Multi-stage injection method of ammonia fuel in engine cylinder

Abstract

Provided is a multi-stage injection method for ammonia fuel in an engine cylinder. This method combines the environmental conditions at each stage in the cylinder and realizes the injection of ammonia fuel in stages. When the temperature in the engine cylinder is higher than the boiling point of liquid ammonia, flash boiling injection is adopted for liquid ammonia to reduce the liquid phase penetration distance at low back pressure and avoid hitting the wall, realizing rapid heat absorption and reducing the compression work. When the environmental pressure in the engine cylinder is less than the critical pressure of ammonia, compressed liquid atomization injection is adopted for liquid ammonia, which can increase the liquid phase penetration distance under high back pressure and make full use of the cylinder space in a large-bore internal combustion engine. When the environmental pressure in the engine cylinder is greater than the critical pressure of ammonia, fuel transcritical injection is adopted for liquid ammonia, enabling the ammonia fuel to evaporate rapidly and mix with the surrounding air. The above method can make full use of the physical and chemical properties of ammonia and enable the efficient use of ammonia fuel in a reciprocating engine.

Description

Technical Field

[0001] The present invention relates to the field of engines, and more particularly to the field of ammonia fuel combustion in engines. Background Art

[0002] As the most economical and energy-saving mode of transportation, 80% of international trade is achieved by sea shipping. According to the greenhouse gas research report released by the International Maritime Organization (IMO) in 2020, the global share of emissions from the shipping industry has increased from 2.76% to 2.89%. The report also shows that if no measures are taken, with the growth of seaborne trade demand, ship carbon emissions in 2050 are expected to be 90%-130% higher than in 2008. For this reason, the 72nd session of the Marine Environment Protection Committee of the IMO held in 2018 adopted the "IMO Initial Strategy for Reducing Greenhouse Gas Emissions from Ships", which put forward the quantitative carbon emission reduction requirements that the international shipping carbon emission intensity in 2030 should be at least 40% lower than in 2008, strive to reduce it by 70% by 2050, and the total annual greenhouse gas emissions in 2050 should be at least 50% lower than in 2008, and achieve zero carbon emissions by the end of this century.

[0003] Measures such as slow steaming, route optimization, and on-time arrival at ports play a positive role in promoting the "decarbonization" of the international shipping industry, but their contribution to achieving the ship carbon reduction goal is very limited. Whether it is ocean-going or inland river and coastal ships, the optimized path of design energy efficiency coupled with operation energy efficiency can only meet the medium- and short-term carbon reduction requirements of IMO 2030 and the strategic deployment of China's "carbon peak" before 2030, and there are difficulties in achieving the long-term IMO carbon reduction goal and China's "carbon neutrality" before 2060.

[0004] Therefore, the research, development and utilization of marine alternative fuels, especially low-carbon and zero-carbon fuels, are of great significance at present. On the one hand, it can get rid of the dependence on traditional petrochemical fuels and avoid energy shortage problems; on the other hand, it can effectively utilize the physical and chemical properties of clean fuels to reduce nitrogen oxides (NO x x), particulate matter (PM) and greenhouse gas emissions. At present, common marine low-carbon fuels mainly include liquefied natural gas (LNG), liquefied petroleum gas (LPG), methanol, biodiesel, ammonia and hydrogen, etc.

[0005] Ammonia fuel is a gas at normal temperature and pressure, can become a liquid when pressurized at normal temperature, and belongs to a superheated liquid fuel after normal temperature liquefaction. Under the current situation of rising fuel prices and increasingly strict domestic and international emission control, ammonia fuel engines are becoming more and more popular in the market.

[0006] Liquid ammonia fuel has a low viscosity, a high heat of vaporization, a narrow flammable range, and a low volumetric calorific value after vaporization. There is a risk of fire, and advanced mixture control and combustion organization technologies must be adopted to improve the combustion performance of ammonia fuel engines. The current combustion organization methods for ammonia fuel engines under research mainly include two schemes: one is to inject liquid ammonia or ammonia gas into the intake duct before or after the engine turbocharger using a relatively low injection pressure. The ammonia fuel is brought into the engine cylinder by air during the intake stroke, and then ignited by high-activity fuel injection or the jet flame of a pre-chamber, a spark plug, plasma, or laser; the other is to use a high injection pressure to inject liquid ammonia into the engine cylinder in a manner similar to a traditional diesel engine, and then ignite it by diesel injection.

[0007] However, both of the above-mentioned schemes have significant drawbacks: when injecting ammonia fuel at low pressure in the intake duct, there is an intake-exhaust overlap period in most reciprocating internal combustion engines, resulting in ammonia escaping into the exhaust pipe during cylinder scavenging, so there is unburned ammonia in the emissions, and it also increases the possibility of unburned ammonia catching fire and exploding in the intake and exhaust systems; when injecting ammonia fuel at high pressure in the cylinder, due to the high heat of vaporization of liquid ammonia, the cold liquid ammonia will rapidly evaporate when hitting the hot engine components, causing problems such as large local thermal stress; in addition, since injecting a large flow of liquid ammonia fuel once in the combustion chamber will cause uneven mixing of ammonia and air, resulting in an extended combustion duration; injecting liquid ammonia in the later stage of the compression stroke will reduce the effect of liquid ammonia cooling and reducing the compression work, thereby reducing the engine thermal efficiency; and due to the relatively high local temperature of diffusion combustion, the emission of nitrogen oxides is relatively high. Therefore, there is currently a lack of an injection strategy for liquid ammonia in the compression stroke suitable for large-bore high-power internal combustion engines. Summary of the Invention

[0008] An object of the present invention is to provide a method for organizing the injection of ammonia fuel in the engine cylinder, which can achieve staged injection of ammonia fuel and has better injection and mixing effects of ammonia fuel and air.

[0009] The method for organizing the injection of ammonia fuel in the engine cylinder to achieve the above object includes the following methods: when the temperature in the engine cylinder is higher than the boiling point of liquid ammonia, flash boiling injection is used for liquid ammonia; when the ambient pressure in the engine cylinder is less than the critical pressure of ammonia, compressed liquid atomization injection is used for liquid ammonia; when the ambient pressure in the engine cylinder is greater than the critical pressure of ammonia, fuel transcritical injection is used for liquid ammonia.

[0010] In one or more embodiments, flash boiling injection, compressed liquid atomization injection, and fuel transcritical injection are carried out in the early, middle, and later stages of the engine compression stroke.

[0011] In one or more embodiments, when the engine is cold-started or under light load conditions, compressed liquid atomization injection is used for liquid ammonia to form an air-fuel mixture; when the engine operates under medium load conditions, a combined injection method of flash boiling injection and compressed liquid atomization injection is adopted to form an air-fuel mixture; when the engine operates under high load conditions, a combined injection method of flash boiling injection, compressed liquid atomization injection, and fuel transcritical injection is adopted to form an air-fuel mixture.

[0012] In one or more embodiments, the injection ratios of the combined injection method are determined according to different target parameters, and the target parameters include load, speed, injection pressure, injection pulse width, and emission requirements.

[0013] In one or more embodiments, fuel reactivity controlled compression ignition or prechamber jet flame ignition or spark plug ignition or plasma ignition or laser ignition is used to ignite ammonia fuel.

[0014] In one or more embodiments, when fuel reactivity controlled compression ignition is adopted, high-reactivity fuel is premixed with ammonia fuel during the compressed liquid atomization injection stage and then injected or ignited during the fuel transcritical injection stage or in the late stage of the piston compression stroke.

[0015] In one or more embodiments, when fuel reactivity controlled compression ignition is adopted, high-reactivity fuel is injected and ignited during the fuel transcritical injection stage or in the late stage of the piston compression stroke.

[0016] In one or more embodiments, when prechamber jet flame ignition is adopted, a gas fuel jet flame is used to inject and ignite ammonia fuel during the fuel transcritical injection stage or in the late stage of the piston compression stroke.

[0017] In one or more embodiments, when a spark plug or plasma or laser is used for ignition, a spark plug or plasma or laser is used to trigger and ignite ammonia fuel during the fuel transcritical injection stage or in the late stage of the piston compression stroke.

[0018] The above method for organizing ammonia fuel injection in the engine cylinder utilizes the characteristics of the changing environment in the cylinder of a reciprocating internal combustion engine and combines the characteristics of ammonia being difficult to ignite. A staged injection strategy is adopted when the environment in the cylinder of the reciprocating engine is in different stages, and appropriate injection methods are selected according to different stages. A better injection strategy matching the different compression strokes is adopted, resulting in better injection and ammonia-air mixture effects. Description of the Drawings

[0019] The above and other features, properties, and advantages of the present invention will become more apparent through the following description in conjunction with the drawings and embodiments, where:

[0020] Figure 1is the comprehensive phase diagram of ammonia fuel and the in-cylinder environmental pressure-temperature in a reciprocating engine;

[0021] Figure 2A is a schematic diagram of ammonia fuel in the flash boiling injection stage (the early stage of the piston compression stroke);

[0022] Figure 2B is a schematic diagram of ammonia fuel in the compressed liquid atomization injection stage (the middle stage of the piston compression stroke);

[0023] Figure 2C is a schematic diagram of ammonia fuel in the fuel transcritical injection stage (the late stage of the piston compression stroke);

[0024] Figure 3A is a schematic diagram of the in-cylinder environment when ammonia fuel is in the flash boiling injection state using fuel reactivity controlled compression ignition;

[0025] Figure 3B is a schematic diagram of the in-cylinder environment of the pilot fuel and ammonia fuel in the premixed state when using fuel reactivity controlled compression ignition;

[0026] Figure 3C is a schematic diagram of the in-cylinder environment when pilot fuel reactivity controlled compression ignition of ammonia fuel;

[0027] Figure 4A is a schematic diagram of the in-cylinder environment when ammonia fuel is in the flash boiling injection state using prechamber jet flame ignition;

[0028] Figure 4B is a schematic diagram of the in-cylinder environment when ammonia fuel is in the atomization injection state using prechamber jet flame ignition;

[0029] Figure 4C is a schematic diagram of the in-cylinder environment when prechamber jet flame ignites;

[0030] Figure 5A is a schematic diagram of the in-cylinder environment when ammonia fuel is in the flash boiling injection state using spark plug ignition;

[0031] Figure 5B is a schematic diagram of the in-cylinder environment when compressed liquid ammonia is atomized and injected using spark plug ignition;

[0032] Figure 5C is a schematic diagram of the in-cylinder environment when spark plug ignites ammonia fuel. Specific implementation manners

[0033] The present invention will be further described below in conjunction with specific embodiments and the accompanying drawings. In the following description, more details are set forth in order to fully understand the present invention. However, the present invention is obviously capable of being implemented in many other ways different from this description. Those skilled in the art can make similar generalizations and deductions according to the actual application situation without departing from the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0034] It should be noted that these and subsequent other drawings and characteristic data are only examples, and they are not drawn under the condition of equal proportion, and should not be used to limit the actual protection scope required by the present invention.

[0035] Figure 1 The P-T phase diagram of ammonia and the P-T phase diagram of the in-cylinder environment of a reciprocating engine are shown. The ordinate P is the pressure, and the abscissa T is the temperature. The critical temperature T of ammonia C is 132.3 °C, and the critical pressure P C is 11.2 MPa. The boiling point T at normal pressure boil is -33.5 °C, and the saturated vapor pressure of ammonia at normal temperature (25 °C) is 1.0 MPa.

[0036] It should be noted that the above data is a reference for the characteristics of ammonia and should not be considered as limiting the actual protection scope required by the present invention.

[0037] Figure 1 The solid line in [Figure] represents the ammonia saturated vapor pressure curve, and the dashed line represents the in-cylinder environment curve of a reciprocating internal combustion engine. There are three points A, B, and C on it, representing different in-cylinder injection environments. Point A represents the fuel flash boiling injection environment, point B represents the compressed liquid atomization injection environment, and point C represents the fuel transcritical injection environment. The area where L is located in the phase diagram represents the liquid phase region of ammonia, CL represents the compressed liquid region of ammonia, G represents the gas phase region of ammonia, IG represents the ideal gas region, and S represents the supercritical region. Among them, point D represents the position of the initial state when the fuel is injected.

[0038] Utilizing the characteristics of the in-cylinder environment change of a reciprocating internal combustion engine and combining the characteristics of ammonia being difficult to catch fire, the method described in the present disclosure can inject liquid ammonia fuel into the cylinder in stages according to different stroke stages to organize and form an ammonia-air mixture.

[0039] In this method, when the in-cylinder temperature of the engine is higher than the boiling point T of liquid ammonia boil , the flash boiling injection method is used for liquid ammonia; when the in-cylinder environment pressure of the engine is less than the critical pressure P of ammonia C , the compressed liquid atomization injection method is used for liquid ammonia; when the in-cylinder environment pressure of the engine is greater than the critical pressure P of ammonia CWhen the time is right, fuel transcritical injection of liquid ammonia is adopted. By the above multi-stage injection method, the problem of slow and incomplete combustion after single injection of liquid ammonia fuel can be reduced.

[0040] Specifically, as shown in combination with Figure 2A and Figure 1 the dotted line, after the engine exhaust valve is closed and in the early stage of the compression stroke of the piston 10, at this time, the temperature in the engine cylinder 15 is higher than the boiling point T of liquid ammonia boil . When liquid ammonia is injected into the cylinder 15 by the liquid ammonia injector 20 at this time, a flash boiling atomization effect will be generated. The change process of ammonia fuel changes from point D to point A, as shown by line ①. In the following introduction, this process will be called the first stage. The flash boiling injection has a short penetration distance. The liquid ammonia fuel will quickly boil and vaporize, which will not cause wet wall phenomenon in the cylinder, nor will it hit the hot engine components and cause problems such as large local thermal stress. In addition, the latent heat of vaporization of liquid ammonia is high. A large amount of heat in the cylinder will be absorbed during the flash boiling injection process, reducing the cylinder temperature, thereby indirectly reducing the work done in the piston compression stroke and improving the engine thermal efficiency.

[0041] Continuing to understand in combination with Figure 2B and Figure 1 the dotted line shown, when the piston is in the middle of the compression stroke, the ambient pressure in the engine cylinder has not reached the critical pressure P of ammonia c , at this time, taking advantage of the characteristic that the density of compressed liquid ammonia is large, compressed liquid atomization injection method is used to inject liquid ammonia. The change process of ammonia fuel is from point D to point B, as shown by line ②. In the following introduction, this process will be called the second stage. At this time, injecting liquid ammonia with high injection momentum, the formed liquid mist has a long penetration distance, which can solve the problem that the large cylinder diameter of a high-power engine cannot fully utilize the combustion space.

[0042] As the piston further compresses, when the ambient pressure in the engine cylinder exceeds the critical pressure P of ammonia c , at this time, fuel transcritical injection method is adopted. For example, liquid ammonia can be injected within 20°CA before the piston top dead center. Utilizing the high-temperature and high-pressure environment in the cylinder, liquid ammonia quickly forms a combustible mixture. The change process of ammonia fuel is from point D to point C, as shown by line ③. In the following introduction, this process will be called the third stage. This method can effectively reduce unburned ammonia and ammonia escape.

[0043] The above-mentioned method for organizing ammonia fuel injection in the engine cylinder makes full use of the characteristics of the temperature and pressure environment changes in the cylinder of a reciprocating internal combustion engine, and combines the characteristics of ammonia being easy to liquefy but not easy to ignite. Different multi-stage injection strategies are adopted according to different strokes. Fuel transcritical injection in the late stage of piston compression and the early stage of power stroke can effectively reduce unburned ammonia and ammonia escape, and use the high-temperature and high-pressure environment in the cylinder to quickly form a combustible mixture; compressed liquid atomization injection in the middle stage of piston compression can make full use of the combustion space of a high-power engine; fuel flash boiling injection in the early stage of piston compression can quickly vaporize the liquid ammonia fuel, without causing wet wall phenomenon in the cylinder, nor generating problems such as large local thermal stress caused by the impact of liquid ammonia on the hot parts of the engine. The flash boiling injection process can also absorb a large amount of heat in the cylinder, reduce the cylinder temperature, and indirectly reduce the compression work, so as to make full use of the physical and chemical properties of ammonia fuel and efficiently use it in a reciprocating engine.

[0044] Under the high-load condition of a marine engine, the above-mentioned flash boiling injection, compressed liquid atomization injection, and fuel transcritical injection respectively correspond to three stroke stages of the early, middle, and late stages of compression in an internal combustion engine. However, under low-load conditions, the fuel transcritical injection method is generally not considered.

[0045] The aforementioned method based on the physical and chemical properties of ammonia fuel and using multi-stage injection also needs to consider factors such as different loads, speeds, injection pressures, injection pulse widths, and emission requirements in the engine cylinder pressure. After comprehensively considering various factors in the cylinder, the following injection organization scheme for ammonia fuel ammonia-air mixture suitable for high-power engines can be formed.

[0046] When the engine is cold-started or under low-load conditions, due to the low temperature and pressure in the cylinder, it is necessary to avoid the problem of misfire risk caused by the rapid heat absorption during flash boiling injection. Therefore, compressed liquid atomization injection is used for liquid ammonia to form a fuel-air mixture.

[0047] When the engine operates under medium-load conditions, since the pressure at the start of combustion in the cylinder does not reach the critical pressure of ammonia fuel, which is 11.2 MPa, a combined injection method of flash boiling injection and compressed liquid atomization injection can be adopted according to target parameters such as different loads, speeds, injection pressures, injection pulse widths, and emission requirements to form a fuel-air mixture.

[0048] When the engine operates under high-load conditions, the pressure at the start of combustion in the cylinder exceeds the critical pressure of ammonia fuel. A combined injection method of flash boiling injection, compressed liquid atomization injection, and fuel transcritical injection can be adopted according to target parameters such as different loads, speeds, injection pressures, injection pulse widths, and emission requirements to form a fuel-air mixture.

[0049] The proportion of the combined injection method in the above-mentioned method is specifically determined by different target parameters such as load, speed, injection pressure, injection pulse width, and emission requirements.

[0050] In addition, methods such as reactivity controlled compression ignition of fuel, pre-chamber jet flame ignition, spark plug ignition, plasma ignition, and laser ignition can be used to ignite the ammonia fuel - air mixture after the above-mentioned multi-stage injection.

[0051] Reactivity Controlled Compression Ignition (RCCI) is a method of using highly reactive fuels such as fuel for injection ignition. As Figure 3B shown, in some embodiments, the highly reactive fuel can be pre-mixed with ammonia fuel through the fuel injector 30 during the second-stage compression liquid atomization injection process, and then ignite the ammonia fuel during the third-stage fuel transcritical injection; in other embodiments, as Figure 3C shown, the highly reactive fuel can also directly ignite the ammonia fuel during the third-stage fuel transcritical injection or in the later stage of the piston compression stroke.

[0052] When using the pre-chamber jet flame ignition method, based on the pre-chamber, a jet flame 40 is generated using a gaseous fuel such as hydrogen, and in the third stage, that is, during the fuel transcritical injection or in the later stage of the piston compression stroke, a jet flame is directly generated to ignite the ammonia fuel, as Figure 4C shown.

[0053] Ignition methods such as spark plug, plasma, or laser ignition can also be used, and a spark plug, plasma, or laser is used to trigger the ignition of ammonia fuel in the third stage, that is, during the fuel transcritical injection. As Figure 5C shown, the spark plug 50 is directly triggered in the later stage of the internal combustion engine compression and the early stage of the power stroke to complete the ignition of ammonia fuel in the cylinder.

[0054] The above-mentioned multi-stage injection method of ammonia fuel in the engine cylinder and the corresponding ignition methods fully consider the in-cylinder environmental factors and the inherent characteristics of liquid ammonia, and propose a hierarchical injection, combined injection, and corresponding ignition organization strategy, which promotes the ammonia - air mixing degree, avoids problems such as excessive local thermal stress and ammonia misfire deflagration, thereby making full use of the physical and chemical properties of ammonia fuel and efficiently using it in a reciprocating engine, and further enabling the ammonia fuel engine to have better performance.

[0055] It should be noted that the use of terms such as "first" and "second" to limit components in the above introduction is only for the convenience of distinguishing the corresponding components. Without additional declaration, the above terms have no special meaning and do not represent primary or secondary, so it should not be understood as a limitation on the protection scope of this application.

[0056] Meanwhile, this application uses specific terms to describe the embodiments of this application. For example, "an embodiment", "one embodiment", and / or "some embodiments" mean a certain feature, structure, or characteristic related to at least one embodiment of this application. Therefore, it should be emphasized and noted that the "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more at different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this application can be appropriately combined.

[0057] Although the present invention is disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. Method for multi-stage injection of ammonia fuel in an engine cylinder, characterized in that, The method includes the following ways: When the temperature in the engine cylinder is higher than the boiling point of liquid ammonia, flash boiling injection is adopted for the liquid ammonia; When the ambient pressure in the engine cylinder is less than the critical pressure of ammonia, compressed liquid atomization injection is adopted for the liquid ammonia; When the ambient pressure in the engine cylinder is greater than the critical pressure of ammonia, fuel transcritical injection is adopted for the liquid ammonia; Flash boiling injection, compressed liquid atomization injection and fuel transcritical injection are carried out in the early, middle and late stages of the engine compression stroke; when the engine is operating under high load conditions, a combined injection method of flash boiling injection, compressed liquid atomization injection and fuel transcritical injection is adopted to form an air-fuel mixture.

2. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 1, characterized in that, When the engine is cold started or operating under low load conditions, compressed liquid atomization injection is adopted for the liquid ammonia to form an air-fuel mixture; When the engine is operating under medium load conditions, a combined injection method of flash boiling injection and compressed liquid atomization injection is adopted to form an air-fuel mixture.

3. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 2, characterized in that, Determine the injection ratios of the combined injection method according to different target parameters.

4. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 3, characterized in that, The target parameters include load, speed, injection pressure, injection pulse width, and emission requirements.

5. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 1 or 2, characterized in that, Fuel reactivity controlled compression ignition or pre-chamber jet flame ignition or spark plug ignition or plasma ignition or laser ignition is adopted to ignite the ammonia fuel.

6. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 1, characterized in that, When fuel reactivity controlled compression ignition is adopted, the high-reactivity fuel and the ammonia fuel are premixed in the compressed liquid atomization injection stage and then the ammonia fuel is injected and ignited in the fuel transcritical injection stage or the late stage of the piston compression stroke.

7. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 1, characterized in that, When fuel reactivity controlled compression ignition is adopted, the high-reactivity fuel is injected and ignited in the fuel transcritical injection stage or the late stage of the piston compression stroke.

8. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 1, characterized in that, When pre-chamber jet flame ignition is adopted, the gas fuel jet flame is used to inject and ignite the ammonia fuel in the fuel transcritical injection stage or the late stage of the piston compression stroke.

9. The method for multi-stage injection of ammonia fuel in an engine cylinder according to claim 1, characterized in that, When spark plug or plasma or laser ignition is adopted, the spark plug or plasma or laser is used to trigger and ignite the ammonia fuel in the fuel transcritical injection stage or the late stage of the piston compression stroke.

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