Control strategy for reducing NH3 emission of hydrogen ammonia engine

Abstract

The invention discloses a control strategy for reducing NH3 emission of a hydrogen-ammonia engine. The control strategy comprises the steps that the rotating speed, the load, the pressure in an air cylinder, the air flow entering the air cylinder, the hydrogen injection amount, the ammonia injection amount and the exhaust temperature of the engine are monitored in real time; the maximum value of the in-cylinder pressure at the moment is calculated from a cylinder pressure model according to the rotating speed and the load of the engine, the maximum value of the in-cylinder temperature at the moment is calculated from an exhaust model according to the exhaust temperature detected by a sensor in front of a catalytic converter, and the in-cylinder air-fuel ratio at the moment is calculated according to the hydrogen injection amount, the ammonia injection amount and the air flow; an unburned ammonia model is established according to the characteristics affecting ammonia emission, and the unburned ammonia proportion at the moment is calculated through the unburned ammonia model; according to the size of the ammonia unburned proportion, the ammonia emission risk at the moment is recognized; and the maximum value of the hydrogen-ammonia injection amount is calculated through the ammonia leakage limiting coefficient, the theoretical air-fuel ratio and the air inflow and used for restraining the total hydrogen-ammonia injection amount. And the unburned ammonia proportion of the ammonia gas in the air cylinder can be effectively controlled.

Description

Technical Field

[0001] The present invention relates to the field of engine design and manufacturing, and in particular to a control strategy for reducing NH3 emissions from hydrogen-ammonia engines. Background Art

[0002] At present, commercial vehicles mainly use diesel engines as power systems. After diesel combustion, a large amount of CO2 is produced. Although CO2 is not a pollutant, it is a greenhouse gas. As greenhouse gases increase, the earth's temperature is getting higher and higher, which has seriously affected human life. Reducing greenhouse gas emissions is imminent. In order to achieve the national carbon peak and carbon neutrality goals, commercial vehicles have currently carried out research on low-carbon and zero-carbon internal combustion engines.

[0003] There are many technical routes for low-carbon and zero-carbon internal combustion engines, among which hydrogen and ammonia, two zero-carbon fuels, have become hot topics of research. Hydrogen and ammonia are both renewable resources. Hydrogen is easy to burn and does not produce polluting gases, but hydrogen is currently expensive to manufacture and difficult to transport and store. Ammonia currently has a mature manufacturing industry and is easy to store and transport, but ammonia is difficult to burn and has low combustion efficiency. Hydrogen-ammonia engines can just make up for the shortcomings of these two fuels, using a small amount of hydrogen to ignite ammonia, and a large amount of ammonia to burn and drive the vehicle.

[0004] Ammonia in an ammonia engine burns in the cylinder, but the ammonia cannot react with oxygen completely, so some unburned ammonia will be discharged from the cylinder. Ammonia is a polluting gas, and the current National VI regulations have strict emission requirements. The next stage of the National VII regulations will require lower ammonia emissions. How to reduce NH3 emissions is a difficult problem that must be solved for the commercial application of hydrogen-ammonia engines.

[0005] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0006] The object of the present invention is to provide a control strategy for reducing NH3 emissions from a hydrogen-ammonia engine, which can effectively control the unburned ammonia ratio in the cylinder and effectively reduce the discharge of unburned ammonia from the cylinder.

[0007] To achieve the above-mentioned purpose, the present invention provides a control strategy for reducing NH3 emissions from a hydrogen-ammonia engine, comprising: real-time monitoring of the engine speed, load, cylinder pressure, air flow into the cylinder, hydrogen injection amount, ammonia injection amount and exhaust temperature; calculating the maximum cylinder pressure value at this time from a cylinder pressure model according to the engine speed and load, calculating the maximum cylinder temperature at this time from an exhaust model according to the exhaust temperature detected by a pre-catalyst sensor, and calculating the cylinder air-fuel ratio at this time according to the hydrogen injection amount, the scheduled injection amount and the air flow; establishing an unburned ammonia model according to the characteristics that affect ammonia emissions, and calculating the unburned ammonia ratio at this time through the unburned ammonia model; identifying the ammonia emission risk at this time according to the size of the ammonia unburned ratio; and calculating the maximum hydrogen-ammonia injection amount through an ammonia leakage limitation coefficient, a theoretical air-fuel ratio and an air intake amount, and using it to constrain the total hydrogen-ammonia injection amount.

[0008] In a preferred embodiment, the cylinder air-fuel ratio at this time=air flow rate / (hydrogen injection amount+ammonia injection amount).

[0009] In a preferred embodiment, the unburned ammonia ratio at this time = a×the air-fuel ratio in the cylinder at this time+b×the maximum temperature in the cylinder at this time+c×the maximum pressure in the cylinder at this time, wherein a, b, and c are constants and can be obtained by fitting the test data.

[0010] In a preferred embodiment, the cylinder air-fuel ratio at this time has the greatest influence on the ammonia unburned ratio at this time, the cylinder temperature maximum value at this time is second, and the cylinder pressure maximum value at this time is the smallest.

[0011] In a preferred embodiment, the ammonia emission risk at this time is divided into a very small ammonia unburned ratio, a small ammonia unburned ratio, a medium ammonia unburned ratio, or a high ammonia unburned ratio.

[0012] In a preferred embodiment, when the accelerator is suddenly pressed, the air-fuel ratio is very low and the proportion of unburned ammonia is very high. At this time, the maximum value of the hydrogen-ammonia injection amount = air intake amount / (theoretical air-fuel ratio×ammonia leakage limiting coefficient), wherein the air intake amount is a real-time monitoring output value, the theoretical air-fuel ratio can be calculated according to the current ammonia and hydrogen injection amounts through the chemical reaction equation, and the value of the ammonia leakage limiting coefficient is based on the engine speed and the circulating air intake amount as input conditions, and is obtained from a control model with low ammonia leakage established during the engine development stage.

[0013] In a preferred embodiment, when the combustion conditions are very good and the proportion of unburned ammonia is very small, the current combustion control is maintained.

[0014] In a preferred embodiment, if it is identified that the unburned ammonia ratio is small, the injection angle is corrected and the ammonia is injected into the cylinder in advance to allow a longer time for the ammonia and air to mix. The uniform mixing is conducive to the complete combustion of the ammonia and reduces the unburned ammonia ratio.

[0015] In a preferred embodiment, if the unburned ammonia ratio is identified to be medium, the proportional coefficient of the hydrogen-ammonia injection amount is adjusted to reduce the ammonia injection amount and increase the hydrogen injection amount, thereby increasing the hydrogen ratio and reducing the unburned ammonia ratio, while ensuring that the power output remains unchanged and does not affect the user's driving.

[0016] In a preferred embodiment, if a transient acceleration condition with a high unburned ammonia ratio is identified, ammonia and hydrogen are injected based on the maximum hydrogen-ammonia injection amount to avoid a situation where a large amount of ammonia leakage occurs due to a very small air-fuel ratio.

[0017] Compared with the prior art, the control strategy for reducing NH3 emissions from hydrogen-ammonia engines of the present invention has the following beneficial effects: First, according to the characteristics of ammonia leakage in ammonia-hydrogen engines, an unburned ammonia model is established based on pressure, temperature, and air-fuel ratio to calculate the proportion of unburned ammonia, and the risk of NH3 emissions is identified in real time. Second, an ammonia leakage limitation coefficient is established. When the air-fuel ratio is very small and the proportion of unburned ammonia is very large, the ammonia-hydrogen injection amount is constrained to increase the air-fuel ratio to avoid large-scale ammonia leakage. Third, according to the risk of unburned ammonia in the cylinder, targeted control adjustments are made to maintain a low NH3 emission level. Maintain the original control when the unburned ammonia is very small, advance the ammonia injection when the unburned ammonia is small, increase the proportion of hydrogen when the unburned ammonia proportion is medium, and limit the maximum ammonia-hydrogen injection amount when the unburned ammonia proportion is large. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of control logic of a control strategy according to an embodiment of the present invention.

[0019] Description of main reference numerals:

[0020] p-the maximum value of the cylinder pressure at this time, t-the maximum value of the cylinder temperature at this time, i-the air-fuel ratio in the cylinder at this time, α-ammonia unburned ratio, β-ammonia leakage limitation coefficient. DETAILED DESCRIPTION

[0021] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation modes.

[0022] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0023] like Figure 1As shown, a control strategy for reducing NH3 emissions from a hydrogen-ammonia engine according to a preferred embodiment of the present invention includes: real-time monitoring of the engine speed, load, cylinder pressure, air flow into the cylinder, hydrogen injection amount, ammonia injection amount and exhaust temperature; calculating the maximum cylinder pressure value p at this time from the cylinder pressure model according to the engine speed and load, calculating the maximum cylinder temperature value t at this time from the exhaust model according to the exhaust temperature detected by the pre-catalyst sensor, and calculating the cylinder air-fuel ratio i at this time according to the hydrogen injection amount, the scheduled injection amount and the air flow; establishing an unburned ammonia model according to the characteristics that affect ammonia emissions, and calculating the unburned ammonia ratio α at this time through the unburned ammonia model; identifying the ammonia emission risk at this time according to the size of the ammonia unburned ratio; and calculating the maximum hydrogen-ammonia injection amount through the ammonia leakage limitation coefficient β, the theoretical air-fuel ratio and the air intake amount, and using it to constrain the total hydrogen-ammonia injection amount.

[0024] In some embodiments, the cylinder pressure model refers to the real-time prediction of the maximum pressure change in the cylinder based on the actual operating state and control parameters of the engine; the exhaust model refers to the real-time prediction of the maximum temperature change in the cylinder based on the temperature before the catalyst and the state operating parameters of the engine.

[0025] In some embodiments, the cylinder air-fuel ratio at this time is i=air flow rate / (hydrogen injection amount+ammonia injection amount).

[0026] In some embodiments, according to research, the higher the in-cylinder pressure, the higher the temperature, the greater the air-fuel ratio, the more complete the ammonia combustion, and the less unburned ammonia. The unburned ammonia ratio at this time = a×the in-cylinder air-fuel ratio at this time i+b×the maximum in-cylinder temperature at this time t+c×the maximum in-cylinder pressure at this time p, where a, b, and c are constants that can be obtained by fitting the test data.

[0027] In some embodiments, the cylinder air-fuel ratio i at this time has the greatest influence on the ammonia unburned ratio at this time, the cylinder temperature maximum value t at this time is second, and the cylinder pressure maximum value p at this time is the smallest.

[0028] In some embodiments, the ammonia emission risk at this time is divided into a very small ammonia unburned ratio, a small ammonia unburned ratio, a medium ammonia unburned ratio, or a high ammonia unburned ratio.

[0029] In some embodiments, when the accelerator is suddenly pressed, the air-fuel ratio is generally very small, and the proportion of unburned ammonia may be very high. At this time, the maximum value of hydrogen-ammonia injection amount = air intake amount / (theoretical air-fuel ratio×ammonia leakage limitation coefficient β), wherein the air intake amount is the real-time monitoring output value, the theoretical air-fuel ratio can be calculated according to the current ammonia and hydrogen injection amounts through the chemical reaction equation, and the value of the ammonia leakage limitation coefficient β is based on the engine speed and the circulating intake amount as input conditions, and is obtained from the control model with small ammonia leakage established during the engine development stage.

[0030] In some embodiments, when the combustion conditions are very good and the unburned ammonia ratio is very low, the current combustion control is maintained.

[0031] In some embodiments, if it is detected that the unburned ammonia ratio is small, the injection angle is corrected and the ammonia is injected into the cylinder in advance to allow ammonia and air to mix for a longer time. The uniform mixing is conducive to the complete combustion of ammonia and reduces the unburned ammonia ratio.

[0032] In some embodiments, if a medium ammonia unburned ratio is detected, the ratio coefficient of hydrogen-ammonia injection is adjusted to reduce the ammonia injection amount and increase the hydrogen injection amount, thereby increasing the hydrogen ratio and reducing the ammonia unburned ratio, while ensuring that the power output remains unchanged and does not affect the user's driving.

[0033] In some embodiments, if a transient acceleration condition with a high unburned ammonia ratio is identified, the total injection amount of ammonia is constrained based on the maximum injection amount of ammonia to avoid a situation where a large amount of ammonia leakage occurs due to a very small air-fuel ratio.

[0034] In summary, the control strategy for reducing NH3 emissions from hydrogen-ammonia engines of the present invention has the following advantages: First, according to the characteristics of ammonia leakage in ammonia-hydrogen engines, an unburned ammonia model is established based on pressure, temperature, and air-fuel ratio to calculate the proportion of unburned ammonia, and the risk of NH3 emissions is identified in real time. Second, an ammonia leakage limitation coefficient is established. When the air-fuel ratio is very small and the proportion of unburned ammonia is very large, the ammonia-hydrogen injection amount is constrained to increase the air-fuel ratio to avoid large-scale leakage of ammonia. Third, according to the risk of unburned ammonia in the cylinder, targeted control adjustments are made to maintain a low NH3 emission level. Maintain the original control when the amount of unburned ammonia is very small, advance ammonia injection when the amount of unburned ammonia is small, increase the proportion of hydrogen when the proportion of unburned ammonia is medium, and limit the maximum injection amount of ammonia-hydrogen when the proportion of unburned ammonia is large.

[0035] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A control strategy for reducing NH3 emissions from a hydrogen-ammonia engine, characterized in that: include: Real-time monitoring of engine speed, load, cylinder pressure, air flow into the cylinder, hydrogen injection amount, ammonia injection amount and exhaust temperature; The maximum cylinder pressure at this time is calculated from the cylinder pressure model according to the engine speed and load, and the maximum cylinder temperature at this time and the cylinder air-fuel ratio at this time are calculated from the exhaust model according to the exhaust temperature detected by the pre-catalyst sensor; Establishing an unburned ammonia model according to the characteristics that affect ammonia emissions, and calculating the unburned ammonia ratio at this time by using the unburned ammonia model; According to the size of the unburned ammonia ratio, the ammonia emission risk at this time is identified; as well as The maximum amount of hydrogen and ammonia injection is calculated by the ammonia slip limitation coefficient, the theoretical air-fuel ratio and the air intake volume, and is used to constrain the total amount of hydrogen and ammonia injection.

2. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 1, characterized in that: The in-cylinder air-fuel ratio at this time=air flow rate / (hydrogen injection amount+ammonia injection amount).

3. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 1, characterized in that: The unburned ammonia ratio at this time=a×the air-fuel ratio in the cylinder at this time+b×the maximum temperature in the cylinder at this time+c×the maximum pressure in the cylinder at this time, wherein a, b, and c are constants and can be obtained by fitting test data.

4. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 3, characterized in that: The cylinder air-fuel ratio at this time has the greatest influence on the ammonia unburned ratio at this time, the cylinder temperature maximum value at this time is second, and the cylinder pressure maximum value at this time is the smallest.

5. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 1, characterized in that: The ammonia emission risk at this time is divided into a very small ammonia unburned ratio, a small ammonia unburned ratio, a medium ammonia unburned ratio, or a high ammonia unburned ratio.

6. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 5, characterized in that: When the accelerator is suddenly pressed, the air-fuel ratio is very low and the proportion of unburned ammonia is very high. At this time, the maximum value of the hydrogen-ammonia injection amount = air intake amount / (theoretical air-fuel ratio×ammonia leakage limitation coefficient), wherein the air intake amount is the real-time monitoring output value, the theoretical air-fuel ratio can be calculated according to the chemical reaction equation based on the current ammonia and hydrogen injection amounts, and the value of the ammonia leakage limitation coefficient is based on the engine speed and the circulating intake amount as input conditions, and is obtained from the control model with small ammonia leakage established during the engine development stage.

7. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 5, characterized in that: When the combustion conditions are very good and the proportion of unburned ammonia is very small, maintain the current combustion control.

8. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 5, characterized in that: If a small amount of unburned ammonia is detected, the injection angle is corrected to inject ammonia into the cylinder in advance, allowing ammonia and air to mix for a longer time. Even mixing is conducive to the complete combustion of ammonia and reduces the unburned ammonia ratio.

9. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 5, characterized in that: If the unburned ammonia ratio is detected to be medium, the ratio coefficient of hydrogen-ammonia injection will be adjusted to reduce the ammonia injection amount and increase the hydrogen injection amount, thereby increasing the hydrogen ratio and reducing the unburned ammonia ratio, while ensuring that the power output remains unchanged and does not affect the user's driving.

10. The control strategy for reducing NH3 emissions from a hydrogen-ammonia engine as claimed in claim 5, characterized in that: If a transient acceleration condition with a high proportion of unburned ammonia is identified, ammonia and hydrogen are injected based on the maximum hydrogen-ammonia injection amount to avoid a situation where a very small air-fuel ratio causes a large amount of ammonia leakage.

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