Construction method of hydrogen turbulent combustion thickened flame surface model

Abstract

The invention provides a method for constructing a thickened flame surface model of hydrogen turbulent combustion, which belongs to the technical field of hydrogen fuel engines, and specifically comprises the following steps: modeling a diffusion enhancement effect and a flame surface wrinkle effect caused by multi-scale turbulent flow by constructing a hydrogen fuel turbulent flame speed scale rate under a wide working condition; and the combustion process of the hydrogen fuel can be described more accurately. In addition, on the basis of a thin reaction zone combustion mode, key physical quantities are extracted, a combustion efficiency function is optimized, multi-scale turbulence and a difference diffusion effect are considered, and the thickened flame surface model is further perfected. The development of the method provides powerful technical support for the forward design of the hydrogen fuel engine based on numerical simulation, promotes the engineering application of the hydrogen fuel engine, and assists the hydrogen fuel engine to play a greater role in efficient, clean and safe energy transformation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hydrogen fuel engines, and in particular to a method for constructing a hydrogen turbulent combustion thickened flame surface model. BACKGROUND

[0002] With the growing global demand for clean energy, hydrogen fuel engines have received widespread attention due to their high efficiency and clean combustion characteristics. However, the development of hydrogen fuel engines faces many challenges. Backfiring and thermoacoustic oscillations are prone to occur when hydrogen fuel is burned, which affects the performance of the engine. Backfiring refers to the reverse propagation of the flame into the fuel supply system, while thermoacoustic oscillations are instabilities caused by the interaction of the combustion process with the acoustic characteristics of the combustion chamber. In addition, hydrogen fuel has low ignition energy and is prone to deflagration, which poses a potential safety hazard to the safe operation of the equipment. Numerical simulation is of great significance to the design of hydrogen fuel engines. Traditional engine design usually relies on a large number of experimental trial and error, which not only has high cost, but also is time-consuming and laborious. Numerical simulation can simulate and predict the combustion process inside the engine based on physical models and numerical methods, providing a scientific basis for the design and optimization of the engine. Through numerical simulation, engineers can evaluate different combustion organization schemes in the design stage, predict the performance and emission characteristics of the engine, identify and solve potential problems in advance, reduce experimental cost and risk, and shorten the development cycle. However, hydrogen combustion numerical simulation also faces a series of challenges. The unstable combustion of hydrogen fuel has strong transient characteristics, which puts high requirements on the accuracy of the combustion model and the stability of the numerical method. In the actual working condition of the engine, the combustion process involves complex interactions between turbulent flow and chemical reactions. However, the conventional large eddy simulation grid is difficult to accurately analyze the fine structure of the hydrogen flame, which limits the accuracy of the simulation results and further limits the guidance significance for engine development. SUMMARY

[0003] Therefore, the present application provides a method for constructing a hydrogen turbulent combustion thickened flame surface model, which solves the problems in the prior art and accurately simulates the combustion process in a hydrogen fuel engine.

[0004] The method for constructing a hydrogen turbulent combustion thickened flame surface model provided by the present application adopts the following technical scheme: A method for constructing a hydrogen turbulent combustion thickened flame surface model, comprising: Step 1, constructing a multi-source data set of hydrogen turbulent flame propagation velocity under wide operating conditions, and determining the main control parameter of hydrogen turbulent flame propagation velocity based on the multi-source data set, and then modeling the diffusion enhancement effect and flame surface wrinkling effect corresponding to multi-scale turbulence, and constructing a hydrogen turbulent flame propagation velocity scaling rate in a wide operating range; Step 2, the thin reaction zone hydrogen turbulent flow combustion process is simulated by using a numerical simulation method, physical quantities in the combustion field are extracted, and an optimal expression form of a hydrogen turbulent flow combustion efficiency function is determined based on the extracted physical quantities; Step 3, for the deviation of the combustion characteristics caused by the unanalyzed flame fold in the thickened flame surface model, a physical model of the flame fold is modeled, and a compensation method for weakening the thickened flame fold is designed; Step 4, the combustion efficiency function determined in step 2, the flame fold physical model and the compensation method in step 3, and the hydrogen turbulent flow flame propagation speed scaling rate set in step 1 are integrated into the thickened flame surface initial model under the large eddy simulation framework, and the effective diffusion coefficient in the energy equation and the component equation is calculated dynamically to form the hydrogen turbulent flow combustion thickened flame surface model considering the multi-scale turbulent flow and the differential diffusion effect.

[0005] Optionally, in step 1, the construction of the wide working condition hydrogen turbulent flow flame propagation speed multi-source data set includes hydrogen fuel turbulent flow flame propagation speed data under different pressures, temperatures, fuel equivalence ratios and turbulent intensities.

[0006] Optionally, in step 1, the specific steps of determining the main control parameters of the hydrogen turbulent flow flame propagation speed based on the multi-source data set include: using the active subspace method to reduce the dimension of the working condition parameters in the multi-source data set, and extracting the turbulent fluctuation velocity, laminar flame speed, laminar flame thickness and turbulent integral scale as the main control parameters by analyzing the correlation between each working condition parameter and the hydrogen turbulent flow flame propagation speed.

[0007] Optionally, in step 1, the expression of the wide working condition hydrogen turbulent flow flame propagation speed scaling rate is: ; ; ; Wherein, is the turbulent flame propagation speed; is the laminar flame speed; is the flame area after folding; is the flame area before folding; is the additional diffusion coefficient caused by turbulence; is the molecular diffusion coefficient; is the turbulent fluctuation velocity; is the laminar flame speed; is the laminar flame thickness; is the turbulent integral scale; is the Karlovitz number.

[0008] Optionally, in step 2, the physical quantities in the combustion field include the turbulent fluctuation velocity , flame stretch, laminar flame speed , laminar flame thickness , and grid characteristic scale .

[0009] Optionally, in the step 2, the optimal expression form of the hydrogen turbulent flame burning efficiency function is: ; wherein, is the efficiency function; is the first model parameter; is the turbulent fluctuation velocity; is the laminar flame speed; is the grid characteristic scale; is the laminar flame thickness; is the thickening factor.

[0010] Optionally, in the step 3, the compensation method for designing the thickening flame fold weakening specifically comprises: introducing a correction term in the thickening flame surface model, the correction term being related to the morphological characteristics and scale of the flame fold, and the deviation of the burning efficiency and the flame propagation speed caused by the unanalyzed flame fold is compensated through the correction term.

[0011] Optionally, in the step 4, the formula for dynamically calculating the effective diffusion coefficient in the energy equation and the component equation is: ; wherein, ; is the effective diffusion coefficient; is the molecular diffusion coefficient; is the turbulent diffusion coefficient; is the efficiency function; is the thickening factor; is the flame detection function; is the second model parameter; is the absolute value of the reaction rate.

[0012] In summary, the present application includes the following beneficial technical effects: The thickening flame surface model considering the multi-scale turbulent flow and the differential diffusion effect in the present application enables the hydrogen fuel unsteady combustion simulation to accurately simulate the combustion process in the hydrogen fuel engine within a wide range of working conditions, provides strong technical support for the positive design of the engine, and helps to improve the performance and safety of the engine, and reduce the research and development cost and period.

[0013] By considering the thickened flame surface model of multi-scale turbulent flow and differential diffusion effect, the requirement of grid resolution can be reduced under the premise of ensuring the simulation accuracy, the calculation efficiency of numerical simulation is improved, and it is more suitable for engineering practical application. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only represent some of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings.

[0015] Figure 1 The flow chart of the construction method of the hydrogen turbulent combustion thickened flame surface model of the embodiments of the present application. DETAILED DESCRIPTION

[0016] The embodiments of the present application will be described in detail below with reference to the drawings.

[0017] The embodiments of the present application are described below through specific concrete examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. Obviously, the described embodiments are only some of the embodiments of the present application, not all. The present application can also be implemented or applied by other different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0018] It should be noted that the various aspects of the embodiments described below are within the scope of the appended claims. It should be apparent that the aspects described herein can be embodied in a wide variety of forms and that any specific structure and / or function described herein is merely illustrative. Based on the present application, those skilled in the art should understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, the devices and / or methods can be implemented using any number of the aspects set forth herein. In addition, this device and / or method can be implemented using other structures and / or functionality in addition to or other than one or more of the aspects set forth herein.

[0019] It is also necessary to explain that the drawings provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and only show the components related to the present application in the drawings, not drawn according to the number, shape and size of the components in actual implementation. The type, number and proportion of each component in actual implementation can be a random change, and the component layout type can be more complex.

[0020] In addition, in the following description, specific details are provided in order to facilitate a thorough understanding of examples. However, one skilled in the art will understand that the aspects described can be practiced without these specific details.

[0021] The embodiment of the present application provides a construction method of a hydrogen turbulent combustion thickened flame surface model.

[0022] As shown in Figure 1 A construction method of a hydrogen turbulent combustion thickened flame surface model, comprising: Step 1, constructing a multi-source data set of hydrogen turbulent flame propagation velocity under wide working conditions, and determining the main control parameter of hydrogen turbulent flame propagation velocity based on the multi-source data set, and then modeling the diffusion enhancement effect and the flame surface folding effect corresponding to multi-scale turbulence respectively. The diffusion enhancement effect model is for small-scale turbulence, considers the promotion effect of small-scale turbulence on the mixing of hydrogen fuel and oxidant, and the promotion effect on the hydrogen turbulent flame propagation velocity, and the promotion effect is quantified by the ratio of the additional diffusion coefficient caused by turbulence to the molecular diffusion coefficient. The flame surface folding effect model is for large-scale turbulence, describes the stretching, folding and breaking phenomenon of large-scale turbulence on the hydrogen flame surface, quantifies the influence of flame surface folding on hydrogen turbulent flame propagation velocity through the ratio of the flame area after folding to the flame area before folding, and develops the scaling rate of hydrogen turbulent flame propagation velocity in a wide working condition range.

[0023] Step 2, simulating the hydrogen turbulent combustion process in the thin reaction zone by using a high-fidelity numerical simulation method, extracting key physical quantities in the combustion field, and determining the best expression form of the hydrogen turbulent combustion efficiency function based on the extracted key physical quantities.

[0024] Step 3, modeling the physical model of flame folding and designing a compensation method for weakening the thickened flame folding for the deviation of combustion characteristics caused by the unresolved flame folding in the thickened flame surface model.

[0025] Step 4, integrating the combustion efficiency function determined in step 2, the flame folding physical model and the compensation method in step 3, and the scaling rate of hydrogen turbulent flame propagation velocity in a wide working condition range in step 1 into the thickened flame surface initial model under the large eddy simulation framework, and forming the hydrogen turbulent combustion thickened flame surface model considering multi-scale turbulence and differential diffusion effect by dynamically calculating the effective diffusion coefficient in the energy equation and the component equation.

[0026] This application aims to develop a simulation method for unsteady combustion of hydrogen fuel based on a thickened flame surface model to address the challenges faced in hydrogen combustion simulation. The thickened flame surface model, by artificially thickening the flame surface, reduces the mesh resolution requirement while ensuring accurate flame propagation velocity, effectively alleviating the mismatch between mesh analytical scale and flame thickness in combustion chamber simulation. By constructing a hydrogen fuel turbulent flame velocity scaling rate under wide operating conditions, and modeling the diffusion enhancement effect and flame surface wrinkling effect caused by multi-scale turbulence, the hydrogen fuel combustion process can be described more accurately. Furthermore, based on a thin reaction zone combustion mode, key physical quantities are extracted, the combustion efficiency function is optimized, and multi-scale turbulence and differential diffusion effects are considered to further improve the thickened flame surface model. The development of this method will provide strong technical support for realizing forward design of hydrogen fuel engines based on numerical simulation, promote the engineering application of hydrogen fuel engines, and help them play a greater role in the efficient, clean, and safe energy transition.

[0027] In step 1, a multi-source dataset of hydrogen turbulent flame propagation velocity under wide operating conditions is constructed, including hydrogen fuel turbulent flame propagation velocity data under different pressures, temperatures, fuel equivalence ratios, and turbulence intensities to ensure the dataset's broad applicability and representativeness. Specifically, the pressure range is 0.1-1 MPa, the temperature range is 300-800 K, the fuel equivalence ratio range is 0.3-3.0, and the turbulent fluctuation velocity range is 0.1-10 m / s.

[0028] In step 1, the specific steps for determining the master control parameters of hydrogen turbulent flame propagation velocity based on multi-source datasets include: using the active subspace method to reduce the dimensionality of the operating parameters in the multi-source datasets; and extracting the turbulent fluctuation velocity, laminar flame velocity, laminar flame thickness, and turbulent integral scale as master control parameters by analyzing the correlation between each operating parameter and the hydrogen turbulent flame propagation velocity. By analyzing the correlation between the operating parameters and the flame propagation velocity, the main sensitive parameters, i.e., the master control parameters of hydrogen turbulent flame propagation velocity, are determined, providing a foundation for developing the scaling rate of hydrogen turbulent flame propagation velocity.

[0029] In step 1, the expression for the scaling factor of the hydrogen turbulent flame propagation velocity over a wide operating range is: ; ; ; in, The propagation speed of turbulent flame; Laminar flame velocity; The area of ​​the flame after folding; The flame area before the folds; The additional diffusion coefficient caused by turbulence; The molecular diffusion coefficient; For turbulent fluctuation velocity; Laminar flame velocity; The thickness of the laminar flame; The integral scale is for turbulence. It is a Karlovy Vu number.

[0030] The scaling factor for hydrogen turbulent flame propagation velocity over a wide operating range can reflect the quantitative relationship between flame propagation velocity and operating parameters, providing a foundation for subsequent combustion model development.

[0031] In step 2, the key physical quantities extracted from the combustion field include turbulent fluctuation velocity. Flame elongation, laminar flame velocity Laminar flame thickness and grid feature scale These physical quantities reflect important information such as turbulence characteristics, flame structure, and combustion reaction rate during the combustion process.

[0032] In step 2, the optimal expression of the hydrogen turbulent combustion efficiency function is: ; in, Let it be the efficiency function; These are the parameters for the first model, with values ​​ranging from 0.1 to 10. For turbulent fluctuation velocity; Laminar flame velocity; The grid feature scale; The thickness of the laminar flame; The thickening factor has a value range of 5-50.

[0033] The optimal expression of the hydrogen turbulent combustion efficiency function should be able to more accurately describe the relationship between combustion efficiency and key physical quantities, thereby improving the prediction accuracy of the combustion model.

[0034] In step 3, the specific compensation method for reducing the thickness of flame folds includes: introducing a correction term into the thickened flame surface model. The correction term is related to the morphological characteristics and scale of the flame folds. The correction term compensates for the deviation in combustion efficiency and flame propagation speed caused by the lack of resolution of flame folds.

[0035] In step 4, the formula for dynamically calculating the effective diffusion coefficient in the energy equation and composition equation is as follows: ; in, ; The effective diffusion coefficient; The molecular diffusion coefficient; The turbulent diffusion coefficient; Let it be the efficiency function; For thickening factor; This is a flame detection function; These are the parameters for the second model, with values ​​ranging from 3 to 10. This represents the absolute value of the reaction rate.

[0036] Step 4: Specifically, using the large eddy simulation framework as the numerical calculation vehicle, the hydrogen turbulent combustion efficiency function determined in Step 2, the flame wrinkling physical model constructed in Step 3, and the thickened flame wrinkling reduction compensation method are initially embedded into the basic thickened flame surface model to form an initial model of hydrogen turbulent combustion thickened flame surface considering multi-scale turbulence and differential diffusion effects. Then, the wide-range hydrogen turbulent flame propagation velocity scaling rate model constructed in Step 1 is used as the accuracy verification benchmark model, and the parameters of the current simulation condition are substituted: including turbulent fluctuation velocity. Laminar flame velocity Laminar flame thickness Turbulent integral scale The theoretical turbulent flame propagation velocity is calculated. The aforementioned initial model for hydrogen turbulent combustion with a thickened flame surface is run, and the turbulent flame propagation velocity output by the initial model is extracted from the calculation results of the large eddy simulation framework. The deviation between the theoretical turbulent flame propagation velocity and the turbulent flame propagation velocity output by the initial model for hydrogen turbulent combustion with a thickened flame surface is compared. If the deviation exceeds a preset accuracy threshold, the parameters of the initial model for hydrogen turbulent combustion with a thickened flame surface are adjusted, such as the parameters of the first model. Flame detection function The second model parameter Thickening factor The above process is repeated until the deviation between the theoretical turbulent flame propagation speed and the turbulent flame propagation speed output by the initial model of hydrogen turbulent combustion thickened flame surface meets the accuracy requirements, and finally the hydrogen turbulent combustion thickened flame surface model considering multi-scale turbulence and differential diffusion effects is obtained.

[0037] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for constructing a hydrogen turbulent combustion thickened flame surface model, characterized in that... ,include: Step 1: Construct a multi-source dataset of hydrogen turbulent flame propagation velocity under wide operating conditions, and determine the main control parameters of hydrogen turbulent flame propagation velocity based on the multi-source dataset. Then, model the diffusion enhancement effect and flame surface wrinkling effect corresponding to multi-scale turbulence respectively, and construct a scaling rate of hydrogen turbulent flame propagation velocity over a wide operating range. Step 2: The hydrogen turbulent combustion process in the thin reaction zone is simulated using numerical simulation methods. Physical quantities in the combustion field are extracted, and the optimal expression of the hydrogen turbulent combustion efficiency function is determined based on the extracted physical quantities. Step 3: To address the combustion characteristic deviation caused by the unresolved flame folds in the thickened flame surface model, a physical model of the flame folds is modeled, and a compensation method for reducing the thickness of the flame folds is designed. Step 4: Integrate the combustion efficiency function determined in Step 2, the flame folding physical model and compensation method in Step 3, and the wide operating range hydrogen turbulent flame propagation velocity scaling rate in Step 1 into the thickened flame surface initial model under the large eddy simulation framework. By dynamically calculating the effective diffusion coefficient in the energy equation and composition equation, a hydrogen turbulent combustion thickened flame surface model considering multi-scale turbulence and differential diffusion effects is formed.

2. The method for constructing the hydrogen turbulent combustion thickened flame surface model according to claim 1, characterized in that, In step 1, the construction of a multi-source dataset of hydrogen turbulent flame propagation velocity under wide operating conditions includes hydrogen fuel turbulent flame propagation velocity data under different pressures, temperatures, fuel equivalence ratios, and turbulence intensities.

3. The method for constructing a hydrogen turbulent combustion thickened flame surface model according to claim 1, characterized in that, In step 1, the specific steps for determining the master control parameters of hydrogen turbulent flame propagation speed based on multi-source datasets include: using the active subspace method to reduce the dimensionality of the operating parameters in the multi-source datasets, and extracting the turbulent pulsation velocity, laminar flame velocity, laminar flame thickness, and turbulent integral scale as master control parameters by analyzing the correlation between each operating parameter and hydrogen turbulent flame propagation speed.

4. The method for constructing the hydrogen turbulent combustion thickened flame surface model according to claim 1, characterized in that, In step 1, the expression for the scaling factor of the hydrogen turbulent flame propagation velocity over a wide operating range is: ； ； ； in, The propagation speed of turbulent flame; Laminar flame velocity; The area of ​​the flame after folding; The flame area before the folds; The additional diffusion coefficient caused by turbulence; The molecular diffusion coefficient; For turbulent fluctuation velocity; Laminar flame velocity; The thickness of the laminar flame; The integral scale is for turbulence. It is a Karlovy Vu number.

5. The method for constructing a hydrogen turbulent combustion thickened flame surface model according to claim 1, characterized in that, In step 2, the physical quantities extracted from the combustion field include turbulent pulsation velocity. Flame elongation, laminar flame velocity Laminar flame thickness and grid feature scale .

6. The method for constructing a hydrogen turbulent combustion thickened flame surface model according to claim 5, characterized in that, In step 2, the optimal expression of the hydrogen turbulent combustion efficiency function is: ； in, Let it be the efficiency function; These are the parameters of the first model; For turbulent fluctuation velocity; Laminar flame velocity; The grid feature scale; The thickness of the laminar flame; This is a thickening factor.

7. The method for constructing a hydrogen turbulent combustion thickened flame surface model according to claim 1, characterized in that, In step 3, the specific compensation method for reducing the thickness of flame wrinkles includes: A correction term is introduced into the thickened flame surface model. The correction term is related to the morphological characteristics and scale of the flame folds. The correction term compensates for the deviations in combustion efficiency and flame propagation speed caused by the lack of resolution of flame folds.

8. The method for constructing a hydrogen turbulent combustion thickened flame surface model according to claim 1, characterized in that, In step 4, the formula for dynamically calculating the effective diffusion coefficient in the energy equation and composition equation is as follows: ； in, ; The effective diffusion coefficient; The molecular diffusion coefficient; The turbulent diffusion coefficient; Let it be the efficiency function; For thickening factor; This is a flame detection function; These are the parameters for the second model; This represents the absolute value of the reaction rate.

Images