A method for controlling the combustion heat flow and its application to an opposed two-stroke engine

Abstract

The application discloses a combustion heat flow control method, belonging to the technical field of engines, comprising asymmetric combustion chamber design, flame development and heat insulation coupling design and structure parameterization design based on heat flow directional guidance. The intake side piston adopts an improved double-curl flow structure, the exhaust side piston adopts a flat top structure, and oil is only sprayed to the intake side space; heat insulation regions are more accurately selected based on the spatial field distribution characteristics of flames, and different combined heat insulation schemes are finely and differentially designed according to different heat transfer parameters, the highest heat insulation measure is selected for the high near-wall heat flow region, and the ordinary heat insulation measure is selected for the low near-wall heat flow region; structure parameterization design is performed, and combustion chamber parameters are adjusted to realize active control of heat flow in the whole space. The method can solve the problem of overheating of the exhaust side piston and improve the thermal efficiency. On this basis, the application further provides an opposed two-stroke engine applying the heat flow control method, which is high in efficiency, compact and reliable.

Description

Technical Field

[0001] This invention belongs to the field of engine technology, and in particular relates to a combustion heat flow control method and its application in an opposed two-stroke engine. Background Technology

[0002] Compared to traditional four-stroke engines, opposed two-stroke engines double the power frequency. The elimination of the cylinder head and valve train results in a more compact structure and reduced weight, leading to their widespread use as power sources in both military and civilian applications. However, the increased power frequency eliminates the cooling system's cooling pathway through the cylinder head, resulting in higher combustion temperatures and increased thermal load within the engine cylinders. Simultaneously, the "one-sided intake, one-sided exhaust" scavenging process in direct-flow scavenging mode means that the exhaust port and piston are subjected to high-frequency, high-temperature working fluid scouring without adequate cooling from the fresh impulse. Therefore, opposed piston two-stroke engines suffer from excessive thermal load on the exhaust port and piston, making them prone to overheating and erosion.

[0003] Excessive heat load on the exhaust side is mainly caused by uneven heat flow distribution within the cylinder of an opposed two-stroke engine. In the "opposed piston + direct scavenging" operating mode, the exhaust side is constantly in contact with high-temperature combustion gases during combustion and scavenging, meaning that combustion heat is concentrated primarily on the exhaust side. This leads to increased temperature of structural components and a greater susceptibility to ablation failures. Furthermore, with the continuous improvement in engine performance, higher combustion temperatures result in significantly increased heat transfer losses, making improved thermal efficiency a critical issue that urgently needs to be addressed.

[0004] Given the inherent structural characteristics of opposed two-stroke engines, including symmetrical piston arrangement and combustion in both combustion chambers, there are currently no effective methods for dissipating heat accumulation on the combustion walls, resulting in persistently high heat loads on key exhaust-side components. Heat flow distribution is closely related to flame development; the flame's spatial distribution determines both heat load and overall engine thermal efficiency. Traditional enclosed combustion chambers cannot achieve directional guidance of fuel-air mixtures and flames in the spatial field. Combustion chamber insulation technology is widely used to improve thermal efficiency. However, current technology focuses too broadly on the selection of insulation areas, lacking precise implementation of specific insulation measures. For example, insulating the entire piston, especially due to a lack of understanding of the flame's spatial distribution, often results in low heat transfer loss in the selected insulation area, failing to achieve the desired thermal efficiency improvement. The combustion chamber configuration significantly affects in-cylinder spray development and airflow organization, thus determining flame development and combustion heat release processes; therefore, the combustion chamber configuration is crucial and requires reasonable parametric design. For the purpose of guiding heat flow in a directional manner, the existing parameterization methods for the combustion chamber of opposed piston two-stroke engines can only determine the relevant linear size range such as the diameter of the inner and outer chambers. They lack a systematic construction of the combustion chamber configuration and effective separation of independent variables, which also delays the design and optimization process.

[0005] In summary, existing opposed two-stroke engines have symmetrical piston arrangements and fuel injection combustion in both combustion chambers. The heat accumulation on the exhaust side piston and port cannot be dissipated, and excessive heat load can easily lead to burning failure. The current heat insulation technology is too crude in the selection of heat insulation areas and the heat insulation measures are not refined enough, which restricts the improvement of engine thermal efficiency.

[0006] In view of this, there is an urgent need to develop an in-cylinder combustion heat flow control method to effectively solve the problem of excessive heat load in opposed piston two-stroke engines and improve thermal efficiency. Summary of the Invention

[0007] To address the aforementioned deficiencies, the technical problem solved by this invention is to provide a combustion heat flow control method, including asymmetric combustion chamber design, flame development and thermal insulation coupling design, and structural parameterization design based on heat flow directional guidance. This method can achieve heat flow rebalancing of both pistons in a opposed two-stroke engine, solve the problem of exhaust-side piston overheating, and improve thermal efficiency, while also facilitating rapid design and optimization. Furthermore, this invention also provides an opposed two-stroke engine applying this heat flow control method.

[0008] The asymmetric combustion chamber design and the flame development and thermal insulation coupling design are both based on GT-Power software to calculate the boundary conditions of the opposed two-stroke engine. The boundary conditions include intake and exhaust parameters, fuel injection parameters, temperature, pressure, etc.

[0009] Preferably, the specific process of the asymmetric combustion chamber design is as follows:

[0010] Step A1: Using Fire software, establish a three-dimensional CFD simulation model of the opposed two-stroke engine, including a spray fragmentation model, an evaporation model, a turbulence model, and a combustion model.

[0011] Step A2: Design different combustion chamber configurations using Creo software, including a double-shell symmetrical combustion chamber, a double-wedge symmetrical combustion chamber, a double-wedge + shell asymmetrical combustion chamber, a double-wedge + guide-flow asymmetrical combustion chamber, and a double-wedge + flat-top asymmetrical combustion chamber.

[0012] Step A3: Import the different combustion chamber configurations from Step 2 into Fire software, and perform combustion simulation calculations in conjunction with the calibrated model to complete the design of the optimal combustion chamber configuration.

[0013] Preferably, the spray breakup model, the evaporation model, the turbulence model, and the combustion model are respectively the Wave model, the Dukowicz model, the k-zeta-f model, and the ECFM-3Z model.

[0014] Preferably, the combustion simulation calculation includes the calculation of air utilization rate, in-cylinder fuel-air / turbulent mixing rate, and heat flux density, as detailed below:

[0015] Air utilization rate represents the ratio of the total volume of meshes in the CFD computation region where the fuel-air equivalence ratio satisfies the constraint condition to the total mesh volume. The specific calculation formula is as follows:

[0016]

[0017] Among them, V i V is the total volume of gas inside the cylinder. tol The total volume of the grid is 0.5≤φ≤1.5, where φ is the air-fuel equivalence ratio;

[0018] The in-cylinder air-fuel / turbulent mixing rate is proportional to the reciprocal of the turbulent mixing time. The reciprocal of the turbulent mixing time characterizes the rate of change of turbulent kinetic energy in the cylinder. The specific calculation formula is as follows:

[0019]

[0020] Where Δ is the reciprocal of the turbulent mixing time, m i For the mass of the infinitesimal element, E i Let k be the turbulent dissipation rate within the infinitesimal element. i It represents the turbulent kinetic energy within the infinitesimal element;

[0021] The formula for calculating heat flux density is as follows:

[0022]

[0023] Where, ρ f For fluid density, C p,f For the specific heat capacity of the fluid, u τ T is the frictional velocity based on shear force. + y is a dimensionless temperature value. + =(u τ y c ) / v f y is a dimensionless constant representing the distance near the wall in turbulent conditions. c T c T represents the distance to the near-wall mesh and the temperature, respectively. s For the solid domain temperature.

[0024] Preferably, the intake-side piston adopts an improved dual-flow structure, and the exhaust-side piston adopts a flat-top structure, forming an asymmetrical combustion chamber. The entire profile consists of an inner chamber throat, an outer chamber throat located at one end of the inner chamber throat, an outer chamber recess arc located at the end of the outer chamber throat away from the inner chamber throat, and an inner chamber recess arc located at the end of the outer chamber recess arc away from the outer chamber throat. The combustion chamber length is denoted as L, the inner chamber throat diameter as L1, and the inner chamber elevation angle as θ. a The radius of the inner chamber recess arc is denoted as R1, the diameter of the outer chamber throat is denoted as L2, and the outer chamber elevation angle is denoted as θ. b The radius of the outer chamber recess arc is denoted as R2, and the outer chamber outlet angle is denoted as θ. c The height of the ridge at the connection between the inner and outer rooms is denoted as H.

[0025] Preferably, the specific process of flame development and thermal insulation coupling design is as follows:

[0026] Step B1: Using Fire software, establish a CFD three-dimensional simulation model of the opposed two-stroke engine, including the intake and exhaust ports.

[0027] Step B2: Adjust the fuel injection and intake strategies for the determined optimal combustion chamber configuration to actively guide the flame in the space field and enable rapid combustion. Extract the near-wall temperature field and convective heat transfer coefficient. The near-wall temperature field is the process of the flame transferring heat to the wall, including heat conduction and convective heat transfer.

[0028] Step B3: Calculate the heat flux density based on the extracted near-wall temperature field and convective heat transfer coefficient;

[0029] Step B4: Based on the determined distribution of heat flux density in different areas of the optimal combustion chamber, take refined heat insulation measures;

[0030] Step B5: Use the finite element software Ansys to obtain thermal stress and strain. The specific calculation formula is as follows:

[0031]

[0032] σ=Eδ

[0033] Where ε is thermal strain, α is the coefficient of thermal expansion, and T ref Here, σ is the solid reference temperature, E is the material's elastic modulus, δ is the length of the conductive medium, Δl represents the change in the object's length, l represents the object's original length, and T represents the solid temperature.

[0034] Step B6: Evaluate different insulation measures comprehensively based on their insulation performance, heat load characteristics, and combustion performance, conduct multiple iterations, and finally determine the optimal scheme for the coupling design of flame development and insulation.

[0035] Preferably, the specific calculation expressions for heat conduction, convective heat transfer, convective heat transfer coefficient, and heat flux density are as follows:

[0036] After coupling the fluid surface temperature calculation to the solid surface, the expression for calculating heat conduction in the solid domain is obtained according to Fourier's law:

[0037]

[0038] q=-λ(T1-T2)tA / δ

[0039] Where q is the heat flux density and λ is the thermal conductivity of the material. Let t be the derivative of temperature in the n direction, t be the conduction time, A be the contact area, δ be the length of the conduction medium, T1 be the fluid temperature, and T2 be the wall temperature.

[0040] Based on Fourier's heat conduction equation describing heat conduction in solids and the heat transfer equation describing heat transfer in fluids, the expression for convective heat transfer at the fluid-solid interface is:

[0041]

[0042] Where λ is the thermal conductivity of the material, T is the solid temperature, and α is the coefficient of thermal expansion. w T is the wall temperature. f The temperature of the fluid near the wall;

[0043] The formula for calculating the convective heat transfer coefficient is as follows:

[0044]

[0045] Among them, T s For the solid domain temperature, T ref q is the reference temperature for the solid. s Heat flux density;

[0046] The formula for calculating heat flux density is as follows:

[0047]

[0048] Where, ρ f For fluid density, C p,f For the specific heat capacity of the fluid, u τ T is the frictional velocity based on shear force. + y is a dimensionless temperature value. + =(u τ y c ) / v f y is a dimensionless constant representing the distance near the wall in turbulent conditions. c T c T represents the distance to the near-wall mesh and the temperature, respectively.s For the solid domain temperature.

[0049] Preferably, the specific process of taking refined heat insulation measures in step B4 based on the determined distribution of heat flux density in different regions of the optimal combustion chamber is as follows:

[0050] B41. Based on simulation calculations and optical tests, determine the influence of the characteristic parameters of the thermal insulation coating on the wall heat transfer. The characteristic parameters of the thermal insulation coating include the thermal insulation coating thickness, thermal insulation material, surface roughness, and porosity.

[0051] B42. Considering the reverse effect of the characteristic parameters of the heat insulation coating on combustion, calculate the characterization indicators of combustion efficiency, indicated work, and indicated thermal efficiency.

[0052] B43. Design different groups of insulation measures and analyze the specific insulation effects; determine the preliminary insulation scheme, select the insulation measures with the highest insulation capacity for areas with higher heat flow near the wall, and select insulation measures with ordinary insulation capacity for areas with lower heat flow near the wall.

[0053] Preferably, the specific process of the structural parametric design based on heat flow directional guidance is as follows:

[0054] Step C1: Select θ a ,H,R1,L2,θ c ,R2,θ b Seven variables determine the combustion chamber shape: L2, θ c R2 determines the size and position of the outer chamber arc, R1, θ a H determines the inner chamber arc and its tangent, θ b Determine the common tangent line between the inner and outer chambers;

[0055] Step C2: Calculate the coordinate and slope parameters to complete the parameterized expression of the combustion chamber cross-section. The specific calculation is shown below:

[0056] (1) Slope of the left tangent line of the outer circle: k = tanθ b ;

[0057] (2) Abscissa of the outer circle center: x2 = L2 - R2sinθ c ;

[0058] (3) The ordinate of the outer circle's center: y2 = R2cosθ c ;

[0059] (4) Obtuse of the tangent line on the outer circle:

[0060] Step C3: Calculate the cross-sectional area S of the combustion chamber. A Combustion chamber cross-sectional area S AIt consists of three small cross-sections, denoted as S1, S2, and S3, where S2 is the area of ​​an obtuse triangle; S1 and S3 are the areas of closed figures bounded by two straight line segments and a circular arc, calculated using calculus; the specific calculation method is as follows:

[0061]

[0062] Step C4: Calculate the combustion chamber volume V according to Goulding's theorem. The specific expression is as follows:

[0063] V = 2πS A x b .

[0064] The opposed two-stroke engine provided by this invention employs the combustion heat flow control method described above for in-cylinder heat flow regulation. This invention develops a novel combustion heat flow control method and an opposed two-stroke engine. It features an asymmetric combustion chamber design, with an improved double-flow structure for the intake-side piston and a flat-top structure for the exhaust-side piston, injecting fuel only into the intake space. It incorporates a flame development and heat insulation coupling design, more precisely selecting the heat insulation area based on the flame's spatial distribution characteristics, and meticulously and differentially designing different combinations of heat insulation schemes for different heat transfer parameters. Simultaneously, it considers the in-cylinder combustion process to determine the optimal scheme for flame development and heat insulation coupling design. It also employs a structural parameterization design based on heat flow directional guidance, adjusting combustion chamber parameters to actively control heat flow throughout the entire space. Combined with its own structural features of eliminating the cylinder head and intake / exhaust valves, the opposed two-stroke engine provided by this invention, applying the aforementioned combustion heat flow control scheme, exhibits high efficiency, high compactness, and high reliability.

[0065] Therefore, the combustion heat flow control method and its application in an opposed two-stroke engine described above have the following beneficial effects:

[0066] I. Asymmetric Combustion Chamber Design: ① The intake-side piston features an improved dual-flow configuration, with a long and full outer chamber and a short and gentle inner chamber. This achieves bidirectional flow of fuel against the outer chamber wall and unidirectional flow diffusion within the inner chamber, improving air utilization throughout the combustion chamber, accelerating fuel-air mixing, and shortening the combustion duration. ② The exhaust side uses a flat-top piston that injects fuel only into the intake space, reducing the concentrated heat flow area on the exhaust-side piston and lowering the thermal load on structural components. ③ The asymmetric combustion system design ensures that the exhaust-side temperature is significantly lower than that of the symmetric combustion system, achieving thermal rebalancing of the two pistons and solving problems such as piston and port erosion on the exhaust side of the opposed two-stroke engine.

[0067] II. Flame Development and Thermal Insulation Coupling Design: ① Based on the distribution characteristics of the flame in the spatial field, the thermal insulation area can be selected more accurately, ensuring high-intensity thermal insulation for key high-heat-transfer areas to reduce heat loss and improve heat-work conversion efficiency, while preserving the heat diffusion capacity of non-critical low-heat-transfer areas to reduce the overall heat load; ② Based on clarifying the influence of thermal insulation coating characteristic parameters on wall heat transfer, different combinations of thermal insulation schemes can be finely designed for different heat transfer parameters of the selected thermal insulation area to achieve more efficient thermal insulation; ③ Based on the near-wall heat flux density, combined with fluid-structure interaction and thermo-mechanical interaction calculations, the characteristics of wall temperature and thermal stress changes can be further explored to truly obtain the heat load effect of in-cylinder heat transfer on the wall; ④ Thermal insulation also takes into account the in-cylinder combustion process. After taking thermal insulation measures, multiple rounds of feedback iteration are performed to obtain the combustion and heat load characteristics. The final determined optimal design scheme for flame development and thermal insulation coupling can achieve the optimal comprehensive performance of thermal insulation, heat load, and combustion.

[0068] III. Structural parameterization design based on heat flow directional guidance: ① It enables rapid determination of the combustion chamber structure with minimal individual variables, and the connection between the inner and outer chambers largely realizes the individual parameterization of the inner and outer chambers, simplifying complex problems; ② It focuses on analyzing and adjusting the combustion chamber structural parameters to actively control the combustion heat flow in the entire space, and determines that the inner chamber elevation angle, outer chamber elevation angle, and outer chamber outlet angle are the most critical influencing parameters. Optimization of the inner chamber elevation angle ensures the expansion of the inner chamber space, allowing the flame to roll outward and reducing the inner chamber heat load; further optimization of the outer chamber elevation angle ensures that the flame no longer develops against the wall, significantly reducing the wall heat flow and lowering the outer chamber heat load; further optimization of the outer chamber outlet angle successfully transports the heat flow from the top of the outer chamber to the bottom of the outer chamber, achieving efficient optimization for the purpose of directional guidance of combustion heat flow; ③ The established structural parameterization design serves the rapid design and optimization of the combustion system, which can accelerate the iterative update of opposed two-stroke engines.

[0069] Fourth, by combining its structural features such as eliminating the cylinder head and intake and exhaust valves, the opposed two-stroke engine provided by this invention, which applies the aforementioned combustion heat flow control scheme, has high efficiency, high compactness, and high reliability.

[0070] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0071] Figure 1 This is a comparison diagram of the high temperature distribution areas of different types of combustion chambers in this invention. Among them, (a) is a structural diagram of a double-shell symmetrical combustion chamber, (b) is a structural diagram of a double-wound symmetrical combustion chamber, (c) is a structural diagram of a double-wound + shell asymmetrical combustion chamber, (d) is a structural diagram of a double-wound + guide-flow asymmetrical combustion chamber, and (e) is a structural diagram of a double-wound + flat-top asymmetrical combustion chamber.

[0072] Figure 2 This is a structural diagram of the optimal combustion chamber configuration of the present invention;

[0073] Figure 3 This is a schematic diagram of fuel distribution in the optimal combustion chamber configuration of this invention;

[0074] Figure 4 This is a comparison diagram of the exhaust piston heat flux density of the asymmetric and symmetric combustion chambers of the present invention, wherein (a) is the heat flux density distribution of the symmetric combustion chamber at -2.5°CA, (b) is the heat flux density distribution of the asymmetric combustion chamber at -2.5°CA, (c) is the heat flux density distribution of the symmetric combustion chamber at 2.5°CA, and (d) is the heat flux density distribution of the asymmetric combustion chamber at 2.5°CA.

[0075] Figure 5 This is a comparison diagram of heat transfer between the exhaust piston in the asymmetric and symmetric combustion chambers of the present invention, wherein (a) is a comparison diagram of instantaneous heat transfer and (b) is a comparison diagram of total heat transfer.

[0076] Figure 6 This is the flame spatial field orientation guidance diagram of the present invention;

[0077] Figure 7 This is a diagram illustrating the selection of insulation zones and refined insulation measures according to the present invention;

[0078] Figure 8 This is an overall flowchart of the flame development and thermal insulation coupling design of this invention;

[0079] Figure 9 This is a simplified parameterized diagram of the asymmetric combustion chamber structure of the present invention;

[0080] Figure 10 This is a schematic diagram of the combustion chamber structure of the opposed two-stroke engine of the present invention;

[0081] Figure 11 These are diagrams illustrating the effect of the structural variables based on parametric design of this invention on the spatial orientation of heat flow. (a) shows the effect of the inner chamber elevation angle variable on the spatial orientation of heat flow, (b) shows the effect of the outer chamber elevation angle variable on the spatial orientation of heat flow, and (c) shows the effect of the outer chamber outlet angle variable on the spatial orientation of heat flow.

[0082] Figure 12 This is a schematic diagram of the principle of an opposed two-stroke engine to which the combustion heat flow control method of the present invention is applied. Detailed Implementation

[0083] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0084] The core of this invention is to provide a combustion heat flow control method, achieved through asymmetric combustion chamber design, flame development and thermal insulation coupling design, and structural parameterization design based on heat flow directional guidance. This method can ensure heat flow rebalancing of both pistons in an opposed two-stroke engine, solve the problem of exhaust-side piston overheating and improve thermal efficiency, while also facilitating rapid design and optimization. The specific implementation of this method is described below with reference to the accompanying drawings.

[0085] Please see Figure 1-11 This is a combustion heat flow control method, which includes asymmetric combustion chamber design, flame development and thermal insulation coupling design, and structural parameterization design based on heat flow directional guidance. Both the asymmetric combustion chamber design and the flame development and thermal insulation coupling design are based on GT-Power software to calculate the boundary conditions of the opposed two-stroke engine. The boundary conditions include intake and exhaust parameters, fuel injection parameters, temperature, pressure, etc.

[0086] The specific process of asymmetric combustion chamber design is as follows:

[0087] Step A1: Using Fire software, establish a three-dimensional CFD simulation model of the opposed two-stroke engine, including a spray fragmentation model, an evaporation model, a turbulence model, and a combustion model. The spray fragmentation model, evaporation model, turbulence model, and combustion model adopt the Wave model, Dukowicz model, k-zeta-f model, and ECFM-3Z model, respectively.

[0088] Step A2: Design different combustion chamber configurations using Creo software, including a double-shell symmetrical combustion chamber, a double-wedge symmetrical combustion chamber, a double-wedge + shell asymmetrical combustion chamber, a double-wedge + guide-flow asymmetrical combustion chamber, and a double-wedge + flat-top asymmetrical combustion chamber.

[0089] Step A3: Import the different combustion chamber configurations from Step 2 into Fire software, and perform combustion simulation calculations using the calibrated model to complete the design of the optimal combustion chamber configuration. The combustion simulation calculations include the calculation of air utilization rate, in-cylinder air-fuel / turbulent mixing rate, and heat flux density, as detailed below:

[0090] Air utilization rate represents the ratio of the total volume of meshes in the CFD computation region where the fuel-air equivalence ratio satisfies the constraint condition to the total mesh volume. The specific calculation formula is as follows:

[0091]

[0092] Among them, V i V is the total volume of gas inside the cylinder. tol The total volume of the grid is 0.5≤φ≤1.5, where φ is the air-fuel equivalence ratio;

[0093] The in-cylinder air-fuel / turbulent mixing rate is proportional to the reciprocal of the turbulent mixing time. The reciprocal of the turbulent mixing time characterizes the rate of change of turbulent kinetic energy in the cylinder. The specific calculation formula is as follows:

[0094]

[0095] Where Δ is the reciprocal of the turbulent mixing time, m i For the mass of the infinitesimal element, E i Let k be the turbulent dissipation rate within the infinitesimal element. i It represents the turbulent kinetic energy within the infinitesimal element;

[0096] The formula for calculating heat flux density is as follows:

[0097]

[0098] Where, ρ f For fluid density, C p,f For the specific heat capacity of the fluid, u τ T is the frictional velocity based on shear force. + y is a dimensionless temperature value. + =(u τ y c ) / v f y is a dimensionless constant representing the distance near the wall in turbulent conditions. c T c T represents the distance to the near-wall mesh and the temperature, respectively. s For the solid domain temperature.

[0099] The optimal combustion chamber configuration is an asymmetric combustion chamber with an improved dual-flow structure for the intake piston and a flat-top structure for the exhaust piston. The overall profile consists of an inner chamber throat, an outer chamber throat located at one end of the inner chamber throat, an outer chamber recess arc located at the end of the outer chamber throat away from the inner chamber throat, and an inner chamber recess arc located at the end of the outer chamber recess arc away from the outer chamber throat. The combustion chamber length is denoted as L, the inner chamber throat diameter as L1, and the inner chamber elevation angle as θ. a The radius of the inner chamber recess arc is denoted as R1, the diameter of the outer chamber throat is denoted as L2, and the outer chamber elevation angle is denoted as θ. b The radius of the outer chamber recess arc is denoted as R2, and the outer chamber outlet angle is denoted as θ. c The height of the ridge at the connection between the inner and outer rooms is denoted as H.

[0100] The specific process of flame development and thermal insulation coupling design is as follows:

[0101] Step B1: Using Fire software, establish a CFD three-dimensional simulation model of the opposed two-stroke engine, including the intake and exhaust ports.

[0102] Step B2: Adjust the fuel injection and intake strategies for the determined optimal combustion chamber configuration to actively guide the flame in the space field and enable rapid combustion. Extract the near-wall temperature field and convective heat transfer coefficient. The near-wall temperature field is the process of the flame transferring heat to the wall, including heat conduction and convective heat transfer.

[0103] Step B3: Calculate the heat flux density based on the extracted near-wall temperature field and convective heat transfer coefficient;

[0104] The specific calculation expressions for heat conduction, convective heat transfer, convective heat transfer coefficient, and heat flux density are as follows:

[0105] After coupling the fluid surface temperature calculation to the solid surface, the expression for calculating heat conduction in the solid domain is obtained according to Fourier's law:

[0106]

[0107] q=-λ(T1-T2)tA / δ

[0108] Where q is the heat flux density and λ is the thermal conductivity of the material. Let t be the derivative of temperature in the n direction, t be the conduction time, A be the contact area, δ be the length of the conduction medium, T1 be the fluid temperature, and T2 be the wall temperature.

[0109] Based on Fourier's heat conduction equation describing heat conduction in solids and the heat transfer equation describing heat transfer in fluids, the expression for convective heat transfer at the fluid-solid interface is:

[0110]

[0111] Where λ is the thermal conductivity of the material, T is the solid temperature, and α is the coefficient of thermal expansion. w T is the wall temperature. f The temperature of the fluid near the wall;

[0112] The formula for calculating the convective heat transfer coefficient is as follows:

[0113]

[0114] Among them, T s For the solid domain temperature, T ref q is the reference temperature for the solid. s Heat flux density;

[0115] The formula for calculating heat flux density is as follows:

[0116]

[0117] Where, ρ f For fluid density, C p,f For the specific heat capacity of the fluid, u τ T is the frictional velocity based on shear force. + y is a dimensionless temperature value. + =(u τ y c ) / v f y is a dimensionless constant representing the distance near the wall in turbulent conditions. c T c T represents the distance to the near-wall mesh and the temperature, respectively. s For the solid domain temperature.

[0118] Step B4: Based on the determined distribution of heat flux density in different regions of the optimal combustion chamber, implement refined heat insulation measures; the specific process is as follows:

[0119] B41. Based on simulation calculations and optical tests, determine the influence of the characteristic parameters of the thermal insulation coating on the wall heat transfer. The characteristic parameters of the thermal insulation coating include the thermal insulation coating thickness, thermal insulation material, surface roughness, and porosity.

[0120] B42. Considering the reverse effect of the characteristic parameters of the heat insulation coating on combustion, calculate the characterization indicators of combustion efficiency, indicated work, and indicated thermal efficiency.

[0121] The maximum chemical energy that fuel can provide is m f Q HV Calculate, m f For fuel quality, Q HV Given the calorific value of the fuel, combustion efficiency is calculated using the following formula:

[0122]

[0123] The formula for calculating indicated work is:

[0124] W i =∮pdv

[0125] Among them, W i p represents the indicated work, v represents the average pressure inside the cylinder, and v represents the cylinder volume.

[0126] The formula for calculating indicated thermal efficiency is:

[0127]

[0128] Among them, Q i To add heat to the working fluid inside the cylinder, H u m is the calorific value of the fuel. fuel This refers to the amount of fuel injected during the cycle.

[0129] B43. Design different groups of insulation measures and analyze the specific insulation effects; determine the preliminary insulation scheme, select the insulation measures with the highest insulation capacity for areas with higher heat flow near the wall, and select insulation measures with ordinary insulation capacity for areas with lower heat flow near the wall.

[0130] Step B5: Use the finite element software Ansys to obtain thermal stress and strain. The specific calculation formula is as follows:

[0131]

[0132] σ=Eδ

[0133] Where ε is thermal strain, α is the coefficient of thermal expansion, and T ref Here, σ is the solid reference temperature, E is the material's elastic modulus, δ is the length of the conductive medium, Δl represents the change in the object's length, l represents the object's original length, and T represents the solid temperature.

[0134] Step B6: Evaluate different insulation measures comprehensively based on their insulation performance, heat load characteristics, and combustion performance, conduct multiple iterations, and finally determine the optimal scheme for the coupling design of flame development and insulation.

[0135] The specific process of structural parametric design based on heat flow directional guidance is as follows:

[0136] Step C1: Select θ a ,H,R1,L2,θ c ,R2,θ b Seven variables determine the combustion chamber shape: L2, θ c R2 determines the size and position of the outer chamber arc, R1, θ a H determines the inner chamber arc and its tangent, θ b Determine the common tangent line between the inner and outer chambers;

[0137] Step C2: Calculate parameters such as coordinates and slope to complete the parametric expression of the combustion chamber cross-section. The specific calculations are shown below:

[0138] (1) Slope of the left tangent line of the outer circle: k = tanθ b ;

[0139] (2) Abscissa of the outer circle center: x2 = L2 - R2sinθ c ;

[0140] (3) The ordinate of the outer circle's center: y2 = R2cosθ c ;

[0141] (4) Obtuse of the tangent line on the outer circle:

[0142] Step C3: Calculate the cross-sectional area S of the combustion chamber.A Combustion chamber cross-sectional area S A It consists of three small cross-sections, denoted as S1, S2, and S3, where S2 is the area of ​​an obtuse triangle; S1 and S3 are the areas of closed figures bounded by two straight line segments and a circular arc, calculated using calculus; the specific calculation method is as follows:

[0143]

[0144] Step C4: Calculate the combustion chamber volume V according to Goulding's theorem. The specific expression is as follows:

[0145] V = 2πS A x b .

[0146] In addition to the aforementioned in-cylinder combustion heat flow control method, this embodiment also provides an opposed two-stroke engine that uses this control method for heat flow regulation. (See also...) Figure 12 Considering the unique opposed piston structure of the opposed two-stroke engine, a side-mounted fuel injection method is adopted.

[0147] Example 1

[0148] A method for controlling in-cylinder combustion heat flux

[0149] (1) Asymmetric combustion chamber design:

[0150] Based on GT-Power software, taking a specific type of opposed two-stroke engine as an example, boundary conditions are calculated, including intake and exhaust parameters, fuel injection parameters, etc., to provide for subsequent three-dimensional calculations.

[0151] A CFD three-dimensional simulation model of a opposed two-stroke engine was established using Fire software. Specifically, the spray dispersion model was the Wave model, the evaporation and turbulence models were the Dukowicz model and the k-zeta-f model, respectively, and the combustion model was the ECFM-3Z model. Optical testing experiments were conducted simultaneously, and the data obtained were used to calibrate the simulation process.

[0152] Different combustor configurations were designed in Creo software and imported into Fire software. Combustion simulation calculations were then performed using the calibrated model to support the optimization of the combustor configuration design. All other initial boundary conditions remained consistent. Combustion process simulation calculations were performed on different combustor configurations, including double-shell symmetrical combustors, double-flow symmetrical combustors, double-flow + shell asymmetrical combustors, double-flow + guide-flow asymmetrical combustors, and double-flow + flat-top asymmetrical combustors, focusing on high-temperature flames and heat flux distribution. Specific details are as follows: Figure 1As shown, for symmetrical combustion chambers, both the intake and exhaust pistons exhibit corresponding high-temperature heat flow distributions. For asymmetrical combustion chambers, the clamshell exhaust piston also exhibits a large near-wall high-temperature region. For a dual-flow + guide-flow asymmetrical combustion chamber, to reduce the thermal load on the exhaust piston, fuel is injected only on the dual-flow intake piston side, and the exhaust piston is only equipped with grooves for guiding the flow, i.e., transporting the fuel drawn out of the outer chamber of the dual-flow piston towards the center of the combustion chamber. However, it was found that a more concentrated high-temperature distribution exists at the groove guidance area. For dual-flow + flat-top combustion chambers, the high-temperature heat flow distribution on the exhaust piston side is significantly reduced.

[0153] Based on the above results, the design concept of an asymmetric combustion chamber, featuring an improved dual-flow structure for the intake piston and a flat-top structure for the exhaust piston, was confirmed. Figure 2 and Figure 3 As shown, the intake side employs a dual-flow structure. After the fuel hits the ridge, it forms a clockwise flow within the inner chamber and distributes towards the near end of the injector, solving the problem of uneven fuel-air distribution that a single injector cannot handle. It also facilitates the transport of heat from the wall to free space. The traditional dual-flow configuration is improved by designing a shorter and gentler inner chamber and a longer and fuller outer chamber. This achieves bidirectional fuel flow after impacting the outer chamber wall and unidirectional diffusion within the inner chamber, improving air utilization throughout the entire space and accelerating the fuel-air mixing rate. Simultaneously, the larger concave radius of the outer chamber ensures that the fuel is primarily distributed on the intake piston side, with the high-temperature heat flow relatively far from the exhaust piston. Considering the unique opposed piston structure of the opposed two-stroke engine, a side-mounted injection method is adopted. To effectively channel the exhaust heat flow, fuel is injected only onto the intake piston side. Figure 4 In (a), (c), and (b), (d), compared to a symmetrical combustion chamber, the heat flux density on the exhaust piston side of an asymmetrical combustion chamber is significantly reduced, such as... Figure 5 In (a) and (b), the instantaneous and total heat transfer also decreased significantly.

[0154] (2) Coupled design of flame development and thermal insulation:

[0155] Based on GT-Power software, taking a real opposed two-stroke engine as an example, boundary conditions such as temperature and pressure are calculated and provided for three-dimensional calculation.

[0156] A CFD 3D simulation model of an opposed two-stroke engine, including intake and exhaust ducts, was established using Fire software. The inclusion of intake and exhaust ducts allows for more accurate thermal boundary conditions of the combustion chamber walls. Specifically, the spray dissipation model used the Wave model, the evaporation and turbulence models used the Dukowicz model and the k-zeta-f model, respectively, and the combustion model used the ECFM-3Z model. Simultaneously, optical tests of spray and flame development were conducted on basic experimental rigs such as constant-volume incendiary bombs, and the obtained data were used to calibrate the simulation process.

[0157] Different combustion chamber wall configurations were designed in Creo software and imported into Fire software. Through further improvements to the dual-flow combustion chamber and the matching of coupled fuel injection and intake strategies, active flame guidance and efficient, rapid combustion in the space field were achieved. Figure 6 As shown, the active transport of the flame to the center of the combustion chamber is achieved through the entrapment of the inner and outer chambers. Further analysis of the heat transfer process from the working fluid to the wall surface is conducted, extracting the near-wall temperature field and convective heat transfer coefficient. Based on the distribution of the near-wall temperature field and convective heat transfer coefficient in different regions of the combustion chamber, the principle is to reduce heat loss and improve heat-work conversion efficiency by insulating key components, while preserving heat diffusion capacity and reducing overall heat load in non-critical components. Figure 7 The diagram shows a finely divided insulation zone. Specifically, low heat transfer zone C is left uninsulated, while high heat transfer zones B and A are insulated. The refined insulation measures include: firstly, combining simulation calculations and optical testing to clarify the impact of insulation coating characteristic parameters such as coating thickness, insulation material, surface roughness, and porosity on wall heat transfer, while also considering their reverse effect on combustion. Combustion is characterized by combustion efficiency, indicated work, and indicated thermal efficiency. Different groups of insulation measures are designed, and their specific insulation effects are analyzed. Based on this, a preliminary insulation scheme is determined: the insulation measure with the highest insulation capacity is selected for zone A, where the near-wall heat flux is higher, followed by zone B, where the near-wall heat flux is lower.

[0158] Using the finite element software Ansys, the near-wall temperature field and convective transfer coefficient field obtained from in-cylinder spray combustion calculations are mapped onto the wall as the thermal boundary for calculating the wall temperature field. At the same time, the temperature field calculation model is verified through wall temperature measurement experimental data, and the wall temperature and heat flow characteristic parameters under the original conditions and with different insulation measures are obtained, clarifying the heat transfer characteristics before and after insulation.

[0159] Furthermore, using the wall temperature field as the boundary condition for calculating the wall thermal stress and strain field, thermo-mechanical coupled stress field calculations were performed on the combustion chamber components to obtain the original stress and strain distribution under different insulation measures, thus clarifying the thermal load characteristics before and after insulation.

[0160] Based on the above, different insulation schemes are comprehensively evaluated using thermal insulation performance, heat load characteristics, and combustion performance. Multiple iterations are conducted, with the optimal overall performance of these three factors used as the evaluation criterion. Finally, the best scheme for the coupled design of flame development and thermal insulation is determined. The overall process is as follows: Figure 8 As shown.

[0161] (3) Structural parameterization based on heat flow directional guidance:

[0162] The combustion chamber of a opposed two-stroke engine is formed by a shared space on the tops of the intake and exhaust pistons. The asymmetric combustion chamber provided by this invention features improved dual-flow and flat-top pistons on the intake and exhaust sides, respectively. Taking the intake piston as an example... Figure 9 and Figure 10 As shown, the combustion chamber length is denoted as L, the inner chamber throat diameter as L1, and the inner chamber elevation angle as θ. a The radius of the inner chamber recess arc is denoted as R1, the diameter of the outer chamber throat is denoted as L2, and the outer chamber elevation angle is denoted as θ. b The radius of the outer chamber recess arc is denoted as R2, and the outer chamber outlet angle is denoted as θ. c The height of the ridge at the connection between the inner and outer rooms is denoted as H.

[0163] By changing any of the aforementioned parameters in several sets, several uniquely determined combustion chamber structures can be obtained. Assuming the total volume of the combustion chamber remains constant, θ a θ b and θ c As a core independent variable, its allocation allows for the proactive control of the distribution characteristics of flame and heat flux within the combustion chamber. The following section will detail the effects of parametrically designed structural variables on the spatial directional guidance of combustion heat flux, using spatial heat flux distribution as a performance indicator:

[0164] Specifically, select θ a Taking the relevant internal room parameters as the research object, the external room parameters and the internal room volume remain unchanged, θ a L1 is the active variable, and L2 and R1 are the passive variables. For example... Figure 11 As shown in (a), θ a When θ is relatively small, L1 is longer and R1 remains essentially constant. In this case, the flame and heat flow develop close to the inner chamber wall, resulting in a smaller vortex space after the flow splits at the ridge, which leads to a higher heat load on the inner chamber wall. Conversely, θ... a When the value is large, L1 is shorter and the inner chamber is fuller. At this time, the swirling space after the fuel impacts the arc ridge is larger, the flame development space is sufficient and it can swirl outwards, and the heat load of the inner chamber is reduced accordingly.

[0165] Select the optimal room parameter from the above steps, θ b The study focuses on the relevant external chamber parameters, while keeping the internal chamber parameters and external chamber volume constant, θ b L1 is the active variable, and L2 and R2 are the passive variables. For example... Figure 11 As shown in (b) in the figure, θ b When θ is smaller, L2 is larger and R2 is slightly increased. At this point, the flame and heat flow develop close to the outer wall, and the oil jet is in contact with air on only one side, which is not conducive to the diffusion and mixing of oil and gas, and will also bring a high heat load to the outer wall. Conversely, θ b When the size is large, L2 is shorter and the outer chamber is fuller. At this time, there is basically no phenomenon of flame and heat flow sticking to the wall. The space above and below the oil jet is sufficient, the flame develops more evenly and is far away from the wall, and the heat load on the outer chamber wall is reduced accordingly.

[0166] Select the optimal inner and outer chamber parameters from the two steps mentioned above, denoted by θ.c The study focuses on parameters related to the interior and exterior chambers, with most parameters remaining constant. θ c As active variables, L and θ b R2 and R2 are dependent variables. For example... Figure 11 As shown in (c), θ c When θ is smaller, L and R2 decrease, and at this time, due to the curvature of the outer chamber, more fuel flows towards the top of the outer chamber, making the top of the combustion chamber a high-heat flow region. Conversely, θ c When the values ​​are large, L and R2 increase, and more fuel flows towards the bottom of the outer chamber, while the heat flow at the top of the outer chamber is successfully transported to the bottom of the outer chamber.

[0167] Example 2

[0168] An opposed two-stroke engine includes a combustion heat flow control method as provided in Embodiment 1 of the present invention. (See also...) Figure 12 This diagram illustrates the principle of a opposed two-stroke engine to which a combustion heat flow control method according to Embodiment 2 of the present invention is applied. Through an asymmetric combustion chamber design, the intake-side piston adopts an improved double-flow structure, and the exhaust-side piston adopts a flat-top structure, injecting fuel only into the intake-side space. This achieves heat flow rebalancing between the two pistons, reducing the heat concentration area of ​​the exhaust-side piston and lowering the thermal load on structural components. Through flame development and insulation coupling design, the insulation area is more accurately selected based on the flame's spatial distribution characteristics. Different combinations of insulation schemes are finely and differentiated for different heat transfer parameters. The highest insulation capacity is selected for high near-wall heat flow areas, while ordinary insulation capacity is selected for low near-wall heat flow areas, which is beneficial for efficient insulation and improved thermal efficiency. Meanwhile, taking into account the in-cylinder combustion process, the optimal design scheme for flame development and heat insulation coupling can achieve the best comprehensive performance of heat insulation, heat load and combustion. Through structural parameterization design based on heat flow directional guidance, the combustion chamber parameters are adjusted to actively control the heat flow in the entire space, serving the rapid design and optimization of the combustion system. Combined with its structural features of eliminating cylinder head, intake and exhaust valves, etc., the opposed two-stroke engine with the aforementioned combustion heat flow control scheme provided by this invention has high efficiency, high compactness and high reliability.

[0169] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for controlling combustion heat flux, characterized in that: This includes asymmetric combustion chamber design, flame development and thermal insulation coupling design, and structural parameterization design based on heat flow directional guidance. Both the asymmetric combustion chamber design and the flame development and thermal insulation coupling design are based on GT-Power software to calculate the boundary conditions of the opposed two-stroke engine. The boundary conditions include intake and exhaust parameters, fuel injection parameters, temperature, and pressure. The specific process of the asymmetric combustion chamber design is as follows: Step A1: Using Fire software, establish a three-dimensional CFD simulation model of the opposed two-stroke engine, including a spray fragmentation model, an evaporation model, a turbulence model, and a combustion model. Step A2: Design different combustion chamber configurations using Creo software, including a double-shell symmetrical combustion chamber, a double-wedge symmetrical combustion chamber, a double-wedge + shell asymmetrical combustion chamber, a double-wedge + guide-flow asymmetrical combustion chamber, and a double-wedge + flat-top asymmetrical combustion chamber. Step A3: Import the different combustion chamber configurations from Step 2 into Fire software, and perform combustion simulation calculations in conjunction with the calibrated model to complete the design of the optimal combustion chamber configuration; The specific process of flame development and thermal insulation coupling design is as follows: Step B1: Use Fire software to create a CFD three-dimensional simulation model of the opposed two-stroke engine, including the intake and exhaust ports. Step B2: Adjust the fuel injection and intake strategies for the determined optimal combustion chamber configuration to actively guide the flame in the space field and enable rapid combustion. Extract the near-wall temperature field and convective heat transfer coefficient. The near-wall temperature field is the process of the flame transferring heat to the wall, including heat conduction and convective heat transfer. Step B3: Calculate the heat flux density based on the extracted near-wall temperature field and convective heat transfer coefficient; Step B4: Based on the determined distribution of heat flux density in different areas of the optimal combustion chamber, take refined heat insulation measures; Step B5: Use the finite element software Ansys to obtain thermal stress and strain. The specific calculation formula is as follows: Where ε is thermal strain and α is the coefficient of thermal expansion. For solid reference temperature, Let E be the thermal stress, E be the elastic modulus of the material, and δ be the length of the conductive medium. It represents the change in the length of an object. Indicates the original length of the object. Indicates the temperature of a solid; Step B6: Evaluate different insulation measures comprehensively based on their insulation performance, heat load characteristics, and combustion performance, conduct multiple iterations, and finally determine the optimal scheme for the coupling design of flame development and insulation. The specific process of the structural parametric design based on heat flow directional guidance is as follows: Step C1, Select Seven variables determine the shape of the combustion chamber. Determine the size and position of the outer chamber arc. Determine the inner chamber arc and its tangent. Determine the common tangent lines of the inner and outer chambers; among which, The elevation angle of the interior room; The height of the ridge at the junction of the inner and outer rooms; The radius of the inner recessed area; The diameter of the outer chamber throat opening; The outer room exit angle; The radius of the outer chamber recess arc; The elevation angle of the outer room; Step C2: Calculate the coordinate and slope parameters to complete the parameterized expression of the combustion chamber cross-section. The specific calculation is shown below: (1) Slope of the left tangent of the outer circle ; (2) Abscissa of the center of the outer circle: ; (3) The ordinate of the outer circle's center: ; (4) Tangent intercept on the outer circle: ; Step C3: Calculate the cross-sectional area of ​​the combustion chamber. Combustion chamber cross-sectional area It consists of three small segmented sections, denoted as follows: , It is the area of ​​the obtuse triangle; The area of ​​each figure is a closed figure bounded by two straight line segments and a circular arc, and is calculated using calculus. The specific calculation method is as follows: Step C4: Calculate the combustion chamber volume according to Goulding's theorem. The specific expression is as follows: 。 2. The combustion heat flux control method according to claim 1, characterized in that, The spray fragmentation model, the evaporation model, the turbulence model, and the combustion model are respectively based on the Wave model, the Dukowicz model, the k-zeta-f model, and the ECFM-3Z model.

3. The combustion heat flux control method according to claim 2, characterized in that, Combustion simulation calculations include calculations of air utilization rate, in-cylinder fuel-air / turbulent mixing rate, and heat flux density, as detailed below: Air utilization rate represents the ratio of the total volume of meshes in the CFD computation region where the fuel-air equivalence ratio satisfies the constraint condition to the total mesh volume. The specific calculation formula is as follows: in, This refers to the total volume of gas inside the cylinder. The total volume of the grid is 0.5≤φ≤1.5, where φ is the air-fuel equivalence ratio; The in-cylinder air-fuel / turbulent mixing rate is proportional to the reciprocal of the turbulent mixing time. The reciprocal of the turbulent mixing time characterizes the rate of change of turbulent kinetic energy in the cylinder. The specific calculation formula is as follows: Where Δ is the reciprocal of the turbulent mixing time, For the mass of the infinitesimal element, The turbulent dissipation rate within the infinitesimal element. It represents the turbulent kinetic energy within the infinitesimal element; The formula for calculating heat flux density is as follows: in, For fluid density, Specific heat capacity of the fluid Friction speed based on shear force, The value is a dimensionless temperature. It is a dimensionless constant representing the distance to the wall when in turbulent flow. These represent the distance to the near-wall mesh and the temperature, respectively. For the solid domain temperature.

4. The combustion heat flux control method according to claim 3, characterized in that, The optimal combustion chamber configuration is an asymmetric combustion chamber with an improved dual-flow structure for the intake piston and a flat-top structure for the exhaust piston. The overall profile consists of an inner chamber throat, an outer chamber throat located at one end of the inner chamber throat, an outer chamber recess arc located at the end of the outer chamber throat away from the inner chamber throat, and an inner chamber recess arc located at the end of the outer chamber recess arc away from the outer chamber throat. The length of the combustion chamber is denoted as... L The diameter of the inner chamber throat is recorded as L 1 The elevation angle of the inner room is recorded as θ a The radius of the inner recess is denoted as . R 1 The diameter of the external ventricular larynx is recorded as L 2 The elevation angle of the outer room is recorded as θ b The radius of the outer chamber recess arc is denoted as R 2 The outer room exit corner is marked as θ c The height of the ridge at the junction of the inner and outer rooms is recorded as H .

5. The combustion heat flux control method according to claim 4, characterized in that, The specific calculation expressions for heat conduction, convective heat transfer, convective heat transfer coefficient, and heat flux density are as follows: After coupling the fluid surface temperature calculation to the solid surface, the expression for calculating heat conduction in the solid domain is obtained according to Fourier's law: Where q is the heat flux density and λ is the thermal conductivity of the material. The derivative of temperature with respect to the n-direction, t is the conduction time, A is the contact area, and δ is the length of the conduction medium. For fluid temperature, The wall temperature; Based on Fourier's heat conduction equation describing heat conduction in solids and the heat transfer equation describing heat transfer in fluids, the expression for convective heat transfer at the fluid-solid interface is: Where λ is the thermal conductivity of the material, T is the solid temperature, and α is the coefficient of thermal expansion. The wall temperature, The temperature of the fluid near the wall; The formula for calculating the convective heat transfer coefficient is as follows: in, For solid-state temperature, For solid reference temperature, Heat flux density; The formula for calculating heat flux density is as follows: in, For fluid density, Specific heat capacity of the fluid Friction speed based on shear force, The value is a dimensionless temperature. It is a dimensionless constant representing the distance to the wall when in turbulent flow. These represent the distance to the near-wall mesh and the temperature, respectively. For the solid domain temperature.

6. The combustion heat flux control method according to claim 5, characterized in that, The specific process of taking refined heat insulation measures based on the determined distribution of heat flux density in different regions of the optimal combustion chamber in step B4 is as follows: B41. Based on simulation calculations and optical tests, determine the influence of the characteristic parameters of the thermal insulation coating on the wall heat transfer. The characteristic parameters of the thermal insulation coating include the thickness of the thermal insulation coating, the thermal insulation material, the surface roughness, and the porosity. B42. Considering the reverse effect of the characteristic parameters of the heat insulation coating on combustion, calculate the characterization indicators of combustion efficiency, indicated work, and indicated thermal efficiency. B43. Design different groups of insulation measures and analyze the specific insulation effects; determine the preliminary insulation scheme, select the insulation measures with the highest insulation capacity for areas with higher heat flow near the wall, and select insulation measures with ordinary insulation capacity for areas with lower heat flow near the wall.

7. A opposed two-stroke engine, characterized in that: The opposed two-stroke engine uses the combustion heat flow control method described in any one of claims 1-6 for in-cylinder heat flow control.

Images