A Model-Based Method for Simulating the Cylinder Blow-by Fault of Marine Engines

Abstract

The present invention provides a model-based method for simulating the cylinder blow-by fault of a marine engine, based on the 7G80MEC9 two-stroke diesel engine, and includes the following steps: constructing an engine cylinder model according to the law of conservation of energy, the law of conservation of mass, and the ideal gas state equation; constructing an engine intake and exhaust model according to the law of conservation of energy and the law of conservation of mass; constructing an engine EGB model according to the map of the supercharged air of the engine; constructing a supercharger model of the engine according to the supercharger characteristic map of the engine; constructing an engine intercooler model according to a mathematical formula; obtaining the change signals of the performance parameters of the engine through model simulation calculation; observing the change rules, trends, and amplitudes of the change signals of the performance parameters of the engine, and analyzing them to judge the degree of the blow-by fault; and simulating the cylinder piston ring blow-by fault under different factors by the control variable method.

Description

Technical Field

[0001] The present invention relates to the technical field of fault simulation, and more particularly to a model-based method for simulating the cylinder blow-by fault of marine engines. Background Art

[0002] In recent years, the strict international regulations on ship energy efficiency and NOx emissions from ocean-going ships have made energy conservation and emission reduction the theme of the shipping industry. Due to their fuel economy and reliability, most large commercial ships are powered by low-speed two-stroke marine diesel engines. However, there are many adverse factors in obtaining data on the fault types of large marine diesel engines through bench tests or actual ships. Therefore, numerical calculations for fault simulation of diesel engines are particularly important, and they are also of great significance for troubleshooting and the construction of data-driven intelligent fault diagnosis systems.

[0003] Most of the current research on engine cylinder blow-by faults focuses on the field of vehicle engines, and there is less research in the field of marine engines. In the case of vehicle engines, with the increasingly stringent automotive emission regulations, the crankcase ventilation system has become an accessory system that cannot be ignored in automotive engines. When the engine is running normally, the exhaust gas generated by fuel combustion in the combustion chamber will leak out through the gap between the piston ring and the cylinder liner. The leaked gas accumulates in the crankcase. If it cannot be discharged in time, it will lead to seal failure, serious lubricating oil leakage, power reduction, and may also cause flash combustion of the gas in the crankcase, resulting in engine damage. In the early stage, the crankcase ventilation system was mainly connected to a one-way valve and directly led to the atmosphere to maintain the normal pressure in the crankcase, that is, the open crankcase ventilation system. Later, to prevent air pollution, researchers introduced the blow-by gas into the intake manifold and re-introduced it into the combustion chamber for combustion, which is the commonly used closed crankcase ventilation system.

[0004] In order to simulate the cylinder blow-by fault of large low-speed marine diesel engines, analyze the influencing factors of cylinder blow-by, and study the detection methods of cylinder blow-by, it is necessary to establish a whole-engine model of a diesel engine considering cylinder blow-by and crankcase ventilation. A method for studying the cylinder blow-by fault by studying the heating effect of the crankcase ventilation system on the intake system is proposed. Summary of the Invention

[0005] In view of the technical problems mentioned in the above background art, a model-based method for simulating the cylinder blow-by fault of marine engines is provided. The technical means adopted by the present invention are as follows:

[0006] A model-based method for simulating the cylinder blow-by fault of marine engines, based on the 7G80MEC9 two-stroke diesel engine, includes the following steps:

[0007] Step 1: Construct an engine cylinder model based on the law of conservation of energy, the law of conservation of mass, and the ideal gas state equation. The engine cylinder model includes: constructing a heat release model, a heat transfer model, fuel properties, a piston ring blow-by model, and a gas exchange model, and deriving thermal performance parameters;

[0008] Step 2: Construct an engine intake and exhaust model based on the law of conservation of energy and the law of conservation of mass to obtain the pressure, temperature, and mass parameters of the intake and exhaust;

[0009] Step 3: Construct an engine EGB model based on the map of the supercharged air of the engine to obtain the transient exhaust gas bypass mass flow rate;

[0010] Step 4: Construct a supercharger model of the engine based on the supercharger characteristic map of the engine to obtain the mass flow rate, outlet temperature, and instantaneous corresponding rotational speed at the supercharger outlet;

[0011] Step 5: Construct an engine intercooler model according to a mathematical formula to obtain the intercooler efficiency and the outlet temperature; the mathematical formula is: T s = T co - η c ·(T co - T ws )

[0012] where, T s represents the outlet temperature surface of the intercooler, T co represents the outlet temperature of the compressor, η c represents the cooling coefficient, and the value range of η c is 0.7 - 0.9, and T ws represents the cooling medium temperature;

[0013] Step 6: Obtain the change signals of the engine's various performance parameters through model simulation calculations; compare the simulation calculation data of the engine's various performance parameters with the engine bench test data. If the error is less than 5%, it indicates that the simulation accuracy of the constructed zero-dimensional engine model meets the requirements of fault simulation, and proceed to Step 7; if the error is greater than or equal to 5%, re-execute Step 1; at the same time, observe the change rules, trends, and amplitudes of the change signals of the engine's various performance parameters, and analyze them to judge the degree of blow-by fault occurrence;

[0014] Step 7: Conduct in-cylinder piston ring blow-by fault simulation under different factors through the control variable method.

[0015] Furthermore, the heat release model describes the combustion process through a double Wibe function. The Wibe function is:

[0016]

[0017]

[0018]

[0019] Among them, χ represents the combustion percentage, χ 1 represents the premixed combustion percentage, χ 2 represents the diffusion combustion percentage, Q d represents the diffusion combustion fraction, θ z represents the start point of premixed combustion, m 1 and m 2 respectively represent the premixed combustion quality coefficient and the diffusion combustion quality coefficient, τ represents the premixed combustion lead angle, represents the start point of diffusion combustion;

[0020] Furthermore, the heat transfer model is estimated by assuming the convective heat transfer of the constant value of the cylinder wall temperature, and the heat transfer model is constructed by the Woschni relation;

[0021] The Woschni relation is:

[0022]

[0023] Among them, i = 1, 2, 3, respectively representing the cylinder head, the piston crown and the cylinder liner; a w represents the instantaneous heat transfer coefficient calculated by the Woschni model; A w,i represents the heat transfer surface area exposed to the cylinder working medium; T Z represents the gas temperature in the cylinder; T w,i represents the average temperature of the heat transfer surface, which is a constant compared with T Z and is a constant.

[0024] Even further, the gas exchange model is constructed based on the opening areas of the scavenging ports and the exhaust valves and the pressure difference between the scavenging chamber and the cylinder; the scavenging mass flow rate of the scavenging ports and the gas mass flow rate of the exhaust valves are estimated by the isentropic flow through the orifices;

[0025] The isentropic flow is described as when the pressures of the upstream and downstream sections of the orifice satisfy the equation the working medium is in the subcritical flow state, and at this time the mass flow is:

[0026]

[0027] When the pressures of the upstream and downstream sections of the orifice do not satisfy the equation the working medium is in the critical flow state, and at this time the mass flow is:

[0028]

[0029] Among them, p eand p z represents the pressure in the exhaust pipe and the pressure in the cylinder; μ is the flow coefficient, A is the orifice flow area; R Z is the ideal gas constant; k is the adiabatic index of the working fluid.

[0030] Furthermore, the piston ring blowby model estimates the blowby mass flow rate and blowby energy loss through the piston ring based on the hole flow model of laminar flow and compressible flow; the hole flow model is:

[0031]

[0032] Among them, C bb Indicates the blowby flow coefficient; A bb Indicates the equivalent area of ​​blowby gas leakage, f m Calculated according to different blowby gas flow conditions.

[0033] Furthermore, in the intake and exhaust model, both the scavenging and exhaust pipes are open systems; the energy conservation, mass conservation and ideal gas state equations are solved to obtain the pressure, temperature, mass and gas composition in each crank angle step.

[0034] Furthermore, the EGB model includes an EGB valve; the opening area of ​​the EGB valve is controlled by an electronic control unit ECU, and the transient EGB mass flow rate is calculated according to the pressure difference before and after the EGB valve and the opening area.

[0035] Furthermore, the supercharger model is derived from the relationship between the pressure ratio, the compressor efficiency and the mass flow rate through the supercharger power and the outlet temperature.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] Combined with the model simulation results, it can be seen that the simulation effect and adjustability of the engine model taking into account the in-cylinder piston ring blowby are accurate and efficient, and the in-cylinder piston ring blowby fault can be effectively detected and simulated. Therefore, the low-speed two-stroke engine model based on the crankcase ventilation system, that is, taking into account the piston ring blowby, can be used as a research model for piston ring blowby, and the piston ring blowby fault simulation method based on the constructed engine model is feasible.

[0038] In the present invention, the blow-by gas that blows into the crankcase through the piston ring is used to detect the heating effect of the crankcase ventilation system on the intake air, thereby avoiding the situation where a single blow-by model is established for the insufficient in-depth research on the blow-by gas fault simulation and detection. By observing the impact of the piston ring blow-by gas failure on the running engine performance parameters, some major factors affecting the piston ring blow-by gas are analyzed, which provides certain guiding significance for preventing serious blow-by gas failures of the piston ring during the daily operation and maintenance of the engine.

[0039] In the research on the blow-by fault simulation method, first, the influence of engine load on the blow-by gas volume of the piston ring is studied. Then, on the equivalent blow-by area calibrated in the present invention, the area size is changed to study the influence of the blow-by fault on the engine performance parameters. The simulation experiment results show that blow-by faults of different degrees have a certain impact on the normal operation of the operating engine. Brief Description of the Drawings

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0041] Figure 1 It is a calculation model diagram of the present invention;

[0042] Figure 2 It is a Simulink model of piston ring blow-by of the present invention;

[0043] Figure 3 It is a Simulink model of the whole engine of the present invention;

[0044] Figure 4 It is a comparison of the model simulation cylinder pressure and the measured cylinder pressure data under the calibrated blow-by area of the present invention;

[0045] Figure 5 It is the change of blow-by mass flow rate and scavenging mass flow rate under different loads of the present invention;

[0046] Figure 6 It is the change of blow-by energy loss and engine effective power under different loads of the present invention;

[0047] Figure 7 It is the change of the intercooler outlet temperature, the intercooler outlet temperature after mixing blow-by gas, and the intercooler outlet temperature rise caused by blow-by under different loads of the present invention;

[0048] Figure 8 It is the change of engine fuel consumption rate and power under different blow-by areas of the present invention;

[0049] Figure 9 It is the change of engine boost pressure and explosion pressure under different blow-by areas of the present invention;

[0050] Figure 10 It is the change of engine turbine speed and exhaust temperature under different blow-by areas of the present invention;

[0051] Figure 11The pressure change of the scavenging box and the exhaust pipe under different blow-by areas of the present invention;

[0052] Figure 12 The temperature change before and after the intercooler under different blow-by areas of the present invention;

[0053] Figure 13 The blow-by mass flow rate and mass loss change under different blow-by areas of the present invention. Detailed implementation manners

[0054] In order to enable those skilled in the art of this technology to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0055] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0056] As Figure 1 shown, the present invention provides a model-based method for simulating the blow-by fault of a marine engine cylinder. Based on the working characteristics of a 7G80MEC9 two-stroke diesel engine, a zero-dimensional thermodynamic model is established. Since the engine cylinder is an open system, the control volume method is used to build the model. The energy conservation, mass conservation, and ideal gas state equation are solved according to the change of the crank angle. The engine model consists of an engine cylinder model and its sub-models, which are used to describe the thermodynamic characteristics of the engine. The sub-models include combustion heat release, heat transfer, scavenging, exhaust, turbocharger, and air cooler models. The calculation model diagram of the present invention is as Figure 1 shown and includes the following steps:

[0057] Step 1: Construct an engine cylinder model based on the law of conservation of energy, the law of conservation of mass, and the ideal gas state equation. The engine cylinder model includes: constructing a heat release model, a heat transfer model, fuel properties, a piston ring blow-by model, and a gas exchange model, and deriving thermal performance parameters;

[0058] Step 2: Construct an engine intake and exhaust model based on the law of conservation of energy and the law of conservation of mass, and obtain the pressure, temperature, and mass parameters of the intake and exhaust;

[0059] Step 3: Construct an engine EGB model based on the map of the engine's supercharged air, and obtain the transient exhaust gas bypass mass flow rate;

[0060] Step 4: Construct a supercharger model of the engine based on the supercharger characteristic map of the engine, and obtain the mass flow rate, outlet temperature, and instantaneous corresponding rotational speed at the supercharger outlet;

[0061] Step 5: Construct an engine intercooler model according to a mathematical formula, and obtain the intercooler efficiency and outlet temperature; the mathematical formula is: T s =T co -η c ·(T co -T ws )

[0062] where, T s represents the outlet temperature surface of the intercooler, T co represents the outlet temperature of the compressor, η c represents the cooling coefficient, and the value range of η c is 0.7 to 0.9, and T ws represents the cooling medium temperature;

[0063] Step 6: Obtain the change signals of the engine's various performance parameters through model simulation calculations; compare the simulation calculation data of the engine's various performance parameters with the engine bench test data. If the error is less than 5%, it means that the simulation accuracy of the constructed zero-dimensional engine model meets the requirements of fault simulation, and proceed to Step 7; if the error is greater than or equal to 5%, re-execute Step 1; at the same time, observe the change rules, trends, and amplitudes of the change signals of the engine's various performance parameters, and analyze them to judge the degree of blow-by fault occurrence;

[0064] Step 7: Conduct in-cylinder piston ring blow-by fault simulation under different factors through the control variable method.

[0065] As a preferred implementation manner, in the present application, the heat release model describes the combustion process through a double Wibe function. The Wibe function is:

[0066]

[0067]

[0068]

[0069] Among them, χ represents the combustion percentage, and χ 1 represents the premixed combustion percentage, and χ 2 represents the diffusion combustion percentage, Q d represents the diffusion combustion fraction, θ z represents the start point of premixed combustion, m 1 and m 2 respectively represent the premixed combustion quality coefficient and the diffusion combustion quality coefficient, τ represents the premixed combustion lead angle, represents the start point of diffusion combustion;

[0070] As a preferred embodiment, in the present application, the heat transfer model is estimated by assuming the convective heat transfer of a constant value of the cylinder wall temperature, and the heat transfer model is constructed by the Woschni relation;

[0071] The Woschni relation is:

[0072]

[0073] where i = 1, 2, 3, respectively representing the cylinder head, the piston crown, and the cylinder liner; a w represents the instantaneous heat transfer coefficient calculated by the Woschni model; A w,i represents the heat transfer surface area exposed to the cylinder working medium; T Z represents the gas temperature in the cylinder; T w,i represents the average temperature of the heat transfer surface, which is a constant compared with T Z compared.

[0074] Furthermore, the gas exchange model is constructed based on the opening areas of the scavenging ports and the exhaust valves and the pressure difference between the scavenging chamber and the cylinder; the scavenging mass flow rate of the scavenging ports and the gas mass flow rate of the exhaust valves are estimated by the isentropic flow through the orifices;

[0075] The isentropic flow is described as when the pressures of the upstream and downstream sections of the orifice satisfy the equation the working medium is in a subcritical flow state, and the mass flow at this time is:

[0076]

[0077] When the pressures of the upstream and downstream sections of the orifice do not satisfy the equation the working medium is in a critical flow state, and the mass flow at this time is:

[0078]

[0079] Among them, p e and p z represent the pressure in the exhaust pipe and the in-cylinder pressure; μ is the flow coefficient, and A is the orifice flow area; R Z is the ideal gas constant; k is the adiabatic index of the working fluid.

[0080] Furthermore, the piston ring blow-by model estimates the blow-by mass flow rate and blow-by energy loss through the piston ring according to the orifice flow model of laminar flow and compressible flow; the orifice flow model is:

[0081]

[0082] Among them, C bb represents the blow-by flow coefficient; A bb represents the equivalent blow-by leakage area, and f m is obtained according to different blow-by flow states.

[0083] As a preferred implementation manner, in this application, an open system is adopted for both scavenging and the exhaust pipe in the intake and exhaust model; through the solution of energy conservation, mass conservation, and the ideal gas state equation, the pressure, temperature, mass, and gas composition in each crank angle step are obtained.

[0084] As a preferred implementation manner, in this application, the EGB model includes an EGB valve; the opening area of the EGB valve is controlled by an electronic control unit ECU, and the transient EGB mass flow rate is calculated according to the pressure difference and the opening area before and after the EGB valve.

[0085] As a preferred implementation manner, in this application, the supercharger model is derived from the relationship between the supercharger power and the outlet temperature by the pressure ratio, the compressor efficiency, and the mass flow rate.

[0086] Example 1

[0087] As Figure 5 , Figure 6 and Figure 7 shown, by controlling different engine operating loads, the piston ring blow-by mass flow rate, piston ring blow-by energy loss, scavenging mass flow rate, and the change of the engine effective power are observed to simulate the blow-by fault.

[0088] Figure 5 shows the variation of the blow-by mass flow rate and the scavenging flow rate with the load. It can be seen from Figure 6 that the blow-by mass flow rate gradually increases with the increase of the engine load, and the variation amplitude is between 0.4 and 0.6 kg. At the same time, with the increase of the engine load, the scavenging flow velocity also increases between 20 - 45 kg / s. The mass flow rate of blow-by is about 1% - 2% of the scavenging mass flow rate.

[0089] Figure 6 shows the blow-by energy loss of the piston ring under different loads. As the load increases, between 800–1200 kW, the blow-by energy loss gradually increases. The blow-by energy loss is mixed with the scavenging air compressed and cooled by the turbocharger and the air cooler respectively, thus heating the intake air.

[0090] Figure 7 shows the air temperature after the air cooler, after the heating effect of the blow-by, and the temperature rise due to the thermal effect of the blow-by. The air temperature after the air cooler and the temperature after the heating effect of the blow-by increase with the increase of the load. And the temperature rise caused by the heating effect of the blow-by on the intake air decreases with the increase of the load, and the temperature rise range is 20–30 K.

[0091] Example 2

[0092] As Figures 8 - 13 , by controlling the size of the blow-by area of the piston ring in the engine cylinder, the change of the engine operating parameters is observed.

[0093] Figures 8 - 13 provides the changes of the main performance parameters of the engine with the change of the blow-by area percentage (compared with the calibrated equivalent blow-by area). The SFOC increases with the increase of the blow-by area. When the blow-by area doubles, the SFOC will increase by 3%. On the contrary, when the blow-by area becomes zero, the SFOC will decrease by 3%.

[0094] However, it is unrealistic to completely avoid the blow-by mass and energy losses to prevent the piston ring from breaking due to excessive pressure difference between the upper and lower surfaces of the piston ring, especially for the top piston ring. As the blow-by area increases, the blow-by mass loss and energy loss almost increase linearly. As the blow-by area increases, the blow-by energy loss and the temperature of the gas entering the cylinder increase, which in turn leads to an increase in the cylinder temperature, exhaust temperature and turbine speed. While the compression pressure and the maximum combustion pressure decrease with the increase of the blow-by area. At the same time, the scavenging pressure, the exhaust receiver pressure and the air temperature after the air cooler increase slightly with the increase of the blow-by area.

[0095] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages and disadvantages of the embodiments. In the above embodiments of the present invention, the descriptions of each embodiment have their own emphases. For the parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments. In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A model - based method for simulating the cylinder blow - by fault of marine engines, based on the 7G80MEC9 two - stroke diesel engine, Characterized in that, It includes the following steps: Step 1: According to the law of conservation of energy, the law of conservation of mass, and the ideal gas state equation, construct an engine cylinder model. The engine cylinder model includes: constructing a heat release model, a heat transfer model, fuel properties, a piston ring blow - by model, and a gas exchange model, and deriving thermal performance parameters; Step 2: According to the law of conservation of energy and the law of conservation of mass, construct an engine intake and exhaust model to obtain the pressure, temperature, and mass parameters of the intake and exhaust; Step 3: According to the map of the engine's supercharged air, construct an engine EGB model to obtain the transient exhaust gas bypass mass flow rate; the EGB model includes an EGB valve; the opening area of the EGB valve is controlled by the electronic control unit ECU, and the transient EGB mass flow rate is calculated based on the pressure difference and the opening area before and after the EGB valve; Step 4: According to the characteristic map of the engine's supercharger, construct an engine supercharger model to obtain the mass flow rate, outlet temperature, and instantaneous corresponding speed at the supercharger outlet; Step Five: Construct a model of the engine intercooler according to the mathematical formula to obtain the intercooler efficiency and the outlet temperature; the mathematical formula is: T s = T co - η c ·(T co - T ws ) Among them, T s represents the temperature of the outlet surface of the intercooler, T co represents the outlet temperature of the compressor, η c represents the cooling coefficient, η c has a value range of 0.7 to 0.9, T ws represents the temperature of the cooling medium; Step 6: Through model simulation, calculate the change signals of each performance parameter of the engine; compare the simulation calculation data of each performance parameter of the engine with the engine bench test data. If the error is less than 5%, it means that the simulation accuracy of the constructed zero - dimensional whole - engine model of the engine meets the requirements of fault simulation, and execute Step 7; if the error is greater than or equal to 5%, re - execute Step 1; at the same time, observe the change rules, trends, and amplitudes of the change signals of each performance parameter of the engine, and analyze them to judge the degree of blow - by fault; Step 7: Through the method of controlling variables, simulate the cylinder piston ring blow - by fault under different factors.

2. A model - based method for simulating the cylinder blow - by fault of marine engines according to claim 1, Characterized in that, The heat release model describes the combustion process through a double Wibe function; The Wibe function is: Among them, χ represents the combustion percentage, χ 1 represents the premixed combustion percentage, χ 2 represents the diffusion combustion percentage, Q d represents the diffusion combustion fraction, θ z represents the starting point of premixed combustion, m 1 and m 2 respectively represent the premixed combustion quality coefficient and the diffusion combustion quality coefficient, τ represents the premixed combustion lead angle, represents the starting point of diffusion combustion.

3. A model - based method for simulating the cylinder blow - by fault of marine engines according to claim 1, Characterized in that, The heat transfer model is estimated by convective heat transfer assuming a constant value of the cylinder wall temperature, and the heat transfer model is constructed through the Woschni relation; The Woschni relation is: where \(i = 1, 2, 3\) respectively represent the cylinder head, the piston crown and the cylinder liner; \(a\) w represents the instantaneous heat transfer coefficient calculated by the Woschni model; \(A\) w,i represents the heat transfer surface area exposed to the cylinder working medium; \(T\) Z represents the gas temperature in the cylinder; \(T\) w,i represents the average temperature of the heat transfer surface, which is a constant compared to \(T\) Z and is a constant compared to \(T\).

4. A model - based method for simulating the cylinder blow - by fault of marine engines according to claim 1, Characterized in that, The gas exchange model is constructed based on the opening areas of the scavenging ports and exhaust valves and the pressure difference between the scavenging chamber and the cylinder; the scavenging mass flow rate of the scavenging ports and the gas mass flow rate of the exhaust valves are estimated by the isentropic flow of orifices; The isentropic flow is described as when the pressures at the upstream and downstream sections of the orifice satisfy the equation the working fluid is in a subcritical flow state, and the mass flow at this time is: When the pressures of the upstream and downstream cross-sections of the orifice do not satisfy the equation the working fluid is in a critical flow state, and the mass flow rate at this time is: where p e and p z represent the pressure in the exhaust pipe and the in-cylinder pressure; μ is the flow coefficient, A is the orifice flow area; R Z is the ideal gas constant; k is the adiabatic index of the working fluid.

5. A model - based method for simulating the cylinder blow - by fault of marine engines according to claim 1, Characterized in that, The piston ring blow - by model estimates the blow - by mass flow rate and blow - by energy loss through the piston rings according to the orifice flow model of laminar flow and compressible flow; the orifice flow model is: Among them, C bb represents the blow-by flow coefficient; A bb represents the equivalent area of blow-by leakage, f m is obtained according to different blow-by flow states.

6. A model - based method for simulating the cylinder blow - by fault of marine engines according to claim 1, Characterized in that, In the intake and exhaust model, both the scavenging and the exhaust pipe adopt an open system; by solving through the conservation of energy, conservation of mass, and the ideal gas state equation, the pressure, temperature, mass, and gas composition in each crank angle step are obtained.

7. A method for simulating the cylinder blow-by fault of a marine engine based on a model according to claim 1, characterized in that the supercharger model is derived from the relationship between the pressure ratio, compressor efficiency, and mass flow rate through the supercharger power and outlet temperature.

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