A method for reducing a combustion mechanism based on reactive molecular dynamics

Abstract

This invention relates to a simplified method for combustion mechanisms based on reaction molecular dynamics, belonging to the field of combustion dynamics simulation technology. The method first constructs an ammonia-hydrogen combustion system model using Materials Studio software; secondly, it uses the C / H / O / N potential function and performs multi-condition simulations using LAMMPS software; then, it extracts key reaction pathways and core species through reaction trajectory analysis, and removes secondary species and reactions based on species reaction frequencies, constructing a simplified combustion mechanism model; finally, it verifies and optimizes key parameters such as laminar flame velocity and ignition delay time using Chemkin-Pro software under multiple conditions. This invention overcomes the shortcomings of traditional combustion mechanism simplifications that rely on empirical judgment, revealing the essence of combustion reactions at the atomic scale. While ensuring prediction accuracy, it significantly reduces the computational complexity of the mechanism, providing theoretical support for a deeper understanding of combustion dynamics mechanisms and guidance for the efficient organization and optimization of combustion processes.

Description

Technical Field

[0001] This invention belongs to the field of combustion dynamics simulation technology, specifically relating to a simplified method for combustion mechanisms based on reaction molecular dynamics. Background Technology

[0002] In recent years, with the continuous consumption of fossil fuels and the increasingly serious greenhouse gas emissions and environmental pollution problems they cause, the global energy system's transition to a clean and low-carbon model has become imminent. To promote this green and low-carbon energy structure transition, the development and application of zero-carbon / low-carbon clean alternative fuels is becoming an important development direction in the current energy sector.

[0003] Ammonia (NH3), as an energy medium possessing the dual attributes of "hydrogen carrier" and "zero-carbon fuel," is considered an important component in building a future low-carbon energy system. Ammonia combustion does not produce carbon dioxide and features high calorific value, high octane number, low storage and transportation costs, and high energy density. However, ammonia suffers from combustion characteristic defects such as low laminar combustion velocity, high ignition energy, and a narrow flammability limit, severely restricting its direct application as a fuel. Research shows that mixing hydrogen (H2) with NH3 for combustion can significantly improve the instability of NH3 combustion, broaden its flammability limit, and increase combustion efficiency.

[0004] In the study of combustion characteristics, chemical reaction mechanisms are an important tool for predicting fuel combustion processes, enabling the establishment of chemical reaction kinetic models. Existing methods for simplifying combustion mechanisms are mostly based on chemical kinetic techniques such as sensitivity analysis and reaction flow analysis. However, these methods lack objective data support at the atomic scale during species screening and reaction pathway determination, failing to provide comprehensive atomic-scale data support for mechanism construction.

[0005] Reactive molecular dynamics simulations can dynamically demonstrate the breaking and formation of chemical bonds during combustion, revealing reaction mechanisms at the atomic scale and obtaining complete information on species evolution trajectories and reaction pathways. While significantly reducing computational costs and increasing simulation speed, they can achieve computational accuracy comparable to quantum chemical methods, providing a novel technical approach for simplifying the exploration of chemical reactions and combustion mechanisms in complex molecular systems. Summary of the Invention

[0006] The purpose of this invention is to provide a simplified method for combustion mechanism based on reaction molecular dynamics, realize reaction molecular dynamics simulation under different operating conditions, obtain atomic-scale combustion reaction information through reaction molecular dynamics simulation, observe the bond breaking and bonding process of substances, analyze the concentration changes of reactants, intermediates and products, construct combustion reaction pathways, extract core species and reaction pathways, construct a simplified combustion mechanism and verify it.

[0007] To achieve the above objectives, the technical solution of the present invention is: a simplified method for combustion mechanism based on reaction molecular dynamics, comprising:

[0008] The combustion system reaction molecular dynamics model was constructed by using Materials Studio software to build an initial model of the combustion system of ammonia-hydrogen mixed fuel, determining the fuel composition and proportion parameters, and using LAMMPS software to set the simulation boundary conditions and ensemble parameters to complete the construction of the combustion system reaction molecular dynamics model.

[0009] The ReaxFF reactive force field was used to simulate the combustion of the constructed NH3 / H2 mixture under multiple operating conditions using LAMMPS software. The simulation results were obtained and stored in the output file.

[0010] Based on the results of the reaction force field simulation, combustion reaction path analysis was conducted to screen core reactant species and key elementary reactions, and a combustion mechanism framework model containing the core reaction network was constructed.

[0011] The simplified combustion mechanism model was applied to Chemkin software, and the model parameters were adjusted through multi-condition verification of key combustion characteristic parameters, including laminar flame velocity and ignition delay time, to finally obtain the simplified combustion mechanism.

[0012] Furthermore, the construction of the molecular dynamics model of the combustion system reaction specifically includes:

[0013] A combustion system model of a target fuel and oxidant was constructed using Materials Studio software. The target fuel was an ammonia-hydrogen mixture. By setting different H2 volume fractions and equivalence ratios, the molecular ratio of each component in the ammonia-hydrogen mixture combustion system was determined. An initial model of the ammonia-hydrogen mixture was constructed using the Amorphous Cell module in Materials Studio software. The Forcite module was used to perform structural optimization, annealing, and kinetic simulation on the constructed model.

[0014] The C / H / O / N potential function is selected to describe the interatomic interactions in the combustion system;

[0015] The initial model was imported into the LAMMPS software, periodic boundary conditions were set, NVT canonical ensembles were used, temperature was controlled by a Nose-Hoover thermostat, and simulation time step, total simulation duration and atomic trajectory data were set.

[0016] The initial model was relaxed and then heated to a predetermined temperature for combustion simulation at high temperature.

[0017] Furthermore, the H2 volume fraction is set in the range of 0.0 to 0.4.

[0018] Furthermore, the equivalent ratio is set in the range of 0.5 to 1.5.

[0019] Furthermore, the simulation time step is set to 0.1 fs, and the total simulation duration is 20 ns.

[0020] Furthermore, the relaxation process of the initial model followed by heating includes: relaxing the model at 298 K for 50 ps, ​​then heating it to 2500 K at a heating rate of 10 K / ps, and continuing the simulation at 2500 K.

[0021] Furthermore, the multi-condition combustion simulation using the ReaxFF reactive force field includes:

[0022] Perform reaction molecular dynamics simulations of the combustion system, record the concentration changes of each species over time during the simulation, and obtain the changing patterns of reactants, intermediates, and products.

[0023] The Reacnetgenerator tool was used to post-process the atomic trajectory data output from the simulation, identify chemical reaction events, count the net number of reactions for each elementary reaction, and determine the dominant reaction pathway.

[0024] Based on the reaction pathway analysis results and the concentration changes of each species, the core reactants, highly active intermediates and major products of the entire combustion process were identified, forming a set of key species.

[0025] Furthermore, chemical reaction events in atomic trajectory data are identified using bond-level truncation.

[0026] Furthermore, the simplified combustion mechanism model was applied to verify the following:

[0027] The simplified mechanism model was imported into Chemkin-Pro software to perform multi-condition simulation calculations of laminar flame velocity and ignition delay time.

[0028] The simulation results of the simplified mechanism are compared with experimental data and the simulation results of the original detailed mechanism. The relative error is calculated to verify the feasibility of the mechanism.

[0029] Furthermore, the simplified combustion mechanism framework model constructed includes 26 species and 177 elementary reactions.

[0030] Compared with existing technologies, this invention has the following advantages: This invention reveals the combustion reaction mechanism of ammonia-hydrogen blended fuels at the atomic scale through reaction molecular dynamics, and simplifies and verifies the mechanism based on simulation results. The simplified mechanism significantly reduces the computational complexity of the combustion mechanism and improves computational efficiency while ensuring the accuracy of combustion characteristic prediction. It can provide solid theoretical support for a deeper understanding of the ammonia-hydrogen combustion kinetic mechanism, and at the same time provide important technical guidance for the efficient organization and optimization of the combustion process of ammonia-hydrogen blended fuels and the engineering application of zero-carbon / low-carbon fuels. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method according to an embodiment of the present invention.

[0032] Figure 2 This is the ammonia-hydrogen mixed combustion model in the embodiments of the present invention.

[0033] Figure 3 This shows the change in the number of NH3 molecules as reactants in the embodiments of the present invention over time.

[0034] Figure 4 This refers to the net number of reactions of NH3 under different equivalence ratios and volume fractions in the embodiments of the present invention.

[0035] Figure 5 This represents the main reaction pathway of N atoms under different equivalence ratios during the ammonia-hydrogen combustion process in the embodiments of the present invention.

[0036] Figure 6 This is a comparison of laminar flame velocities with experimental values ​​for different mechanisms in the embodiments of the present invention.

[0037] Figure 7 This is a comparison of the ignition delay time of different mechanisms with experimental values ​​in the embodiments of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0040] This invention provides a simplified method for combustion mechanisms based on reaction molecular dynamics, comprising:

[0041] The combustion system reaction molecular dynamics model was constructed by using Materials Studio software to build an initial model of the combustion system of ammonia-hydrogen mixed fuel, determining the fuel composition and proportion parameters, and using LAMMPS software to set the simulation boundary conditions and ensemble parameters to complete the construction of the combustion system reaction molecular dynamics model.

[0042] The ReaxFF reactive force field was used to simulate the combustion of the constructed NH3 / H2 mixture under multiple operating conditions using LAMMPS software. The simulation results were obtained and stored in the output file.

[0043] Based on the results of the reaction force field simulation, combustion reaction path analysis was conducted to screen core reactant species and key elementary reactions, and a combustion mechanism framework model containing the core reaction network was constructed.

[0044] The simplified combustion mechanism model was applied to Chemkin software, and the model parameters were adjusted through multi-condition verification of key combustion characteristic parameters, including laminar flame velocity and ignition delay time, to finally obtain the simplified combustion mechanism.

[0045] The following are specific implementation examples of the present invention.

[0046] like Figure 1 As shown, this embodiment provides a simplified method for combustion mechanisms based on reaction molecular dynamics. The specific steps are as follows:

[0047] Step S1: Construct an initial model of the ammonia-hydrogen mixed combustion system using Materials Studio software. Set combustion systems with different equivalence ratios (0.5~1.5) and H2 volume fractions (0.0~0.4). The ammonia-hydrogen mixed combustion model is as follows: Figure 2 As shown, the constructed model was converted into a LAMMPS-recognizable data file. The C / H / O / N force field parameters developed by Hong et al. were used, periodic boundary conditions were set, an NVT ensemble was employed, and a Nose-Hoover thermostat was used to control the temperature. The time step was 0.1 fs, the total simulation duration was 20 ns, and atomic trajectory data were output every 1 ps. The model was relaxed at 298 K for 50 ps, ​​then heated to 2500 K at a rate of 10 K / ps, and the simulation continued at 2500 K.

[0048] Step S2: Use LAMMPS software to perform multi-condition combustion simulations on the constructed NH3 / H2 mixture model, and record the changes in the concentration of each species over time. Use the Reacnetgenerator tool to analyze atomic trajectories, count the net number of reactions for each elementary reaction, and construct the combustion reaction pathway.

[0049] Step S3: Extract the key reactive species in the combustion process, exclude minor species with extremely low concentrations and negligible impact on the combustion process in the simulation, integrate the simplified species and reaction network to form a simplified mechanism of combustion reaction kinetics.

[0050] Step S4: Import the simplified mechanism into Chemkin-Pro software to simulate and verify the laminar flame velocity and ignition delay time, and compare the experimental data with the original mechanism.

[0051] In this embodiment, in step S1, the molecular ratio of each component in the system is determined by setting different equivalence ratios and H2 volume fractions; a mixed combustion system model of the target fuel and oxidant is constructed using Materials Studio software; and the constructed model is structurally optimized, annealed, and kinetics simulated using the Forcite module.

[0052] In this embodiment, in step S1, the potential function of the corresponding material is selected, and the C / H / O / N potential function is selected to describe the interatomic interaction in the combustion system;

[0053] In this embodiment, in step S1, the constructed initial model is imported into LAMMPS software, periodic boundary conditions are set, NVT canonical ensemble is used, temperature is controlled by Nose-Hoover thermostat, and simulation time step, total simulation duration and atomic trajectory data are set.

[0054] In this embodiment, in step S1, the initial model is relaxed and then heated to a specific temperature to perform combustion simulation at high temperature.

[0055] In this embodiment, in step S1, the model built by Materials Studio software is converted into a data file that LAMMPS can recognize using the msi2lmp tool that comes with LAMMPS.

[0056] In this embodiment, in step S2, a molecular dynamics simulation of the combustion system is performed, and the concentration changes of each species over time are recorded during the simulation. The changing patterns of reactants, intermediates, and products are obtained. The change in the number of NH3 molecules over time is shown below. Figure 3 As shown.

[0057] In this embodiment, in step S2, the atomic trajectory data output from the simulation is post-processed using the Reacnetgenerator tool. Chemical reaction events are identified using the bond-level truncation method, and the net number of reactions for each elementary reaction is counted to determine the net number of reactions for the dominant reaction pathway NH3 under different equivalence ratios and volume fractions. Figure 4 As shown.

[0058] In this embodiment, in step S2, based on the reaction pathway analysis results and the concentration changes of each species, the core reactants, highly reactive intermediates, and main products of the entire combustion process are determined, forming a key species set. The main reaction pathways of N atoms under different equivalence ratios during ammonia-hydrogen combustion are as follows: Figure 5 As shown.

[0059] In this embodiment, in step S3, the Zhang mechanism (38 components, 263 reaction) is simplified based on the results of reaction molecular dynamics simulation, and the key reactant species in the NH3 / H2 combustion process are extracted, including reactants: NH3, H2, O2 and products: H2O, N2, NO. x Secondly, important intermediate substances, such as NH2, OH, and O, were extracted based on the combustion reaction pathway. Finally, for other elementary elements, the reaction species that generated a large number of reactions were extracted by statistically analyzing the occurrence frequency of species. The final simplified framework mechanism of the NH3 / H2 combustion reaction kinetics consists of 26 species and 177 elementary reactions.

[0060] In this embodiment, in step S4, the simplified mechanism model is imported into Chemkin-Pro software to perform multi-condition simulation calculations of laminar flame velocity (LBV) and ignition delay time (IDT). Figure 6 and Figure 7 The comparisons between LBV and IDT with experimental values ​​for different mechanisms are shown.

[0061] In this embodiment, in step S4, the simulation results of the simplified mechanism are compared with the experimental data and the simulation results of the original detailed mechanism. The relative error is calculated to verify the feasibility of the mechanism. The calculation speed of the simplified mechanism is about 2.14 times faster than that of the original detailed mechanism. Moreover, in terms of LBV and IDT prediction, it is comparable to or even slightly improved with the original mechanism, with the average error being within 8%.

[0062] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A simplified method for combustion mechanisms based on reaction molecular dynamics, characterized in that, include: The combustion system reaction molecular dynamics model was constructed by using Materials Studio software to build an initial model of the combustion system of ammonia-hydrogen mixed fuel, determining the fuel composition and proportion parameters, and using LAMMPS software to set the simulation boundary conditions and ensemble parameters to complete the construction of the combustion system reaction molecular dynamics model. The ReaxFF reactive force field was used to simulate the combustion of the constructed NH3 / H2 mixture under multiple operating conditions using LAMMPS software. The simulation results were obtained and stored in the output file. Based on the results of the reaction force field simulation, combustion reaction path analysis was conducted to screen core reactant species and key elementary reactions, and a combustion mechanism framework model containing the core reaction network was constructed. The simplified combustion mechanism model was applied to Chemkin software, and the model parameters were adjusted through multi-condition verification of key combustion characteristic parameters, including laminar flame velocity and ignition delay time, to finally obtain the simplified combustion mechanism.

2. The simplified method for combustion mechanism based on reaction molecular dynamics according to claim 1, characterized in that, The construction of the molecular dynamics model for the combustion system reaction specifically includes: A combustion system model of a target fuel and oxidant was constructed using Materials Studio software. The target fuel was an ammonia-hydrogen mixture. By setting different H2 volume fractions and equivalence ratios, the molecular ratio of each component in the ammonia-hydrogen mixture combustion system was determined. An initial model of the ammonia-hydrogen mixture was constructed using the Amorphous Cell module in Materials Studio software. The Forcite module was used to perform structural optimization, annealing, and kinetic simulation on the constructed model. The C / H / O / N potential function is selected to describe the interatomic interactions in the combustion system; The initial model was imported into the LAMMPS software, periodic boundary conditions were set, NVT canonical ensembles were used, temperature was controlled by a Nose-Hoover thermostat, and simulation time step, total simulation duration and atomic trajectory data were set. The initial model was relaxed and then heated to a predetermined temperature for combustion simulation at high temperature.

3. The simplified method for combustion mechanism based on reaction molecular dynamics according to claim 2, characterized in that, The H2 volume fraction is set in the range of 0.0 to 0.

4.

4. The simplified method for combustion mechanism based on reaction molecular dynamics according to claim 2, characterized in that, The equivalent ratio is set in the range of 0.5 to 1.

5.

5. A simplified method for combustion mechanism based on reaction molecular dynamics according to claim 2, characterized in that, The simulation time step is set to 0.1 fs, and the total simulation duration is 20 ns.

6. A simplified method for combustion mechanism based on reaction molecular dynamics according to claim 2, characterized in that, The relaxation process of the initial model followed by heating includes: relaxing the model at 298 K for 50 ps, ​​then heating it to 2500 K at a heating rate of 10 K / ps, and continuing the simulation at 2500 K.

7. A simplified method for combustion mechanism based on reaction molecular dynamics according to claim 2, characterized in that, The multi-condition combustion simulation using the ReaxFF reactive force field includes: Perform reaction molecular dynamics simulations of the combustion system, record the concentration changes of each species over time during the simulation, and obtain the changing patterns of reactants, intermediates, and products. The Reacnetgenerator tool was used to post-process the atomic trajectory data output from the simulation, identify chemical reaction events, count the net number of reactions for each elementary reaction, and determine the dominant reaction pathway. Based on the reaction pathway analysis results and the concentration changes of each species, the core reactants, highly active intermediates and major products of the entire combustion process were identified, forming a set of key species.

8. A simplified method for combustion mechanism based on reaction molecular dynamics according to claim 7, characterized in that, Chemical reaction events in atomic trajectory data can be identified using bond-level truncation.

9. A simplified method for combustion mechanism based on reaction molecular dynamics according to claim 1, characterized in that, The simplified combustion mechanism model was applied to the verification process, including: The simplified mechanism model was imported into Chemkin-Pro software to perform multi-condition simulation calculations of laminar flame velocity and ignition delay time. The simulation results of the simplified mechanism are compared with experimental data and the simulation results of the original detailed mechanism. The relative error is calculated to verify the feasibility of the mechanism.

10. A simplified method for combustion mechanism based on reaction molecular dynamics according to any one of claims 3-6, characterized in that, The simplified combustion mechanism framework model constructed includes 26 species and 177 elementary reactions.

Images