Thermal load analysis method and system for free piston type internal combustion engine generator

Abstract

The invention provides a thermal load analysis method and system for a free piston type internal combustion engine generator, and relates to the technical field of internal combustion engine generator cylinder body and cylinder cover stress analysis, and the method comprises the following steps: collecting cylinder pressure, piston displacement and cooling water temperature data under a calibration working condition, generating a smooth displacement curve by using Fourier series, and carrying out equidistant sampling; establishing a combustion model through Converge, using equidistant displacement data as a boundary condition of the model, calculating an in-cylinder average temperature and a heat exchange coefficient after calibration with cylinder pressure data, and determining a steady-state temperature boundary condition in combination with cooling water temperature data; constructing a cylinder cover system model, performing polyhedral mesh division, setting the boundary layer mesh thickness of a turbulence model, and calculating normal thermal resistance by using a thin shell heat transfer model; and based on the steady-state temperature boundary conditions, the heat load of the free piston type internal combustion engine generator is analyzed through a finite element method by means of the cylinder cover system model and the calculated steady-state temperature field.

Description

Technical Field

[0001] The invention relates to the technical field of stress analysis of a cylinder block and a cylinder head of an internal combustion generator, and in particular to a heat load analysis method and system for a free piston internal combustion generator. Background Art

[0002] With the rapid development of modernization and industrialization, environmental protection and energy efficiency have gradually become the focus of global attention. In this context, traditional internal combustion engines face huge challenges and need to meet more stringent environmental protection standards and energy efficiency requirements. The research and application of new power devices, especially FPLG (free piston internal combustion generator), has become a hot topic in the industry.

[0003] Traditional internal combustion engines use a crank-connecting rod mechanism to convert fossil energy into mechanical energy through the combustion chamber. This structure has gradually matured in long-term application and has high reliability. However, the working process of the internal combustion engine involves a complex mechanical transmission system and mainly relies on fossil fuels, resulting in low energy conversion efficiency and environmental pollution. In recent years, FPLG, as a new type of power device, has gradually attracted widespread attention from academia and industry due to its simple structure, variable compression ratio and adaptability to multiple fuel types.

[0004] However, due to the unique combustion mode of FPLG, which is completely different from traditional internal combustion engines, the research on the thermal load of its combustion chamber structure under multi-physical field coupling is still blank, which leads to the lack of effective evaluation of its structural reliability under working conditions, which may affect its safety, performance stability and durability for long-term operation. Summary of the invention

[0005] In order to solve the technical problem that FPLG has a unique combustion mode that is completely different from that of traditional internal combustion engines, so that the research on the thermal load of its combustion chamber structure under multi-physical field coupling is still blank, which leads to a lack of effective evaluation of its structural reliability under working conditions, thereby possibly affecting its safety, performance stability and durability for long-term operation, the present invention provides a thermal load analysis method and system for a free piston internal combustion generator.

[0006] The technical solution provided by the embodiment of the present invention is as follows:

[0007] First aspect:

[0008] An embodiment of the present invention provides a method for analyzing heat load of a free piston internal combustion generator, comprising:

[0009] S1: Collect cylinder pressure data, piston displacement data and cooling water temperature data under calibration conditions;

[0010] S2: performing curve fitting on the piston displacement data using Fourier series, and obtaining a smooth displacement curve by minimizing the error between the fitting curve and the original piston displacement data;

[0011] S3: performing equidistant sampling on the smooth displacement curve to obtain equidistant piston displacement data;

[0012] S4: Use Converge to build a combustion model with the same size as the actual prototype;

[0013] S5: using the equidistant piston displacement data as the boundary condition of the combustion model, calibrating with the cylinder pressure data, and calculating the average temperature in the cylinder and the average heat transfer coefficient in the cylinder;

[0014] S6: determining a steady-state temperature boundary condition according to the cooling water temperature data, the average temperature in the cylinder, and the average heat transfer coefficient in the cylinder;

[0015] S7: Construct a simplified model of the cylinder head system;

[0016] S8: performing polyhedral mesh division on the simplified model of the cylinder head system, setting a boundary layer mesh thickness adapted to the turbulence model, and setting a thin shell heat transfer model on the inner surface of the cylinder head and the cylinder body to calculate the normal thermal resistance, thereby forming a cylinder head system model;

[0017] S9: Based on the steady-state temperature boundary condition, calculate the steady-state temperature field through the cylinder head system model;

[0018] S10: Taking the steady-state temperature field as a heat load condition, the heat load of the free-piston internal combustion generator is analyzed by a finite element method.

[0019] Second aspect:

[0020] An embodiment of the present invention provides a thermal load analysis system for a free piston internal combustion generator, comprising:

[0021] processor;

[0022] A memory having computer-readable instructions stored thereon, wherein when the computer-readable instructions are executed by the processor, the thermal load analysis method of the free-piston internal combustion generator as described in the first aspect is implemented.

[0023] The third aspect:

[0024] An embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the method for analyzing the thermal load of a free-piston internal combustion generator as described in the first aspect is implemented.

[0025] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0026] (1) In the present invention, the piston displacement data is curve-fitted by using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions, combining with cylinder pressure data for calibration, calculating the average temperature and heat transfer coefficient in the cylinder, and determining the steady-state temperature boundary conditions in combination with cooling water temperature data. Based on these boundary conditions, the heat load is analyzed by the finite element method, thereby providing effective support for the reliability evaluation of the combustion chamber structure under the unique combustion mode of FPLG, solving the gap in heat load research under multi-physical field coupling, and effectively conducting heat load research and structural reliability evaluation, thereby improving the safety and performance stability of FPLG. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A schematic flow chart of a heat load analysis method for a free-piston internal combustion generator provided in an embodiment of the present invention;

[0029] Figure 2 A schematic structural diagram of a thermal load analysis system for a free-piston internal combustion generator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0031] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0032] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they intend to express are the same. "of", "corresponding, relevant" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they intend to express are the same.

[0033] In the embodiments of the present invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are consistent.

[0034] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0035] Reference Manual Attached Figure 1 , showing a schematic flow chart of a thermal load analysis method for a free-piston internal combustion generator provided in an embodiment of the present invention.

[0036] The embodiment of the present invention provides a method for analyzing the thermal load of a free piston internal combustion generator. The method can be implemented by a thermal load analysis device for a free piston internal combustion generator. The thermal load analysis device for a free piston internal combustion generator can be a terminal or a server. The processing flow of the method for analyzing the thermal load of a free piston internal combustion generator can include the following steps:

[0037] S1: Collect cylinder pressure data, piston displacement data and cooling water temperature data under calibration conditions.

[0038] Among them, calibration conditions refer to the process of evaluating and adjusting the performance of equipment or systems under specific experimental or test conditions. These conditions usually include ambient temperature, pressure, flow, and load to ensure the accuracy and repeatability of the measurement results.

[0039] Specifically, a cylinder pressure sensor is installed to record the pressure changes in the cylinder in real time, and a displacement sensor is used to monitor the displacement of the piston.

[0040] In the present invention, by installing a cylinder pressure sensor and a displacement sensor, the changes in the cylinder pressure and the piston displacement can be recorded in real time, providing accurate data support. At the same time, by measuring under the calibration conditions, the interference of external factors on the data can be eliminated, ensuring the accuracy and reliability of the collected data.

[0041] S2: The piston displacement data is curve-fitted using Fourier series, and a smooth displacement curve is obtained by minimizing the error between the fitting curve and the original piston displacement data.

[0042] Among them, Fourier series is an important tool in mathematics, which is used to express periodic functions as the sum of a series of sine and cosine functions. It is widely used in signal processing, audio analysis, image processing, heat conduction and other fields.

[0043] It should be noted that the original displacement data needs to be filtered due to the presence of interference.

[0044] In a possible implementation, S2 specifically includes:

[0045] S201: Use Fourier series to perform curve fitting on the piston displacement data, and optimize the error between the fitting curve and the original piston displacement data by the least square method to obtain the optimal Fourier coefficient:

[0046]

[0047] Among them, S represents the square of error, N represents the amount of displacement data, and t i represents the time value of the data point, M represents the number of Fourier series terms, f0 represents the fundamental frequency, y i Indicates the actual displacement of the data point, a0, a n , b n All represent Fourier coefficients.

[0048] In the present invention, the error between the fitting curve and the original data is optimized by the least square method, and the optimal Fourier coefficient can be obtained to ensure the best fitting effect and further improve the reliability of the model. At the same time, the Fourier series has strong adaptability and can process signals with different frequency components. It is suitable for various types of piston motion data and adapts to different working conditions.

[0049] S202: Obtain a smooth displacement curve through a Fourier fitting method according to the optimal Fourier coefficients.

[0050] In a possible implementation, the smooth displacement curve is specifically:

[0051]

[0052] Among them, y(t) represents the smooth displacement curve, M represents the number of Fourier series terms, f0 represents the fundamental frequency, t represents the independent variable time, a0, a n , b n All represent Fourier coefficients.

[0053] In the present invention, by smoothing the displacement curve, the subsequent calculation and analysis process can be simplified, the calculation complexity can be reduced, and the accuracy and reliability of data processing can be improved.

[0054] S3: Perform equidistant sampling on the smooth displacement curve to obtain equidistant piston displacement data.

[0055] Specifically, the fitted displacement-time function is sampled at equal intervals to obtain uniformly distributed displacement data points.

[0056] In the present invention, uniformly distributed displacement data points can be obtained by equidistant sampling, ensuring the consistency of data on the time axis and making subsequent analysis more accurate. At the same time, uniform sampling helps to eliminate potential biases caused by data concentration or sparseness, so that each data point has equal importance in the analysis.

[0057] S4: Use Converge to create a combustion model with the same size as the actual prototype.

[0058] Among them, Converge is a software specifically used for simulating fluid dynamics (CFD), also known as Converge fluid simulation software, which is widely used in the fields of internal combustion engines, injectors, combustion and heat conduction. The software can handle complex flow and heat transfer problems through efficient calculation methods and flexible grid generation technology.

[0059] Specifically, the combustion chamber structure was extracted in a 1:1 ratio with the physical prototype using SolidWorks software, exported to STL format, and imported into Converge to check whether the geometric model had defects, and then set the model parameters to ensure that the boundary conditions were the same as those of the physical prototype under the calibration conditions. In this process, by adjusting the model initial condition parameters, the cylinder pressure curve of the simulation results was highly consistent with the actual measured cylinder pressure curve, thereby improving the reliability of the model.

[0060] In the present invention, the combustion chamber structure created by SolidWorks at a 1:1 ratio ensures that the model is highly consistent with the actual prototype in size and shape, providing an accurate basis for subsequent simulation. At the same time, through a meticulous construction and verification process, the deviation between the model and the actual situation can be reduced, significantly improving the accuracy and reliability of the simulation.

[0061] S5: Using the equidistant piston displacement data as the boundary condition of the combustion model, the average in-cylinder temperature and the average in-cylinder heat transfer coefficient are calculated by calibration with the cylinder pressure data.

[0062] Among them, the average heat transfer coefficient (Average Heat Transfer Coefficient) describes the relationship between the amount of heat transferred per unit area per unit time and the temperature difference during heat transfer. It is an important indicator for evaluating the heat transfer capacity within a system and is usually used in the fields of engineering thermodynamics, heat transfer and fluid dynamics.

[0063] In a possible implementation manner, the calculation formula for the average temperature in the cylinder in S5 is:

[0064]

[0065] Among them, T mrepresents the average temperature of the gas in the cylinder, T represents the cycle period, h g Represents the transient heat transfer coefficient in the cylinder, T g represents the transient temperature of the gas in the cylinder, and t represents the time.

[0066] In a possible implementation manner, the calculation formula for the average heat transfer coefficient in the cylinder in S5 is:

[0067]

[0068] Among them, h m represents the average heat transfer coefficient in the cylinder, T represents the cycle period, h g represents the transient heat transfer coefficient in the cylinder, and t represents time.

[0069] In the present invention, the piston displacement data sampled at equal intervals ensures the consistency of the time step and spatial distribution when the boundary conditions are applied in the combustion model. This can more accurately reflect the impact of the actual piston movement on the combustion process and heat transfer. At the same time, by integrating and averaging the transient heat transfer coefficient and transient temperature in a cycle in the formula, more comprehensive temperature information can be obtained.

[0070] Furthermore, by comprehensively utilizing the piston's equidistant sampling data and cylinder pressure data calibration, more accurate in-cylinder temperature and heat transfer coefficient can be obtained, which can not only reflect the actual combustion and heat transfer process, but also simplify complex transient analysis, providing reliable data support for the thermal design and optimization of the internal combustion engine system.

[0071] S6: Determine the steady-state temperature boundary condition based on the cooling water temperature data, the average temperature in the cylinder, and the average heat transfer coefficient in the cylinder.

[0072] In a possible implementation, S6 specifically includes:

[0073] It should be noted that the heat transfer boundary conditions on the cylinder body surface are the third type of boundary conditions. Considering that the heat transfer amount on the cylinder body heating surface varies with space, dimensionless parameters are used to calculate the corresponding temperature distribution and heat transfer coefficient distribution at different spatial positions on the cylinder body heating surface.

[0074] S601: Determine the temperature distribution and heat transfer coefficient distribution at different spatial positions on the cylinder body heating surface based on the average temperature in the cylinder:

[0075] If 0≤β≤1

[0076]

[0077] If β>1,

[0078]

[0079] k1=0.537(S / D) 0.24 ,k2=1.45k1,k3=D / S

[0080] Where, β represents the ratio of the distance from the piston to TDC to the piston stroke, h β represents the heat transfer coefficient related to the piston position β, T β represents the temperature associated with the piston position β, h m represents the average heat transfer coefficient in the cylinder, k1, k2, k3 are dimensionless parameters, T m It represents the average temperature of the gas in the cylinder, S represents the piston stroke, and D represents the cylinder diameter.

[0081] Specifically, considering that the required gas temperature is a transient temperature, in order to simplify the solution of the heat load, the steady-state equation is used to solve the thermal stress model. Therefore, it is necessary to average the transient temperature and the transient heat transfer coefficient, calculate the spatially distributed steady-state temperature boundary conditions, and thus impose constraints in the model.

[0082] In the present invention, by accurately calculating the temperature and heat transfer coefficient at different positions, suitable boundary conditions can be provided for cylinder structures with complex geometric shapes. This helps to truly reproduce the actual conditions of complex flow and heat transfer in numerical simulation, thereby improving the credibility of the model.

[0083] S602: Calculate the heat transfer coefficient distribution at different spatial positions on the cylinder head heating surface based on the average temperature in the cylinder:

[0084] h r =h m (-1.9401x 3 +1.1356x 2 +0.6834x+0.602)

[0085] x=r / R

[0086] Among them, h r It represents the heat transfer coefficient distribution at different spatial positions on the cylinder head heating surface, h m represents the average heat transfer coefficient in the cylinder, x represents a dimensionless parameter, r represents the radius from the combustion chamber to the center of the circle, and R represents the radius of the combustion chamber.

[0087] Specifically, the heat transfer boundary conditions on the inner surface of the cylinder head are the third type of boundary conditions. Considering that the heat flux on the heated surface of the cylinder head has different distributions with spatial changes, dimensionless parameters are used to calculate the corresponding heat transfer coefficient distribution at different spatial positions on the heated surface of the cylinder head.

[0088] S603: The temperature distribution and heat transfer coefficient distribution results at different spatial positions on the heating surface of the cylinder block and the heat transfer coefficient distribution results at different spatial positions on the heating surface of the cylinder head are used as steady-state temperature boundary conditions.

[0089] In the present invention, the temperature distribution and heat transfer coefficient distribution of the cylinder block and cylinder head are calculated and used as steady-state temperature boundary conditions, which can accurately reflect the spatial variation of heat transfer in the cylinder, effectively simplify the processing of transient problems, and improve the accuracy, stability and efficiency of numerical calculations.

[0090] S7: Build a simplified model of the cylinder head system.

[0091] S8: Perform polyhedral meshing on the simplified model of the cylinder head system, set the boundary layer mesh thickness that is suitable for the turbulence model, and set a thin shell heat transfer model on the inner surface of the cylinder head and the cylinder body to calculate the normal thermal resistance and form a cylinder head system model.

[0092] Among them, normal thermal resistance is the thermal resistance perpendicular to the surface or layer structure of an object during heat conduction. It is a parameter that measures the degree of resistance of a material to heat transfer in the direction perpendicular to the heat flow, and is often used to describe the thermal insulation performance of materials such as films and coatings.

[0093] Specifically, the assembly model is divided into polyhedral meshes in fluent meshing, and the topology is shared between fluid and solid, and between solid and solid, to ensure the continuity of energy transmission.

[0094] It should be noted that different fuels have different requirements for the material and thickness of the cylinder coating. In order to repeatedly divide the coating grid on the wall, the thickness and material of the coating and adhesive layer are defined, and thin shell heat transfer is used instead of coating grid division for calculation to analyze the heat transfer performance of the coating.

[0095] In the present invention, a thin shell heat transfer model is used instead of the actual coating meshing, which significantly reduces the number and complexity of meshes and reduces the resource consumption and time cost of numerical calculations.

[0096] In a possible implementation, the calculation formula of normal thermal resistance is:

[0097]

[0098] Among them, R n represents normal thermal resistance, d represents coating thickness, k represents material thermal conductivity, and A represents heat flow cross-sectional area.

[0099] In the present invention, the polyhedral grid has stronger geometric adaptability and can generate high-quality grids on complex geometric surfaces to ensure the continuity of energy transfer between fluids and solids. At the same time, the normal thermal resistance mainly describes the thermal resistance of the coating in the direction of heat flow. The thin shell heat transfer model can accurately calculate the normal thermal resistance according to the thickness and material properties, so that the numerical model can accurately reflect the thermal insulation effect of the coating, effectively reduce the heat loss of the cylinder wall, and improve the overall efficiency of the engine.

[0100] S9: Based on the steady-state temperature boundary conditions, the steady-state temperature field is calculated through the cylinder head system model.

[0101] Among them, the cylinder head system model is a simplified or detailed description of the geometry, material properties, thermodynamics and structural properties of the engine cylinder head and cylinder block, which is used for numerical simulation and analysis.

[0102] Among them, the steady-state temperature field refers to the temperature distribution formed when the temperature of each point in the system does not change over time. In a steady-state temperature field, the temperature value of any point in the system is constant, that is, it does not change over time. Steady-state temperature fields often appear in systems that have reached thermal equilibrium, when heat conduction and heat exchange between points remain balanced.

[0103] In a possible implementation manner, calculating the steady-state temperature field in S9 specifically includes:

[0104] S901: Perform polyhedral mesh division on the solid and fluid regions, and calculate the flow field and temperature field using the finite volume method based on the steady-state temperature boundary conditions.

[0105] Among them, the finite volume method (FVM) is a numerical method for solving partial differential equations, especially suitable for numerical calculations of fluid mechanics and heat conduction problems. It divides the calculation area into multiple finite control volumes (grid units), applies conservation equations on each control volume, and thus obtains the distribution of physical quantities in the entire calculation area.

[0106] In the present invention, the finite volume method can be used to process complex turbulent flow fields. By setting appropriate boundary layer grid thickness and dimensionless distance values, the flow characteristics of turbulence can be accurately simulated, especially the thermal boundary layer and velocity boundary layer in the near-wall area. This accurate turbulence simulation helps to improve the prediction accuracy of the flow and heat transfer process in the cooling channel.

[0107] S902: Obtain the steady-state temperature field through fluid-solid coupling field calculation.

[0108] Among them, Fluid-Structure Interaction (FSI) refers to a computational method that simultaneously considers the interaction between fluid and solid in numerical simulation. It combines fluid mechanics and solid mechanics to solve complex problems of fluid-solid interaction. The goal of fluid-structure interaction is to simulate the force of fluid on solid structure (such as pressure, shear force, etc.) and the effect of deformation of solid structure on fluid flow.

[0109] Specifically, since the fluid-solid coupling model is relatively complex, the solid and fluid regions are meshed with polyhedrons, and the finite volume method is used to calculate the flow field and temperature field. The boundary layer mesh thickness is re-divided according to the dimensionless distance value of the fluid near the wall boundary layer to obtain the dimensionless distance value of the boundary layer that satisfies the turbulence model used. The fluid-solid coupling field is calculated to obtain a more accurate temperature field.

[0110] In the present invention, fluid-solid coupling refers to the interaction between the fluid domain and the solid domain. Through fluid-solid coupling, the heat exchange process between the coolant and the cylinder head and cylinder block materials can be simulated to accurately reflect the heat transfer phenomenon under actual working conditions. In an internal combustion engine, the coolant takes away the heat generated during the combustion process through the cooling channels in the cylinder head and cylinder block, and this heat is conducted to the coolant through the cylinder head and cylinder block materials. The calculation of the fluid-solid coupling field can accurately capture the dynamic characteristics of these heat exchanges and improve the accuracy of the temperature field simulation.

[0111] S10: Using the steady-state temperature field as the heat load condition, the heat load of the free-piston internal combustion generator is analyzed by the finite element method.

[0112] Among them, the finite element method (FEM) is a powerful numerical analysis technology used to solve complex partial differential equations and integral equations, especially in the fields of solid mechanics, heat conduction, electromagnetism, fluid mechanics, etc. The finite element method divides the complex solution domain into many small, simple units and performs local approximation in each unit, thereby converting the original complex global problem into a simple local problem.

[0113] In a possible implementation, S10 specifically includes:

[0114] S101: performing interpolation processing on the steady-state temperature field.

[0115] In the present invention, by interpolating the steady-state temperature field, the discrete temperature field data can be smoothed to generate a more accurate temperature distribution model. This processing can eliminate the discreteness and discontinuity in the data, making the temperature field smoother and more continuous, thereby improving the accuracy when used as a heat load condition.

[0116] S102: Using the interpolated steady-state temperature field as a heat load condition, the heat load of the free-piston internal combustion generator is analyzed by a finite element method.

[0117] Optionally, in order to avoid stress concentration, multiple faces are selected to apply displacement constraints in different directions to achieve the purpose of fixation.

[0118] In the present invention, by applying displacement constraints in different directions on multiple surfaces, the direction of displacement can be limited, so that the structural stress is more evenly distributed, the local stress concentration phenomenon is reduced, and excessive stress and fatigue damage of the material can be avoided. At the same time, by applying reasonable displacement constraints, the overall displacement change can be limited, and the influence of thermal deformation on the structural stress distribution can be reduced.

[0119] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0120] (1) In the present invention, the piston displacement data is curve-fitted by using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions, combining with cylinder pressure data for calibration, calculating the average temperature and heat transfer coefficient in the cylinder, and determining the steady-state temperature boundary conditions in combination with cooling water temperature data. Based on these boundary conditions, the heat load is analyzed by the finite element method, thereby providing effective support for the reliability evaluation of the combustion chamber structure under the unique combustion mode of FPLG, solving the gap in heat load research under multi-physical field coupling, and effectively conducting heat load research and structural reliability evaluation, thereby improving the safety and performance stability of FPLG.

[0121] Reference Manual Attached Figure 2 , showing a structural schematic diagram of a thermal load analysis system for a free piston internal combustion generator provided by the present invention.

[0122] The present invention further provides a free piston internal combustion generator heat load analysis system 20, which is applied to the above-mentioned free piston internal combustion generator heat load analysis method, comprising:

[0123] Processor 201;

[0124] The memory 202 stores computer-readable instructions, and when the computer-readable instructions are executed by the processor 201, the thermal load analysis method of the free-piston internal combustion generator as described in the method embodiment is implemented.

[0125] The thermal load analysis system 20 for a free-piston internal combustion generator provided by the present invention can execute the above-mentioned thermal load analysis method for a free-piston internal combustion generator and achieve the same or similar technical effects. To avoid repetition, the present invention will not elaborate on them.

[0126] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0127] (1) In the present invention, the piston displacement data is curve-fitted by using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions, combining with cylinder pressure data for calibration, calculating the average temperature and heat transfer coefficient in the cylinder, and determining the steady-state temperature boundary conditions in combination with cooling water temperature data. Based on these boundary conditions, the heat load is analyzed by the finite element method, thereby providing effective support for the reliability evaluation of the combustion chamber structure under the unique combustion mode of FPLG, solving the gap in heat load research under multi-physical field coupling, and effectively conducting heat load research and structural reliability evaluation, thereby improving the safety and performance stability of FPLG.

[0128] It should be understood that the processor in the embodiment of the present invention may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0129] It should also be understood that the memory in the embodiments of the present invention may be a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories. Among them, the non-volatile memory may be a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), which is used as an external cache. By way of example and not limitation, many forms of random access memory (RAM) are available, such as static RAM (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous link DRAM (SLDRAM), and direct rambus RAM (DR RAM).

[0130] The above embodiments can be implemented in whole or in part by software, hardware (such as circuits), firmware or any other combination. When implemented by software, the above embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center by wired (such as infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server or data center that contains one or more available media sets. The available medium can be a magnetic medium (for example, a floppy disk, a hard disk, a tape), an optical medium (for example, a DVD), or a semiconductor medium. The semiconductor medium can be a solid-state hard disk.

[0131] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0132] In the present invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, c can be single or multiple.

[0133] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0134] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0135] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described equipment, devices and units can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0136] In the several embodiments provided by the present invention, it should be understood that the disclosed devices, apparatuses and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0137] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0138] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0139] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0140] An embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the method for analyzing the thermal load of a free-piston internal combustion generator as described in the method embodiment is implemented.

[0141] A computer-readable storage medium provided by the present invention can implement the steps and effects of the thermal load analysis method for a free-piston internal combustion generator of the above method embodiment, and to avoid repetition, the present invention will not elaborate on them.

[0142] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0143] (1) In the present invention, the piston displacement data is curve-fitted by using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions, combining with cylinder pressure data for calibration, calculating the average temperature and heat transfer coefficient in the cylinder, and determining the steady-state temperature boundary conditions in combination with cooling water temperature data. Based on these boundary conditions, the heat load is analyzed by the finite element method, thereby providing effective support for the reliability evaluation of the combustion chamber structure under the unique combustion mode of FPLG, solving the gap in heat load research under multi-physical field coupling, and effectively conducting heat load research and structural reliability evaluation, thereby improving the safety and performance stability of FPLG.

[0144] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0145] There are a few points to note:

[0146] (1) The drawings of the embodiments of the present invention only relate to the structures related to the embodiments of the present invention, and other structures may refer to the general design.

[0147] (2) For the sake of clarity, in the drawings used to describe the embodiments of the present invention, the thickness of the layers or regions is exaggerated or reduced, that is, these drawings are not drawn according to the actual scale. It is understood that when an element such as a layer, film, region or substrate is referred to as being "on" or "under" another element, the element may be "directly" "on" or "under" the other element or there may be intermediate elements.

[0148] (3) In the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to obtain new embodiments.

[0149] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for analyzing the thermal load of a free piston internal combustion generator, characterized in that: include: S1: Collect cylinder pressure data, piston displacement data and cooling water temperature data under calibration conditions; S2: performing curve fitting on the piston displacement data using Fourier series, and obtaining a smooth displacement curve by minimizing the error between the fitting curve and the original piston displacement data; S3: performing equidistant sampling on the smooth displacement curve to obtain equidistant piston displacement data; S4: Use Converge to build a combustion model with the same size as the actual prototype; S5: using the equidistant piston displacement data as the boundary condition of the combustion model, calibrating with the cylinder pressure data, and calculating the average temperature in the cylinder and the average heat transfer coefficient in the cylinder; S6: determining a steady-state temperature boundary condition according to the cooling water temperature data, the average temperature in the cylinder, and the average heat transfer coefficient in the cylinder; S7: Construct a simplified model of the cylinder head system; S8: performing polyhedral mesh division on the simplified model of the cylinder head system, setting a boundary layer mesh thickness adapted to the turbulence model, and setting a thin shell heat transfer model on the inner surface of the cylinder head and the cylinder body to calculate the normal thermal resistance, thereby forming a cylinder head system model; S9: Based on the steady-state temperature boundary condition, calculate the steady-state temperature field through the cylinder head system model; S10: Taking the steady-state temperature field as a heat load condition, the heat load of the free-piston internal combustion generator is analyzed by a finite element method.

2. The heat load analysis method of a free piston internal combustion generator according to claim 1, characterized in that: The S2 specifically includes: S201: Perform curve fitting on the piston displacement data using Fourier series, and optimize the error between the fitting curve and the original piston displacement data using the least squares method to obtain the optimal Fourier coefficient: Among them, S represents the square of error, N represents the amount of displacement data, and t i represents the time value of the data point, M represents the number of Fourier series terms, f0 represents the fundamental frequency, y i Indicates the actual displacement of the data point, a0, a n , b n All represent Fourier coefficients; S202: Obtain a smooth displacement curve through a Fourier fitting method according to the optimal Fourier coefficients.

3. The heat load analysis method of a free piston internal combustion generator according to claim 2, characterized in that: The smooth displacement curve is specifically: Among them, y(t) represents the smooth displacement curve, M represents the number of Fourier series terms, f0 represents the fundamental frequency, t represents the independent variable time, a0, a n , b n All represent Fourier coefficients.

4. The heat load analysis method of a free piston internal combustion generator according to claim 1, characterized in that: The calculation formula of the average temperature in the cylinder in S5 is: Among them, T m represents the average temperature of the gas in the cylinder, T represents the cycle period, h g Represents the transient heat transfer coefficient in the cylinder, T g represents the transient temperature of the gas in the cylinder, and t represents the time.

5. The heat load analysis method of a free piston internal combustion generator according to claim 1, characterized in that: The calculation formula of the average heat transfer coefficient in the cylinder in S5 is: Among them, h m represents the average heat transfer coefficient in the cylinder, T represents the cycle period, h g represents the transient heat transfer coefficient in the cylinder, and t represents time.

6. The heat load analysis method of a free piston internal combustion generator according to claim 1, characterized in that: The S6 specifically includes: S601: Determine the temperature distribution and heat transfer coefficient distribution at different spatial positions on the heating surface of the cylinder body according to the average temperature in the cylinder: If 0≤β≤1 Ifβ>1, k1=0.537(S / D) 0.24 ,k2=1.45k1,k3=D / S Where, β represents the ratio of the distance from the piston to TDC to the piston stroke, h β represents the heat transfer coefficient related to the piston position β, T β represents the temperature associated with the piston position β, h m represents the average heat transfer coefficient in the cylinder, k1, k2, k3 are dimensionless parameters, T m It represents the average temperature of the gas in the cylinder, S represents the piston stroke, and D represents the cylinder diameter; S602: Calculate the heat transfer coefficient distribution at different spatial positions on the heating surface of the cylinder head according to the average temperature in the cylinder: h r =h m (-1.9401x 3 +1.1356x 2 +0.6834x+0.602) x=r / R Among them, h r It represents the heat transfer coefficient distribution at different spatial positions on the cylinder head heating surface, h m represents the average heat transfer coefficient in the cylinder, x represents a dimensionless parameter, r represents the radius from the combustion chamber to the center of the circle, and R represents the radius of the combustion chamber; S603: The temperature distribution and heat transfer coefficient distribution results at different spatial positions on the heating surface of the cylinder block and the heat transfer coefficient distribution results at different spatial positions on the heating surface of the cylinder head are used as steady-state temperature boundary conditions.

7. The heat load analysis method of a free piston internal combustion generator according to claim 1, characterized in that: The calculation formula of the normal thermal resistance is: Among them, R n represents normal thermal resistance, d represents coating thickness, k represents material thermal conductivity, and A represents heat flow cross-sectional area.

8. The heat load analysis method of a free piston internal combustion generator according to claim 1, characterized in that: The calculation of the steady-state temperature field in S9 specifically includes: S901: performing polyhedral mesh division on the solid and fluid regions, and calculating the flow field and the temperature field using the finite volume method based on the steady-state temperature boundary condition; S902: Obtain the steady-state temperature field through fluid-solid coupling field calculation.

9. The heat load analysis method of a free piston internal combustion generator according to claim 1, characterized in that: The S10 specifically includes: S101: performing interpolation processing on the steady-state temperature field; S102: Using the interpolated steady-state temperature field as a heat load condition, the heat load of the free-piston internal combustion generator is analyzed by a finite element method.

10. A thermal load analysis system for a free piston internal combustion generator, characterized in that: include: processor; A memory having computer-readable instructions stored thereon, wherein when the computer-readable instructions are executed by the processor, the thermal load analysis method of the free-piston internal combustion generator according to any one of claims 1 to 9 is implemented.

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