A combustion system and combustion method for a dual-fuel engine with direct injection of ammonia and diesel

Abstract

The purpose of the present invention is to provide a combustion system and a combustion method for a direct-injection ammonia diesel dual-fuel engine, including a piston, a cylinder liner, a direct-injection ammonia injector, a cylinder head, an exhaust valve, a high-pressure common rail injector, an intake valve and other structures; the engine has two operating modes, namely, a pure diesel operating mode at start-up and idling to ensure smooth engine start-up, and a diesel / ammonia dual-fuel operating mode at other operating conditions, using ammonia fuel high-low pressure injection and diesel multiple injections, adjusting the injection ratio and injection timing of ammonia and diesel according to the change of operating conditions, and cooperating with the Miller cycle to improve the combustion efficiency and combustion stability of the ammonia fuel engine on the basis of reducing carbon emissions. The present invention can reduce the carbon oxide and sulfur oxide emissions caused by the combustion of fossil fuels in traditional engines, as well as the ignition difficulties caused by the slow combustion speed of ammonia fuel and the high ignition energy.

Description

Technical Field

[0001] The present invention relates to an engine device, in particular to an engine combustion system and a combustion method. Background Art

[0002] Ammonia has a liquefaction temperature of -33°C and is easy to store and transport. The energy density per unit volume of liquid ammonia is comparable to that of gasoline. Ammonia is considered an ideal zero-carbon alternative fuel because of its good long-term stability in storage and transportation, its ease of preparation, and the fact that its combustion products do not contain greenhouse gases.

[0003] Compared with typical hydrocarbon fuels, direct use of ammonia in combustion systems has the characteristics of slow combustion speed, high ignition energy, narrow flammable range, high auto-ignition temperature, long quenching distance, and long ignition delay time. In terms of maximum power, efficiency and emissions, it is far inferior to the performance achieved by using hydrocarbon fuels under similar operating conditions. Existing technologies tend to use highly reactive fuels to ignite ammonia or improve ammonia combustion, while highly reactive diesel is widely used and well-equipped, and using diesel to ignite ammonia is safe and reliable.

[0004] Most existing patents improve the combustion of ammonia by adding hydrogen. Patent CN115217622A mentions an ammonia-hydrogen fusion fuel control system based on reaction activity regulation, which uses an on-board hydrogen production device to produce hydrogen, uses intake duct injection to supply ammonia and mix it with hydrogen, and uses hydrogen jet ignition. The device achieves zero carbon emissions, but because it contains hydrogen storage equipment, there is a risk of hydrogen leakage and explosion, and there is also a risk of backfire during hydrogen jet combustion. Patent CN115111089A mentions a pre-combustion chamber ammonia fuel engine system, which uses ammonia catalytic decomposition to produce hydrogen, and uses hydrogen fuel cells and other equipment to provide energy for ammonia catalysis. It uses direct injection in the cylinder to supply ammonia and ignite hydrogen in the pre-combustion chamber to ignite ammonia. This invention only needs to provide ammonia and does not use carbon-containing fuels, but the cost of using hydrogen fuel cells is high, the requirements for hydrogen purification are high, and the reliability is poor. Summary of the invention

[0005] The purpose of the present invention is to provide a combustion system and a combustion method for a dual-fuel engine with direct injection of ammonia and diesel, which can reduce the carbon oxide and sulfur oxide emissions caused by the combustion of fossil fuels in traditional engines, as well as the ignition difficulties caused by the slow combustion speed and high ignition energy of ammonia fuel.

[0006] The object of the present invention is achieved in that:

[0007] The present invention discloses a combustion system of a direct-injection ammonia diesel dual-fuel engine, which is characterized by comprising a cylinder, a diesel fuel tank, a liquid ammonia tank, a high-pressure fuel rail, and a liquid ammonia common rail pipe. The cylinder comprises a cylinder sleeve, a cylinder head, and a piston. The cylinder head is provided with a high-pressure common rail injector, a direct-injection ammonia injector, an intake valve, and an exhaust valve. The diesel fuel tank is connected to the high-pressure common rail injector through a fuel pump and a high-pressure fuel rail. The liquid ammonia tank is connected to the direct-injection ammonia injector through a liquid ammonia pump and a liquid ammonia common rail pipe. The cylinder is connected to an intake passage through an intake valve. The cylinder is connected to an exhaust passage through an exhaust valve. The axis of the high-pressure common rail injector coincides with the axis of the cylinder. The axis of the in-cylinder direct injection ammonia injector is in the same plane as the cylinder axis, and the angle with the vertical direction is 30-60°. The spray hole of the in-cylinder direct injection ammonia injector adopts a non-axisymmetric design, and the intersection of the axial extension line of the spray hole and the piston surface is in the same plane. At the same time, the spray hole close to the cylinder axis adopts a larger spray hole diameter, so that the liquid ammonia injected by the in-cylinder direct injection ammonia injector is evenly distributed in the cylinder; the central axis of the in-cylinder direct injection ammonia injector intersects with the central axis of the high-pressure common rail injector, so that the ammonia spray injected by the in-cylinder direct injection ammonia injector is distributed on the oil beam path injected by the high-pressure common rail injector.

[0008] The invention discloses a combustion method for a dual-fuel engine of direct-injection ammonia and diesel, which is characterized by comprising a pure diesel mode, in which only a high-pressure common rail injector injects diesel for combustion; when the engine is in starting and idling conditions, the high-pressure common rail injector performs a single injection, and the injection timing is 5-20°CA before compression top dead center; in other conditions, the high-pressure common rail injector performs two injections, the first injection timing is 60°CA before compression top dead center, and the second injection timing is 5-20°CA before compression top dead center.

[0009] The combustion method of a dual-fuel engine with direct injection of ammonia and diesel in the cylinder of the present invention may also include:

[0010] 1. Including ammonia / diesel dual-fuel mode, diesel is injected by high-pressure common rail injectors, and liquid ammonia is injected by direct-injection ammonia injectors. The injection ratio of diesel and liquid ammonia is adjusted according to the load;

[0011] When the engine is running at high load, ammonia is used as the main fuel and diesel is used as the pilot fuel. The calorific value of diesel accounts for 5%-25% of the total fuel. At 60°CA before the compression top dead center, the high-pressure common rail injector pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total injected diesel, to produce highly active substances to shorten the ignition delay period of the main injection diesel combustion process. When the piston moves to the top dead center 5-15°CA, the high-pressure common rail injector performs the main injection of diesel into the cylinder, accounting for 60%-85% of the total injected diesel. After the main injection of diesel is completed, diesel is post-injected at 5-15°CA, accounting for 10%-25% of the total injected diesel, to burn out the residual ammonia.

[0012] When the engine is running at medium load, the proportion of diesel increases, and the proportion of diesel in the total fuel calorific value is 25%-45%. At the beginning of the compression stage, the direct injection ammonia injector injects low-pressure liquid ammonia into the cylinder, and its injection timing is delayed under high load conditions, making the ammonia closer to the high-pressure common rail injector more concentrated, forming a concentration stratification. At 60°CA before the top dead center in the compression stage, the high-pressure common rail injector pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total amount of injected diesel, producing highly active substances and shortening the main injection of diesel. During the ignition delay period of the oil combustion process, when the piston moves to the top dead center 5-15°CA, the high-pressure common rail injector performs a main injection of diesel into the cylinder, accounting for 60%-85% of the total injected diesel. The in-cylinder direct injection ammonia injector injects high-pressure liquid ammonia into the cylinder again, which lags 2-5°CA behind the main injection of diesel. The liquid ammonia spray and the diesel spray cross and are ignited by the diesel. After the main injection of diesel is completed, the diesel is post-injected 5-15°CA, accounting for 10%-25% of the total injected diesel, so that all the unburned ammonia is burned out.

[0013] When the engine is running at low load, the proportion of diesel is further increased, and the proportion of diesel in the total fuel calorific value is between 45% and 65%. Diesel is used as the main fuel and ammonia is used as the alternative fuel. At 60°CA before the top dead center in the compression stage, the high-pressure common rail injector pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total injected diesel; when the piston moves to 5-15°CA before the top dead center, the high-pressure common rail injector performs the main injection of diesel into the cylinder, accounting for 60%-85% of the total injected diesel; the in-cylinder direct-injection ammonia injector injects high-pressure liquid ammonia into the cylinder, which lags 2-5°CA behind the main injection of diesel, and the liquid ammonia spray and diesel spray cross and are ignited by the diesel.

[0014] The advantages of the present invention are:

[0015] 1. Using diesel to ignite ammonia is safer and more reliable than hydrogen ignition, and the equipment cost is lower.

[0016] 2. Using different fuel injection schemes for different loads can achieve stable operation of the engine under all working conditions and meet the emission and power requirements of the engine under different working conditions.

[0017] 3. Direct injection can realize more ammonia and diesel injection schemes, which is conducive to flexible setting of injection timing to adapt to different working conditions. At the same time, since ammonia is easy to evaporate, direct injection can avoid intake charge loss.

[0018] 4. Using an in-cylinder direct injection ammonia injector and a liquid ammonia common rail with variable rail pressure, high-pressure and low-pressure injection of liquid ammonia can be achieved while using one ammonia injector, making the arrangement of the in-cylinder direct injection ammonia injector on the cylinder head more flexible and adaptable to engines of different sizes. In addition, the in-cylinder direct injection ammonia injector can achieve high-pressure and low-pressure injection of liquid ammonia, which can meet the precise requirements of large and small flow injection amounts.

[0019] 5. The use of Miller cycle can reduce compression work, improve thermal efficiency, reduce fuel consumption, and effectively suppress engine knock under high load. It can also reduce the combustion temperature in the cylinder, reduce heat load, and reduce NOx emissions.

[0020] 6. The present invention is not only applicable to Miller cycle engines but also to other compression ignition engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 The cylinder radial distribution diagram of ammonia and diesel mist beams in the combustion system under the ammonia / diesel dual fuel mode;

[0023] Figure 3 The working flow diagram of the combustion system in ammonia / diesel dual fuel mode;

[0024] Figure 4 The in-cylinder state diagram of the combustion system at the end of the compression phase under high load conditions in the ammonia / diesel dual-fuel mode;

[0025] Figure 5 Low load injection flow diagram of the combustion system in ammonia / diesel dual fuel mode;

[0026] Figure 6 The mid-load injection flow diagram of the combustion system in ammonia / diesel dual-fuel mode;

[0027] Figure 7 High load injection flow diagram of the combustion system in ammonia / diesel dual-fuel mode. DETAILED DESCRIPTION

[0028] The present invention is described in more detail below with reference to the accompanying drawings:

[0029] Combination Figure 1-7The present invention provides a combustion system of a direct-injection ammonia / diesel dual-fuel engine, comprising a piston 1, a cylinder liner 2, a direct-injection ammonia injector 3, a cylinder head 4, an exhaust valve 5, a high-pressure common rail injector 6, and an intake valve 7. The cylinder head 4 is mounted on the top of the cylinder liner 2, and the piston 1 is mounted inside the cylinder liner 2. The enclosed space enclosed by the three is a cylinder. The cylinder is connected to the intake passage through the intake valve 7 and to the exhaust passage through the exhaust valve 6. Diesel is transported from the diesel tank 13 to the high-pressure fuel rail 10 through the fuel pump 11, and is supplied to the high-pressure common rail injector 6. Liquid ammonia is transported from the liquid ammonia tank 14 to the liquid ammonia common rail pipe 8 through the liquid ammonia pump 12, and is supplied to the direct-injection ammonia injector 3. The ECU 9 controls the operation of the fuel pump 11 and the liquid ammonia pump 12 according to the engine operating conditions, and controls the injection of the direct-injection ammonia injector 3 and the high-pressure common rail injector 6.

[0030] The combustion system adopts the Miller cycle to achieve that the actual compression ratio in the intake stage is less than the expansion ratio in the power stage, thereby reducing the compression work, improving the thermal efficiency, reducing the fuel consumption rate, and effectively suppressing the engine knock, and also reducing the temperature in the cylinder, reducing the heat load, and suppressing the generation of NOx. The implementation method of the Miller cycle includes realizing the Miller cycle by closing the intake valve 7 in advance before the bottom dead center.

[0031] Combination Figure 2 , a high-pressure common rail injector 6 and an in-cylinder direct injection ammonia injector 3 are arranged in the cylinder head 4, and the heads of the two are separated by a certain distance and are both exposed in the cylinder, wherein the axis of the high-pressure common rail injector 6 coincides with the axis of the cylinder, and the axis of the in-cylinder direct injection ammonia injector 3 is on the same plane as the axis of the cylinder, and the angle with the vertical direction is 30-60°, and the inclination angle of the in-cylinder direct injection ammonia injector 3 and the distance separated from the high-pressure common rail injector 6 are determined by the specific structure of the engine. The spray hole of the in-cylinder direct injection ammonia injector 6 adopts a non-axisymmetric design, and the intersection of the axial extension line of the spray hole and the surface of the piston 1 is on the same plane. At the same time, the spray hole near the cylinder axis adopts a larger spray hole diameter, so that the liquid ammonia injected by the in-cylinder direct injection ammonia injector 6 is evenly distributed in the cylinder; the central axis of the in-cylinder direct injection ammonia injector 3 intersects with the central axis of the high-pressure common rail injector 6, so that the ammonia spray injected by the in-cylinder direct injection ammonia injector 3 is distributed on the oil beam path injected by the high-pressure common rail injector 6.

[0032] The engine adopts the injection mode of direct injection in the cylinder to supply diesel and ammonia. Different injection modes can be realized by changing the injection state of the high-pressure common rail injector 6 and the direct injection ammonia injector 3, including the pure diesel mode and the ammonia / diesel dual-fuel mode. The injection state includes injection timing and injection pulse width. The injection state of the high-pressure common rail injector 6 and the direct injection ammonia injector 3 is flexibly controlled according to the load change to realize the switching and backup of the dual-fuel mode and the pure diesel mode. Especially in the transitional working condition, diesel and ammonia are coupled and injected multiple times to meet the requirements of transient working conditions and emission regulations, ensuring the coverage of the entire working range of the engine and the reliability of operation.

[0033] The high-pressure common rail injector 6 is a spray hole type high-pressure common rail injector, which can realize single or multiple injections in one cycle, and adjust the number of injections, injection pulse width and injection timing according to actual needs. When the in-cylinder direct injection ammonia injector 3 fails, it can be used as a backup fuel supply device to meet the engine power demand by increasing the injection amount, adjusting the injection timing and number, and maintaining the engine operation.

[0034] The rail pressure of the liquid ammonia common rail pipe 8 that supplies ammonia fuel to the in-cylinder direct injection ammonia injector 3 is a common rail pipe with a variable rail pressure, which realizes the supply of high-pressure liquid ammonia and low-pressure liquid ammonia to the in-cylinder direct injection ammonia injector 3, and adjusts the liquid ammonia supply pressure according to actual needs. The in-cylinder direct injection ammonia injector 3 injects high-pressure liquid ammonia under low-load conditions. The use of high-pressure injection ensures better atomization of liquid ammonia, which is conducive to accelerating the gasification of liquid ammonia, and at the same time ensures that the injection is completed within the required pulse width. The in-cylinder direct injection ammonia injector 3 injects low-pressure liquid ammonia under medium-load and high-load conditions, and uses low-pressure injection to reduce equipment loss.

[0035] The pure diesel mode is that only the high-pressure common rail injector 6 injects diesel for combustion, which is mainly used for engine starting and idling. The number of injections, injection amount and injection timing are flexibly controlled according to load changes. When the engine is in the starting and idling conditions, the high-pressure common rail injector 6 injects once, and the injection timing is 5-20°CA before the compression top dead center. Due to the low temperature of the engine parts and the low temperature of the compression end point in the cylinder, and the ignition point of diesel (527K) is much lower than the ignition point of ammonia (930K), the selection of diesel can reduce the occurrence of incomplete combustion or misfire. The pure diesel operation mode can be used as a backup operation mode of the diesel / ammonia dual-fuel operation mode and can be switched at any time when needed, that is, the pure diesel mode is used instead of the ammonia / diesel dual-fuel mode to maintain the engine operation. At this time, the high-pressure common rail injector 6 performs two injections, the first injection timing is 60°CA before the compression top dead center, and the second injection timing is 5-20°CA before the compression top dead center.

[0036] Combination Figures 3 to 7In the ammonia / diesel dual fuel mode, the high pressure common rail injector 6 injects diesel, and the in-cylinder direct injection ammonia injector 3 injects liquid ammonia. The injection ratio of diesel and liquid ammonia is adjusted according to the load. When the engine is running at high load, ammonia is used as the main fuel and diesel is used as the pilot fuel. The calorific value of diesel accounts for 5%-25% of the total fuel. At the beginning of the compression stage, the direct injection ammonia injector 3 injects low-pressure liquid ammonia into the cylinder, which is conducive to uniform mixing with the intake air, avoiding local excessive concentration of fuel, resulting in violent combustion, causing excessive temperature in the cylinder and generating more NOx. Near 60°CA before the compression top dead center, the high-pressure common rail injector 6 pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total injected diesel, producing more highly active substances to shorten the ignition delay period of the main injection diesel combustion process. When the piston moves to 5-15°CA before the top dead center, the high-pressure common rail injector 6 performs the main injection of diesel into the cylinder, accounting for 60%-85% of the total injected diesel, forming multiple ignition sources. After the main injection of diesel, the diesel post-injection is performed at 5-15°CA, accounting for 10%-25% of the total injected diesel, burning out the residual ammonia and preventing ammonia from being discharged from the cylinder. When the engine is running at medium load conditions, the diesel ratio is increased, and the diesel accounts for 25%-45% of the total fuel calorific value. At the beginning of the compression stage, the direct injection ammonia injector 3 injects low-pressure liquid ammonia into the cylinder, and its injection timing is delayed under high load conditions, so that the ammonia near the high-pressure common rail injector 6 is more concentrated, forming a certain concentration stratification. Near 60°CA before the top dead center in the compression stage, the high-pressure common rail injector 6 pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total amount of injected diesel, producing more highly active substances to shorten the ignition delay period of the main injection diesel combustion process. When the piston moves to 5-15°CA before the top dead center, the high-pressure common rail injector 6 performs the main injection of diesel into the cylinder, accounting for 60%-85% of the total amount of injected diesel, forming multiple ignition sources, and the direct injection ammonia injector 3 injects high-pressure liquid ammonia into the cylinder again, which is 2-5°CA later than the main injection of diesel. The liquid ammonia spray and the diesel spray cross and are ignited by the diesel. After the main injection of diesel is completed, the diesel is post-injected 5-15°CA, accounting for 10%-25% of the total amount of injected diesel, so that all the unburned ammonia is burned out. When the engine is running at low load, the proportion of diesel is further increased, and the proportion of diesel in the total fuel calorific value is 45%-65%. When the engine is in low load condition, diesel is used as the main fuel and ammonia is used as an alternative fuel. At about 60°CA before the top dead center in the compression stage, the high-pressure common rail injector 6 pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total amount of injected diesel; when the piston moves to the top dead center 5-15°CA, the high-pressure common rail injector 6 performs the main diesel injection into the cylinder, accounting for 60%-85% of the total amount of injected diesel; the in-cylinder direct injection ammonia injector 3 injects high-pressure liquid ammonia into the cylinder, which lags 2-5°CA behind the main diesel injection, and the liquid ammonia spray and diesel spray cross and are ignited by the diesel. At low load, the amount of liquid ammonia injection is small. Using low-pressure injection of liquid ammonia can increase the injection pulse width, which is conducive to precise control of the injection amount.

[0037] The appearance of concentration and activity stratification allows the ignition process to proceed in stages. First, the local area has high reactivity and spontaneous combustion, and then the low reactivity area is ignited, and finally the spontaneous combustion and combustion phase are effectively controlled. Controlling the concentration and activity stratification in the cylinder can not only effectively control the ignition time and combustion reaction rate, but also has great advantages in controlling emissions. The RCCI combustion mode can form concentration and activity stratification, realize stratified combustion of the mixture, thereby broadening the operating range, and has flexible control over the combustion phase and pressure rise rate, achieving extremely low NOx and carbon smoke emissions in a wide range of engine loads, and having an acceptable pressure rise rate and extremely high indicated efficiency.

Claims

1. A combustion method for a dual-fuel engine with direct injection of ammonia and diesel, Its characteristics are: A dual-fuel engine combustion system of direct injection ammonia and diesel is adopted, the system includes a cylinder, a diesel tank, a liquid ammonia tank, a high-pressure fuel rail, and a liquid ammonia common rail pipe. The cylinder includes a cylinder liner, a cylinder head, and a piston. The cylinder head is provided with a high-pressure common rail injector, a direct injection ammonia injector, an intake valve, and an exhaust valve. The diesel tank is connected to the high-pressure common rail injector through a fuel pump and a high-pressure fuel rail. The liquid ammonia tank is connected to the direct injection ammonia injector through a liquid ammonia pump and a liquid ammonia common rail pipe. The cylinder is connected to the intake passage through an intake valve, and the cylinder is connected to the exhaust passage through an exhaust valve. The axis of the high-pressure common rail injector coincides with the axis of the cylinder. The axis of the direct injection ammonia injector is in the same plane as the cylinder axis, and the angle with the vertical direction is 30-60 degrees. The spray hole of the direct injection ammonia injector adopts a non-axisymmetric design, and the intersection of the axial extension line of the spray hole and the piston surface is in the same plane. At the same time, the spray hole close to the cylinder axis adopts a larger spray hole diameter, so that the liquid ammonia injected by the direct injection ammonia injector is evenly distributed in the cylinder; the central axis of the direct injection ammonia injector intersects with the central axis of the high-pressure common rail injector, so that the ammonia spray injected by the direct injection ammonia injector is distributed on the oil beam path injected by the high-pressure common rail injector; The method includes a pure diesel mode, in which only the high-pressure common rail injector injects diesel for combustion. When the engine is in the starting and idling conditions, the high-pressure common rail injector performs a single injection, and the injection timing is 5-20°CA before the compression top dead center. In other conditions, the high-pressure common rail injector performs two injections, the first injection timing is 60°CA before the compression top dead center, and the second injection timing is 5-20°CA before the compression top dead center. The method also includes an ammonia / diesel dual fuel mode, wherein the high pressure common rail injector injects diesel, the in-cylinder direct injection ammonia injector injects liquid ammonia, and the injection ratio of diesel and liquid ammonia is adjusted according to the load; The method also includes that when the engine is running under high load conditions, ammonia is used as the main fuel and diesel is used as the pilot fuel, the diesel accounts for 5%-25% of the total fuel calorific value, 60°CA before compression top dead center, a small amount of diesel is pre-injected by the high-pressure common rail injector for low-temperature reaction, accounting for 5%-15% of the total amount of injected diesel, to produce highly active substances to shorten the ignition delay period of the main injection diesel combustion process, 5-15°CA before the piston moves to the top dead center, the high-pressure common rail injector performs a main injection of diesel into the cylinder, accounting for 60%-85% of the total amount of injected diesel, and 5-15°CA after the main injection of diesel is completed, diesel is post-injected, accounting for 10%-25% of the total amount of injected diesel, to burn out the residual ammonia; When the engine is running at medium load, the proportion of diesel increases, and the proportion of diesel in the total fuel calorific value is 25%-45%. At the beginning of the compression stage, the in-cylinder direct injection ammonia injector injects low-pressure liquid ammonia into the cylinder, and its injection timing is delayed under high load conditions, making the ammonia closer to the high-pressure common rail injector more concentrated, forming a concentration stratification. At 60°CA before the top dead center in the compression stage, the high-pressure common rail injector pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total amount of injected diesel, producing highly active substances and shortening the main injection of diesel. During the ignition delay period of the oil combustion process, when the piston moves to the top dead center 5-15°CA, the high-pressure common rail injector performs the main injection of diesel into the cylinder, accounting for 60%-85% of the total injected diesel. The in-cylinder direct injection ammonia injector injects high-pressure liquid ammonia into the cylinder again, 2-5°CA later than the main injection of diesel. The liquid ammonia spray and the diesel spray cross and are ignited by the diesel. After the main injection of diesel is completed, the post-injection of diesel is performed 5-15°CA, accounting for 10%-25% of the total injected diesel, so that all the unburned ammonia is burned out. When the engine is running at low load, the proportion of diesel is further increased, and the proportion of diesel in the total fuel calorific value is between 45% and 65%. Diesel is used as the main fuel and ammonia is used as the alternative fuel. At 60°CA before the top dead center in the compression stage, the high-pressure common rail injector pre-injects a small amount of diesel for low-temperature reaction, accounting for 5%-15% of the total injected diesel; when the piston moves to the top dead center 5-15°CA, the high-pressure common rail injector performs the main injection of diesel into the cylinder, accounting for 60%-85% of the total injected diesel; the in-cylinder direct-injection ammonia injector injects high-pressure liquid ammonia into the cylinder, which lags 2-5°CA behind the main injection of diesel, and the liquid ammonia spray and diesel spray cross and are ignited by the diesel.

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