A thermal load analysis method and system for a free-piston internal combustion generator

Abstract

The present invention provides a thermal load analysis method and system for a free-piston internal combustion generator, which relates to the technical field of stress analysis of a cylinder block and a cylinder head of an internal combustion generator. The method comprises: collecting cylinder pressure, piston displacement, and cooling water temperature data under calibration conditions, generating a smooth displacement curve using a Fourier series, and performing equidistant sampling; establishing a combustion model through Converge, using the equidistant displacement data as the boundary conditions of the model, calculating the average temperature and heat transfer coefficient in the cylinder after calibration with the cylinder pressure data, and determining the steady-state temperature boundary conditions in combination with the cooling water temperature data; constructing a cylinder head system model, performing polyhedral meshing, setting the boundary layer mesh thickness of the turbulence model, and calculating the normal thermal resistance using a thin shell heat transfer model; and analyzing the thermal load of the free-piston internal combustion generator through a finite element method based on the steady-state temperature boundary conditions and the calculated steady-state temperature field using the cylinder head system model.

Description

Technical Field

[0001] The present invention relates to the technical field of stress analysis of a cylinder block and a cylinder cover of an internal combustion generator, and in particular to a thermal 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 become increasingly important global concerns. Against this backdrop, traditional internal combustion engines face significant challenges, needing to meet increasingly stringent environmental standards and energy efficiency requirements. The research and application of novel power plants, particularly free-piston internal combustion generators (FPLGs), has become a hot topic in the industry.

[0003] Traditional internal combustion engines utilize a crank-connecting rod mechanism to convert fossil fuels into mechanical energy through the combustion chamber. This structure has matured over time and boasts high reliability. However, the operation of internal combustion engines involves a complex mechanical transmission system and relies primarily on fossil fuels, resulting in low energy conversion efficiency and environmental pollution. In recent years, FPLG, as a new type of power unit, has 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. This leads to a lack of effective evaluation of its structural reliability under working conditions, which may affect its safety, performance stability and durability during long-term operation. Summary of the Invention

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

[0006] The technical solutions provided by the embodiments of the present invention are as follows:

[0007] First aspect:

[0008] An embodiment of the present invention provides a method for analyzing the thermal 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: Using Converge, a combustion model with the same size as the actual prototype is created.

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

[0014] S6: determining a 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;

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

[0016] S8: performing polyhedral meshing 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: Calculating a steady-state temperature field using the cylinder head system model based on the steady-state temperature boundary condition;

[0018] S10: Analyze the thermal load of the free-piston internal combustion generator using the finite element method, taking the steady-state temperature field as a thermal load condition.

[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 using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions. The model is calibrated in combination with cylinder pressure data, and the average temperature and heat transfer coefficient in the cylinder are calculated. The steady-state temperature boundary conditions are determined 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, effectively conducting heat load research and structural reliability evaluation, and 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 an "exemplary" in the present invention should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner. Furthermore, in the embodiments of the present invention, "and / or" can mean both or either of the two.

[0032] In the embodiments of the present invention, the terms "image" and "picture" may be used interchangeably. It should be noted that, when the distinction between them is not emphasized, their intended meanings are the same. The terms "of," "corresponding," and "corresponding" may be used interchangeably. It should be noted that, when the distinction between them is not emphasized, their intended meanings 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 form such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

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

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

[0036] An embodiment of the present invention provides a method for analyzing the thermal load of a free-piston internal combustion generator. This method can be implemented using a thermal load analysis device for a free-piston internal combustion generator, which can be a terminal or a server. The process flow of the thermal load analysis method for a free-piston internal combustion generator may include the following steps:

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

[0038] Calibration is the process of evaluating and adjusting the performance of a device or system under specific experimental or test conditions. These conditions typically include ambient temperature, pressure, flow rate, and load to ensure the accuracy and repeatability of 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 this invention, by installing a cylinder pressure sensor and a displacement sensor, changes in cylinder pressure and piston displacement can be recorded in real time, providing accurate data support. Furthermore, by performing measurements under calibrated working conditions, external factors can be eliminated from interfering with the data, ensuring the accuracy and reliability of the collected data.

[0041] S2: Use Fourier series to perform curve fitting on the piston displacement data, and obtain a smooth displacement curve by minimizing the error between the fitting curve and the original piston displacement data.

[0042] The Fourier series is an important mathematical tool used to represent periodic functions as the sum 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 using the least squares method to obtain the optimal Fourier coefficient:

[0046]

[0047] Among them, S represents the square of error, N represents the amount of displacement data, 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 Both represent Fourier coefficients.

[0048] In this paper, the error between the fitted curve and the original data is optimized using the least squares method to obtain the optimal Fourier coefficients, ensuring the best fitting effect and further improving the reliability of the model. Furthermore, the Fourier series is highly adaptable and can process signals with different frequency components, making it suitable for a variety of piston motion data and adapting to different operating conditions.

[0049] S202: Obtain a smooth displacement curve using 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 Both 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 this invention, evenly spaced sampling is used to obtain evenly distributed displacement data points, ensuring data consistency along the time axis and making subsequent analysis more accurate. Uniform sampling also helps eliminate potential bias caused by data concentration or sparsity, ensuring 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] Converge, also known as Converge fluid simulation software, is specialized in fluid dynamics (CFD) simulations and is widely used in fields such as internal combustion engines, fuel injectors, combustion, and heat transfer. Through efficient computational methods and flexible mesh generation technology, the software can handle complex flow and heat transfer problems.

[0059] Specifically, the combustion chamber structure was extracted using SolidWorks at a 1:1 scale with the physical prototype and exported to STL format. The STL file was then imported into Converge, where the geometric model was inspected for defects. The model parameters were then set to ensure the boundary conditions were identical to those of the physical prototype under calibration conditions. During this process, the model's initial condition parameters were adjusted to ensure that the cylinder pressure curves from the simulations were highly consistent with the measured ones, thereby improving the model's reliability.

[0060] In this invention, the combustion chamber structure was created in SolidWorks at a 1:1 scale, ensuring a high degree of consistency in size and shape between the model and the actual prototype, providing an accurate foundation for subsequent simulations. Furthermore, a meticulous construction and verification process reduced deviations between the model and actual conditions, 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, calibrate it with the cylinder pressure data to calculate the average in-cylinder temperature and the average in-cylinder heat transfer coefficient.

[0062] The average heat transfer coefficient (AHT) 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 a system's heat transfer capacity and is commonly used in fields such as engineering thermodynamics, heat transfer, and fluid dynamics.

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

[0064]

[0065] Among them, T mIndicates the average temperature of the gas in the cylinder, T indicates the cycle period, h g Indicates 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 one possible implementation, 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 this invention, equidistantly sampled piston displacement data ensures consistency in time step length and spatial distribution when applying boundary conditions in the combustion model. This more accurately reflects the impact of actual piston motion on the combustion process and heat transfer. Furthermore, by integrating and averaging the transient heat transfer coefficient and transient temperature within a cycle, 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 conditions 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 condition on the cylinder body surface is a third-type boundary condition. 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: Based on the average temperature in the cylinder, determine the temperature distribution and heat transfer coefficient distribution at different spatial locations on the heating surface of the cylinder body:

[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 related to the piston position β, h m Indicates the average heat transfer coefficient in the cylinder, k1, k2, k3 are all 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 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 transient heat transfer coefficient, calculate the spatially distributed steady-state temperature boundary conditions, and thus impose constraints in the model.

[0082] By accurately calculating the temperature and heat transfer coefficient at different locations, this method can provide appropriate boundary conditions for cylinder structures with complex geometries. This helps to realistically reproduce the actual conditions of complex flow and heat transfer in numerical simulations, thereby improving the credibility of the model.

[0083] S602: Calculate the heat transfer coefficient distribution at different spatial locations 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 condition on the inner surface of the cylinder head is a third-type boundary condition. 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 changes in 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 cylinder head system model, set the boundary layer mesh thickness to match the turbulence model, and set a thin shell heat transfer model on the inner surface of the cylinder head and cylinder body to calculate the normal thermal resistance to form the cylinder head system model.

[0092] Normal thermal resistance describes the thermal resistance perpendicular to the surface or layer structure of an object during heat conduction. It measures the degree to which a material hinders heat transfer perpendicular to the heat flow and is often used to describe the thermal insulation properties 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 solids 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, by defining the thickness and material of the coating and adhesive layer, thin shell heat transfer is used instead of coating grid division for calculation and analysis of the coating's heat transfer performance.

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

[0096] In one possible implementation, the calculation formula for normal thermal resistance is:

[0097]

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

[0099] In this invention, polyhedral meshes offer enhanced geometric adaptability, enabling the generation of high-quality meshes on complex geometric surfaces, ensuring continuity of energy transfer between fluids and solids. Furthermore, the thin-shell heat transfer model accurately calculates the normal thermal resistance, which primarily describes the thermal resistance of the coating in the direction of heat flow, based on thickness and material properties. This allows the numerical model to accurately reflect the thermal insulation effect of the coating, effectively reducing heat loss from the cylinder wall and improving overall engine efficiency.

[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] A steady-state temperature field refers to the temperature distribution that occurs when the temperature at each point in a system remains constant over time. In a steady-state temperature field, the temperature at any point in the system is constant, meaning it does not change over time. A steady-state temperature field often occurs in systems that have reached thermal equilibrium, where heat conduction and heat exchange between points remain balanced.

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

[0104] S901: Perform polyhedral meshing 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] The finite volume method (FVM) is a numerical method for solving partial differential equations, particularly suitable for numerical calculations of problems such as fluid dynamics and heat conduction. It divides the computational domain into multiple finite control volumes (grid cells) and applies conservation equations to each control volume to determine the distribution of physical quantities across the entire computational domain.

[0106] In this paper, the finite volume method can handle complex turbulent flow fields. By setting appropriate boundary layer mesh thickness and dimensionless distance values, the flow characteristics of turbulence can be accurately simulated, especially the thermal boundary layer and velocity boundary layer near the wall. This precise turbulence simulation helps improve the prediction accuracy of flow and heat transfer processes in cooling channels.

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

[0108] Fluid-Structure Interaction (FSI) is a computational method that simultaneously considers the interaction between fluids and solids in numerical simulations. It combines the concepts of fluid mechanics and solid mechanics to address complex problems involving the interaction between fluids and solids. The goal of FSI is to simulate the forces exerted by fluids on solid structures (such as pressure and shear), as well as the effects of solid deformation on fluid flow.

[0109] Specifically, due to the complexity of the fluid-structure interaction model, a polyhedral mesh was created for the solid and fluid regions, and the finite volume method was used to calculate the flow and temperature fields. The boundary layer mesh thickness was rescaled based on the dimensionless distance of the fluid near the wall to obtain a dimensionless distance that satisfies the turbulence model used. Fluid-structure interaction field calculations were then performed to obtain a more accurate temperature field.

[0110] In this paper, fluid-structure interaction refers to the interaction between the fluid and solid domains. Through fluid-structure interaction, the heat exchange process between the coolant and the cylinder head and block materials can be simulated, accurately reflecting the heat transfer phenomena under actual operating conditions. In an internal combustion engine, the coolant removes the heat generated during combustion through cooling channels within the cylinder head and block. This heat is then transferred to the coolant through the cylinder head and block materials. Calculation of the fluid-structure interaction field accurately captures the dynamic characteristics of this heat exchange, improving the accuracy of temperature field simulations.

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

[0112] The finite element method (FEM) is a powerful numerical analysis technique used to solve complex partial differential equations and integral equations, and is particularly widely used in fields such as solid mechanics, heat conduction, electromagnetism, and fluid mechanics. The finite element method divides the complex solution domain into many small, simple units and performs local approximations within each unit, thereby transforming the original complex global problem into a simple local problem.

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

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

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

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

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

[0118] In this invention, by applying displacement constraints in different directions on multiple surfaces, the direction of displacement can be limited, resulting in a more uniform distribution of structural stress, reducing local stress concentrations, and avoiding excessive stress and fatigue damage in the material. Furthermore, by applying reasonable displacement constraints, the overall displacement variation can be limited, reducing the impact of thermal deformation on the structural stress distribution.

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

[0120] (1) In the present invention, the piston displacement data is curve-fitted using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions. The model is calibrated in combination with cylinder pressure data, and the average temperature and heat transfer coefficient in the cylinder are calculated. The steady-state temperature boundary conditions are determined 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, effectively conducting heat load research and structural reliability evaluation, and improving the safety and performance stability of FPLG.

[0121] Reference Manual 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 thermal load analysis system 20, which is applied to the above-mentioned free-piston internal combustion generator thermal load analysis method, comprising:

[0123] Processor 201;

[0124] The memory 202 stores computer-readable instructions. When the computer-readable instructions are executed by the processor 201 , the thermal load analysis method for a 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 it again.

[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 using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions. The model is calibrated in combination with cylinder pressure data, and the average temperature and heat transfer coefficient in the cylinder are calculated. The steady-state temperature boundary conditions are determined 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, effectively conducting heat load research and structural reliability evaluation, and improving the safety and performance stability of FPLG.

[0128] It should be understood that the processor in the embodiments 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 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 through software, hardware (such as circuits), firmware, or any other combination. When implemented using 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 program are loaded or executed on a computer, the processes or functions described in accordance with the embodiments of the present invention are 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. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via a wired method (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 a collection of one or more available media. The available medium can be a magnetic medium (such as a floppy disk, hard disk, or magnetic tape), an optical medium (such as a DVD), or a semiconductor medium. The semiconductor medium can be a solid-state drive.

[0131] It should be understood that the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. A and B can be singular or plural. Furthermore, the character " / " as used herein generally indicates an "or" relationship between the associated objects, but it may also indicate an "and / or" relationship. For specific understanding, please refer to the context.

[0132] In this disclosure, "at least one" means one or more, and "plurality" 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 mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or plural.

[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. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0135] Those skilled in the art will 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 merely illustrative. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, 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 interface, indirect coupling or communication connection of the device or unit, which can be electrical, mechanical or other forms.

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

[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, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. 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, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment 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] The 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. 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 using Fourier series to obtain a smooth displacement curve, thereby establishing accurate combustion model boundary conditions. The model is calibrated in combination with cylinder pressure data, and the average temperature and heat transfer coefficient in the cylinder are calculated. The steady-state temperature boundary conditions are determined 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, effectively conducting heat load research and structural reliability evaluation, and improving the safety and performance stability of FPLG.

[0144] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection 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. Other structures may refer to conventional designs.

[0147] (2) For the sake of clarity, the thickness of layers or regions in the drawings used to describe the embodiments of the present invention are exaggerated or reduced, that is, these drawings are not drawn to 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 intervening elements may be present.

[0148] (3) In the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to form 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: Using Converge, a combustion model with the same size as the actual prototype is created. S5: using the equidistant piston displacement data as the boundary condition of the combustion model and calibrating it with the cylinder pressure data to calculate the average in-cylinder temperature and the average in-cylinder heat transfer coefficient; S6: determining a 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; S7: Construct a simplified model of the cylinder head system; S8: performing polyhedral meshing 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: Calculating a steady-state temperature field using the cylinder head system model based on the steady-state temperature boundary condition; S10: Analyze the thermal load of the free-piston internal combustion generator using the finite element method, taking the steady-state temperature field as a thermal load condition.

2. The thermal 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, 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 using a Fourier fitting method according to the optimal Fourier coefficients.

3. The thermal 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 Both represent Fourier coefficients.

4. The thermal load analysis method of a free-piston internal combustion generator according to claim 1, characterized in that: The calculation formula for the average temperature in the cylinder in S5 is: Among them, T m Indicates the average temperature of the gas in the cylinder, T indicates the cycle period, h g Indicates 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 thermal 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 locations on the heating surface of the cylinder body based on 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 related to the piston position β, h m Indicates the average heat transfer coefficient in the cylinder, k1, k2, k3 are all 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 heated surface of the cylinder head based on 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 thermal 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 the normal thermal resistance, d represents the coating thickness, k represents the thermal conductivity of the material, and A represents the 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: Perform polyhedral meshing 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 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 thermal load condition, a finite element method is used to analyze the thermal load of the free-piston internal combustion generator.

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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