A numerical calculation method for calculating the stretch rate of hydrogen-ammonia mixed turbulent combustion

Abstract

The application discloses a numerical calculation method for calculating the stretch rate of hydrogen-ammonia mixed turbulent flow combustion, and belongs to the field of clean energy combustion numerical simulation calculation. The steps comprise the following steps: constructing a small flame database based on one-dimensional reactant-product equations and combining a strain rate parameterization; mapping the database to a trajectory variable space of a mixing fraction, a reaction progress variable and a normalized hydrogen mass fraction to generate a small flame lookup table; solving control equations by adopting large eddy simulation, and obtaining components, chemical source terms, differential diffusion terms and stretch rate terms by looking up the table; and comparing experimental data by prior verification and posterior verification to quantify the differential diffusion effect and the stretch effect. The application optimizes the small flame model by extension, can further consider the stretch effect while considering the differential diffusion effect, can accurately predict the main component mass fraction distribution in the hydrogen-ammonia mixed premixed flame, and provides theoretical support for the design and optimization of a hydrogen-ammonia burner.

Description

Technical Field

[0001] This invention belongs to the field of numerical simulation calculation of clean energy combustion, specifically a numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion. Background Technology

[0002] Currently, carbon emissions from traditional fossil fuels are a major concern, making research into clean energy increasingly urgent. However, while ammonia, as a clean energy source, has the potential for zero carbon emissions, it also faces a series of challenges that urgently need to be addressed, such as low flammability, low radiation intensity, and high nitrogen oxide emissions. Research indicates that by co-firing ammonia with partially cracked hydrogen, properties similar to methane fuel can be achieved, partially addressing these challenges. However, in high-intensity turbulent hydrogen-ammonia premixed flames, the flame is pushed into the thin reaction zone of the premixed region, and a strong stretching effect in curvature and strain is expected, significantly impacting the flame structure and characteristics, posing a major challenge to modeling premixed hydrogen-ammonia turbulent flames. Therefore, for such hydrogen-ammonia co-firing flames with significant stretching effects, it is crucial to calculate the stretching rate in hydrogen-ammonia co-firing turbulent combustion using numerical methods to ensure its safe and efficient operation in energy systems. Currently, the modeling process for hydrogen-ammonia blended combustion typically utilizes large eddy simulation (LES) methods from computational fluid dynamics. For premixed flames, a differential diffusion small flame model is used in conjunction with an artificially thickened flame model to predict component distribution changes caused by the different diffusion rates of hydrogen and ammonia. However, this process neglects the stretching effect. Furthermore, some models that consider the stretching effect, such as those based on scalar dissipation rate, OH mass fraction, H radical mass fraction, or H2 mass fraction, are used to simulate methane or hydrogen flames. These models have not been sufficiently validated in hydrogen-ammonia blended flames with strong differential diffusion effects. In other words, there is currently no method that can simultaneously consider the influence of differential diffusion and stretching effects in hydrogen-ammonia blended turbulent premixed flames. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a technical solution: a numerical calculation method for calculating the elongation rate of hydrogen-ammonia blended turbulent combustion. This invention couples a differential diffusion small flame model considering elongation rate with an artificially thickened flame model, and incorporates detailed chemical reaction mechanisms to simulate and predict the mass fraction of major components in a hydrogen-ammonia blended turbulent premixed flame.

[0004] The technical solution of the present invention is as follows:

[0005] A numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion includes the following steps:

[0006] Step 1: Construct a small flame database based on the one-dimensional reactant-product equation and strain rate parameterization;

[0007] Step 2: Map the database to the trajectory variable space of mixture fraction, reaction progress variable and normalized hydrogen mass fraction, and generate a small flame lookup table;

[0008] Step 3: Solve the governing equations using large eddy simulation, and obtain the components, chemical source terms, differential diffusion terms, and stretching rate terms by looking up tables;

[0009] Step 4: Quantify the difference diffusion effect and stretching effect by comparing experimental data through prior and posterior verification.

[0010] In the above technical solution, in step 1:

[0011] The global equivalent ratio covering the hydrogen-ammonia blending experimental conditions is 1.6;

[0012] The strain rate covers the upper and middle branches of the S-shaped curve to characterize the tensile effect.

[0013] In the above technical solution, in step 2:

[0014] Mixed fractions for:

[0015]

[0016] in, and These are the local mixing fractions of hydrogen and oxygen elements in the main components. This represents the relative atomic mass of hydrogen. The value represents the relative atomic mass of oxygen. The subscript ox indicates the oxidant flow rate, and the subscript fuel indicates the fuel flow rate.

[0017] Reaction progress variable: mass fraction Defined as the mass fraction of water ;

[0018] Normalized hydrogen mass fraction , Hydrogen mass fraction The maximum value.

[0019] In the above technical solution, in step 2:

[0020] Extrapolation was used for the mixture fraction region exceeding the flammability limit;

[0021] The small flame lookup table contains the efficiency factor, thickening factor, and flame sensor parameters of the artificially thickened flame model.

[0022] In the above technical solution, in step 3:

[0023] The governing equations include the component transport equations:

[0024]

[0025] in, and These are the efficiency function, the thickness factor, and the flame sensor. It is the diffusion coefficient, extracted from a small flame lookup table considering / not considering differential diffusion / stretching effects, where t is time. For average density, The solution is in the i-th direction. This is the subgrid eddy current diffusivity, with the main components k selected as H2, NH3, H2O, and O2. Let it be the Farve average mass fraction of its corresponding principal component k. Let be the average Farve velocity in the i-direction. For the Farve average source term of component k, It is a spatial average quantity. This represents the Farve average obtained through large eddy simulation.

[0026] In the above technical solution, step 4:

[0027] Prior verification involves directly inputting experimental data into a small flame lookup table and comparing the output components with the experimental data.

[0028] Posterior validation was performed by comparing the output results of large eddy simulation with experimental data.

[0029] In the above technical solution, the formula for quantifying the differential diffusion effect in step 4 is:

[0030]

[0031] in, Item and The terms are the diffusion terms in the principal component equations. The differential diffusion parameter is defined.

[0032] In the above technical solution, the formula for quantifying the stretching effect in step 4 is:

[0033]

[0034] in, For the elongation term, For strain rate, Let be the curvature term, where The flame displacement velocity, For curvature.

[0035] In the above technical solution, in step 3:

[0036] The computational domain adopts a cylindrical structure, including a central hydrogen-ammonia fuel jet, an annular ignition nozzle, and an outer nitrogen isolation zone; the mesh is a non-orthogonal structure.

[0037] In the above technical solution, step 1 adopts a hydrogen-ammonia blending mechanism that includes 31 components and 203 reactions.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] This invention, based on a one-dimensional reactant-product (R2P) small flame table incorporating strain rate and combined with a detailed hydrogen-ammonia mixing mechanism, introduces the stretching effect into a differential diffusion small flame model. The model is then fully validated by comparing it with experimental data, demonstrating its ability to accurately predict the distribution of major components in hydrogen-ammonia mixed turbulent premixed flames. Compared to models that do not consider the stretching effect, this model effectively solves the problem of inaccurate predictions caused by the stretching effect, providing research ideas and methods for subsequent simulations of flames exhibiting both differential diffusion and significant stretching effects. Attached Figure Description

[0040] Figure 1 This is a flowchart of a numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to the present invention.

[0041] Figure 2 This is a comparison chart (a) of the main component mass fraction distribution between the table lookup results and experimental data at the flow direction 3.5D (D is the diameter of the central fuel jet) position in the prior verification of the embodiments of the present invention.

[0042] Figure 3 This is a comparison chart (II) of the main component mass fraction distribution between the table lookup results and experimental data at the flow direction 3.5D (D is the diameter of the central fuel jet) position in the prior verification of the embodiments of the present invention.

[0043] Figure 4 This is a comparison of the mass fraction distribution of the main components in the large eddy simulation and experimental data at the 3.5D flow direction in an embodiment of the present invention.

[0044] Figure 5 This is a quantitative comparison chart of the differential diffusion coefficients of the main components in the embodiments of the present invention;

[0045] Figure 6 This is a distribution diagram of the normalized tensile rate, strain rate, and curvature terms along the flow direction in an embodiment of the present invention. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0047] Example:

[0048] This invention, within the framework of large eddy simulation and based on a small flame table incorporating the stretching effect, calculates the stretching rate of a hydrogen-ammonia mixed turbulent flame, thus integrating the stretching effect into a differential diffusion small flame model. This enables accurate prediction of the main components in a hydrogen-ammonia mixed turbulent premixed flame. Furthermore, a comparison is made using a model that does not consider the stretching effect.

[0049] An embodiment of the numerical calculation method of the present invention for calculating the elongation ratio of hydrogen-ammonia mixed turbulent combustion is shown below. Figure 1 As shown, the main steps are as follows: Step 1: Establish a one-dimensional small flame database; Step 2: Map the small flame table to the trajectory variable dimension and convert it into an OpenFOAM readable form; Step 3: Perform model verification, which is divided into prior and posterior. The prior verifies the small flame table for use in the posterior. The posterior is the large eddy simulation, which sets the computational domain, mesh generation, initial conditions, and boundary conditions according to the experimental design, and then performs numerical solution; Step 4: Perform quantitative analysis on the differential diffusion effect and stretching effect.

[0050] Step 1: Establishing a one-dimensional small flame database. The detailed process is as follows:

[0051] The ULF software was used to solve the equations for a one-dimensional reactant-product (R2P) flame in physical space, under different equivalence ratios and strain rates. The equivalence ratio range was... Covering low to high flammability, including the global equivalence ratio corresponding to hydrogen-ammonia blending experimental conditions. The strain rate is varied at each equivalent ratio to represent the tensile effect, with the strain rate range being... This process covers the upper and middle branches of the S-shaped curve. A detailed chemical reaction mechanism for hydrogen-ammonia blended combustion is used, involving 31 components and 203 chemical reactions. Furthermore, a mixture-averaging method is employed in the solution process to account for differential diffusion effects. This solution process yields results including component mass fractions. ,temperature Equivalent ratio strain rate Component diffusion coefficient Data files containing information such as laminar small flames, i.e., a one-dimensional laminar small flame database, hence the thermochemical quantities It can be expressed as an equivalent ratio Component mass fraction ,temperature Component diffusion coefficient strain rate The function is as follows:

[0052] (1)

[0053] To highlight the effects of stretching and differential diffusion, additional small flame libraries were established using a similar method to obtain operating conditions where differential diffusion or stretching effects were neglected. Specifically, the FlameMaster software was used to obtain small flame libraries without considering stretching effects based on the one-dimensional free propagation (FPP) flame equation; and a small flame library without considering differential diffusion effects was obtained based on the unified Lewis number assumption. The importance of differential diffusion and stretching effects can be fully demonstrated through the simulations based on the above small flame libraries described later.

[0054] Step 2: Map the small flame table to the trajectory variable dimension and convert it into an OpenFOAM-readable form. The specific process is as follows:

[0055] Step (1): Calculate the mixed fraction To characterize the fuel stratification phenomenon caused by differential diffusion, the mixing fraction proposed by Bilger et al. was used. Definition of calculation. Since it is not directly obtained from the small flame table in step 1, the component mass fraction needs to be solved using the equivalence ratio as shown in formula (2) during the mapping of the small flame table, and then calculated. As shown in formula (3). The specific calculation formula is as follows:

[0056] (2)

[0057] in, This represents the actual molar ratio / mass ratio of fuel to oxidizer. It is the molar ratio / mass ratio of fuel to oxidant under stoichiometry (i.e., the ratio in which fuel and oxidant react completely in a complete combustion reaction).

[0058] (3)

[0059] in, and These represent the local mixing fractions of hydrogen and oxygen elements in the main components, with the subscripts fuel and ox indicating pure fuel and pure air fluid, respectively. and This represents the relative atomic masses of elements hydrogen and oxygen. The mixing fraction outside the equivalence ratio range in step 1. Extrapolation calculations are performed using the OpenFOAM mapping solver.

[0060] Step (2): Determine the variables in the reaction process For the hydrogen-ammonia co-combustion condition, since water is the main product and can fully represent the reaction progress, the reaction process variable is defined as follows: .

[0061] Step (3): Define the trajectory variable for the reaction stretching effect. Studies have shown that for pure hydrogen and methane-air mixed flame conditions, combining the hydrogen mass fraction with the progress variable as a parameterized tabulation for the strain-limited flame model can simultaneously consider the stretching effect and the differential diffusion effect. Good prediction results are also expected for hydrogen-ammonia mixed flames. Therefore, this invention also uses the hydrogen mass fraction to characterize the stretching effect of the hydrogen-ammonia mixed flame, while considering the differential diffusion effect. Furthermore, since hydrogen, as one of the fuels, exhibits a decreasing trend, the hydrogen mass fraction is normalized: ,in, This represents the maximum hydrogen mass fraction in the small flame table. This process is the core of the invention. Through this process, the stretching effect is incorporated into the differential diffusion small flame model to achieve quantitative calculation of stretching rate, strain rate, and curvature. Through steps (1)-(3), the thermochemical state space of the one-dimensional floor-to-ceiling small flame library in step 1 can be parameterized into a trajectory variable (mixing fraction sum, reaction process variable, hydrogen mass fraction) space, expressed as:

[0062] (4)

[0063] Step (4): Considering that the actual flame surface thickness of the premixed flame is too small and does not reach the grid resolution threshold of the large eddy simulation, the flame surface needs to be thickened and corrected. After obtaining the efficiency factor, thickening factor and flame detector parameters corresponding to the premixed flame through relevant numerical calculation methods, they are uniformly stored in the small flame lookup table (FLT) to provide data support for the parameter reading and numerical solution process in step 3.

[0064] In addition to mapping a small flame table that considers both differential diffusion and stretching effects (R2P), the above process also maps a small flame table that does not consider stretching effects (FPP) to compare and demonstrate the importance of the stretching effect. Similarly, a small flame table that does not consider differential diffusion effects (Le1) is mapped to compare and demonstrate the importance of the differential diffusion effect.

[0065] Step 3, model validation, is divided into prior validation and posterior validation. Posterior validation is large eddy simulation.

[0066] The specific steps of prior analysis are as follows: First, use the experimental data as input to calculate the trajectory variables. , and Based on the small flame lookup table in step 2 of the trajectory variable lookup above, the lookup result is output as formula (5), thereby making the thermochemical state space Such as component mass fraction The temperature T is expressed as formula (6).

[0067] (5)

[0068] (6)

[0069] Because the experimental dataset is included in the flow direction The main components at position (D is the diameter of the central jet flame) were compared with the mass fractions of the main components obtained from the lookup table to verify the correctness of the small flame lookup table. The comparison results are as follows: Figure 2 and Figure 3 As shown, the data fits well with the experimental data, proving the accuracy of the small flame lookup table, which can be used for subsequent large eddy simulations.

[0070] Large eddy simulation (post-hoc verification), namely, the large eddy simulation of a three-dimensional hydrogen-ammonia mixed turbulent premixed flame, the specific calculation process is as follows:

[0071] Step (1): Referring to the turbulent premixed hydrogen-ammonia blending experiment conducted by Robin Schultheis et al., the computational domain, geometry, initial conditions, and boundary conditions were designed. The computational domain was a cylindrical field with a diameter of 135 mm and a length of 200 mm. The burner consisted of three fuel inlets: the center was a jet of hydrogen-ammonia blended fuel with a blending ratio of NH3 / H2 / N2 = 40 / 45 / 15 (volume fraction), a global equivalence ratio of 1.6, a diameter of 4.5 mm, and a jet velocity of 50 m / s; surrounding the central jet fuel were annular igniter nozzles, composed of nitrogen-diluted dilute hydrogen flames with a specific ratio of H2 / N2 = 45 / 15 (volume fraction), an equivalence ratio of 0.57, simulating the exhaust gas from the dilute cracking of NH3, with a diameter of 60.5 mm and a velocity of 2.5 m / s; the outermost annular co-current nozzle had a diameter of 73.5 mm, providing pure nitrogen to isolate the external gas environment, and a velocity of 1 m / s. A non-orthogonal mesh was selected, with a total of approximately six million cells. The initial temperature of the premixed fuel was 293 K, and the pressure was set to atmospheric pressure.

[0072] Step (2): Using the finite volume method, the set of control equations to be solved is numerically discretized, including the density equation, velocity equation, main component equation, and pressure equation. The time integral adopts the first-order Euler implicit integral, and the spatial integral adopts the second-order linear restricted integral scheme.

[0073] Step (3): Solve the equation in step (2). Specifically, solve the equation as follows:

[0074] The governing equation for density is:

[0075] (7)

[0076] in, It is a spatial average quantity. This represents the Farve average obtained through large eddy simulation. Density; The gradient operator, It is the velocity vector; For time.

[0077] The governing equations for velocity are:

[0078] (8)

[0079] in, For pressure, For gravitational acceleration, and It is the viscous stress tensor.

[0080] The main component equation is:

[0081] (9)

[0082] in, and These are the efficiency function, the thickness factor, and the flame sensor. It is the diffusion coefficient, extracted from the small flame lookup table in step 2 considering differential diffusion and stretching effects (R2P), without stretching effects (FPP), and without differential diffusion effects (Le1), where t is time. For average density, The solution is in the i-th direction. This refers to the subgrid eddy current diffusivity. Under the hydrogen-ammonia mixing condition, the main components k are selected as H2, NH3, H2O, and O2. Let it be the Farve average mass fraction of its corresponding principal component k. Let be the average Farve velocity in the i-direction. For the Farve average source term of component k, This refers to the subgrid eddy diffusion rate. Studies have shown that by selecting the main components instead of calculating all components in the chemical reaction mechanism, the computational load can be greatly reduced, computational resources saved, and computational efficiency improved while ensuring relatively accurate results. This method can accurately predict the differential diffusion effect in pure hydrogen-methane blended flames. Therefore, this invention can verify its applicability in hydrogen-ammonia blended flames and verify its accuracy in predicting differential diffusion and stretching effects.

[0083] Step (4): By solving the equations in step (3), the estimated values ​​of density and velocity, as well as the Farve average values ​​of the main components, are obtained. Based on the main components obtained from the solution, the Farve average trajectory variables can be calculated according to the definitions of trajectory variables (mixing fraction, reaction process variables, and hydrogen mass fraction) in step 2.

[0084] Step (5): Based on the trajectory variables obtained in step (4), look up the small flame lookup table (FLT) obtained in step 2, which considers / does not consider differential diffusion / stretching effects, to obtain the components, temperature, chemical reaction source terms, differential diffusion terms, stretching rate terms, etc.

[0085] Step (6): Determine whether the calculation error is satisfied, i.e., whether it has converged or reached the specified end time. If not, continue to step (2) for iterative correction and solution. If satisfied, output the solution and table lookup results in step (5), which can be represented as the following function:

[0086] (10)

[0087] This section only shows the component mass fraction. and temperature Other thermochemical quantities It can also be obtained by looking up a table, which will not be explained in detail here.

[0088] Step (7): Therefore, by matching the output of the table lookup in step (6) above with the experimental data flow... The mass fraction of the main components and temperature at the location were compared to verify the model's accuracy. This process is called post-hoc validation, and the comparison results are as follows: Figure 4 As shown, the R2P model that considers both differential diffusion and stretching effects has the most accurate prediction results, while the model that does not consider the differential diffusion / stretching effects all have under-predictive results. This proves the importance of differential diffusion and stretching effects in hydrogen-ammonia mixed turbulent premixed flames.

[0089] Step 4: Perform a comprehensive analysis of the model, namely, conduct budget analysis on the difference diffusion term and the stretching rate term (strain rate term, curvature term) to quantify the difference diffusion effect and the stretching effect.

[0090] For the quantitative analysis of differential diffusion effects, a differential diffusion parameter of the principal components is defined. This reflects the magnitude of the influence of differential diffusion effect on each major component:

[0091] (11)

[0092] in, Item and The terms are diffusion terms in the principal component equation (Equation (9)), and are specifically defined as follows:

[0093] (12)

[0094] (13)

[0095] in, and These are the efficiency function, the thickness factor, and the flame sensor. As the main component diffusion coefficient, It is the turbulent viscosity coefficient (which describes the momentum transport capacity of turbulence). It is the Schmidt number (characterizing the ratio of momentum diffusion to mass diffusion), and the ratio of the two represents the turbulent mass diffusion coefficient (describing the transport capacity of turbulence for components). It is the thermal conductivity of a fluid (describing the ability of heat to be transferred through the thermal motion of molecules). It is the average isobaric specific heat capacity, and the ratio of the two corresponds to the molecular thermal diffusivity, which is used to characterize the heat diffusion capacity at the molecular level.

[0096] The method was used to calculate the differential diffusion coefficients of the principal components for three models: one considering differential diffusion and stretching effects (R2P), one not considering stretching effects (FPP), and one not considering differential diffusion effects (Le1). The results are as follows: Figure 5 As shown, the differential diffusion coefficient of hydrogen is about three times that of the case where differential diffusion effect is not considered, indicating that it is most affected by differential diffusion effect, while the other components are not significantly affected by differential diffusion effect.

[0097] To quantify the tensile effect, the elongation, strain rate, and curvature are calculated using the following formulas:

[0098] (14)

[0099] in, For the elongation term, For strain rate, This is the curvature term. Among them, This refers to the flame displacement velocity; The curvature is calculated using the following formula:

[0100] (15)

[0101] in, Calculated based on reaction process variables, defined as , The mass fraction of the reaction progress variable is defined as the mass fraction of the product water. .

[0102] The tensile rate, strain rate, and curvature terms are obtained by spatial averaging along the flow direction, and plotted as follows: Figure 6 Based on its distribution pattern, it is divided into 3 regions (shaded areas in the figure). It can be seen that in the middle region 2 ( Figure 6 In Zone 2, the stretching effect is relatively small, while in Zone 1 ( Figure 6 Zone 1 and Zone 3 Figure 6 Zone 3 corresponds to the upstream and downstream of the hydrogen-ammonia mixed flame. Both strain rate and curvature terms are large in these zones, indicating a significant tensile effect. The posterior verification comparison in large eddy simulation is performed in upstream zone 1, which explains... Figure 3 The model considering the stretching effect in this invention yields significantly better prediction results than other models. Therefore, it can be concluded that the stretching effect is very important in the hydrogen-ammonia co-combustion process and needs to be carefully considered in calculations. The model proposed in this invention for calculating the stretching rate of hydrogen-ammonia co-combustion turbulent combustion can predict the combustion of hydrogen-ammonia co-combustion turbulent premixed flames very well.

[0103] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined in this invention may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this invention.

Claims

1. A numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion, characterized in that, include: Step 1: Construct a small flame database based on the one-dimensional reactant-product equation and strain rate parameterization; Step 2: Map the small flame database to the trajectory variable space of mixture fraction, reaction progress variable, and normalized hydrogen mass fraction to generate a small flame lookup table. The normalized hydrogen mass fraction is used as the trajectory variable characterizing the stretching effect. , Hydrogen mass fraction The maximum value; extrapolation is used for the mixed fraction region that exceeds the flammability limit. The small flame lookup table contains the efficiency factor, thickening factor and flame sensor parameters of the artificially thickened flame model. Step 3: Solve the governing equations using large eddy simulation. Obtain the components, chemical source terms, differential diffusion terms, and stretching rate terms by looking up tables, and substitute them into the governing equations to iterate until convergence. Step 4: Quantify the differential diffusion effect and stretching effect by comparing experimental data through prior and posterior verification. For prior verification, the experimental data is directly input into the small flame lookup table, and the output components are compared with the experimental data. For posterior verification, the results are compared with the experimental data through large eddy simulation.

2. The numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to claim 1, characterized in that, In step 1: The global equivalent ratio covering the hydrogen-ammonia blending experimental conditions is 1.6; The strain rate covers the upper and middle branches of the S-shaped curve to characterize the tensile effect.

3. The numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to claim 1, characterized in that, In step 2: Mixed fractions for: ； in, and These are the local mixing fractions of hydrogen and oxygen elements in the main components. This represents the relative atomic mass of hydrogen. The value represents the relative atomic mass of oxygen. The subscript ox indicates the oxidant flow rate, and the subscript fuel indicates the fuel flow rate. Reaction progress variable: mass fraction Defined as the mass fraction of water .

4. The numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to claim 1, characterized in that, In step 3: The governing equations include the component transport equations: ； in, and These are the efficiency function, the thickness factor, and the flame sensor. It is the diffusion coefficient, extracted from a small flame lookup table considering / not considering differential diffusion / stretching effects, where t is time. For average density, The solution is in the i-th direction. This is the subgrid eddy current diffusivity, with the main components k selected as H2, NH3, H2O, and O2. Let it be the Farve average mass fraction of its corresponding principal component k. Let be the average Farve velocity in the i-direction. For the Farve average source term of component k, It is a spatial average quantity. This represents the Farve average obtained through large eddy simulation.

5. The numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to claim 1, characterized in that, The formula for quantifying the differential diffusion effect in step 4 is: ； in, Item and The terms are the diffusion terms in the principal component equations. The differential diffusion parameter is defined.

6. The numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to claim 1, characterized in that, The formula for quantifying the stretching effect in step 4 is: ； in, For the elongation term, For strain rate, Let be the curvature term, where The flame displacement velocity, For curvature.

7. The numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to claim 1, characterized in that, In step 3: The computational domain adopts a cylindrical structure, including a central hydrogen-ammonia fuel jet, an annular ignition nozzle, and an outer nitrogen isolation zone; the mesh is a non-orthogonal structure.

8. The numerical calculation method for calculating the elongation rate of hydrogen-ammonia mixed turbulent combustion according to claim 1, characterized in that, Step 1 employs a hydrogen-ammonia blending mechanism involving 31 components and 203 reactions.

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