Engine combustion chamber fuel injection point source loading method based on flame surface model

Abstract

The invention belongs to the field of engines and computational fluid mechanics, and discloses an engine combustion chamber fuel injection point source loading method based on a flame surface model. According to the engine combustion chamber fuel injection point source loading method based on the flame surface model, the point source is arranged at the center point of the fuel injection hole under the condition that the numerical simulation precision of the combustion chamber is not reduced according to the rapid, efficient and accurate numerical simulation requirements of fuel injection, mixing and combustion processes in the aerospace engine combustion chamber; a mass source item, a momentum source item, an energy source item and a mixed fraction source item are added in a control equation set, so that the generation difficulty of a complex grid is reduced, the physical characteristics of the fuel injection process are well represented, a combustion chamber numerical simulation CFD program is slightly changed, the operability is high, and the method is suitable for large-scale popularization and application. And the modeling difficulty and the grid number of the combustion chamber grid with the complex engineering configuration are reduced, the engine evaluation design efficiency is greatly improved, and the engineering practical value is achieved.

Description

Technical Field

[0001] The invention belongs to the field of engines and computational fluid dynamics, and in particular relates to a method for loading a fuel injection point source in an engine combustion chamber based on a flame surface model. Background Art

[0002] In the numerical simulation of the engine combustion chamber, it is necessary to solve the Navier-Stokes equations. For compressible flow, the equations are derived from the three conservation laws of mass conservation, momentum conservation, and energy conservation. The specific control equations are as follows: ; If fuel injection is considered, the mixture fraction conservation equation needs to be added: .

[0003] by Figure 1a Taking the fuel injection holes of the combustion chamber support plate model shown in the figure as an example, in the traditional combustion chamber numerical simulation, in order to simulate the fuel injection, mixing and combustion process of the combustion chamber support plate, it is necessary to divide all the fuel injection holes of the combustion chamber support plate into Figure 1b The grid shown.

[0004] In order to achieve efficient combustion, the combustion chamber usually contains dozens or even hundreds of fuel injection holes. Since the fuel injection holes are small (usually in the order of 0.5mm~1mm in diameter) and numerous (for engineering combustion chamber configurations, the number of fuel injection holes is usually in the order of tens to hundreds), the difficulty of combustion chamber mesh modeling is greatly increased.

[0005] In order to simulate the fuel injection process, traditional combustion chamber numerical simulation adopts the method of directly dividing the grid of the fuel nozzle. The advantage of this is high-fidelity grid modeling of the injection process, which can better describe the near-field physical characteristics of the nozzle. The disadvantage is that high-quality grid generation is difficult, time-consuming, and the grid size is large, which reduces the efficiency of numerical simulation.

[0006] In recent years, with the rise of AI, digital evaluation, digital design, and digital intelligence have become synonymous with the aerospace field. In order to achieve efficient digital design and evaluation of aerospace engine combustion chambers, efficient and reliable numerical simulation technology is a key technology, which poses a great challenge to high-quality grid generation.

[0007] Currently, there is an urgent need to develop a point source loading method for fuel injection in the engine combustion chamber based on the flame surface model. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for loading a fuel injection point source in an engine combustion chamber based on a flame surface model, so as to simulate a fuel injection process.

[0009] The method for loading a fuel injection point source in an engine combustion chamber based on a flame surface model of the present invention comprises the following steps: S10. Grouping the fuel nozzles according to the injection flow rate of each fuel nozzle; If there are m fuel nozzles in the engine combustion chamber, and the injection flow rate of each fuel nozzle is f(m), then {f(1), ...f(m)} constitutes the fuel injection flow rate set A. The elements in A are sorted by bubble sorting, and duplicate elements are deleted to obtain set B = {f(1), ...f(k)}. The number of elements in set B is the number of groups of fuel nozzles. S20. For each group of fuel injection holes, organize the injection information and write it into a file inject.dat; Treat each group of fuel nozzles as a set and organize the injection information, which includes: the injection flow rate of the fuel nozzles in this group, the name and mass fraction of the injected fuel component, the injected fuel temperature, the injected fuel speed, the number of fuel nozzles in this group, and the center point position coordinates of each fuel nozzle; S30. Treat the fuel nozzle as a solid wall and divide the grid; Determine the coordinate origin for a certain engine combustion chamber O and x, y, z Three coordinate axes, treat the fuel nozzle as a solid wall and divide the grid; S40. Establish a control equation group for numerical simulation of the combustion chamber and compile a corresponding CFD calculation program; The control equations for the numerical simulation of the combustion chamber are: ; in, is the fluid density, For pressure, is the total energy, is a mixed fraction, is the diffusion coefficient, is the enthalpy, for Direction speed, for Direction speed, is the energy flux, is the shear stress, is the Dirichilet constant, For time, for Direction and location; S50. Start the numerical simulation of the combustion chamber, calculate to the Nth step, and determine whether to inject fuel; S60. If no fuel is injected, the calculation continues until convergence, and the combustion chamber numerical simulation calculation ends; S70. If fuel is injected, a point source loading method is used to simulate the fuel injection process; Read the inject.dat file to obtain the injection information of each fuel nozzle; based on the injection information, calculate the mass source term of each fuel nozzle injection , momentum source term , Energy source term and the mixed fraction source term ; S80. Equivalently treat each fuel injection hole as a point at the center of the fuel injection hole, and load injection information through the grid unit where the point at the center of the fuel injection hole is located; According to the center position coordinates of each fuel nozzle, find the number of the fuel nozzle in the entire combustion chamber grid, and according to the number, the mass source item injected by the fuel nozzle is , momentum source term , Energy source term and the mixed fraction source term Etc. are loaded as source terms to the right side of the CFD control equation, namely: ; S90. Solve the above control equations, update the physical quantities of each grid unit at the same time, return to S70, iterate until convergence, and the numerical simulation calculation of the combustion chamber with point source loading is completed.

[0010] The flame surface model-based engine combustion chamber fuel injection point source loading method of the present invention is aimed at the needs of fast, efficient and accurate numerical simulation of fuel injection, mixing and combustion processes in the combustion chamber of an aerospace engine. Without reducing the numerical simulation accuracy of the combustion chamber, a point source is set at the center point of the fuel nozzle, and mass source terms, momentum source terms, energy source terms and mixed fraction source terms are added to the control equation group, thereby reducing the difficulty of complex grid generation and better characterizing the physical characteristics of the fuel injection process. It has little change to the combustion chamber numerical simulation CFD program and has strong operability, reduces the difficulty of grid modeling and the number of grids in the combustion chamber of complex engineering configuration, greatly improves the efficiency of engine evaluation and design, and has practical engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1a It is the combustion chamber support plate model (physical model); Figure 1b is the combustion chamber support plate model (computational mesh); Figure 2 The present invention is a flow chart of a method for loading a fuel injection point source in an engine combustion chamber based on a flame surface model; Figure 3 This is a schematic diagram of the combustion chamber configuration of the DLR engine; Figure 4a Loading diagram for point source (2D); Figure 4b Schematic diagram of point source loading (3D); Figure 5a is the mixture fraction distribution in the unburned case (point source simulated injection); Figure 5b is the mixture fraction distribution in the unburned case (real physical fuel nozzle); Figure 6a The static pressure distribution of the flow field under unburned conditions (point source simulated injection); Figure 6b The static pressure distribution of the flow field under unburned conditions (real physical fuel nozzle); Figure 7a is the OH mass fraction distribution under combustion conditions (point source simulation injection); Figure 7b is the OH mass fraction distribution under combustion conditions (real physical fuel nozzle); Figure 8a The temperature profiles at different flow positions under combustion conditions (x=67mm); Figure 8b The temperature profiles at different flow positions under combustion conditions (x=110mm); Figure 8c It is the temperature profile at different flow positions under combustion conditions (x=218mm). DETAILED DESCRIPTION

[0012] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0013] like Figure 2 As shown, the method for loading a fuel injection point source in an engine combustion chamber based on a flame surface model of the present invention comprises the following steps: S10. Grouping the fuel nozzles according to the injection flow rate of each fuel nozzle; If there are m fuel nozzles in the engine combustion chamber, and the injection flow rate of each fuel nozzle is f(m), then {f(1), ...f(m)} constitutes the fuel injection flow rate set A. The elements in A are sorted by bubble sorting, and duplicate elements are deleted to obtain set B = {f(1), ...f(k)}. The number of elements in set B is the number of groups of fuel nozzles. S20. For each group of fuel injection holes, organize the injection information and write it into a file inject.dat; Treat each group of fuel nozzles as a set and organize the injection information, which includes: the injection flow rate of the fuel nozzles in this group, the name and mass fraction of the injected fuel component, the injected fuel temperature, the injected fuel speed, the number of fuel nozzles in this group, and the center point position coordinates of each fuel nozzle; S30. Treat the fuel nozzle as a solid wall and divide the grid; Determine the coordinate origin for a certain engine combustion chamber O and x, y, z Three coordinate axes, treat the fuel nozzle as a solid wall and divide the grid; S40. Establish a control equation group for numerical simulation of the combustion chamber and compile a corresponding CFD calculation program; The control equations for the numerical simulation of the combustion chamber are: ; in, is the fluid density, For pressure, is the total energy, is a mixed fraction, is the diffusion coefficient, is the enthalpy, for Direction speed, for Direction speed, is the energy flux, is the shear stress, is the Dirichilet constant, For time, for Direction and location; S50. Start the numerical simulation of the combustion chamber, calculate to the Nth step, and determine whether to inject fuel; S60. If no fuel is injected, the calculation continues until convergence, and the combustion chamber numerical simulation calculation ends; S70. If fuel is injected, a point source loading method is used to simulate the fuel injection process; Read the inject.dat file to obtain the injection information of each fuel nozzle; based on the injection information, calculate the mass source term of each fuel nozzle injection , momentum source term , Energy source term and the mixed fraction source term ; S80. Equivalently treat each fuel injection hole as a point at the center of the fuel injection hole, and load injection information through the grid unit where the point at the center of the fuel injection hole is located; According to the center position coordinates of each fuel nozzle, find the number of the fuel nozzle in the entire combustion chamber grid, and according to the number, the mass source item injected by the fuel nozzle is , momentum source term , Energy source term and the mixed fraction source term Etc. are loaded as source terms to the right side of the CFD control equation, namely: ; S90. Solve the above control equations, update the physical quantities of each grid unit at the same time, return to S70, iterate until convergence, and the numerical simulation calculation of the combustion chamber with point source loading is completed.

[0014] Embodiment: This embodiment is a DLR engine combustion chamber. The configuration of the DLR engine combustion chamber is shown in Figure 3 The DLR engine combustion chamber inlet is 50mm high and 40mm wide. The combustion chamber support plate is 32mm long and 6mm high. Hydrogen is injected into the combustion chamber through 15 fuel injection holes on the bottom of the support plate. The fuel injection hole diameter is 1mm, the fuel injection hole spacing is 2.4mm, the incoming flow Mach number Ma=2, and the injection flow Mach number Ma=1. The schematic diagram of the point source loading of this embodiment is shown in Figure 4a , Figure 4b For the two-dimensional case, no mesh is divided on the boundary of the fuel nozzle, the entire fuel nozzle boundary is treated as a wall, and a source term is added at the center point of the fuel nozzle. For the three-dimensional case, no mesh is divided on the boundary of the fuel nozzle, the entire fuel nozzle boundary is treated as a wall, and a source term is added at the center point of the fuel nozzle.

[0015] The incoming flow and injection conditions of this embodiment are shown in Table 1. In order to reduce the amount of calculation, two-dimensional calculation is adopted, the total grid volume is about 200,000, the wall surface adopts the adiabatic wall surface condition, the combustion model adopts the flame surface model, and the chemical reaction kinetic mechanism adopts the 7 components and 8 equations of hydrogen. For the convenience of comparison, two methods are used to carry out the calculation, one is to use real physical fuel nozzles to simulate the fuel injection combustion process, and the other is to use the engine combustion chamber fuel injection point source loading method based on the flame surface model of the present invention to simulate the fuel injection combustion process.

[0016] Table 1

[0017] Figure 5a The Z-mixf distribution of the mixture fraction in the unburned case (point source simulation injection) is given. Figure 5b The mixture fraction Z-mixf distribution in the unburned case (real physical fuel nozzle) is given; Figure 6a The static pressure P distribution of the flow field under unburned conditions (point source simulation injection) is given. Figure 6b The static pressure P distribution of the flow field under unburned conditions (real physical fuel nozzle) is given. It can be seen that near the fuel nozzle, there are some differences between the results of point source simulation injection and the real physical fuel nozzle. As the fuel moves downstream, the difference between the two gradually decreases, so that it will not affect the overall flow field structure.

[0018] Figure 7a The OH mass fraction distribution under combustion conditions (point source simulation injection) is given. Figure 7bThe OH mass fraction distribution under combustion conditions (real physical fuel nozzle) is given, where OH represents hydroxyl group; it can be seen that the flame structure, morphology and flame zone width are consistent in the two modes, indicating that the engine combustion chamber fuel injection point source loading method based on the flame surface model of the present invention can achieve the effect of a real physical fuel nozzle in simulating the combustion process after fuel injection, confirming the feasibility of the engine combustion chamber fuel injection point source loading method based on the flame surface model of the present invention.

[0019] Figure 8a The temperature profile at the flow position x=67mm under combustion is given. Figure 8b The temperature profile at the flow position x=110mm under combustion conditions is given. Figure 8c The temperature profile at the flow direction position x=218mm under combustion is given. It can be seen that except for the vicinity of the fuel injection hole ( x =67mm), the calculation and prediction results of the engine combustion chamber fuel injection point source loading method based on the flame surface model of the present invention are consistent with the real physical fuel nozzles, and can replace the real physical fuel nozzles in the numerical simulation process, thereby reducing the difficulty of mesh modeling in complex engineering configurations and improving the efficiency of the early design of the engine combustion chamber.

[0020] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and the embodiments, and can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional improvements and modifications can be easily realized without departing from the principles of the present invention. Therefore, without departing from the general concept defined by the claims and equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.

Claims

1. A method for loading a fuel injection point source into an engine combustion chamber based on a flame surface model, characterized in that: The following steps are involved: S10. Grouping the fuel nozzles according to the injection flow rate of each fuel nozzle; If there are m fuel nozzles in the engine combustion chamber, and the injection flow rate of each fuel nozzle is f(m), then {f(1), ...f(m)} constitutes the fuel injection flow rate set A. The elements in A are sorted by bubble sorting, and duplicate elements are deleted to obtain set B = {f(1), ...f(k)}. The number of elements in set B is the number of groups of fuel nozzles. S20. For each group of fuel injection holes, organize the injection information and write it into a file inject.dat; Treat each group of fuel nozzles as a set and organize the injection information, which includes: the injection flow rate of the fuel nozzles in this group, the name and mass fraction of the injected fuel component, the injected fuel temperature, the injected fuel speed, the number of fuel nozzles in this group, and the center point position coordinates of each fuel nozzle; S30. Treat the fuel nozzle as a solid wall and divide the grid; Determine the coordinate origin for a certain engine combustion chamber O and x, y, z Three coordinate axes, treat the fuel nozzle as a solid wall and divide the grid; S40. Establish a control equation group for numerical simulation of the combustion chamber and compile a corresponding CFD calculation program; The control equations for the numerical simulation of the combustion chamber are: ； in, is the fluid density, For pressure, is the total energy, is a mixed fraction, is the diffusion coefficient, is the enthalpy, for Direction speed, for Direction speed, is the energy flux, is the shear stress, is the Dirichilet constant, For time, for Direction and location; S50. Start the numerical simulation of the combustion chamber, calculate to the Nth step, and determine whether to inject fuel; S60. If no fuel is injected, the calculation continues until convergence, and the combustion chamber numerical simulation calculation ends; S70. If fuel is injected, a point source loading method is used to simulate the fuel injection process; Read the inject.dat file to obtain the injection information of each fuel nozzle; based on the injection information, calculate the mass source term of each fuel nozzle injection , momentum source term , Energy source term and the mixed fraction source term ; S80. Equivalently treat each fuel injection hole as a point at the center of the fuel injection hole, and load injection information through the grid unit where the point at the center of the fuel injection hole is located; According to the center position coordinates of each fuel nozzle, find the number of the fuel nozzle in the entire combustion chamber grid, and according to the number, the mass source item injected by the fuel nozzle is , momentum source term , Energy source term and the mixed fraction source term Etc. are loaded as source terms to the right side of the CFD control equation, namely: ； S90. Solve the above control equations, update the physical quantities of each grid unit at the same time, return to S70, iterate until convergence, and the numerical simulation calculation of the combustion chamber with point source loading is completed.

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