Diesel and ammonia dual-fuel engine combustion system and combustion method using hybrid gas active reforming

Abstract

The object of the present invention is to provide a combustion system and a combustion method for a diesel and ammonia dual-fuel engine using hybrid gas reforming. A vertically-mounted concentric double-needle valve injector and an inclined in-cylinder direct injection ammonia injector are provided on the cylinder head. The intake valve and the exhaust valve are driven by a variable valve train system to adjust the valve timing and the valve motion law according to various operating conditions of the engine, so as to achieve functional requirements such as Miller cycle, exhaust trapping and fuel reforming. The main and auxiliary fuel supply systems are used to independently supply fuel to the concentric double-needle valve injector. The present invention can flexibly adjust the proportion, injection law and injection timing of diesel and ammonia fuels, realize multi-mode combustion of the engine, and cover all operating conditions with stable operation while achieving high-efficiency clean combustion.

Description

Technical Field

[0001] The present invention relates to an ammonia fuel engine, specifically to an ammonia fuel engine combustion system and method. Background Art

[0002] As a renewable carbon-free energy source, ammonia is widely available and has extremely low production costs. It is an excellent alternative energy source. An engine using ammonia as fuel can significantly reduce the emissions of CO 2 greenhouse gases. However, the flame propagation speed of ammonia is extremely slow, and its autoignition temperature is high. It is very difficult for a compression ignition engine of pure ammonia to ignite and stably burn. It is necessary to blend other fuels and adopt more organizational methods and optimization technologies to solve the defects such as poor combustion stability, insufficient mixing, and large compression loss.

[0003] Currently, the patents on internal combustion engines fueled by ammonia mainly focus on two aspects: one is the hydrogen jet ignition combustion system of the ammonia engine in the patent with the publication number CN114294129A. The design of the prechamber and hydrogen jet aims to solve the problems of difficult ignition and low overall combustion efficiency of the ammonia engine. However, it has high requirements for the ignition device, insufficient engine system control, and poor stability. The other is the system and method for reducing unburned ammonia emissions of an ammonia engine in the patent with the publication number CN114483299A. The waste heat of the exhaust gas is used to crack unburned ammonia gas to generate hydrogen, realizing hydrogen-doped combustion of the engine, thereby improving the combustion speed and efficiency of the ammonia engine. However, the ammonia cracking temperature is relatively high, and it is difficult for the waste heat of the exhaust gas in most working conditions of the engine to make the ammonia cracking efficiency meet the requirements of actual application, and the reduction of the unburned ammonia content in the emission concentration cannot meet the demand.

[0004] Based on a series of problems existing in the ammonia fuel engine, the present invention realizes Miller cycle and fuel reforming through variable valve timing, and cooperates with diesel ignition mode and pure diesel mode to improve the stability of the engine system, make up for the disadvantages of long ignition delay period and slow laminar flame speed of ammonia fuel, reduce negative power loss, improve combustion efficiency, and improve exhaust gas emissions. Summary of the Invention

[0005] The purpose of the present invention is to provide a diesel and ammonia dual-fuel engine combustion system and combustion method using mixed gas active reforming, which can flexibly adjust the proportion, injection law, and injection timing of diesel and ammonia fuel, realize multi-mode combustion of the engine, achieve high-efficiency clean combustion, and cover all working conditions for stable operation.

[0006] The purpose of the present invention is achieved as follows:

[0007] The present invention adopts a diesel and ammonia dual-fuel engine combustion system using mixed gas active reforming, which is characterized in that it includes a cylinder, a cylinder head, a piston, a main and auxiliary fuel supply system, and an ammonia supply device;

[0008] The cylinder, cylinder head and piston form a combustion chamber. A concentric double needle valve injector and an in-cylinder direct injection ammonia injector are installed on the cylinder head. The concentric double needle valve injector includes an external large flow rate injector and an internal small flow rate injector. The external large flow rate injector includes an external large flow rate injector needle valve body and an internal small flow rate injector needle valve body. The external large flow rate injector needle valve body is located outside the internal small flow rate injector needle valve body, and an external large flow rate injector oil passage is formed between the two. The internal small flow rate injector includes an internal small flow rate injector needle valve body and an internal small flow rate injector needle valve. The internal small flow rate injector needle valve body is located outside the internal small flow rate injector needle valve, and an internal small flow rate injector oil passage is formed between the two. The end of the internal small flow rate injector needle valve body is the external large flow rate injector pintle;

[0009] The main and auxiliary fuel supply systems include a high-pressure common rail fuel supply system and an electronically controlled unit pump fuel supply system. The high-pressure common rail fuel system includes a common rail pipe, a fuel pump, a high-pressure common rail system fuel tank, a filter, and a pressure relief valve. Diesel oil in the high-pressure common rail system fuel tank is pumped into the common rail pipe by the fuel pump through the filter. The common rail pipe is connected to the internal small flow rate injector. The common rail pipe is connected to the high-pressure common rail system fuel tank through a return pipe. The pressure relief valve is installed on the return pipe. The fuel pump is connected to the return pipe before the pressure relief valve; The electronically controlled unit pump fuel supply system includes an electronically controlled unit pump, a unit pump system fuel tank, and a low-pressure oil pump. The electronically controlled unit pump is respectively connected to the high-pressure oil circuit and the low-pressure oil pump. The low-pressure oil pump is connected to the unit pump system fuel tank through a low-pressure oil circuit. The high-pressure oil circuit is connected to the external large flow rate injector;

[0010] The ammonia supply device includes an ammonia storage tank, a supply pump, an ammonia rail, and an ammonia pressure relief valve. The ammonia storage tank is connected to the ammonia rail through the supply pump. The supply pump and the ammonia rail are connected to the ammonia storage tank through a return ammonia pipe. An ammonia pressure relief valve is provided on the return ammonia tank.

[0011] The combustion system of the diesel and ammonia dual-fuel engine adopting the mixed gas active reforming of the present invention may further include:

[0012] 1. The external large flow rate injector is a pintle injector, and the internal small flow rate injector is a multi-hole injector. The number of spray holes is 6-8. Both the external large flow rate injector and the internal small flow rate injector include independent needle valves, needle valve bodies, springs, solenoid valves, and oil passages.

[0013] 2. The flow rate of the internal small flow rate injector needle valve body reaches the linearity range earlier than that of the external large flow rate injector needle valve body.

[0014] 3. The in-cylinder direct injection ammonia injector has a multi-hole structure, and the spray holes are axially symmetrically distributed about the central axis of the in-cylinder direct injection ammonia injector.

[0015] 4. The central axis of the concentric double needle valve injector coincides with the central axis of the cylinder.

[0016] 5. The central axis of the in-cylinder direct injection ammonia injector and the central axis of the concentric double needle valve injector are in the same spatial plane and point to the center of the combustion chamber, and the included angle between the two central axes is less than 90 degrees.

[0017] The combustion method of the diesel and ammonia dual-fuel engine using mixture active reforming in the present invention is characterized in that it includes a pure diesel mode:

[0018] In the pure diesel mode, during starting, idling and low load conditions, the needle valve of the internal small flow injector in the concentric double needle valve injector lifts before top dead center, and the shaft needle of the external large flow injector moves down to inject a small amount of diesel. As the fuel flow requirement increases and exceeds the fuel supply capacity of the small flow injector, it switches to the large flow injector of the concentric double needle valve injector to inject fuel. The needle valve of the internal small flow injector in the concentric double needle valve injector drops, the injection holes of the internal small flow injector close, and the shaft needle of the external large flow injector moves up. After the upward movement height exceeds the set distance, the diesel flow area at the injection holes increases rapidly. Under high load conditions, the large flow and small flow injectors of the concentric double needle valve injector work simultaneously.

[0019] The combustion method of the diesel and ammonia dual-fuel engine using mixture active reforming in the present invention may further include:

[0020] 1. It includes a dual-fuel mode:

[0021] In the dual-fuel mode, when the engine is at medium and low loads, the diffusion combustion of diesel is the main, and the concentric double needle valve injector and the in-cylinder direct injection ammonia injector work together. During the exhaust stage, the exhaust valve is closed in advance. The needle valve of the internal small flow injector in the concentric double needle valve injector lifts, and the shaft needle of the external large flow injector moves down to inject a small amount of diesel, and an oxidation reaction occurs under the high temperature condition of the exhaust gas to generate OH and H active free radicals. During the intake stage, fresh air flows into the cylinder and mixes with the high temperature exhaust gas and active free radicals. In the second half of the compression stroke, the needle valve of the in-cylinder direct injection ammonia injector lifts to inject high-pressure liquid ammonia into the cylinder. The injection duration is less than half of the compression stroke. The ammonia fuel and air are unevenly mixed. Before top dead center, the needle valve of the internal small flow injector in the concentric double needle valve injector lifts, and the shaft needle of the external large flow injector moves down to inject a small amount of diesel, so that the diesel injection duration and the ammonia fuel injection duration partially overlap, forming a concentration gradient stratification, and realizing the coupled stratified combustion of high-reactivity diesel and ammonia fuel.

[0022] In the dual-fuel mode, when the engine is at high load, the engine mainly burns ammonia fuel. The concentric dual-needle valve injector and the in-cylinder direct injection ammonia injector work together. During the intake stage, the intake valve is closed in advance to achieve an expansion ratio greater than the compression ratio. In the first half of the compression stroke, the needle valve of the in-cylinder direct injection ammonia injector lifts to inject low-pressure liquid ammonia, and the injection duration is greater than half of the compression stroke to obtain a lean mixture with a low concentration gradient. At the top dead center, the shaft needle of the large-flow injector outside the concentric dual-needle valve injector moves downward, and the needle valve of the small-flow injector inside lifts to inject a small amount of ignition diesel fuel, realizing the ignition and stable combustion of the mixed fuel mainly composed of ammonia fuel in the cylinder.

[0023] The advantages of the present invention are as follows: The present invention provides a specific combustion mode for the combustion of ammonia fuel in an internal combustion engine. By flexibly adjusting parameters such as the ratio of diesel and ammonia fuel, injection law, and injection timing, the flexible switching of the combustion mode, precise control of the combustion start point and heat release rate can be achieved. The use of a concentric dual-needle valve injector avoids arranging too many injectors on the cylinder head. Under high load in the dual-fuel mode, the intake valve is closed in advance to achieve an expansion ratio greater than the compression ratio, reducing the in-cylinder temperature at the top dead center and solving the problem of easy knocking under high load. In the medium and low load of the dual-fuel mode, the fuel reforming technology is adopted to oxidize and reform diesel by the high temperature of the exhaust gas, generating a large number of free radicals such as OH and H, improving the reaction activity of ammonia fuel, solving the problem of difficult ignition of ammonia as the main fuel, and realizing efficient, clean, and stable combustion. While meeting the high-power requirements, it covers the entire operating conditions and meets the requirements of fuel economy and emission regulations. In addition, the present invention can select the pure diesel mode / dual-fuel mode according to the actual working conditions of the engine by controlling the concentric dual-needle valve injector. The pure diesel mode is only used for starting, idling conditions or when the dual-fuel mode fails, and pure diesel is supplied; while the dual-fuel mode is used for normal conditions, and low-pressure / high-pressure ammonia supply is selected by adjusting the ammonia supply rail pressure to achieve efficient and clean combustion of the fuel in the cylinder. The atomization effect of high-pressure direct injection of liquid ammonia is good, the combustion is more complete, the concentration gradient is large, and the required pilot fuel quantity is less; the low-pressure direct injection of liquid ammonia is pre-mixed sufficiently, the ammonia supply rail and injector bear less pressure, the maximum combustion temperature is low, and the NO X emission is low, and the ignition and flame propagation are controlled by the turbulence intensity and the mixture composition. And to save costs, the present invention adopts a main and auxiliary fuel supply system. The unit pump fuel supply system uses heavy diesel oil (HFO) with low cost during normal driving in deep sea areas, and uses ordinary diesel oil (MDO) or light diesel oil (MGO) with slightly higher cost when approaching the shore in coastal areas or ports. Brief Description of the Drawings

[0024] Figure 1 is a schematic structural diagram of the present invention;

[0025] Figure 2 is a schematic structural diagram of the concentric dual-needle valve injector;

[0026] Figure 3 Schematic diagram of large-flow injection outside the concentric double needle valve injector;

[0027] Figure 4 Schematic diagram of small-flow injection inside the concentric double needle valve injector;

[0028] Figure 5 Schematic diagram of the initial stage of fuel reforming;

[0029] Figure 6 Schematic diagram of the end stage of fuel reforming;

[0030] Figure 7 Schematic diagram of in-cylinder fuel distribution in pure diesel mode;

[0031] Figure 8 Schematic diagram of in-cylinder fuel distribution in dual fuel mode. Detailed implementation manners

[0032] The present invention will be described in more detail with reference to the accompanying drawings as follows:

[0033] Combined with Figure 1-8 , as shown in the accompanying Figure 1 is the overall structural schematic diagram of the present invention, which includes: piston 1, cylinder 2, combustion chamber 3, exhaust passage 4, cylinder head 5, exhaust valve 6, concentric double needle valve injector 7, intake valve 8, in-cylinder direct injection ammonia injector 9, intake passage 10, ammonia storage tank 11, supply pump 12, ammonia rail 13, ammonia pressure relief valve 14, ECU 15, camshaft 16, other components 17, common rail pipe 18, fuel pump 19, high-pressure common rail system fuel tank 20, oil filter 21, diesel pressure relief valve 22, high-pressure oil circuit 23, electronic unit pump 24, low-pressure oil pump 25, low-pressure oil circuit 26, unit pump system fuel tank 27. The concentric double needle valve injector 7 adopts a nested double needle valve structure, and the two needle valves have independent oil passages, which can respectively achieve precise control of the injection pulse width and injection timing of the two needle valves. It is vertically installed on the cylinder head 5, and its central axis coincides with the central axis of the cylinder 2, and is connected with the main and auxiliary fuel supply systems; the in-cylinder direct injection ammonia injector 9 is inclined and installed on the cylinder head, and its axis and the central axis of the cylinder are in the same spatial plane, and the included angle between the two axes is less than 90 degrees. The specific angle is determined according to the actual structure of the cylinder head 5, and it is connected with an ammonia supply device. The combustion chamber 3 is a hemispherical combustion chamber, which is composed of the upper surface of the piston 1, part of the cylinder liner of the cylinder 2 and the lower surface of the cylinder head 5. It can shorten the flame propagation distance and has strong squish flow, which can improve the turbulence intensity of the mixed gas and contribute to rapid ignition and combustion.

[0034] The main and auxiliary fuel supply systems include two independent fuel supply systems, namely the electronic control unit injector and the high-pressure common rail system. The electronic control unit injector fuel supply system includes an electronic control unit injector 24, a unit injector system fuel tank 27, a high-pressure oil circuit 23, a low-pressure oil circuit 26, a low-pressure oil pump 25, etc., which are used to supply fuel to external large-flow injectors; the high-pressure common rail fuel supply system includes a common rail pipe 18, a fuel pump 19, a high-pressure common rail system fuel tank 20, a fuel filter 21, a pressure relief valve 22, and sensors, etc., which are used to supply fuel to the internal small-flow injectors. The diesel in the high-pressure common rail system fuel tank 20 is pumped into the common rail pipe 18 by the fuel pump 19 through the fuel filter 21. When the pressure exceeds the limit value, the oil pressure relief valve 22 is opened to make the diesel flow back to reduce the pressure, realizing flexible control of injection pressure, injection quantity, injection timing, and injection law, and meeting the requirements of engine fuel supply, concentration stratification, and active reforming, etc.

[0035] The in-cylinder direct injection ammonia injector 9 is a multi-hole injector with 6 - 8 injection holes. The ammonia supply device consists of an ammonia storage tank 11, a supply pump 12, an ammonia rail 13, and an ammonia pressure relief valve 14. The liquid ammonia in the ammonia storage tank 11 is supplied to the ammonia rail 13 by the supply pump 12. When the pressure exceeds the limit value, the ammonia pressure relief valve 14 is opened to make the liquid ammonia flow back to reduce the pressure, realizing high and low pressure injection in the cylinder, eliminating ammonia scavenging leakage caused by the ammonia supply valve overlap angle in the intake manifold, and meeting the full operating conditions of the ammonia fuel engine. Low-pressure injection is applied under high-load conditions. The ECU 15 adjusts the rail pressure limit to reach the limit pressure, controls the opening of the ammonia pressure relief valve to reduce the ammonia supply rail pressure, the injection pressure is about 10 - 20 MPa, and the early injection method is adopted to make the ammonia fuel fully mix with air to form a uniform mixture; high-pressure injection is applied under medium and low-load conditions, and the injection pressure is about 20 - 50 MPa, and the ammonia fuel and air are non-uniformly mixed.

[0036] The specific implementation method of variable valve timing is as follows: Under high load in the dual-fuel mode, the ECU 15 controls the camshaft 16 to make the intake valve 8 close late to reduce the actual compression ratio in the intake stroke, and the expansion ratio in the power stroke is greater than the actual compression ratio in the intake stroke, reducing the in-cylinder temperature at the top dead center and solving the problem of easy knocking under high load; the exhaust timing is controlled to change according to the load. Under medium and low load in the dual-fuel mode, the exhaust valve 6 is closed early so that part of the exhaust gas cannot be completely exhausted, and the residual exhaust gas enters the next working cycle. There is a small negative valve overlap angle interval after the exhaust valve 6 is closed. The concentric double-needle valve injector 7 injects a small amount of diesel, and the high temperature of the exhaust gas is used to make the diesel undergo an oxidation reaction to generate active free radicals such as OH and H, improving the reaction activity of the fuel in the cylinder and shortening the ignition delay period, which helps to improve the combustion efficiency.

[0037] As shown in the Figure 2 accompanying figure is the specific structural schematic diagram of the concentric double-needle valve injector 7 of the present invention. Figure 3-4 is the injection schematic diagram of the concentric double-needle valve injector 7 of the present invention. Combining Figure 2-4A detailed introduction to the concentric double needle valve injector 7 is given. The figure includes: the external large flow injector pintle 28, the external large flow injector needle valve body oil passage 29, the internal small flow injector needle valve body oil passage 30, the internal small flow injector needle valve 31, the internal small flow injector needle valve body 32, and the external large flow injector needle valve body 33. The concentric double needle valve injector 7 is composed of the external large flow injector needle valve body 33 and the internal small flow injector needle valve body 32. The external large flow injector needle valve body 33 and the internal small flow injector needle valve body 32 are coaxially arranged inside the concentric double needle valve injector 7, pointing directly downward to the combustion chamber system. Both the external large flow injector needle valve body 33 of the concentric double needle valve injector and the internal small flow injector needle valve body 32 of the concentric double needle valve injector have independent needle valves, springs, solenoid valves, and fuel supply channels. The needle valve diameter of the external large flow injector needle valve body 33 of the concentric double needle valve injector is much larger than that of the internal small flow injector needle valve body 32 of the concentric double needle valve injector. It should be noted that the small flow injector needle valve body 32 is installed in the large flow injector needle valve body 33, and the small flow injector needle valve body 32 also serves as the pintle of the large flow injector needle valve body 33. The external large flow injector is a pintle type injector, and the internal small flow injector is a multi-hole type injector with 6 - 8 injection holes. The opening and closing of the two injectors and the injection volume are regulated by controlling the rail pressure and the solenoid valve through the ECU15. Under the condition of the same injection pulse width, the flow rate of the internal small flow injector needle valve body 32 is much smaller than that of the external large flow injector needle valve body 33, but the linearity intervals are different. The flow rate of the internal small flow injector needle valve body 32 reaches the linearity interval earlier, and more precise control can be achieved when less fuel is required during starting, idling, low load, or reforming stages. The external large flow injector and the internal small flow injector are supplied with fuel by a main and auxiliary fuel supply system with different fuel supply modes. The external large flow injector adopts a unit pump fuel supply system, and the internal small flow injector adopts a high pressure common rail fuel injection system.

[0038] Combined with Figure 1-8 A detailed introduction to the characteristics of the combustion organization method of the present invention is given:

[0039] Specifically, it includes two operating modes: pure diesel and dual fuel.

[0040] The power in the pure diesel mode can cover the entire operating conditions of the engine. The fuel injection schematic diagram before top dead center is as Figure 7As shown in the figure; under starting, idle, and low-load conditions, the internal small-flow injector needle valve 31 of the concentric dual-needle valve injector 7 before top dead center is lifted, and the external large-flow injector pintle 28 moves downward to inject small-flow diesel. When the engine is in the starting condition, due to the low temperature of the components and the low temperature at the end of cylinder compression, selecting diesel can reduce incomplete combustion or misfire. Moreover, the fuel quantity required for starting, idle, and low-load conditions is small. Therefore, using the internal small-flow injector to inject diesel can achieve more precise control and reduce incomplete combustion or misfire. As the required flow increases and exceeds the fuel supply capacity of the small-flow injector, it switches to the large-flow injector of the concentric dual-needle valve injector 7 to inject fuel. The internal small-flow injector needle valve 31 of the concentric dual-needle valve injector 7 drops, the spray holes of the internal small-flow injector close, and the external large-flow injector pintle 28 moves upward. After moving upward by a certain distance, the diesel flow area at the spray holes increases rapidly; under high-load conditions, the large-flow and small-flow injectors of the concentric dual-needle valve injector work simultaneously to ensure the stable operation of the engine.

[0041] In the dual-fuel mode, the schematic diagram of fuel injection before top dead center is as Figure 8 shown. When the engine is at medium and low loads, the diffusion combustion of diesel is the main process, and the concentric dual-needle valve injector 7 and the in-cylinder direct injection ammonia injector 9 work together. During the exhaust stage, the control system controls the variable valve system to close the exhaust valve 6 in advance according to the working conditions to achieve the capture of high-temperature exhaust gas and increase the initial temperature in the cylinder in the next cycle. After the exhaust valve 6 is closed, the internal small-flow injector needle valve 31 of the concentric dual-needle valve injector 7 is lifted, and the external large-flow injector pintle 28 moves downward to inject a small amount of diesel. Oxidation reactions occur under the high-temperature conditions of the exhaust gas to generate active free radicals such as OH and H, solving problems such as the difficulty of ignition and incomplete combustion of ammonia fuel at medium and low loads, as Figure 5 shown; during the intake stage, fresh air flows into the cylinder and mixes with the high-temperature exhaust gas and active free radicals, as Figure 6 shown; in the second half of the compression stroke, the needle valve of the in-cylinder direct injection ammonia injector 9 is lifted to inject high-pressure liquid ammonia into the cylinder. The injection duration is less than half of the compression stroke. The ammonia fuel and air are non-uniformly mixed. Before top dead center, the internal small-flow injector needle valve 31 of the concentric dual-needle valve injector 7 is lifted, and the external large-flow injector pintle 28 moves downward to inject small-flow diesel. The ignition diesel timing and flow are precisely controlled to achieve partial overlap between the diesel injection duration and the ammonia fuel injection duration, forming a large concentration gradient stratification, and realizing the efficient coupling stratified combustion of high-reactivity diesel and ammonia fuel;

[0042] In the dual-fuel mode, when the engine is at high load, the engine mainly burns ammonia fuel, and the concentric dual-needle valve injector 7 and the in-cylinder direct injection ammonia injector 9 work together. During the intake stage, the ECU 15 controls the variable valve system to close the intake valve 8 in advance according to the working conditions, so as to achieve an expansion ratio greater than the compression ratio, reduce the in-cylinder temperature at the top dead center, and solve the problem of easy knocking at high load; in the first half of the compression stroke, the needle valve of the in-cylinder direct injection ammonia injector 9 lifts to inject low-pressure liquid ammonia, and the injection duration is greater than half of the compression stroke, obtaining a lean mixture with a low concentration gradient. At the top dead center, the outer large-flow injector pintle 28 of the concentric dual-needle valve injector 7 moves down, and the inner small-flow injector needle valve 31 lifts to inject a small amount of ignition diesel fuel, precisely controlling the timing and flow rate of the ignition diesel fuel, and realizing the ignition and stable combustion of the mixed fuel mainly composed of ammonia fuel in the cylinder.

[0043] Among them, the fuel spray does not limit the form of the fuel. The fuel is not only liquid but also gaseous or supercritical fluid.

Claims

1. A combustion system for a diesel and ammonia dual-fuel engine using hybrid gas reactive reforming, characterized in that: it includes a cylinder, a cylinder head, a piston, a main and auxiliary fuel supply system, and an ammonia supply device; the cylinder, the cylinder head and the piston form a combustion chamber. A concentric double-needle valve injector and an in-cylinder direct injection ammonia injector are installed on the cylinder head. The concentric double-needle valve injector includes an external large-flow injector and an internal small-flow injector. The external large-flow injector includes an external large-flow injector needle valve body and an internal small-flow injector needle valve body. The external large-flow injector needle valve body is located outside the internal small-flow injector needle valve body, and an external large-flow injector oil passage is formed between them. The internal small-flow injector includes an internal small-flow injector needle valve body and an internal small-flow injector needle valve. The internal small-flow injector needle valve body is located outside the internal small-flow injector needle valve, and an internal small-flow injector oil passage is formed between them. The end of the internal small-flow injector needle valve body is the external large-flow injector pintle; the main and auxiliary fuel supply system includes a common rail fuel supply system and an electronically controlled unit pump fuel supply system. The common rail fuel system includes a common rail pipe, a fuel pump, a common rail system fuel tank, a filter, and a pressure relief valve. Diesel in the common rail system fuel tank is pumped into the common rail pipe by the fuel pump through the filter. The common rail pipe is connected to the internal small-flow injector. The common rail pipe is connected to the common rail system fuel tank through a return pipe. The pressure relief valve is installed on the return pipe. The fuel pump is connected to the return pipe before the pressure relief valve; the electronically controlled unit pump fuel supply system includes an electronically controlled unit pump, a unit pump system fuel tank, and a low-pressure oil pump. The electronically controlled unit pump is respectively connected to the high-pressure oil circuit and the low-pressure oil pump. The low-pressure oil pump is connected to the unit pump system fuel tank through a low-pressure oil circuit. The high-pressure oil circuit is connected to the external large-flow injector; the ammonia supply device includes an ammonia storage tank, a supply pump, an ammonia rail, and an ammonia pressure relief valve. The ammonia storage tank is connected to the ammonia rail through the supply pump. The supply pump and the ammonia rail are connected to the ammonia storage tank through a return ammonia pipe. An ammonia pressure relief valve is provided on the return ammonia tank; a combustion system for a diesel and ammonia dual-fuel engine using hybrid gas reactive reforming includes a dual-fuel mode: In the dual-fuel mode, when the engine is at medium and low loads, it mainly uses the diffusion combustion of diesel. The concentric double-needle valve injector and the in-cylinder direct injection ammonia injector work together. In the exhaust stage, the exhaust valve is closed in advance. The needle valve of the internal small-flow injector of the concentric double-needle valve injector is lifted, and the external large-flow injector pintle moves downward to inject a small amount of diesel. Under the high-temperature condition of the exhaust gas, an oxidation reaction occurs to generate OH and H active free radicals; in the intake stage, fresh air flows into the cylinder and mixes with the high-temperature exhaust gas and active free radicals; in the second half of the compression stroke, the needle valve of the in-cylinder direct injection ammonia injector is lifted to inject high-pressure liquid ammonia into the cylinder. The injection duration is less than half of the compression stroke. The ammonia fuel and air are non-uniformly mixed. Before top dead center, the needle valve of the internal small-flow injector of the concentric double-needle valve injector is lifted, and the external large-flow injector pintle moves downward to inject a small amount of diesel, so that the diesel injection duration and the ammonia fuel injection duration partially overlap, forming a concentration gradient stratification, and realizing the coupled stratified combustion of high-reactivity diesel and ammonia fuel; In the dual-fuel mode, when the engine is at high load, the engine mainly burns ammonia fuel. The concentric dual-needle valve injector and the in-cylinder direct injection ammonia injector work together. In the intake stage, the intake valve is closed in advance to achieve an expansion ratio greater than the compression ratio. In the first half of the compression stroke, the needle valve of the in-cylinder direct injection ammonia injector lifts to inject low-pressure liquid ammonia, and the injection duration is greater than half of the compression stroke to obtain a lean mixture with a low concentration gradient. At the top dead center, the shaft needle of the large-flow injector outside the concentric dual-needle valve injector moves down, and the needle valve of the small-flow injector inside lifts to inject a small amount of ignition diesel, realizing the ignition and stable combustion of the mixed fuel mainly composed of ammonia fuel in the cylinder.

2. The diesel and ammonia dual-fuel engine combustion system using mixture gas activity reforming according to claim 1, characterized in that: the large-flow injector outside is a shaft needle injector, the small-flow injector inside is a multi-hole injector, the number of spray holes is 6 - 8, and both the large-flow injector outside and the small-flow injector inside include independent needle valves, needle valve bodies, springs, solenoid valves and oil channels.

3. The diesel and ammonia dual-fuel engine combustion system using mixture gas activity reforming according to claim 1, characterized in that: The flow of the needle valve body of the small-flow injector inside reaches the linearity range earlier than that of the needle valve body of the large-flow injector outside.

4. The diesel and ammonia dual-fuel engine combustion system using mixture gas activity reforming according to claim 1, characterized in that: The in-cylinder direct injection ammonia injector has a porous structure, and the spray holes are axially symmetrically distributed about the central axis of the in-cylinder direct injection ammonia injector.

5. The diesel and ammonia dual-fuel engine combustion system using mixture gas activity reforming according to claim 1, characterized in that: The central axis of the concentric dual-needle valve injector coincides with the central axis of the cylinder.

6. The diesel and ammonia dual-fuel engine combustion system using mixture gas activity reforming according to claim 1, characterized in that: The central axis of the in-cylinder direct injection ammonia injector and the central axis of the concentric dual-needle valve injector point to the center of the combustion chamber in the same spatial plane, and the included angle between the two central axes is less than 90 degrees.

7. The diesel and ammonia dual-fuel engine combustion system using mixture gas activity reforming according to claim 1, characterized in that: including the pure diesel mode: In the pure diesel mode, during startup, idle speed and low-load conditions, the needle valve of the small-flow injector inside the concentric dual-needle valve injector lifts before the top dead center, and the shaft needle of the large-flow injector outside moves down to inject a small amount of diesel; As the fuel flow requirement increases and exceeds the fuel supply capacity of the small-flow injector, it switches to the large-flow injector of the concentric dual-needle valve injector to inject fuel. The needle valve of the small-flow injector inside the concentric dual-needle valve injector drops, the spray holes of the small-flow injector inside close, and the shaft needle of the large-flow injector outside moves up. When the upward movement height exceeds the set distance, the diesel flow area at the spray holes increases rapidly; under high-load conditions, the large-flow and small-flow injectors of the concentric dual-needle valve injector work simultaneously.

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