Liquid ammonia direct injection machine internal and external collaborative purification system and purification method thereof

Abstract

The application provides a liquid ammonia direct injection engine internal and external collaborative purification system and a purification method thereof, relates to the technical field of marine internal combustion engine emission control and alternative fuel combustion control, and comprises an engine, an air intake system and an exhaust system are arranged on the engine, the air intake system comprises a liquid ammonia supply unit and a diesel pilot injection unit, the liquid ammonia supply unit is provided with a liquid ammonia injector, a combustion chamber is arranged in the engine, a combustion state monitoring unit is arranged in the combustion chamber, and the combustion state monitoring unit comprises a cylinder pressure module, a crankshaft angle encoder module and a cylinder temperature module. Through the collaborative cooperation of the above structure, online identification and regulation and control of the liquid ammonia spray state, closed-loop control of the diesel pilot ignition kernel, collaborative optimization of the cylinder pre-denitration and the external deep denitration can be realized, so that the efficient, stable and low-emission operation of the engine under the condition of liquid ammonia direct injection can be ensured in a wide operating condition range.

Description

Technical Field

[0001] This invention relates to the field of emission control and alternative fuel combustion control technology for marine internal combustion engines, and more specifically, to a liquid ammonia direct injection engine internal and external synergistic purification system and purification method thereof. Background Technology

[0002] With increasingly stringent restrictions on nitrogen oxide emissions from ships, marine diesel engines must meet higher standards such as Tier III in emission control areas. Traditional solutions that rely solely on external SCR aftertreatment are not adaptable to low loads, wide operating conditions, and alternative fuel applications.

[0003] In existing technologies, one approach focuses on achieving NOx control through the addition of reducing agents to the post-treatment system, such as refluxing liquid ammonia or injecting it separately into the SCR reactor inlet to improve post-treatment denitrification efficiency. While these methods improve upon certain aspects of the entire ammonia supply and combustion process, they have not yet formed a comprehensive system method for synergistic optimization across the entire process. This makes it difficult for existing technologies to achieve optimal synergy between pre-denitrification and deep denitrification under different operating conditions, or to have insufficient adaptability across a wide range of operating conditions. Summary of the Invention

[0004] The present invention aims to solve the problem that existing purification schemes in liquid ammonia direct injection machines are difficult to achieve the optimal solution for denitrification under different operating conditions.

[0005] To address the aforementioned problems, in a first aspect, the present invention provides a liquid ammonia direct injection engine internal and external synergistic purification system, comprising an engine, wherein the engine is equipped with an intake system and an exhaust system, the intake system includes a liquid ammonia supply unit and a diesel ignition injection unit, the liquid ammonia supply unit has a liquid ammonia injector, the engine is equipped with a combustion chamber, the combustion chamber is equipped with a combustion state monitoring unit, the combustion state monitoring unit includes a cylinder pressure module, a crankshaft angle encoder module and a cylinder temperature module, one end of the exhaust system is connected to an aftertreatment denitrification device, the exhaust system is equipped with an exhaust parameter detection unit, the exhaust parameter detection unit includes an exhaust temperature sensor, an exhaust pressure sensor and an exhaust component concentration sensor group, the engine is also equipped with a control unit, the control unit is electrically connected to the liquid ammonia supply unit, the diesel ignition injection unit, the combustion state monitoring unit, the aftertreatment denitrification device and the exhaust parameter detection unit respectively.

[0006] The liquid ammonia direct injection machine internal and external synergistic purification system and purification method provided by this invention have, but are not limited to, the following beneficial effects compared with the prior art: Through the coordinated operation of the above structures, online identification and control of liquid ammonia spray status, closed-loop control of diesel ignition core, and synergistic optimization of in-cylinder pre-denitrification and external deep denitrification can be achieved, thereby ensuring efficient, stable and low-emission operation of the engine under a wide range of operating conditions under liquid ammonia direct injection.

[0007] Furthermore, the exhaust gas component concentration sensor group includes a NOx concentration sensor, an ammonia concentration sensor, and an oxygen concentration sensor.

[0008] Furthermore, the exhaust component concentration sensor group also includes an N2O concentration sensor.

[0009] Secondly, the present invention also provides a method for coordinated internal and external purification of a liquid ammonia direct injection machine, applied to the aforementioned coordinated internal and external purification system for a liquid ammonia direct injection machine, comprising: the control unit constructing a multi-objective optimization function, with NO x Emissions, ammonia slip, N2O generation, combustion efficiency, and engine combustion cycle fluctuations are the comprehensive optimization targets.

[0010] Furthermore, the method for achieving the comprehensive optimization objective includes one or more of the following steps: S1. Control the initial liquid ammonia injection parameters through the liquid ammonia injector; S2. The diesel injection parameters and ignition parameters are controlled by the diesel ignition injection unit.

[0011] Furthermore, it also includes: step S3, injecting supplementary liquid ammonia through a liquid ammonia injector in the later stage of combustion, and controlling the injection parameters of the supplementary liquid ammonia.

[0012] Furthermore, step S3 is triggered when any of the following detection results are met: NO was detected x Concentration is higher than the predicted value / threshold; The actual load on the post-treatment denitrification unit exceeded 90% of its maximum load; The combustion chamber contains both a first temperature range and a second temperature range, wherein the second temperature range is higher than the first temperature range. The ammonia concentration in the combustion chamber is lower than the predicted value / threshold.

[0013] Furthermore, it also includes: step S4, whereby the exhaust parameter detection unit transmits the detection parameters to the control unit, and the control unit controls the liquid ammonia supply unit and / or diesel ignition injection unit to actively adjust according to the first signal set; The first set of signals includes at least: actual ignition time delay exceeding expected ignition time delay; actual pressure rise rate exceeding expected pressure rise rate; and generated NO. x Concentration exceeds predicted value / threshold; ammonia slip exceeds predicted value / threshold; exhaust system temperature is lower than predicted value / threshold.

[0014] Furthermore, it also includes: step S5, supplying an ammonia-containing reducing agent into the aftertreatment denitrification device, so that the ammonia-containing reducing agent mixes with the gas discharged from the exhaust system and reacts under the action of the catalyst in the aftertreatment denitrification device, and controlling the ammonia-nitrogen ratio at the inlet of the aftertreatment denitrification device to be between 0.8 and 1.2 by the control unit.

[0015] Furthermore, the multi-objective optimization function is: , where w1, w2, w3, w4 and w5 are weighting coefficients. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the internal and external coordinated purification system of the liquid ammonia direct injection machine in this invention; Figure 2 This is a schematic diagram of the combustion state monitoring unit system in this invention.

[0017] Explanation of reference numerals in the attached figures: 1. Engine; 2. Intake system; 3. Exhaust system; 4. Combustion chamber; 5. Combustion status monitoring unit; 6. Aftertreatment denitrification device; 7. Exhaust parameter detection unit; 8. Control unit; 21. Liquid ammonia supply unit; 22. Diesel ignition injection unit; 51. Cylinder pressure module; 52. Crankshaft angle encoder module; 53. Cylinder temperature module; 71. Exhaust temperature sensor; 72. Exhaust pressure sensor; 73. NOx concentration sensor; 74. Ammonia concentration sensor; 75. Oxygen concentration sensor; 76. N2O concentration sensor; 211. Liquid ammonia injector. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort will fall within the scope of protection of this application.

[0019] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising," "including," "having," "containing," etc., in the specification, claims, and accompanying drawings of this application are open-ended terms. Therefore, "comprising," "including," or "having" refers to, for example, a method or apparatus having one or more steps or elements, but is not limited to having only these one or more elements. The terms "first," "second," etc., in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0020] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0021] It should be emphasized that when the term "including / comprises" is used in this specification, it is used to expressly indicate the presence of a feature, integer, step, or component, but does not exclude the presence or addition of one or more other features, integers, steps, parts, or groups of features, integers, steps, or parts.

[0022] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0023] See Figure 1 and Figure 2The liquid ammonia direct injection engine internal and external synergistic purification system of this invention includes an engine 1, an intake system 2 and an exhaust system 3. The intake system 2 includes a liquid ammonia supply unit 21 and a diesel ignition injection unit 22. The liquid ammonia supply unit 21 has a liquid ammonia injector 211. The engine 1 has a combustion chamber 4. The combustion chamber 4 has a combustion state monitoring unit 5. The combustion state monitoring unit 5 includes a cylinder pressure module 51, a crankshaft angle encoder module 52 and a cylinder temperature module 53. One end of the exhaust system 3 is connected to an aftertreatment denitrification device 6. The exhaust system 3 is equipped with an exhaust parameter detection unit 7. The exhaust parameter detection unit 7 includes an exhaust temperature sensor 71, an exhaust pressure sensor 72 and an exhaust component concentration sensor group. The engine 1 is also equipped with a control unit 8. The control unit 8 is electrically connected to the liquid ammonia supply unit 21, the diesel ignition injection unit 22, the combustion state monitoring unit 5, the aftertreatment denitrification device 6 and the exhaust parameter detection unit 7.

[0024] In this embodiment, engine 1 can be a marine medium-speed or low-speed compression-ignition engine, including a cylinder block, cylinder head, and piston. Engine 1 provides power for ship propulsion, and its operating state determines the air supply of the intake system 2, the exhaust parameters of the exhaust system 3, and the combustion conditions in the combustion chamber 4.

[0025] The engine speed and load signals of engine 1 serve as important input parameters for closed-loop control of control unit 8, which are used to determine the optimal liquid ammonia injection strategy and diesel ignition parameters under different operating conditions.

[0026] The engine 1 has a combustion chamber 4 inside. The combustion chamber 4 is the main place where liquid ammonia mixes with air, ignites and burns, and selective non-catalytic reduction reaction occurs. Its structure and volume determine the spray penetration distance, mixing time and temperature distribution characteristics.

[0027] Combustion chamber 4 is equipped with a combustion status monitoring unit 5, which is used to monitor various parameters of the combustion process in real time.

[0028] Combustion chamber 4 typically employs a shallow basin or deep pit structure to optimize airflow and flame propagation path.

[0029] The intake system 2 is used to provide clean air to the engine 1 and works in conjunction with the liquid ammonia supply unit 21 and the diesel ignition injection unit 22 to complete the fuel supply and the formation of the air-fuel mixture.

[0030] The intake system 2 may include components such as an air filter, an intake manifold, a turbocharger, and an intake duct.

[0031] The intake system 2 introduces ambient air into the combustion chamber 4, and its airflow and pressure affect the entrainment effect of liquid ammonia spray and the quality of mixture formation.

[0032] The intake system 2 coordinates with the injection timing of the liquid ammonia supply unit 21 and the diesel ignition injection unit 22 to ensure that fuel injection and mixture preparation are completed under appropriate air atmosphere.

[0033] The exhaust system 3 is used to discharge the exhaust gas after combustion from the engine 1. One end of the exhaust system 3 is connected to the aftertreatment denitrification device 6 to achieve deep denitrification outside the engine.

[0034] The exhaust system 3 may include components such as an exhaust manifold, an exhaust pipe, and an exhaust valve.

[0035] The back pressure characteristics of the exhaust system 3 affect the amount of residual exhaust gas and the quality of air exchange in the combustion chamber 4, which in turn affects the combustion stability and emission characteristics.

[0036] The exhaust system 3 is equipped with an exhaust parameter detection unit 7, which is used to collect exhaust status parameters in real time and provide closed-loop feedback signals for the external after-processing of the control unit 8.

[0037] The liquid ammonia supply unit 21 is used to inject liquid ammonia fuel into each cylinder combustion chamber 4 at a fixed time and pressure, and to make the liquid ammonia form a target spray state from the nozzle outlet to the cylinder environment through pressure and temperature regulation.

[0038] The liquid ammonia injection pressure is preferably 20-120 MPa, more preferably 30-80 MPa; The liquid ammonia supply temperature can be controlled within the range of -20℃ to 40℃; The injection timing of the liquid ammonia injector 211 can be arranged relative to the top dead center in the late compression stroke or the early combustion phase, preferably in the range of 40°CA before top dead center to 20°CA after top dead center.

[0039] Top dead center (TDC) serves as the reference position (0°CA) for calculating crankshaft angles, and all injection times are expressed as crankshaft angles relative to TDC. For example, "40°CA before TDC" means that the injection occurs when the crankshaft has rotated 40 degrees before the piston reaches TDC; "20°CA after TDC" means that the injection occurs when the crankshaft has rotated 20 degrees after the piston reaches TDC.

[0040] Symbol representation: θ=0°CA (top dead center of the compression stroke) or θ=180°CA (top dead center of the power stroke).

[0041] Both liquid ammonia and diesel can be injected directly into the cylinder. The adjustment method is to control and change the amount of fuel injected. From the perspective of control hardware, this means controlling the injection pulse width of different fuels.

[0042] Injection pulse width refers to the duration of the electronically controlled pulse signal sent by the control unit to the injector, measured in milliseconds (ms). The injection pulse width determines the length of time the injector is open, thus directly determining the amount of fuel injected each time. Both liquid ammonia and diesel fuel use direct injection, and the adjustment is achieved by controlling the injection quantity; from a control hardware perspective, this means controlling the injection pulse width of different fuels. The control unit 8, based on the target fuel injection quantity, injection pressure, and injector characteristics, converts the target injection mass into a corresponding injection pulse width correction and outputs it to the liquid ammonia injector 211 or the diesel injector.

[0043] The liquid ammonia supply unit 21 injects liquid ammonia into the combustion chamber 4 under high pressure through the liquid ammonia injector 211. The liquid ammonia injector 211 is usually a multi-hole or single-hole high-pressure nozzle. The number of nozzles, nozzle diameter and spray cone angle affect the spatial distribution and atomization quality of liquid ammonia.

[0044] The liquid ammonia injector 211 interacts with the air introduced by the air intake system 2 to form a liquid ammonia-air mixture suitable for diesel ignition.

[0045] The diesel ignition injection unit 22 is independently controlled from the liquid ammonia injection unit. It is used to inject a small amount of diesel before, simultaneously with, or after the liquid ammonia injection to form a local high-reactivity zone and induce the liquid ammonia mixture to ignite.

[0046] The diesel ignition injection function can be implemented by single injection or pre-injection plus main injection. The diesel substitution rate can be adjusted according to the operating conditions and liquid ammonia energy substitution rate.

[0047] The diesel injection timing is preferably set within the range of 10°CA before to 10°CA after the main liquid ammonia injection, and the injection pressure is preferably 40-180MPa.

[0048] The diesel ignition injection unit 22 injects diesel into the combustion chamber 4 through an independent diesel injector. The diesel spray and liquid ammonia spray form a localized highly active combustible zone in space, which promotes the preferential generation of the fire nucleus in the coupling area between the high temperature zone of diesel and the liquid ammonia mixing zone.

[0049] The combustion status monitoring unit 5 is used to obtain parameters such as combustion phase, pressure rise rate, ignition time delay, heat release rate, and indicated work in real time, so as to determine whether the diesel flame core is stably formed and to use it for closed-loop correction of injection parameters.

[0050] The combustion phase refers to the position of the combustion process in the crankshaft angular coordinate system, usually represented by a characteristic angle. The combustion phase reflects characteristics such as the start of combustion, the position of the combustion center of gravity, and the duration of combustion. The control unit 8 calculates the apparent heat release rate and determines the combustion phase based on data from the cylinder pressure module 51 and the crankshaft angle encoder module 52. The combustion phase is characterized by the following characteristic angles: CA10: The crankshaft angle at which the accumulated heat release reaches 10% of the total heat release, used to characterize the initial fire nucleus formation time; CA50: The crankshaft angle corresponding to when the accumulated heat release reaches 50% of the total heat release, used to characterize the main combustion phase (the position of the combustion center of gravity). CA90: The crankshaft angle at which the accumulated heat release reaches 90% of the total heat release, used to characterize the moment when combustion ends.

[0051] Pressure rise rate refers to the rate of change of cylinder pressure with crankshaft angle, typically measured in MPa / °CA (megapascals per degree Celsius). It reflects the intensity of combustion and is a crucial parameter for evaluating combustion quality and engine roughness. The control unit 8 calculates the maximum pressure rise rate per cycle based on the cylinder pressure data collected by the cylinder pressure module 51. An excessively high pressure rise rate indicates overly vigorous combustion, potentially leading to excessive engine mechanical load, increased noise, and worsened emissions; a too-low pressure rise rate indicates insufficient combustion development and weak flame intensity.

[0052] Ignition delay refers to the time interval or crankshaft rotation interval between the start of fuel injection and the start of combustion. Ignition delay includes the physical ignition delay period (the time required for fuel atomization, evaporation, and mixing) and the chemical ignition delay period (the time required for fuel oxidation reaction preparation). Control unit 8 calculates the diesel ignition delay based on the characteristics of cylinder pressure signal changes. Ignition delay is a key parameter for judging the stability of diesel flame core formation. An excessively long ignition delay indicates insufficient mixture formation or a low chemical reaction rate, which may lead to misfire, delayed combustion, and cycle fluctuations.

[0053] The heat release rate refers to the rate of change of heat released by fuel combustion with crankshaft rotation angle, usually expressed in J / °CA. The heat release rate reflects the intensity and pattern of the combustion heat release process and is a core parameter for analyzing the combustion process. The control unit 8 calculates the apparent heat release rate based on the cylinder pressure p(θ) collected by the cylinder pressure module 51 and the cylinder volume V(θ) obtained by the crankshaft angle encoder module 52. The apparent heat release rate takes into account the influence of gas compression and expansion on temperature, and can more accurately reflect the actual combustion heat release process.

[0054] Indicated work refers to the work done by the force exerted by the gas on the piston, reflected in the actual work done by the piston's reciprocating motion. Indicated work is a fundamental parameter for evaluating the thermal-to-work conversion efficiency of an engine's working cycle, used to calculate indicated thermal efficiency and indicated power. The combustion state monitoring unit 5 calculates the indicated work per cycle using data from the cylinder pressure module 51 and the crankshaft angle encoder module 52. Changes in indicated work reflect changes in combustion quality and can serve as an auxiliary parameter for judging flame core stability and combustion efficiency.

[0055] The combustion status monitoring unit 5 includes a cylinder pressure module 51, a crankshaft angle encoder module 52, and a cylinder temperature module 53.

[0056] The cylinder pressure module 51 is used to collect the pressure signal in the combustion chamber 4 in real time. The cylinder pressure module 51 can use a quartz piezoelectric or strain gauge sensor, which is installed on the cylinder head or cylinder wall and can measure the cylinder pressure waveform for each cycle.

[0057] The cylinder pressure p(θ) collected by the cylinder pressure module 51 is the basic data for calculating the apparent heat release rate, pressure rise rate and ignition delay.

[0058] The crankshaft angle encoder module 52 is used to measure the crankshaft angle position. The crankshaft angle encoder module 52 typically uses a photoelectric or magnetoelectric encoder, which can provide angular resolution per degree or per 0.5 degrees.

[0059] The cylinder volume V(θ) and cylinder pressure p(θ) obtained by the crankshaft angle encoder module 52 together constitute the basic parameter pair for combustion analysis.

[0060] The cylinder temperature module 53 is used to estimate the temperature distribution and transient temperature changes in the combustion chamber 4. The cylinder temperature module 53 can be directly measured by the in-cylinder temperature sensor or estimated in real time based on the thermodynamic model and combustion parameters.

[0061] The temperature information provided by the cylinder temperature module 53 is crucial for determining whether there is a suitable temperature window (850–1400 K) for selective non-catalytic reduction reactions in the cylinder.

[0062] The control unit 8 calculates the apparent heat release rate, combustion phase, pressure rise rate, ignition delay and cycle fluctuation parameters based on the cylinder pressure p(θ) collected by the cylinder pressure module 51 and the cylinder volume V(θ) obtained by the crankshaft angle encoder module 52.

[0063] The apparent heat release rate can be calculated using the following formula: In the formula, θ is the crankshaft angle, p is the cylinder pressure, V is the cylinder volume, and κ is the specific heat ratio of the working fluid, preferably ranging from 1.30 to 1.38.

[0064] The cumulative heat release Q(θ) is obtained by integrating the apparent heat release rate, and the crankshaft angles corresponding to the cumulative heat release reaching 10%, 50% and 90% of the total heat release are defined as CA10, CA50 and CA90, respectively; where CA10 is used to characterize the initial fire core formation time, CA50 is used to characterize the main combustion phase, and CA90 is used to characterize the combustion end time.

[0065] Through the coordinated operation of the cylinder pressure module 51 and the crankshaft angle encoder module 52, the control unit 8 can obtain the combustion parameters for each cycle in real time and determine the stability of the flame core accordingly.

[0066] The ignition delay can be calculated using the following formula:

[0067]

[0068] In the formula, θ SOI,d θ is the start time of diesel ignition injection. SOC The moment of combustion initiation can be determined by the first significant increase in the apparent heat release rate or by the cumulative heat release reaching a preset proportion.

[0069] The rate of pressure rise can be calculated using the following formula:

[0070] The cyclic fluctuation coefficient can be calculated using the following formula:

[0071] In the formula, σ IMEP The standard deviation of the mean effective pressure is given for a number of consecutive cycles, and IMEP is the corresponding mean.

[0072] When the cylinder pressure module 51 detects an abnormal increase rate of cylinder pressure, or the crankshaft angle encoder module 52 detects that the combustion phase deviation exceeds the set threshold, the control unit 8 can issue a correction command to the diesel ignition injection unit 22 to adjust the diesel ignition parameters.

[0073] Control unit 8 uses 10 to 50 consecutive cycles as a judgment window. When any two or more of the following conditions are met, the diesel flame core formation is determined to be in an unstable state: ignition delay Δθid is greater than 8–12°CA, or greater than 1.25 times the reference value under the same operating conditions; CA50 is later than 15–20°CA after top dead center, or the deviation from the target combustion phase is greater than 5°CA; the maximum apparent heat release rate is less than 60%–70% of the reference value under the same operating conditions, or the maximum pressure rise rate is less than 0.10–0.20 MPa / °CA, indicating insufficient flame core development; the maximum pressure rise rate exceeds the engine safety limit, preferably exceeding 0.8–1.2 MPa / °CA, indicating excessively violent ignition; COV IMEP The value is greater than 5%, or there are instances of misfire, delayed combustion, or significant fluctuations in the peak heat release rate during continuous cycles.

[0074] When it is determined that the ignition core formation is insufficient or the combustion phase is delayed, the control unit 8 prioritizes implementing corrective measures such as advancing the diesel ignition injection by 1-3°CA, increasing the diesel ignition quantity by 2%-10%, increasing the diesel injection pressure by 5-20MPa, reducing the single injection quantity of liquid ammonia, or appropriately advancing the liquid ammonia injection timing. When it is determined that the pressure rise rate is too high or the combustion phase is too early, corrective measures such as delaying the diesel ignition injection by 1-3°CA, reducing the diesel ignition quantity by 2%-8%, adopting pre-injection-main injection staged ignition, or appropriately delaying the liquid ammonia main injection are implemented to bring CA50, pressure rise rate, and cycle fluctuation back to the target range.

[0075] The exhaust parameter detection unit 7 is used to collect various parameters in the exhaust system 3 in real time, providing feedback signals for the control of the after-treatment denitrification device 6 and the coordinated optimization of internal and external systems.

[0076] The exhaust parameter detection unit 7 includes an exhaust temperature sensor 71, an exhaust pressure sensor 72, and an exhaust component concentration sensor group.

[0077] The exhaust temperature sensor 71 is used to measure the temperature of the exhaust gas in the exhaust system 3. The exhaust temperature sensor 71 can be a thermocouple or a resistance temperature detector (RTD) sensor and is installed on the exhaust manifold or the front pipe of the aftertreatment denitrification device 6 (SCR).

[0078] Exhaust temperature is a key parameter for determining whether the catalyst in the aftertreatment denitrification device 6 is operating within the high-efficiency temperature window (200-550℃), and it is also an important basis for the control unit 8 to determine whether exhaust temperature management is required.

[0079] The exhaust pressure sensor 72 is used to measure the exhaust back pressure in the exhaust system 3. The exhaust pressure sensor 72 can be a piezoelectric or piezoresistive sensor.

[0080] Exhaust back pressure affects the amount of residual exhaust gas and the charging efficiency in combustion chamber 4, which in turn affects the combustion process and emission characteristics.

[0081] Control unit 8 can adjust intake system 2 or injection parameters based on back pressure changes detected by exhaust pressure sensor 72 to maintain optimal combustion. The exhaust component concentration sensor group includes various gas concentration sensors to monitor the concentrations of components such as NOx, ammonia (NH3), O2, and N2O in the exhaust in real time, providing feedback for closed-loop control of external aftertreatment to control unit 8.

[0082] The exhaust parameter detection unit 7 is electrically connected to the control unit 8, and transmits the detected exhaust temperature, pressure and component concentration and other parameters to the control unit 8 in real time. Based on this, the control unit 8 calculates key indicators such as ammonia nitrogen ratio and NOx conversion efficiency at the inlet of the aftertreatment denitrification device 6, and issues corresponding control commands to the aftertreatment denitrification device 6.

[0083] The aftertreatment denitrification device 6 is used to perform deep denitrification treatment on the exhaust gas discharged from the exhaust system 3. The aftertreatment denitrification device 6 is located downstream of the exhaust gas of the engine 1 and may include an ammonia injector, a mixer, a catalytic reactor, and an ammonia escape oxidation unit (ASC) if necessary.

[0084] The ammonia injector of the aftertreatment denitrification device 6 injects an appropriate amount of ammonia-containing reducing agent according to the instructions of the control unit 8, so that it is fully mixed with the gas discharged from the exhaust system 3 and undergoes a selective catalytic reduction reaction under the action of the catalyst, reducing NOx to N2 and H2O.

[0085] The post-treatment denitrification device 6 works in conjunction with the air intake system 2, the liquid ammonia supply unit 21, and the exhaust parameter detection unit 7 to achieve deep denitrification outside the machine.

[0086] The control unit 8 maintains the ammonia-to-nitrogen ratio at the inlet of the post-treatment denitrification unit 6 within the range of 0.8 to 1.2 to obtain the optimal NOx conversion efficiency.

[0087] The exhaust from engine 1 enters the aftertreatment denitrification device 6 through the exhaust system 3, and is discharged into the atmosphere after deep denitrification under the action of SCR catalyst.

[0088] Through the coordinated operation of the above structures, online identification and control of liquid ammonia spray status, closed-loop control of diesel ignition core, and synergistic optimization of in-cylinder pre-denitrification and external deep denitrification can be achieved, thereby ensuring efficient, stable and low-emission operation of the engine under a wide range of operating conditions under liquid ammonia direct injection.

[0089] Optionally, the exhaust gas component concentration sensor group includes a NOx concentration sensor 73, an ammonia concentration sensor 74, and an oxygen concentration sensor 75.

[0090] In this embodiment, the NOx concentration sensor 73 is used to detect the NOx concentration in the combustion chamber 4 or the exhaust system 3. It can be an electrochemical, catalytic combustion, or optical sensor, with a preferred measurement range of 0 to 5000 ppm and a preferred response time of less than 1 second.

[0091] The ammonia concentration sensor 74 is used to detect the NH3 concentration in the combustion chamber 4 or the exhaust system 3. It can be an infrared absorption sensor or a semiconductor sensor, and the measurement range is preferably 0 to 1000 ppm.

[0092] The oxygen concentration sensor 75 is used to detect the oxygen content in the exhaust system 3, and can be a zirconia type or a limit current type sensor.

[0093] The exhaust component concentration sensor group can monitor changes in exhaust components in real time and provide closed-loop feedback signals to the control unit 8.

[0094] By coordinating the detection of NOx concentration sensor 73, ammonia concentration sensor 74 and oxygen concentration sensor 75, the concentration information of NOx, NH3 and O2 in the exhaust gas can be obtained. This information can be used by control unit 8 to judge the effect of in-machine pre-denitrification and the working status of external SCR.

[0095] When the NOx concentration sensor 73 detects that the NOx concentration is higher than the predicted value or the threshold, it indicates that the original emissions are too high. The control unit 8 can increase the amount of ammonia added inside the machine or the amount of ammonia injected outside the machine. When the ammonia concentration sensor 74 detects that the NH3 concentration is too high, it indicates that the reducing agent may be in excess. The control unit 8 can reduce the amount of ammonia injected or improve the utilization rate of the in-cylinder reduction reaction.

[0096] Optionally, the exhaust component concentration sensor group also includes an N2O concentration sensor 76.

[0097] In this embodiment, the N2O concentration sensor 76 is used to detect the N2O concentration in the exhaust system 3. It can be an infrared absorption sensor or an ultraviolet spectroscopy sensor, with a preferred measurement range of 0 to 500 ppm and a preferred response time of less than 2 seconds.

[0098] N2O is a potent greenhouse gas and may be generated under specific temperature conditions during the SCR process, therefore it needs to be monitored.

[0099] By using the N2O concentration sensor 76, N2O byproducts can be controlled synchronously, thus avoiding an increase in N2O emissions during the process of reducing NOx.

[0100] When the N2O concentration sensor 76 detects that the N2O concentration exceeds the preset emission limit, the control unit 8 may take the following measures: appropriately reduce the SCR operating temperature or adjust the ammonia-nitrogen ratio to suppress N2O generation; or increase the pre-denitrification sharing ratio in the machine and reduce the load on the external SCR, thereby reducing the conditions for N2O generation.

[0101] A method for coordinated internal and external purification of liquid ammonia direct injection engine, applied to the aforementioned coordinated internal and external purification system of liquid ammonia direct injection engine, includes: a control unit 8 constructing a multi-objective optimization function, with NOx emissions, ammonia slip, N2O generation, combustion efficiency, and engine combustion cycle fluctuation as comprehensive optimization objectives.

[0102] In this embodiment, the control unit 8 can take engine speed, load, liquid ammonia energy substitution rate, liquid ammonia injection pressure, liquid ammonia injection time, diesel ignition timing, diesel ignition amount, in-engine ammonia replenishment amount, exhaust temperature, NOx concentration, NH3 concentration, and the inlet boundary parameters of the aftertreatment denitrification device 6 as input quantities, and take the NOx emission amount, NH3 slip amount, N2O generation amount, combustion efficiency value, and engine combustion cycle fluctuation amount as comprehensive optimization targets.

[0103] For example, the emissions of NOx, the slip of NH3, the amount of N2O generated, the value of combustion efficiency, and the fluctuation of engine combustion cycle are weighted, and then the weighted values ​​are summed. Zonghua's optimization objective is to minimize the summed value.

[0104] This control strategy can be implemented using rule-based control, model predictive control, or data-driven methods based on mechanistic constraints.

[0105] This enables liquid ammonia marine engines to maintain high denitrification efficiency, low ammonia slip, and good combustion stability under different operating conditions such as low load, partial load, and high load, thereby achieving integrated and coordinated purification inside and outside the engine.

[0106] Optionally, the method for achieving the comprehensive optimization objective includes one or more of the following steps: S1. The initial liquid ammonia injection parameters are controlled by the liquid ammonia injector 211; S2. The diesel injection parameters and ignition parameters are controlled by the diesel ignition injection unit 22.

[0107] In this embodiment, in step S1, the initial liquid ammonia injection parameters include at least the liquid ammonia injection pressure, liquid ammonia supply temperature, liquid ammonia injection time, and single injection volume.

[0108] Control unit 8 can acquire in-cylinder pressure Pc, in-cylinder temperature Tc, engine speed n, load L, and target liquid ammonia injection quantity m in real time. NH3 In conjunction with the saturated properties of liquid ammonia, the superheat index and pressure drop index, which characterize the flash boiling trend, were calculated.

[0109] The liquid ammonia injection pressure, supply temperature, and injection timing are obtained by the control unit 8 based on the target spray state.

[0110] Specifically, when the tendency for local flash boiling after injection is insufficient, the liquid ammonia supply temperature should be increased, the injection time should be advanced, or the effective back pressure difference at the nozzle should be reduced; when the jet is excessively diffused, has insufficient penetration, or is too evaporative, the liquid ammonia supply temperature should be reduced, the injection pressure should be increased, or the injection time should be delayed.

[0111] The control objective is to keep the spray cone angle, penetration length, and evaporation rate within the preset transition flash boiling window.

[0112] The transitional flash boiling spray state can be identified by combining thermodynamic criteria and spray morphology criteria.

[0113] Thermodynamic criteria include: liquid ammonia pre-injection temperature, injection pressure, nozzle pressure drop, cylinder ambient pressure, cylinder ambient temperature, and liquid ammonia saturation temperature and saturation pressure deviation; spray morphology criteria include: spray cone angle, spray penetration length, near-nozzle plume angle, spray axial-radial area ratio, image grayscale fluctuation characteristics, or droplet dispersion.

[0114] When thermodynamic criteria indicate that liquid ammonia is in the range where it has the driving force for phase change but has not reached the point of complete flash evaporation, and the spray pattern simultaneously shows an increased cone angle, finer droplets, and faster evaporation but with the main stem continuously present, the spray is judged to be in a transitional flash boiling state.

[0115] The control unit 8 pre-establishes a correspondence table of "spray status - control parameters" or a multi-dimensional calibration MAP.

[0116] When the identification result indicates insufficient spray flash boiling, control commands are output to increase the supply temperature, advance the liquid ammonia injection timing, reduce the single injection quantity, or adjust the segmented injection ratio. When the identification result indicates excessive jet divergence and insufficient penetration, control commands are output to increase the injection pressure, decrease the supply temperature, delay the injection timing, or reduce the pre-injection ratio. When the identification result indicates that the spray is in the transition flash boiling range but the flame core stability is insufficient, the diesel injection advance angle, diesel ignition quantity, and pre-injection and main injection distribution ratio are further adjusted in conjunction.

[0117] In step S2, the diesel injection parameters and ignition parameters include at least diesel injection pressure, diesel ignition time, diesel ignition quantity, and pre-injection / main injection distribution ratio.

[0118] Control unit 8 calculates the target diesel fuel mass based on ignition time lag deviation, CA10 deviation, peak heat release rate deviation, and cycle fluctuation indicators, and then converts it into diesel injection pulse width correction. The liquid ammonia energy substitution rate is defined as:

[0119] In the formula, m NH3 For single-cycle liquid ammonia injection rate, m d H is the single-cycle diesel ignition rate. NH3 and H d The values ​​are the lower heating values ​​of liquid ammonia and diesel, respectively.

[0120] The amount of diesel fuel used for ignition is determined based on the target liquid ammonia substitution rate and the stability of the ignition core. Preferably, the diesel fuel ignition energy accounts for 3% to 15% of the total fuel energy in a single cycle, and more preferably 5% to 10%.

[0121] By coordinating the execution of steps S1 and S2, the establishment and control of the liquid ammonia transition flash boiling spray state, as well as the formation and flame stabilization control of the diesel ignition nucleus, can be achieved, thus laying the foundation for subsequent in-cylinder pre-denitrification and external deep denitrification.

[0122] Optionally, it also includes: step S3, injecting supplementary liquid ammonia through liquid ammonia injector 211 in the later stage of combustion, and controlling the injection parameters of supplementary liquid ammonia.

[0123] In this embodiment, the injection parameters for replenishing liquid ammonia in step S3 include at least the timing of ammonia replenishment, the amount of ammonia replenished, and the injection pressure.

[0124] The ammonia replenishment should ideally be scheduled during the later stages of combustion or the early stages of expansion, when the temperature distribution inside the cylinder exhibits a gradient characteristic, which is conducive to the formation of a selective non-catalytic reduction reaction window.

[0125] Through step S3, a local reaction window suitable for selective non-catalytic reduction reaction can be formed in the cylinder by jointly adjusting the liquid ammonia spray layered structure, diesel ignition intensity, local temperature field, and equivalence ratio distribution during the middle and late stages of combustion and the early stage of expansion stroke. This allows the nitrogen-containing reducing components such as NH3 and NH2 remaining after the main injection of liquid ammonia to react with the locally generated NOx, thereby reducing the amount of NOx generated in the original exhaust.

[0126] The specific details of the joint adjustment may include: By changing the timing of the main liquid ammonia injection, the segmented injection ratio, and the liquid ammonia injection pressure, the stratified distribution and evaporation rate of NH3 in the cylinder can be adjusted. The location, duration, and intensity of the high-temperature active zone can be adjusted by changing the diesel ignition time, ignition quantity, and pre-injection ratio. The spatiotemporal coexistence of NH3 / NO can be adjusted by changing the timing and amount of ammonia replenishment in the later stages.

[0127] Through the above-mentioned linkage, the volume fraction of NH3 / NO coexistence in the local temperature range of 850-1400K is increased, thereby enhancing the in-cylinder pre-denitrification effect.

[0128] The preferred local reaction temperature window inside the cylinder is 850–1400 K. By increasing the spatiotemporal overlap of the NH3 / NO coexistence region, the conversion ratio of NOx to N2 is increased, while avoiding excessive NH3 residue and the increase of byproducts such as N2O.

[0129] Optionally, step S3 is triggered when any of the following detection results are met: The concentration of generated NOx was detected to be higher than the predicted value / threshold. The actual load of the post-treatment denitrification unit 6 exceeds 90% of its maximum load; The combustion chamber 4 contains both a first temperature range and a second temperature range, wherein the second temperature range is higher than the first temperature range. The ammonia concentration in combustion chamber 4 is lower than the predicted value / threshold.

[0130] In this embodiment, the triggering condition for step S3 may include any one or more of the following situations: predicting or detecting that the original amount of NOx generated in the cylinder is higher than a threshold. This condition can be determined by detecting a sudden increase in NOx concentration by NOx concentration sensor 73, or by predicting that the amount of NOx generated exceeds a set value by combustion model. The actual load of the post-treatment denitrification unit 6 exceeds 90% of the maximum load. This condition can be monitored by the control unit 8, which monitors the NOx concentration and ammonia nitrogen ratio at the SCR inlet. When the actual load approaches the upper limit of the SCR treatment capacity, it is triggered to reduce the instantaneous load of the external SCR. The in-cylinder local temperature falls within the 850–1400K window and there is a usable high-temperature exhaust zone. This condition can be determined by estimating the in-cylinder temperature distribution using the cylinder temperature module 53 or by predicting the temperature window using the combustion model. The 850–1400K window can be considered the first temperature range, and the temperature of the usable high-temperature exhaust zone can be considered the second temperature range. Within the second temperature range, the selective non-catalytic reduction reaction efficiency of NH3 and NOx is relatively high. The in-cylinder residual NH3 is insufficient to support the target pre-denitrification reaction intensity. This condition can be determined by the NH3 concentration detected by the ammonia concentration sensor 74 being lower than the predicted value, indicating that the residual reducing agent after the combustion of the main injection liquid ammonia is insufficient to meet the pre-denitrification requirements. The goal is to reduce the consumption of external SCR reducing agent or suppress insufficient SCR conversion at low temperatures. When the SCR inlet temperature is detected to be too low or the NOx conversion efficiency is insufficient, the overall denitrification efficiency can be improved by increasing in-cylinder ammonia supplementation.

[0131] When any of the above conditions are met, the control unit 8 sends a command to the liquid ammonia injector 211 to add an additional ammonia injection during the later stage of combustion or the early stage of expansion, so as to enhance the in-cylinder pre-denitrification effect.

[0132] Optionally, it also includes: step S4, where the exhaust parameter detection unit 7 transmits the detection parameters to the control unit 8, and the control unit 8 controls the liquid ammonia supply unit 21 and / or the diesel ignition injection unit 22 to actively adjust according to the first signal set; The first set of signals includes at least: the actual ignition time delay exceeds the expected ignition time delay; the actual pressure rise rate exceeds the expected pressure rise rate; the generated NOx concentration exceeds the predicted value / threshold; the ammonia slip exceeds the predicted value / threshold; and the temperature of the exhaust system 3 is lower than the predicted value / threshold.

[0133] In this embodiment, the specific methods of active adjustment in step S4 can be divided into single-factor adjustment and multi-factor linkage adjustment: When the ignition time delay is too long, priority should be given to advancing the diesel ignition time, increasing the diesel ignition quantity, or reducing the single injection quantity of liquid ammonia. The ignition time delay can be calculated using the following formula: In the formula, θ SOI,d θ is the start time of diesel ignition injection. SOC The combustion start time can be determined by the first significant increase in the apparent heat release rate or the cumulative heat release reaching a preset ratio. When Δθid is greater than 8 to 12°CA, or greater than 1.25 times the reference value under the same operating conditions, the ignition time delay is judged to be too long. When the pressure rise rate is too high, delay the main diesel injection timing, reduce the diesel ignition quantity, or adjust the liquid ammonia staged injection ratio. The pressure rise rate is calculated using the following formula:

[0134] when When the pressure rise rate exceeds 0.8–1.2 MPa / °CA, it is considered to be too high, which may lead to excessive mechanical load on the engine or excessively intense combustion. When the NOx in the exhaust is too high, the amount of ammonia added in the engine or the amount of ammonia injected from outside the engine is increased, and the liquid ammonia injection phase is corrected in conjunction to improve the coexistence of NH3 / NO in the cylinder. The NOx concentration detected by the NOx concentration sensor 73 is compared with the predicted value, and the system is triggered when the actual value is higher than the predicted value. When the NH3 slip is too high, the amount of external ammonia injection is reduced first, and the amount of internal ammonia supplementation is reduced or the utilization rate of the in-cylinder reduction reaction is increased. The NH3 concentration detected by the ammonia concentration sensor 74 is compared with the predicted value. When the actual value is higher than the predicted value, it is triggered. When the inlet temperature of the post-treatment denitrification device 6 is too low, the proportion of external ammonia injection is reduced and the proportion of internal pre-denitrification is increased. The device is triggered when the temperature detected by the exhaust temperature sensor 71 is lower than the high-efficiency reaction window (200-550°C) of the post-treatment denitrification device 6.

[0135] If the test results show that the exhaust temperature is too low, the NOx concentration is too high, the residual NH3 is too high, or the ammonia-nitrogen ratio deviates from the set range, the co-control unit will further reverse the liquid ammonia injection parameters, diesel ignition parameters, and in-cylinder ammonia replenishment to actively reconstruct the inlet boundary of the aftertreatment denitrification device 6, so that it falls into the high-efficiency reaction window of the aftertreatment denitrification device 6 as much as possible, rather than passively accepting the fixed exhaust state after in-cylinder combustion.

[0136] Optionally, it also includes: step S5, supplying an ammonia-containing reducing agent into the aftertreatment denitrification device 6, so that the ammonia-containing reducing agent is mixed with the gas discharged from the exhaust system 3 and reacts under the action of the catalyst in the aftertreatment denitrification device 6, and controlling the ammonia-nitrogen ratio at the inlet of the aftertreatment denitrification device 6 to be between 0.8 and 1.2 by the control unit 8.

[0137] In this embodiment, in step S5, the ammonia-containing reducing agent can be gaseous ammonia, urea aqueous solution, or other equivalent ammonia-containing reducing agents.

[0138] When using urea aqueous solution, the urea needs to be decomposed into ammonia gas through a urea hydrolysis device before being injected into the SCR reactor.

[0139] The catalyst in the post-treatment denitrification unit 6 can be Cu-SSZ-13, or iron-based molecular sieves or vanadium-based catalysts can be selected according to the marine exhaust conditions.

[0140] The Cu-SSZ-13 catalyst exhibits good low-temperature catalytic performance and resistance to hydrothermal aging, making it suitable for ship emission control scenarios.

[0141] During the control process, the ammonia injection rate can be adjusted according to the exhaust temperature, NOx concentration, NO / NO2 ratio, residual NH3 concentration and volume hourly space velocity, so that the SCR inlet ammonia-nitrogen ratio is preferably maintained in the range of 0.8 to 1.2 and the operating temperature is preferably maintained in the range of 200 to 550°C.

[0142] The ammonia-to-nitrogen ratio can be calculated using the following formula:

[0143] In the formula, m NH3,in The amount of ammonia injected externally, in m NOx,in M represents the NOx mass flow rate at the inlet of the post-treatment denitrification unit 6. NH3 and M NOx These are the molar masses of ammonia and NOx, respectively.

[0144] When the SCR back end detects that the NH3 slip exceeds the limit, reduce the amount of ammonia injected outside the machine or increase the proportion of pre-denitrification inside the machine; when the NOx conversion is insufficient, increase the amount of ammonia injected outside the machine, improve the mixing uniformity, or improve the catalytic reaction efficiency in conjunction with temperature management measures. If necessary, set up an ammonia escape oxidation unit (ASC) downstream of the post-treatment denitrification unit 6 to further treat unreacted NH3.

[0145] Optionally, the multi-objective optimization function is:

[0146] Among them, w1, w2, w3, w4 and w5 are weighting coefficients.

[0147] In this embodiment, in the multi-objective optimization function, n(NOx) is the normalized NOx emission, n(NH3) is the normalized NH3 slip, n(N2O) is the normalized N2O generation, and COV... IMEP η is the cyclic fluctuation coefficient, and ηcomb is the combustion efficiency.

[0148] The weighting coefficients w1 to w5 can be adjusted according to different operating conditions and optimization priorities. For example, w1 can be increased under high emission control requirements, and w4 can be increased when combustion stability is emphasized.

[0149] The constraints can be written as follows: liquid ammonia injection pressure is between 20 and 120 MPa, preferably between 30 and 80 MPa; liquid ammonia supply temperature is between -20°C and 40°C; liquid ammonia injection timing is between 40°CA before top dead center and 20°CA after top dead center, preferably between 30°CA before top dead center and 10°CA after top dead center; diesel injection pressure is between 40 and 180 MPa; SCR inlet ammonia-nitrogen ratio is maintained between 0.8 and 1.2; SCR inlet temperature is between 200 and 550°C; maximum pressure rise rate, peak burst pressure, and exhaust temperature do not exceed engine safety thresholds; NH3 slip and N2O emissions do not exceed preset emission limits.

[0150] Through the above multi-objective optimization function and constraints, the control unit 8 can comprehensively consider multiple indicators such as NOx emissions, NH3 slip, N2O generation, combustion efficiency and cycle fluctuations. Under the premise of meeting various constraints, it outputs the optimal liquid ammonia injection parameter adjustment, diesel ignition parameter adjustment, in-engine ammonia replenishment, and external ammonia injection, thereby achieving integrated and coordinated purification inside and outside the engine.

[0151] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for coordinated internal and external purification of a liquid ammonia direct injection engine, applied to a coordinated internal and external purification system for a liquid ammonia direct injection engine, the coordinated internal and external purification system for a liquid ammonia direct injection engine includes an engine (1), the engine (1) is provided with an intake system (2) and an exhaust system (3), the engine includes a liquid ammonia supply unit (21) and a diesel ignition injection unit (22), the liquid ammonia supply unit (21) is used to inject liquid ammonia fuel into the combustion chamber of each cylinder at a fixed time and pressure, the liquid ammonia supply unit (21) has a liquid ammonia injector (211), the engine (1) is provided with a combustion chamber (4), the combustion chamber (4) is provided with a combustion state monitoring unit (5), the combustion state monitoring unit (5) The system includes a cylinder pressure module (51), a crankshaft angle encoder module (52), and a cylinder temperature module (53). One end of the exhaust system (3) is connected to an aftertreatment denitrification device (6). An exhaust parameter detection unit (7) is provided on the exhaust system (3). The exhaust parameter detection unit (7) includes an exhaust temperature sensor (71), an exhaust pressure sensor (72), and an exhaust component concentration sensor group. The engine (1) is also provided with a control unit (8). The control unit (8) is electrically connected to the liquid ammonia supply unit (21), the diesel ignition injection unit (22), the combustion state monitoring unit (5), the aftertreatment denitrification device (6), and the exhaust parameter detection unit (7), respectively. Its features are, The method includes: a control unit (8) constructing a multi-objective optimization function, with NO x Emissions, ammonia slip, N2O generation, combustion efficiency, and engine combustion cycle fluctuations are the comprehensive optimization targets; the method for achieving these comprehensive optimization targets includes the following steps: S1. The initial liquid ammonia injection parameters are controlled by the liquid ammonia injector (211). The initial liquid ammonia injection parameters include at least the liquid ammonia injection pressure, liquid ammonia supply temperature, liquid ammonia injection time, and single injection quantity. The control unit (8) acquires the cylinder pressure Pc, cylinder temperature Tc, engine speed n, load L, and target liquid ammonia injection quantity m in real time. NH3 In conjunction with the saturated properties of liquid ammonia, the superheat index and pressure drop index characterizing the flash boiling trend are calculated. When the local flash boiling tendency is insufficient after injection, the liquid ammonia supply temperature is increased, the injection time is advanced, or the effective back pressure difference at the nozzle is reduced. When the jet is excessively divergent, insufficiently penetrated, or too evaporating, the liquid ammonia supply temperature is reduced, the injection pressure is increased, or the injection time is delayed, so that the spray cone angle, penetration length, and evaporation rate are kept within the preset transition flash boiling window. S2. The diesel injection pressure, diesel ignition time, diesel ignition amount and pre-injection and main injection distribution ratio of diesel are controlled by the diesel ignition injection unit (22). The diesel ignition amount is determined according to the target liquid ammonia substitution rate and the stability of the fire core. Step S3: In the later stage of combustion, supplementary liquid ammonia is injected through the liquid ammonia injector (211), and the injection parameters of the supplementary liquid ammonia are controlled.

2. The method for coordinated internal and external purification of liquid ammonia direct injection machine according to claim 1, characterized in that, The exhaust gas component concentration sensor group includes NO x Concentration sensor (73), ammonia concentration sensor (74) and oxygen concentration sensor (75).

3. The method for coordinated internal and external purification of liquid ammonia direct injection machine according to claim 2, characterized in that, The exhaust component concentration sensor group also includes an N2O concentration sensor (76).

4. The method for coordinated internal and external purification of liquid ammonia direct injection machine according to claim 1, characterized in that, Step S3 is triggered when any of the following detection results are met: NO was detected x Concentration above the threshold; The actual load of the post-treatment denitrification unit (6) exceeds 90% of its maximum load; The combustion chamber (4) contains both a first temperature range and a second temperature range, wherein the second temperature range is higher than the first temperature range. The ammonia concentration in the combustion chamber (4) is below the threshold.

5. The method for coordinated internal and external purification of liquid ammonia direct injection machine according to claim 4, characterized in that, It also includes: step S4, where the exhaust parameter detection unit (7) transmits the detection parameters to the control unit (8), and according to the first signal set, the control unit (8) controls the liquid ammonia supply unit (21) and / or the diesel ignition injection unit (22) to actively adjust; The first set of signals includes at least: actual ignition time delay exceeding expected ignition time delay; actual pressure rise rate exceeding expected pressure rise rate; and generated NO. x The concentration exceeds the threshold; the ammonia slip exceeds the threshold; the temperature of the exhaust system (3) is below the threshold.

6. The method for coordinated internal and external purification of liquid ammonia direct injection machine according to claim 5, characterized in that, It also includes: step S5, supplying an ammonia-containing reducing agent into the post-treatment denitrification device (6), mixing the ammonia-containing reducing agent with the gas discharged from the exhaust system (3), and reacting under the action of the catalyst in the post-treatment denitrification device (6), and controlling the ammonia-nitrogen ratio at the inlet of the post-treatment denitrification device (6) to be between 0.8 and 1.2 by the control unit (8).

7. The method for coordinated internal and external purification of liquid ammonia direct injection machine according to claim 1, characterized in that, The multi-objective optimization function is: , where w1, w2, w3, w4 and w5 are weighting coefficients; n(NO) x ) is the normalized NO x Emissions, n(NH3) is the normalized NH3 slip, n(N2O) is the normalized N2O formation, COV IMEP η is the cyclic fluctuation coefficient. comb For combustion efficiency.

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