Method and system for controlling in-cylinder air-fuel ratio of marine methanol dual-fuel engine

Abstract

The invention discloses an in-cylinder air-fuel ratio control method and system for a marine methanol dual-fuel engine. Comprising the following steps: acquiring oxygen concentration data in an exhaust pipeline of the methanol dual-fuel engine, calculating a real-time excess air coefficient in exhaust of the engine according to the oxygen concentration data, and acquiring pressure and temperature of an intake manifold; then, based on the front and back pressure and temperature of the intake manifold, the air mass flow entering the intake manifold is estimated in real time; an air-fuel ratio real-time transmission delay model is established according to an engine operation mechanism and structural characteristics, a delay prediction estimator is designed, and the air-fuel ratio in a cylinder is estimated in real time; according to the air-fuel ratio real-time transmission delay model, a predetermined performance air-fuel ratio control algorithm based on ideal internal dynamics is designed; the method is suitable for accurately controlling the air-fuel ratio of the marine methanol dual-fuel engine, and has a good air-fuel ratio control effect.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control of methanol dual-fuel engines, and specifically to a method and system for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine. Background Art

[0002] In a ship power system, methanol fuel has gradually become an important choice for the ship power system due to its advantages such as low emissions, economy, and easy storage and transportation. However, during the in-cylinder combustion process of a methanol-diesel dual-fuel engine, due to differences in fuel characteristics, combustion non-linearity, and complex working conditions, it faces high control challenges, resulting in high requirements for the control accuracy of the air-fuel ratio. The air-fuel ratio is a key parameter affecting the combustion efficiency, emission level, and power output of an engine. In terms of air-fuel ratio control, well-known engine manufacturers and research institutions at home and abroad mainly conduct research on aspects such as the combustion stability of methanol dual-fuel engines, fuel injection strategies, emission control, and real-time air-fuel ratio optimization to ensure stable in-cylinder combustion and solve problems such as combustion lag and incomplete combustion. In practical applications, due to the response time of sensors, data transmission delays, and complex environmental impacts, the in-cylinder air-fuel ratio data often cannot be obtained in real time, resulting in the inability of traditional control methods to respond in a timely manner, affecting the combustion efficiency and stability of the engine. Therefore, an adaptive control method is needed that can adaptively adjust control parameters according to different working conditions to achieve stable and efficient control. Based on these backgrounds, a method and system for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine are proposed to solve the data delay problem and improve the control accuracy and stability. Summary of the Invention

[0003] This research aims to solve the problem of delayed acquisition and estimation of the in-cylinder air-fuel ratio of a methanol dual-fuel engine, and provides a method and system for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine.

[0004] To achieve the above object, the present invention provides the following technical solution: A method for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine, specifically including the following steps:

[0005] S1. Collect the oxygen concentration data in the exhaust pipeline of the methanol dual-fuel engine, and calculate the real-time excess air coefficient in the engine exhaust according to the oxygen concentration data;

[0006] S2. Collect the temperature and pressure data of the intake manifold;

[0007] S3. Based on the pressure and temperature data before and after the intake manifold, use the physical model of the throttle flow equation to calculate and estimate the air mass flow rate in the intake manifold in real time;

[0008] S4. Establish an air-fuel ratio transmission delay model according to the engine operation mechanism and structural characteristics;

[0009] S5. Input the real-time excess air ratio and air mass flow rate obtained in S1 and S3 into the transmission delay model, and then obtain the real-time transmission delay model of the air-fuel ratio of the methanol dual-fuel engine. Based on the real-time transmission delay model of the air-fuel ratio of the methanol dual-fuel engine, design a delay prediction estimator to estimate the in-cylinder air-fuel ratio of the methanol dual-fuel engine in real time and obtain the real-time estimated value of the in-cylinder air-fuel ratio;

[0010] S6. Construct a dynamic predetermined performance air-fuel ratio control algorithm according to the real-time transmission delay model of the air-fuel ratio in S5;

[0011] S7. Combine the predetermined performance air-fuel ratio control algorithm in S6, and design an engineering predetermined performance convergence with the real-time estimated value of the in-cylinder air-fuel ratio of the methanol dual-fuel engine predicted by the estimator as the target to achieve the adaptive control of the in-cylinder air-fuel ratio of the methanol dual-fuel engine.

[0012] Preferably, the establishment of the air-fuel ratio transmission delay model in S4 includes:

[0013] Combine the standard gas state equation and establish a dynamic expression of the air-fuel ratio at the intake manifold according to the gas inflow and outflow relationship, that is, the air-fuel ratio transmission delay model:

[0014]

[0015]

[0016] The relationship between the air-fuel ratio at the exhaust manifold and the air-fuel ratio at the intake manifold is as follows:

[0017]

[0018] Preferably, in S5, the delay estimator includes a prediction term for the in-cylinder air-fuel ratio and an estimation term for the in-cylinder air-fuel ratio. The in-cylinder air-fuel ratio parameter estimation function is as follows:

[0019] The first step: The gain of the in-cylinder air-fuel ratio input after delay , the gain of the in-cylinder air-fuel ratio prediction state , the correction term of the in-cylinder air-fuel ratio prediction state , where is the observation gain matrix, and by adjusting to make the error dynamics be a Hurwitz matrix. The in-cylinder air-fuel ratio prediction state is as follows:

[0020]

[0021] The second step: Estimate the time-delay state, which can be estimated through the historical values of the input and the known system dynamics. The in-cylinder air-fuel ratio parameter estimation function is as follows:

[0022]

[0023]

[0024] where is the air gas constant of the intake manifold, is the gas pressure of the intake manifold, is the volume of the intake manifold, is the gas temperature of the intake manifold, is the air mass flow rate of the intake manifold, is the integral of the change in the methanol mass flow rate of the intake manifold, is the air-fuel ratio of the exhaust manifold, is the delay from the intake manifold to the exhaust manifold, is the estimated air-fuel ratio at the intake manifold, is the estimated in-cylinder air-fuel ratio, where x is the integration variable and t - x is the time interval from time point x to the current t;

[0025] The delay from the air-fuel ratio of the intake manifold to the in-cylinder air-fuel ratio is , and the in-cylinder air-fuel ratio can be known as:

[0026]

[0027] This delay prediction estimator algorithm can estimate the current state of the system and further predict the future state through this estimation. The in-cylinder air-fuel ratio is the real-time air-fuel ratio at the intake manifold after a time series.

[0028] Preferably, according to the air-fuel ratio real-time transmission delay model in S6, design a predetermined performance air-fuel ratio control algorithm based on the ideal internal dynamics as follows:

[0029] The first step: For the in-cylinder air-fuel ratio system:

[0030]

[0031] In the formula, s is the differential operator;

[0032] Introduce a new variable as the internal dynamics, is the change in the internal dynamics, where is deduced, then it is deduced that:

[0033]

[0034] The control model and the internal dynamics can be deduced as:

[0035]

[0036]

[0037] where , , ; because , the internal dynamics is unstable, is the external disturbance of the system, is the designed air-fuel ratio control input;

[0038] Define the system state error , to obtain the error dynamic model of the air-fuel ratio as:

[0039]

[0040]

[0041] where, is the error of the actual value of the in-cylinder air-fuel ratio, is the error of the internal dynamics, is the target in-cylinder air-fuel ratio, is the bounded ideal internal dynamics, is the designed robust control to force the internal dynamics and the output to track and respectively.

[0042] Step 2: To solve the bounded ideal internal dynamics, the center of the stable system is used to estimate the bounded reference trajectory (i.e., the bounded reference trajectory). , and the central idea is to combine the traditional center of the stable system with a high-order sliding mode parameter observer. Assuming that the reference signal can be piecewise modeled by a linear th-order external system, then the bounded estimate of the ideal internal dynamics that satisfies can be solved by the following differential equation:

[0043]

[0044] In the formula, , , …, are design parameters, represents the order of the assumed external system; , , … , can be calculated by the following formula:

[0045]

[0046] where , , …, are the coefficients of the system characteristic polynomial and can be estimated in real time by a high-order sliding mode estimator;

[0047] Step 3: To ensure and converge quickly, the nonlinear sliding surface based on can be designed as:

[0048]

[0049] where is a design parameter, is a design parameter, is a predefined time, is the nonlinear sliding surface. Once the sliding surface is established, i.e., , the internal dynamics and output dynamics will converge;

[0050] Step 4: To ensure that the error dynamic model of the in-cylinder air-fuel ratio converges to the predefined-time sliding manifold within the predefined time, the adaptive predefined-time air-fuel ratio control law is designed as:

[0051]

[0052] where the design parameter > 0 and , is a design parameter, is a predefined time, is an adaptive parameter used to compensate for the estimation error , sgn(•) is the sign function, is the wave function.

[0053] Preferably, in S7, an adaptive mechanism for the predefined performance convergence of the design project is implemented to achieve the adaptive control of the in-cylinder air-fuel ratio, specifically:

[0054] The adaptive strategy is designed as:

[0055]

[0056] where is a design parameter; and are both positive constants and are related to the design parameters , , i.e., and , is the change amount of the adaptive parameter.

[0057] To solve the above problems, the present invention also provides a system using a method for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine, specifically including:

[0058] An oxygen concentration acquisition and excess air coefficient calculation module, used to collect the oxygen concentration data in the exhaust pipe of the methanol dual-fuel engine and calculate the real-time excess air coefficient in the engine exhaust according to the oxygen concentration data;

[0059] An intake manifold temperature and pressure acquisition module, used to collect the temperature and pressure data of the intake manifold;

[0060] An air mass flow estimation module, used to calculate and estimate the air mass flow in the intake manifold in real time based on the pressure and temperature data before and after the intake manifold through the physical model of the throttle flow equation;

[0061] An air-fuel ratio transmission delay model establishment module, used to establish an air-fuel ratio transmission delay model according to the engine operation mechanism and structural characteristics;

[0062] An air-fuel ratio real-time transmission delay model and prediction estimator module, used to input the real-time excess air coefficient and air mass flow obtained in S1 and S3 into the transmission delay model to obtain the air-fuel ratio real-time transmission delay model of the methanol dual-fuel engine, and design a delay prediction estimator to estimate the in-cylinder air-fuel ratio of the methanol dual-fuel engine in real time;

[0063] A predetermined performance air-fuel ratio control algorithm module, used to construct a dynamic predetermined performance air-fuel ratio control algorithm according to the air-fuel ratio real-time transmission delay model in S5;

[0064] An in-cylinder air-fuel ratio adaptive control module, used to combine the predetermined performance air-fuel ratio control algorithm in S6, aiming at the real-time estimated value of the in-cylinder air-fuel ratio of the methanol dual-fuel engine by the prediction estimator, design an engineering predetermined performance convergence to realize the in-cylinder air-fuel ratio adaptive control of the methanol dual-fuel engine.

[0065] The beneficial effect of this application is that: through the adaptive control method of this application, the control parameters can be adaptively adjusted according to different working conditions to achieve stable and efficient control, so as to solve the data delay problem and improve the control accuracy and stability. Description of the Drawings

[0066] Figure 1 is the step flow chart of the method for controlling the in-cylinder air-fuel ratio of the marine methanol dual-fuel engine described in the present invention;

[0067] Figure 2 is the step flow chart of the method for controlling the in-cylinder air-fuel ratio of the marine methanol dual-fuel engine described in Embodiment 1 of the present invention. Detailed Embodiments

[0068] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, shall be covered by the protection scope of the present invention.

[0069] Embodiment 1

[0070] The present invention provides a technical method, combined with Figures 1 to 2 As shown, a method for controlling the air-fuel ratio in the cylinder of a marine methanol dual-fuel engine includes the following steps:

[0071] S1. Use a wide-range oxygen sensor installed in the exhaust manifold to collect the oxygen concentration signal in the exhaust pipe, and calculate the real-time excess air coefficient in the engine exhaust according to the oxygen concentration signal;

[0072] S2. Collect the intake manifold pressure and temperature through pressure and temperature sensors;

[0073] S3. Based on the collected pressure and temperature before and after the intake manifold, the air mass flow rate in the intake manifold can be calculated in real time through the physical model of the throttle flow equation;

[0074] S4. When methanol is injected into the intake manifold, there is a first-order inertial delay due to the wet wall effect as follows:

[0075]

[0076] Establish a transmission delay model according to the engine operation mechanism and structural characteristics. According to the law of conservation of mass, the change in the mass of the working medium in the system is equal to the sum of the masses exchanged through the system boundary. The law of conservation of mass shows that in an open system (such as the intake manifold), the change in the mass inside the system is equal to the mass flow rate entering the system minus the mass flow rate leaving the system, that is, the change in the mass of the working medium in the intake manifold is equal to the total inflow of fuel and air minus the outflow of the mixture. Combining with the standard gas state equation, establish a dynamic expression of the air-fuel ratio at the intake manifold according to the gas inflow and outflow relationship. The air-fuel ratio transmission delay model is as follows:

[0077]

[0078]

[0079] The relationship between the air-fuel ratio at the exhaust manifold and the air-fuel ratio at the intake manifold is as follows:

[0080]

[0081] S5. Input the excess air ratio and intake manifold air mass flow rate obtained in S1 and S3 into S4 to obtain a transmission delay model, and then obtain a real-time transmission delay model of the air-fuel ratio. Then, design a delay prediction estimator based on the real-time transmission delay model of the methanol dual-fuel engine to estimate the in-cylinder air-fuel ratio in real time. The delay estimator is divided into two parts. One part is the in-cylinder air-fuel ratio prediction term, and the other part is the in-cylinder air-fuel ratio estimation term. The specific description is as follows:

[0082] The first step: The gain of the in-cylinder air-fuel ratio after input delay , the gain of the in-cylinder air-fuel ratio prediction state , the correction term of the in-cylinder air-fuel ratio prediction state , where is the observation gain matrix, and by adjusting to make the error dynamics be a Hurwitz matrix. The in-cylinder air-fuel ratio prediction state is as follows:

[0083]

[0084] The second step: Estimate the time-delay state, which can be estimated through the input historical values and the known system dynamics. The in-cylinder air-fuel ratio parameter estimation function is as follows:

[0085]

[0086]

[0087] The delay from the air-fuel ratio in the intake manifold to the in-cylinder air-fuel ratio is , and the in-cylinder air-fuel ratio is known:

[0088]

[0089] This delay prediction estimator algorithm can estimate the current state of the system and further predict the future state through this estimation. The in-cylinder air-fuel ratio is the real-time air-fuel ratio at the intake manifold after a time series.

[0090] S6. According to the real-time transmission delay model of the air-fuel ratio, design a predetermined performance air-fuel ratio control algorithm based on the ideal internal dynamics:

[0091] The first step: For the in-cylinder air-fuel ratio system:

[0092]

[0093] Introduce a new variable The derivation is as follows:

[0094]

[0095] The control model and internal dynamics can be deduced as follows:

[0096]

[0097]

[0098] where , , ; due to , the internal dynamics is unstable.

[0099] Define the system state error , The error dynamic model of the air-fuel ratio is obtained as follows:

[0100]

[0101]

[0102] where , is the target in-cylinder air-fuel ratio, is the bounded ideal internal dynamics, is the designed robust control to force the internal dynamics and the output to track and respectively.

[0103] Step 2: To solve the bounded ideal internal dynamics, the center of the stable system is used to estimate the bounded reference profile , and the central idea is to combine the traditional center of the stable system with a high-order sliding mode parameter observer. Assuming that the reference signal can be piecewise modeled by a linear -order external system, the bounded estimate of the ideal internal dynamics that satisfies can be solved by the following differential equation:

[0104]

[0105] where , , …, are design parameters, represents the order of the assumed external system; , , … can be calculated by the following formula:

[0106]

[0107] where , , …, are the coefficients of the system characteristic polynomial and can be estimated in real time by a high-order sliding mode estimator.

[0108] Step 3: To ensure and converge quickly, the nonlinear sliding surface based on can be designed as:

[0109]

[0110] where is a design parameter, is a design parameter, is a predefined time. Once the sliding surface is established, i.e., , the internal dynamics and output dynamics will converge.

[0111] The internal dynamic tracking error can be derived as:

[0112]

[0113] Select a Lyapunov function and calculate its derivative to obtain:

[0114]

[0115] The tracking error converges to zero at the predefined time Due to the equation , making converge to zero, so and converge to zero within the predefined time .

[0116] Step 4: To ensure that the error dynamic model of the in-cylinder air-fuel ratio converges to the predefined-time sliding manifold within the predefined time, the adaptive predefined-time air-fuel ratio control law is designed as:

[0117]

[0118] where the design parameter > 0 and .

[0119] S7. Design an adaptive mechanism for the convergence of the engineering predefined performance to achieve the adaptive control of the in-cylinder air-fuel ratio. Combining the predefined performance air-fuel ratio control algorithm in S6, with the real-time estimated value of the in-cylinder air-fuel ratio of the methanol dual-fuel engine by the prediction estimator as the goal, the convergence of the engineering predefined performance means ensuring that the system state reaches the given error range within the preset time and strictly follows the convergence trajectory by adjusting Converge the state of the system within a predefined time. An adaptive mechanism is used to adjust the control parameters online to cope with system uncertainties or external disturbances. When combined, the adaptive mechanism can adjust the control gain or compensation term in real time, enabling the system to always meet the predefined convergence performance requirements of the project, that is, the error converges along a predefined trajectory. In S6, is the adaptive parameter used to compensate for the estimation error of the external disturbance of the system ;

[0120] The adaptive strategy is designed as:

[0121]

[0122] where is the design parameter; and are both positive constants, related to the design parameters 、 , that is and , is the variation of the adaptive parameter.

[0123] Embodiment 2

[0124] A control system for estimating the air-fuel ratio in the cylinder of a marine methanol dual-fuel engine specifically includes:

[0125] An oxygen concentration acquisition and excess air coefficient calculation module for acquiring oxygen concentration data in the exhaust pipe of the methanol dual-fuel engine and calculating the real-time excess air coefficient in the engine exhaust based on the oxygen concentration data;

[0126] An intake manifold temperature and pressure acquisition module for acquiring the temperature and pressure data of the intake manifold;

[0127] An air mass flow rate estimation module for calculating and estimating the air mass flow rate in the intake manifold in real time based on the pressure and temperature data before and after the intake manifold through a physical model of the throttle flow equation;

[0128] An air-fuel ratio transmission delay model establishment module for establishing an air-fuel ratio transmission delay model according to the engine operation mechanism and structural characteristics;

[0129] An air-fuel ratio real-time transmission delay model and prediction estimator module for inputting the real-time excess air coefficient and air mass flow rate obtained in S1 and S3 into the transmission delay model to obtain the air-fuel ratio real-time transmission delay model of the methanol dual-fuel engine, and designing a delay prediction estimator to estimate the air-fuel ratio in the cylinder of the methanol dual-fuel engine in real time;

[0130] A predetermined performance air-fuel ratio control algorithm module is used to construct a dynamic predetermined performance air-fuel ratio control algorithm according to the air-fuel ratio real-time transmission delay model in S5;

[0131] An in-cylinder air-fuel ratio adaptive control module is used to design an engineering predetermined performance convergence in combination with the predetermined performance air-fuel ratio control algorithm in S6 to achieve the in-cylinder air-fuel ratio adaptive control of the methanol dual-fuel engine.

[0132] Finally, it should be noted that the above description is only the preferred embodiment of the present invention. Those of ordinary skill in the art can make various similar representations under the inspiration of the present invention without violating the purpose and claims of the present invention. Such transformations all fall within the protection scope of the present invention.

Claims

1. A method for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine, characterized in that, Specifically, it includes the following steps: S1. Collect the oxygen concentration data in the exhaust pipeline of the methanol dual-fuel engine, and calculate the real-time excess air ratio in the engine exhaust according to the oxygen concentration data; S2. Collect the temperature and pressure data of the intake manifold; S3. Based on the pressure and temperature data before and after the intake manifold, calculate and estimate the air mass flow rate in the intake manifold in real time through the physical model of the throttle flow equation; S4. Establish an air-fuel ratio transmission delay model according to the engine operation mechanism and structural characteristics; S5. Input the real-time excess air ratio obtained in S1 and the air mass flow rate obtained in S3 into the air-fuel ratio transmission delay model to obtain the real-time air-fuel ratio transmission delay model of the methanol dual-fuel engine, and design a delay prediction estimator based on the real-time air-fuel ratio transmission delay model, and use the delay prediction estimator to estimate the in-cylinder air-fuel ratio of the methanol dual-fuel engine in real time; S6. Construct a dynamic predefined performance air-fuel ratio control algorithm according to the real-time air-fuel ratio transmission delay model in S5; S7. Combine the predefined performance air-fuel ratio control algorithm in S6, and design an engineering predefined performance convergence with the real-time estimated value of the in-cylinder air-fuel ratio as the target to achieve the adaptive control of the in-cylinder air-fuel ratio of the methanol dual-fuel engine.

2. A method for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine according to claim 1, characterized in that, Establishing the air-fuel ratio transmission delay model specifically includes: Combined with the standard gas state equation, establish a dynamic expression of the air-fuel ratio at the intake manifold according to the gas inflow and outflow relationship, that is, the air-fuel ratio transmission delay model: ； ； Wherein, is the air gas constant of the intake manifold, is the gas temperature of the intake manifold, is the gas pressure of the intake manifold, is the volume of the intake manifold, is the change in the methanol mass flow rate of the intake manifold, is the change in the air mass flow rate of the intake manifold, is the air-fuel ratio at the mixer, is the air-fuel ratio at the intake manifold, is the mass flow rate of diesel; The relationship between the air-fuel ratio at the exhaust manifold and the air-fuel ratio at the intake manifold is as follows: ； is the air-fuel ratio at the exhaust manifold, is the air-fuel ratio at the intake manifold after eliminating the delay, is the time series, is the delay from the intake manifold to the exhaust manifold.

3. A method for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine according to claim 1, characterized in that, In step S5, the delay prediction estimator includes a prediction term for the air-fuel ratio at the intake manifold and an estimation term for the air-fuel ratio at the intake manifold. The specific steps are as follows: The prediction function of the air-fuel ratio at the intake manifold is as follows: Gain after the input delay of the air-fuel ratio at the intake manifold , gain of the predicted state of the air-fuel ratio at the intake manifold , correction term of the predicted state of the air-fuel ratio at the intake manifold , where is the observation gain matrix, and by adjusting the error dynamics is a Hurwitz matrix, and the change in the predicted value of the air-fuel ratio at the intake manifold is: ； Wherein, is the predicted air-fuel ratio value at the intake manifold, is the correction coefficient; is the air-fuel ratio at the exhaust manifold; The estimation function of the air-fuel ratio at the intake manifold is as follows: Estimate the time-delay state, and the estimation function at the intake manifold is as follows: ； ； In the formula, is the integral of the change in the methanol mass flow rate of the intake manifold, is the air-fuel ratio estimation function of the mixer, is the air-fuel ratio estimation function at the intake manifold, x is the integration variable, and t - x is the time interval from time point x to the current t; The delay from the air-fuel ratio of the intake manifold to the in-cylinder air-fuel ratio is , and the estimated value of the in-cylinder air-fuel ratio is as follows: ； The delay prediction estimator can estimate the current state of the system and further predict the future state through the prediction function of the air-fuel ratio at the intake manifold and the estimation function of the air-fuel ratio at the intake manifold. The estimated value of the in-cylinder air-fuel ratio is the real-time air-fuel ratio at the intake manifold after a time series.

4. A method for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine according to claim 1, characterized in that, In step S6, according to the real-time air-fuel ratio transmission delay model, construct a dynamic predefined performance air-fuel ratio control algorithm as follows: The first step: The actual value of the in-cylinder air-fuel ratio is: ； In the formula, s is the differential operator; Introduce new variables For internal dynamics For the change in internal dynamics, where , it can be deduced that: ； The control model and internal dynamics can be deduced as: ； ； Among them , , ; Since , is unstable, is an external disturbance of the system, is the designed air-fuel ratio control input; Define the system state error , , and the error dynamic model of the air-fuel ratio is obtained as follows: ； ； wherein, is the error of the actual in-cylinder air-fuel ratio, is the error of the internal dynamics, is the target in-cylinder air-fuel ratio, is the bounded standard internal dynamic function, that is, the target value of, is the designed air-fuel ratio control input, which forces the internal dynamics and the actual in-cylinder air-fuel ratio to track and respectively; Step 2: To solve the bounded standard internal dynamics, the bounded standard internal dynamic function is estimated by using the extended stable system center method. is the estimated value of the bounded standard internal dynamic function. The stable system center method is combined with a high-order sliding mode parameter observer. Assume that the air-fuel ratio in the target cylinder can be modeled piecewise by a linear order external system (i.e., the external reference signal generation system). Then, the estimated value of the bounded standard internal dynamic function that satisfies can be solved by the following differential equation: ； wherein, , , …, are design parameters, represents the order of the assumed external system; , , … can be calculated by the following formula: ； Among them, , , …, are the coefficients of the system characteristic polynomial, which can be estimated in real time by a high-order sliding mode estimator; Step 3: In order to ensure and converge quickly, the nonlinear sliding surface based on can be designed as: ； wherein, is a design parameter, is a design parameter, is a predefined time, is a non-linear sliding surface. Once the sliding surface is established, i.e., , the internal dynamics and the output dynamics will converge; The fourth step: To ensure that the error dynamic model of the in-cylinder air-fuel ratio converges to the predefined time sliding manifold within the predefined time, the designed air-fuel ratio control input is: ； Among them, the design parameter > 0 and , is the design parameter, is the predefined time, is an adaptive parameter used to compensate for the estimation error , sgn(•) is the sign function, is the wave function.

5. A method for controlling the in-cylinder air-fuel ratio of a marine methanol dual-fuel engine according to claim 1, characterized in that, In step S7, combine the predefined performance air-fuel ratio control algorithm in S6, and design an engineering predefined performance convergence to achieve the adaptive control of the in-cylinder air-fuel ratio of the methanol dual-fuel engine, where: The adaptive strategy is: ； where is a design parameter; and are both positive constants, related to the design parameters and i.e., and , is the change amount of the adaptive parameter.

6. A system using the in-cylinder air-fuel ratio control method for a marine methanol dual-fuel engine according to any one of claims 1 to 5, characterized in that, Specifically, it includes: The oxygen concentration acquisition and excess air ratio calculation module is used to collect the oxygen concentration data in the exhaust pipeline of the methanol dual-fuel engine and calculate the real-time excess air ratio in the engine exhaust according to the oxygen concentration data; The intake manifold temperature and pressure acquisition module is used to collect the temperature and pressure data of the intake manifold; The air mass flow rate estimation module is used to calculate and estimate the air mass flow rate in the intake manifold in real time based on the pressure and temperature data before and after the intake manifold through the physical model of the throttle flow equation; The air-fuel ratio transmission delay model establishment module is used to establish the air-fuel ratio transmission delay model according to the engine operation mechanism and structural characteristics; An air-fuel ratio real-time transmission delay model and a prediction estimator module are used to input the real-time excess air coefficient and air mass flow rate obtained in S1 and S3 into the transmission delay model, thereby obtaining the air-fuel ratio real-time transmission delay model of the methanol dual-fuel engine, and designing a delay prediction estimator based on the air-fuel ratio real-time transmission delay model, and using the prediction estimator to estimate the in-cylinder air-fuel ratio of the methanol dual-fuel engine in real time; A predetermined performance air-fuel ratio control algorithm module is used to construct a dynamic predetermined performance air-fuel ratio control algorithm according to the air-fuel ratio real-time transmission delay model in S5; An in-cylinder air-fuel ratio adaptive control module is used to combine the predetermined performance air-fuel ratio control algorithm in S6, aiming at the real-time estimated value of the in-cylinder air-fuel ratio of the methanol dual-fuel engine by the prediction estimator, and design an engineering predetermined performance convergence to realize the in-cylinder air-fuel ratio adaptive control of the methanol dual-fuel engine.

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