Numerical calculation method and system for interaction of hydrogen-ammonia mixed combustion flame with wall surface

Abstract

This invention discloses a numerical calculation method and system for the interaction between a hydrogen-ammonia blended combustion flame and the wall, belonging to the field of energy and combustion engineering. Addressing the problem that existing models struggle to simultaneously capture differential diffusion effects and wall heat loss, this invention achieves this through the following steps: Solving the governing equations including wall boundary conditions based on direct numerical simulation (DNS) to generate a high-precision dataset; constructing a small flame database containing one-dimensional free-propagating flames (FPP) and head-on quenched flames (HOQ), embedding the wall heat loss effect; mapping the database to a three-dimensional parameter space of mixing fraction, reaction process variables, and normalized enthalpy to form a small flame lookup table; solving the governing parameter equations and outputting the field variables from the lookup table; and verifying the model accuracy by comparing with DNS data. This method significantly improves near-wall flame quenching and NO reduction. x The accuracy of predictions for key processes such as generation provides technical support for the optimized design of hydrogen-ammonia burners.

Description

Technical Field

[0001] This invention belongs to the field of energy and combustion engineering, and specifically relates to a numerical calculation method and system for the interaction between hydrogen-ammonia co-combustion flame and wall surface. Background Technology

[0002] Hydrogen-ammonia co-combustion, as a feasible technical path to achieve zero-carbon power generation, has significant advantages in reducing carbon emissions. While the addition of hydrogen increases the combustion rate of ammonia fuel, it also significantly alters flame characteristics. Accurate prediction of combustion stability and pollutant emissions is crucial for the engineering application of this technology. Within actual burners, flame-wall interaction is a key physical process affecting flame stability, combustion efficiency, and pollutant generation. The wall, through heat loss and flow field disturbance, can cause flame quenching, structural deformation, and potentially induce flashback, leading to serious consequences such as burner structural damage.

[0003] Especially under lean premixed conditions, the low Lewis number of hydrogen in ammonia-hydrogen flames easily leads to significant thermal diffusion instability, resulting in complex flame structures such as honeycomb and wrinkled shapes. In these cases, the interaction mechanism between the flame and the wall becomes even more difficult to predict and describe. Direct numerical simulation (DNS) can provide a high-precision data foundation for revealing the microscopic mechanism of flame-wall interaction; small-flame models can introduce detailed chemical reactions while ensuring engineering calculation efficiency, making them an effective tool for simulating complex combustion processes. However, existing models still have shortcomings in simultaneously considering the strong differential diffusion effect and wall proximity effect in ammonia-hydrogen flames, making it difficult to comprehensively reflect the dynamic response and pollutant generation characteristics of the near-wall region. Therefore, developing a numerical calculation method for ammonia-hydrogen flames that can accurately characterize the differential diffusion effect and couple the flame-wall interaction, accurately reflecting the flame-wall interaction mechanism, is crucial for revealing the NO in the near-wall region. x The generation path, the improvement of combustion model construction assumptions, and the enhancement of the design reliability of hydrogen-ammonia burners are of great scientific significance and engineering value. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a numerical calculation method and system for the interaction between the flame and the wall in hydrogen-ammonia co-combustion. It focuses on the influence of flame-wall interaction, combining EBIdnsFOAM (an extension of the open-source fluid dynamics software OpenFOAM, specifically designed for high-fidelity chemical reaction flow simulation) to solve the detailed chemical reaction mechanism of hydrogen-ammonia co-combustion and using a small flame model to predict the process. Furthermore, based on the acquired high-precision dataset, it conducts in-depth analysis and exploration of NO... x The generation mechanism and reaction pathway of [the substance].

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface includes the following steps:

[0007] Step 1: Solve the governing equations for hydrogen-ammonia co-combustion based on direct numerical simulation (DNS), and generate the DNS dataset by setting wall boundary conditions;

[0008] Step 2: Construct a small flame database containing free-propagating flames (FPP) and head-on quenched flames (HOQ) using a one-dimensional flame solver;

[0009] Step 3: Map the small flame database to the three-dimensional control parameter space of mixture fraction, reaction process variables and normalized enthalpy, and generate a small flame lookup table;

[0010] Step 4: Solve the transport equations for the mixture fraction, reaction progress variables, and normalized enthalpy. Output the temperature, component mass fraction, and chemical reaction source terms by looking up the small flame lookup table.

[0011] Step 5: Compare the lookup results with the DNS dataset to verify the small flame model's effectiveness on flame quenching distance and NO. x The accuracy of predictions for concentration distribution and heat release rate fields.

[0012] This invention also provides a numerical calculation system for calculating the interaction between a hydrogen-ammonia co-combustion flame and a wall, comprising:

[0013] The DNS solver module is used to generate a high-precision dataset of wall interactions; DNS stands for Direct Numerical Simulation.

[0014] The small flame table construction module realizes the spatial mapping of control parameters in the numerical calculation method of the interaction between the hydrogen-ammonia co-combustion flame and the wall.

[0015] The lookup table solver outputs combustion field variables based on control parameters.

[0016] The present invention also provides a computer-readable storage medium storing program instructions, which, when executed by a processor, implement the above-described numerical calculation method for the interaction between a hydrogen-ammonia co-combustion flame and a wall surface.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. Direct numerical simulation (DNS) based on EBIdnsFOAM was employed to solve the detailed chemical reaction mechanism while precisely setting physical boundary conditions such as no-slip wall, isothermal cooling, and zero species gradient. This provides a high-precision basic dataset that can realistically reflect the interaction between flame and wall for method validation and the construction of a small flame database, fundamentally ensuring the reliability of subsequent model development.

[0019] 2. Improvements to the Small Flame Model: Key innovations were made in the construction of the small flame model in steps 3 and 4. Traditional small flame models are mostly based on adiabatic or constant enthalpy flames, failing to fully consider the strong enthalpy gradient caused by wall heat loss and its accompanying species diffusion effect. This invention introduces head-on quenching (HOQ) flames, enabling the small flame database to inherently include the quantitative impact of heat loss on chemical reaction pathways, thereby greatly improving the model's predictive ability in the near-wall region. Attached Figure Description

[0020] Figure 1 This is a flowchart of the numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to the present invention;

[0021] Figure 2 The mixing fraction without wall conditions in the embodiments of the present invention The instantaneous distribution map is overlaid with black contour lines at 1500K;

[0022] Figure 3 The mixing fraction with wall conditions in the embodiments of the present invention The instantaneous distribution map, overlaid with black contour lines at 1500K;

[0023] Figure 4 This is an instantaneous distribution diagram of nitric oxide (NO) without wall conditions in an embodiment of the present invention;

[0024] Figure 5 This is an instantaneous distribution diagram of nitric oxide (NO) under wall conditions in an embodiment of the present invention;

[0025] Figure 6 This is a comparison chart of key components in the prior analysis of this invention - T;

[0026] Figure 7 A comparison diagram of key components in the prior analysis of this invention. ;

[0027] Figure 8 A comparison diagram of key components in the prior analysis of this invention. ;

[0028] Figure 9 A comparison diagram of key components in the prior analysis of this invention. . Detailed Implementation

[0029] 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.

[0030] Example:

[0031] This embodiment takes the co-combustion of hydrogen and ammonia as the research object, and describes in detail the implementation process of the present invention (e.g. Figure 1 (as shown)

[0032] Step 1, the calculation process for a two-dimensional hydrogen / ammonia / air premixed flame is as follows:

[0033] First, a numerical computation model and solution framework are established. This step uses Direct Numerical Simulation (DNS) to generate a high-precision validation dataset and explore the physical processes. The solver is the EBI-DNS solver in OpenFOAM.

[0034] A two-dimensional rectangular computational domain was designed. To accurately analyze the flame structure and near-wall processes, the mesh resolution was set to 20 mesh points per flame thickness. In this embodiment, the mesh point distribution of the computational domain is 2000 (x-direction) × 3000 (y-direction). The temperature of the unburned hydrogen-ammonia / air premixed gas is 298 K, the pressure is 1 atm, and the equivalence ratio is 0.6. The molar ratio of H2 to NH3 in the fuel is 0.44:0.56. An isothermal wall is set at y=0, with a fixed temperature of 298 K. No-slip conditions are used for velocity, and zero-gradient diffusion conditions are used for species mass fraction. For comparison, a case without a wall is also calculated, which uses periodic boundary conditions in the y-direction.

[0035] A perturbed initial flame front is implanted within the computational domain to promote the development of thermal diffusion instabilities. The fully compressible Navier-Stokes equations (NS) are solved, including the total mass, momentum, species mass, and energy conservation equations. Species diffusion is modeled using a mixture-averaged diffusion model to accurately describe the differential diffusion effects of H2 and NH3 mixing. The chemical reaction mechanism is a detailed mechanism in the Cantera scheme, applicable to hydrogen-ammonia combustion involving 31 components and 203 reactions. The governing equations for the gas-phase energy and transport equations are as follows:

[0036] Energy equation: Energy transfer using total phenomenology To indicate:

[0037] ,

[0038] and ,

[0039] in, It is the thermal conductivity of the mixture. It is isobaric heat capacity. It's temperature. It is the fluid velocity. It's pressure. Components produced or consumed by chemical reactions rate, It is the rate of chemical exothermic reaction. It is the source item from the Lagrange package. This is because the source term of radiation, viscous work, potential energy, radiation, and the Dufour effect are neglected. The gradient operator, Represents the divergence sign. Let t be the heat flux density vector, and t represent time. Indicates density, It is a component The enthalpy of formation, 298K indicates that the wall temperature is set to 298 Kelvin; the species of an ideal gas. enthalpy and the enthalpy of the mixture for:

[0040] ,

[0041] Corrected diffusion mass flux .

[0042] To close this partial differential equation system, density The relationship between pressure p and temperature T is given by the ideal gas equation of state: ,in It is the average molar mass of the mixture. It is the universal gas constant.

[0043] Species mass conservation equation:

[0044] ,

[0045] in, It is a species mass fraction, Species produced or consumed by chemical reactions The rate. Correction speed. , ,in, The total density of the mixture, For the first The diffusion mass flux of the component is expressed in the following form:

[0046] ,

[0047] In the formula, Indicates mass diffusion flux. For heat diffusion flux, It is the pressure diffusion flux. For correction items, This represents the turbulent diffusion flux. The primary mass diffusion flux in the mixture-averaged diffusion model is... According to the approximation calculated by Hirschfelder-Curtiss: ,in It is the average diffusion coefficient of the mixture. It is the average molar mass of the mixture.

[0048] The governing equations are discretized using the finite volume method, and the chemical source term is handled using an operator splitting technique: at the beginning of each hydrodynamic time step, the Sundials CVODE solver is invoked to perform zero-dimensional reactor integration on each grid cell, calculating the average chemical reaction rate within that time step, including the heat release rate. The solution process involves solving the momentum equation, component transport equation, and energy equation sequentially within a PIMPLE loop, ensuring mass conservation through a pressure-velocity coupling algorithm. The final output is the component mass fraction (Y) for each time step. i Field variables such as temperature (T), pressure (p), velocity (U), and heat release rate (Qdot) are used to form a high-precision DNS dataset for subsequent model validation (e.g., Figure 2 and Figure 3 (As shown).

[0049] Based on DNS data, reaction path analysis was performed: Reaction path analysis (RPA) was conducted in the near-wall region to quantify the effect of flame-wall interaction on NO. x The impact of the contribution rate of each generation pathway (such as the NNH pathway, N2O pathway, etc.) Figure 4 and Figure 5 As shown in the figure, this reveals its generation mechanism in depth.

[0050] Step 2: Construct a small flame database that includes wall quenching effects. This step uses ULF software to generate two types of one-dimensional small flame solutions to construct the database.

[0051] Step 2.1 Solve for one-dimensional free-propagating plane flame (FPP): Calculate hydrogen-ammonia / air adiabatic flames with different unburned gas temperatures at equivalence ratios of 0.4 to 1.2, representing the chemical state under no-heat-loss conditions.

[0052] Step 2.2, Solving for One-Dimensional Head-on Quenched Flame (HOQ): The transient process of flame propagation and quenching upon impact with the wall is simulated within a one-dimensional domain containing a cold wall. Computational equivalence ratios ranging from 0.4 to 1.2 and different unburned gas temperatures are also calculated, but wall heat loss, the resulting strong enthalpy gradient, and the accompanying diffusion effects of species (such as H2, NH2, NO, etc.) are included. First, the coordinate system needs to be transformed into a stationary reference frame, with the inlet velocity set to zero at x=0, and the velocities within the domain adjusted accordingly. In this new reference frame, an impermeable wall is located at x=0, and the flame begins to move towards the unburned mixture and the wall. This wall is set as an isothermal cold wall boundary condition, with a lower temperature fixed at the boundary of the simulation domain. Using the heat conduction term in the enthalpy equation, when the flame approaches the cold wall, a large temperature gradient forms between the flame and the wall, driving the heat conduction term to transfer heat from the inside of the flame to the wall. The enthalpy equation to be solved is:

[0053] ,

[0054] in, : Represents the rate of change of total enthalpy per unit volume over time.

[0055] : Represents the transport of total enthalpy in space through convection.

[0056] : Represents the transport of total enthalpy in space through thermal conduction. Under the assumption of constant pressure, total enthalpy This is a conservative quantity, meaning that the chemical reaction does not directly produce or consume total enthalpy. Therefore, the chemical source term on the right-hand side of the equation is zero. This implies that any change in enthalpy comes from convective transport or thermal conduction (typically heat exchange with the external environment, such as wall heat loss). This term is crucial for simulating the wall heat loss effect and is key to the HQQ model capturing the FWI phenomenon.

[0057] Step 3: Construct a three-dimensional small flame table and define control variables: Select the following three variables as control parameters for the manifold: The mixture fraction is calculated using the Bilger formula applicable to hydrogen-ammonia combustion and is used to characterize the equivalence ratio. The calculation formula is as follows:

[0058] ,

[0059] in, and These are the local mixing fractions of elements H and O, respectively. This represents the mass fraction of hydrogen. This represents the mass fraction of hydrogen in the pure fuel stream. This represents the mass fraction of hydrogen in the airflow. This represents the mass fraction of oxygen. This represents the mass fraction of oxygen in the pure fuel stream. This represents the oxygen mass fraction of the airflow. Subscripts 1 and 2 indicate pure fuel and pure air, respectively. Standardized schedule variable. Defined as: ,and definition , and Corresponding to DNS The minimum and maximum values, i.e. It represents the mass fraction of water vapor. The mass fraction of unburned water vapor. The mass fraction of water vapor in fully combusted state is denoted as , and the reaction process variable is defined as a linear combination of the mass fractions of the key product H₂O. Enthalpy is used to characterize the overall thermodynamic state of the system and is directly related to heat loss. Indicates the relative molecular mass of a hydrogen atom; This indicates the relative atomic mass of an oxygen atom.

[0060] Step 4, Data Mapping and Table Creation:

[0061] Using a mapping program developed based on OpenFOAM, all FPP and HOQ flame solutions generated in step 2 are read. All data points of these one-dimensional flames in spacetime (i.e., Z, C, H at each location, and their corresponding temperature, mass fraction of each component, and chemical reaction source terms) are mapped to a mapping program. In a three-dimensional parameter space with coordinates, a continuous and smooth three-dimensional lookup table (i.e., a mini-flame table) is constructed through interpolation. Based on the one-dimensional flame face configuration of head-on quenching (HOQ), a second flame face table is generated for various equivalence ratios and wall temperatures. The thermochemical quantity list is as follows: Based on 1D free-propagating premixed (FPP) flame generation, the thermochemical state list for various equivalence ratios is as follows: ,in, For the set of output variables of a free-propagating flame FPP, For lookup table mapping functions of free-propagating flame FPP, For the set of output variables of HOQ (Head-Quenching Flame), For the lookup table mapping function of HOQ for head-on quenching flame, , and They are The maximum and minimum values, i.e. This is the total enthalpy value. Minimum enthalpy, It is the maximum enthalpy.

[0062] Step 5: Couple the small flame model for model evaluation. In the lookup table solver, instead of directly solving the detailed species transport equations, solve the transport equations for the mixture fraction, reaction process variables, and enthalpy. When solving these equations, the differential diffusion term introduced by the mixture-average diffusion model is explicitly considered. At each grid cell and each time step, the solved instantaneous (mixture fraction) values ​​are... , reaction progress variable Normalized enthalpy The value is used as input and searched in the three-dimensional small flame table generated in step 3 to directly obtain the temperature, mass fraction of all components and chemical reaction source item of that point.

[0063] The lookup results using the above small flame model (based on both FPP and HOQ) will be compared with the high-precision DNS dataset obtained in step 1 (e.g., Figure 6 , Figure 7 , Figure 8 and Figure 9 As shown, DC is the data from direct numerical simulation used for reference and comparison of the HOQ model and the FPP model (see table lookup results). This is achieved by comparing the flame structure, quenching distance, and near-wall NO in the wall-facing case. x The concentration distribution and other key parameters were used to quantitatively evaluate the predictive ability of this invention for the interaction between the hydrogen-ammonia co-combustion flame and the wall. The results show that the model incorporating HOQ significantly improves the prediction of the chemical state in the near-wall region at high PV, particularly for NO in the high PV region. x Accurate captures generated.

[0064] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. 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 the invention. Therefore, the present invention 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 the interaction between a hydrogen-ammonia co-combustion flame and a wall surface, characterized in that, include: Step 1: Solve the governing equations for hydrogen-ammonia co-combustion based on direct numerical simulation (DNS), and generate the DNS dataset by setting wall boundary conditions; Step 2: Construct a small flame database containing free-propagating flames (FPP) and head-on quenched flames (HOQ) using a one-dimensional flame solver; Step 3: Map the small flame database to the three-dimensional control parameter space of mixture fraction, reaction process variables and normalized enthalpy, and generate a small flame lookup table; Step 4: Solve the transport equations for the mixture fraction, reaction progress variables, and normalized enthalpy. Output the temperature, component mass fraction, and chemical reaction source terms by looking up the small flame lookup table. Step 5: Compare the lookup results with the DNS dataset to verify the small flame model's effectiveness on flame quenching distance and NO. x The accuracy of predictions for concentration distribution and heat release rate fields.

2. The numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to claim 1, characterized in that, In step 1: The wall boundary conditions are set as follows: velocity field: no slip; temperature field: isothermal cooling to 298 K; species mass fraction: zero gradient diffusion; The differential diffusion effect of the hydrogen-ammonia mixture is described using a mixture-average diffusion model. The chemical reaction mechanism comprises 31 components and 203 reactions.

3. The numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to claim 1, characterized in that, In step 1: The computational domain grid resolution satisfies 20 grid points per flame thickness; Quantification of NO in the near-wall region through reaction pathway analysis x Contribution rate of the generated path.

4. The numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to claim 1, characterized in that, In step 2: The enthalpy equation for the head-quenched flame (HOQ) is defined as follows: ， in, Represents the rate of change of total enthalpy per unit volume with time t. It represents the transport of total enthalpy in space through convection. It represents the transport of total enthalpy in space through thermal conduction. It is isobaric heat capacity. It is the thermal conductivity of the mixture. Let be the total density of the mixture, h represent the total enthalpy, x represent the spatial position, and u represent the velocity.

5. The numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to claim 1, characterized in that, In step 3: Mixed fractions The calculation formula is: ， in, This represents the mass fraction of hydrogen. This represents the mass fraction of hydrogen in the pure fuel stream. This represents the mass fraction of hydrogen in the airflow. This represents the mass fraction of oxygen. This represents the mass fraction of oxygen in the pure fuel stream. The mass fraction of oxygen in the airflow; Indicates the relative molecular mass of a hydrogen atom; Indicates the relative atomic mass of an oxygen atom; Reaction process variables Defined as: ， in, It represents the mass fraction of water vapor. The mass fraction of unburned water vapor. The mass fraction of water vapor in fully combusted state; Normalized enthalpy for: ， in, This is the total enthalpy value. Minimum enthalpy, It is the maximum enthalpy.

6. The numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to claim 1, characterized in that, In step 4: The transport equations include mixed fraction transport equations, reaction process variable transport equations, and enthalpy transport equations.

7. The numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to claim 1, characterized in that, The small flame lookup table contains two types of data: data based on free-propagating flames (FPPs). and based on head-quenched flame HOQ , For the set of output variables of a free-propagating flame FPP, For lookup table mapping functions of free-propagating flame FPP, For the set of output variables of HOQ (Head-Quenching Flame), For the lookup table mapping function of HOQ for head-on quenching flame, For mixed fractions, As a process variable, It is the normalized enthalpy.

8. The numerical calculation method for the interaction between the hydrogen-ammonia co-combustion flame and the wall surface according to claim 1, characterized in that, The verification process compares the flame quenching distance and NO under wall conditions. x Concentration distribution and heat release rate field realization.

9. A numerical calculation system for calculating the interaction between a hydrogen-ammonia co-combustion flame and a wall surface, characterized in that, include: The DNS solver module is used to generate a high-precision dataset of wall interactions; DNS stands for Direct Numerical Simulation. The small flame table construction module realizes the mapping of the three-dimensional control parameter space in the numerical calculation method of the interaction between the hydrogen-ammonia blended combustion flame and the wall as described in any one of claims 1-8; The lookup table solver outputs combustion field variables based on control parameters.

10. A computer-readable storage medium storing program instructions, characterized in that: When the program instructions are executed by the processor, they implement the numerical calculation method for the interaction between the hydrogen-ammonia blended combustion flame and the wall surface as described in any one of claims 1-8.

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