reduced, and makes the fuel injection amount ratio of each second gas injection valve 14 to be reduced synchronously, that is, the fuel injection amount ratio of the second gas injection valve 14 corresponding to the stable operating condition before deceleration operation is reduced to M times, and the amount of fuel entering each cylinder intake passage 10 is reduced. The electronic control unit ECU2 then adjusts the precise opening ratio of each second gas injection valve 14 through Lambda control according to the detection signal of the oxygen sensor 17. In this step, the fuel injection amount ratio of the second gas injection valve 14 is controlled to be reduced by 0.3 to 0.8 times.

[0056] In the deceleration operating condition, the fuel injection amount of the natural gas engine 1 needs to be decelerated and diluted, so the electronic control unit ECU2 reduces the multi-point injection amount of each of the second gas injection valves 14 through calculation, thereby reducing the fuel amount of the multi-point injection, compensating for the over-rich phenomenon of the mixed gas in the deceleration operating condition, and ensuring the economy of the natural gas engine 1.

[0057] In addition, the application of accelerated enrichment and decelerated dilution can be controlled within a stable range with the help of Lambda. When enriching or diluting, the closed-loop feedback factor of the oxygen sensor 17 and the preset injection demand are combined to act on each of the second gas injection valves 14, which can not only improve the responsiveness of the natural gas engine 1, but also improve the mixed combustion of the natural gas engine 1, effectively reduce the emission of exhaust pollutants, and ultimately reduce the difficulty of emission control.

[0058] The present invention forms a dual fuel injection method by using the first gas injection valve 13 and each of the second gas injection valves 14, which not only solves the problem of poor mixing of the existing fuel injection method, but also improves the responsiveness speed of the fuel injection. Together with the Lambda control of the electronic control unit ECU2 and the oxygen sensor 17, it can effectively reduce the heavy metal content and increase the life of the catalyst 16, thereby reducing the overall cost of the engine.

[0059] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An injection control method for a dual fuel injection system for a natural gas engine, used in conjunction with an electronic control unit (ECU) of a natural gas engine, wherein the dual fuel injection system for a natural gas engine comprises an air filter, a supercharger, an intercooler, an electronic throttle and a gas mixer which are sequentially arranged in series along the direction of gas flow in the gas in the gas pipe on the natural gas engine, wherein the intake pipe at the gas outlet end of the gas mixer is connected to an intake manifold on the natural gas engine, wherein the intake manifold is provided with cylinder intake passages correspondingly connected to each cylinder in the natural gas engine, and further comprises an air storage device, Features: A gas delivery pipe is connected between the gas storage device and the gas mixer, a first gas injection valve is connected in series on the gas delivery pipe, the gas storage device is also connected to each cylinder intake passage through a pipeline, a second gas injection valve is correspondingly installed on the pipeline between each cylinder intake passage and the gas storage device, the electronic throttle, the first gas injection valve and each second gas injection valve are connected to the electronic control unit ECU respectively; The pipeline between the cylinder air intake passage and the gas storage device is arranged as a gas supply structure of a main pipe and a branch pipe, so that the gas outlet end of the second gas injection valve is arranged in the corresponding cylinder air intake passage, and the gas inlet end of the second gas injection valve is connected to the gas supply main pipe of the gas storage device through a branch pipe or a branch pipe; The natural gas engine is also provided with an exhaust device, which is respectively connected to the supercharger, the gas mixer and the electronic control unit ECU; The exhaust device comprises an exhaust pipe connected to the exhaust gas discharge end of each cylinder in the natural gas engine, the tail end of the exhaust pipe is connected to the catalyst, the supercharger is connected in series to the exhaust pipe, an oxygen sensor is arranged in the exhaust pipe between the supercharger and the catalyst, and the oxygen sensor is connected to the electronic control unit ECU; an exhaust gas recirculation pipe is also connected to the exhaust pipe between the supercharger and the natural gas engine, the exhaust gas recirculation pipe is connected to the gas mixer, and an EGR cooler and an EGR valve are connected in series to the exhaust gas recirculation pipe in sequence along the direction of exhaust gas travel in the pipe, and the EGR valve is connected to the electronic control unit ECU; The injection control method of the dual fuel injection system for a natural gas engine comprises the following steps: Step 1: Bench test When the natural gas engine is running, the first gas injection valve and the second gas injection valve inject fuel simultaneously, the amount of fuel injected by the first gas injection valve is a single-point injection amount, the sum of the injection amounts of each of the second gas injection valves is a multi-point injection amount, and the multi-point injection amount is obtained by uniform injection of each of the second gas injection valves; Adjusting the operating condition of the natural gas engine, determining the speed and torque corresponding to the current operating condition, and, with the cooperation of the electronic control unit ECU, calibrating the fuel injection amount ratio of the single-point injection amount to the multi-point injection amount that can ensure the stable operation of the natural gas engine under the speed and torque, and recording; Changing the operating conditions of the natural gas engine, repeating the above test, and recording the fuel injection amount ratio of the single-point injection amount to the multi-point injection amount under the corresponding operating conditions; The fuel injection amount ratio of the single-point injection amount and the multi-point injection amount corresponding to each operating condition of the natural gas engine is formed into an injection amount ratio table, and stored in the electronic control unit ECU for standby use; Step 2: Actual operation judgment The speed sensor provided on the natural gas engine is used to detect the speed of the natural gas engine in real time, and the speed signal is transmitted to the electronic control unit ECU, and the electronic control unit ECU determines the current operating condition of the natural gas engine according to the speed signal; When the electronic control unit ECU determines that the speed of the natural gas engine is stable according to the speed signal, the current operating condition of the natural gas engine is determined to be a stable operating condition, the electronic control unit ECU obtains the corresponding speed and torque according to the current stable operating condition, and queries the pre-stored injection amount ratio table according to the current speed and torque, obtains the fuel injection amount ratio of the single-point injection amount and the multi-point injection amount corresponding to the current speed and torque recorded in the injection amount ratio table, and controls the corresponding openings of the first gas injection valve and the second gas injection valve according to the fuel injection amount ratio; When the electronic control unit ECU learns through the speed signal that the speed of the natural gas engine is increasing, that is, it determines that the current operating condition of the natural gas engine is an acceleration operating condition, then the acceleration control strategy of step three is entered; When the electronic control unit ECU learns through the speed signal that the speed of the natural gas engine is getting smaller and smaller, that is, it determines that the current operating condition of the natural gas engine is a deceleration operating condition, then the deceleration control strategy of step 4 is entered; Step 3: Acceleration control strategy The electronic control unit ECU first controls the fuel injection amount ratio of the multi-point injection amount to increase, and makes the fuel injection amount ratio of each of the second gas injection valves increase synchronously, that is, the fuel injection amount ratio of the second gas injection valve corresponding to the stable operating condition before the acceleration operation is increased to N times, thereby increasing the amount of fuel entering the intake passage of each of the cylinders; The electronic control unit ECU then adjusts the precise opening ratio of each of the second gas injection valves through Lambda closed-loop control according to the detection signal of the oxygen sensor; Step 4: Deceleration control strategy The electronic control unit ECU first controls the fuel injection amount ratio of the multi-point injection amount to be reduced, and makes the fuel injection amount ratio of each of the second gas injection valves to be reduced synchronously, that is, the fuel injection amount ratio of the second gas injection valve corresponding to the stable operating condition before deceleration operation is reduced to M times, thereby reducing the amount of fuel entering the intake passage of each of the cylinders; The electronic control unit ECU then adjusts the precise opening ratio of each of the second gas injection valves through Lambda closed-loop control according to the detection signal of the oxygen sensor.

2. The injection control method of the dual fuel injection system for a natural gas engine according to claim 1, Features: An upper limit of an injection amount of the first gas injection valve is greater than an upper limit of an injection amount of the second gas injection valve.

3. The injection control method of the dual fuel injection system for a natural gas engine according to claim 1, Features: The gas storage device comprises a gas storage tank or a gas storage bottle.

4. The injection control method of the dual fuel injection system for a natural gas engine according to claim 1, Features: In the acceleration control strategy of step 3, the fuel injection amount ratio of each of the second gas injection valves is controlled to increase by 1 to 1.5 times; In the deceleration control strategy of step 4, the fuel injection amount ratio of the second gas injection valve is controlled to be reduced by a multiple of 0.3 to 0.8.

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