Ignition Of Hydrogen Research Articles

Leakage Process and Spontaneous Ignition of Hydrogen within a Tube after Releasing from the Storage Container with Pressures up to 20 MPa

Leakage Process and Spontaneous Ignition of Hydrogen within a Tube after Releasing from the Storage Container with Pressures up to 20 MPa

Autoignition of premixed hydrogen/air mixtures with uniformly dispersed carbon particles

The autoignition of a stoichiometric hydrogen/air mixture laden with uniformly distributed coal char particles is simulated with the Eulerian-Lagrangian approach under isochoric conditions. A zero-dimensional model is adopted to assess the effects of gas temperature, pressure, particle diameter, and concentration on ignition dynamics. Increasing the initial temperature reduces the ignition time and maximum heat release rate of the homogeneous reactions, while the parameters for particle reactions stabilize after reaching a critical temperature. Initial pressure exhibits a non-monotonic influence on gas phase ignition, with higher pressures promoting particle autoignition. An increase in particle diameter decreases the ignition time for the homogeneous reaction, approaching that of particle-free conditions. Meanwhile, particle ignition time first decreases and then linearly increases. Increasing particle concentration reduces the interphase disparities of ignition times, while the two-phase ignition times rapidly rise after exceeding the critical concentration. Moreover, pre-ignition temperature equilibrium (PTE) significantly impacts the ignition parameters and processes. PTE results in a minimal ignition time disparity between the gas and particles, with coal char particles markedly influencing hydrogen ignition. Failure to reach PTE leads to significant two-phase ignition time differences, with negligible impact from the solid phase on gas phase ignition. The particle effect ratio, δ, is introduced to evaluate these effects. Notably, the evolution variations in ignition time and heat release rate are determined by the existence of the PTE under corresponding initial conditions. The findings of this study are crucial for developing strategies to mitigate explosion hazards and enhance the performance of detonation propulsion systems using hybrid fuels.

Effects of internal intervention in tubes on shock wave attenuation, formation and propagation of flame during high-pressure hydrogen release

Experiments on the impacts of the combination of fin structure and expansion chamber on shock wave attenuation, hydrogen ignition, and flame characteristics during high-pressure hydrogen release were carried out. The fin is a four-edged platform hollowed out on all sides. The inflated upper and lower tube walls are located 85, 95, and 105 mm away from the nickel burst disk. With the incident shock wave traveling through the fin, the reflected shock and the superposition of multiple reflected shock waves appear, and the reflected shock wave intensity can equal that of the release pressure. The decrease of the incident shock wave intensity behind the fin leads to the decrease of the non-uniformity of the mixed layer temperature, further causing the decrease of the flame propagation velocity. The presence of fins increases the probability of ignition in the fin region and the critical release pressure for ignition is significantly lower than that in the barrier free tube, mainly because the fin inside intensifies the hydrogen/air mixture, resulting in a lower minimum ignition energy required for self-ignition. Furthermore, the decrease of flame propagation velocity leads to the increase of hydrogen consumption inside the tube and the decrease of shock overpressure outside.

Is hydrogen ignition data from literature practically observed?

Significant and concerning discrepancies exist between the hydrogen ignition data reported in scientific literature and that obtained from practical observations of various real-world applications. This includes data regarding ignition temperatures, minimum ignition energies and flammability limits. These inconsistencies raise critical questions about the reliability and applicability of the existing data. This paper aims to thoroughly investigate these discrepancies, providing a comprehensive and balanced perspective about the underlying causes. By examining the differences between theoretical predictions and practical outcomes, we highlight these gaps' potential risks and challenges. Furthermore, actionable strategies are proposed to rectify these issues, emphasizing the need for improved research methodologies, enhanced data accuracy, and better communication between scientists and practitioners. Our goal is to ensure that hydrogen ignition data is both reliable and applicable, ultimately contributing to safer and more efficient hydrogen utilization in various industries.

Progress in spontaneous ignition of hydrogen during high-pressure leakage with the considerations of pipeline storage and delivery

High-pressure pipeline storage presents a promising method for widespread and efficient hydrogen transfer. However, challenges arise in mitigating pressurized hydrogen leakage due to hydrogen embrittlement issues associated with conventional pipeline materials. Experimental findings indicate that pressurized hydrogen is prone to spontaneous combustion, even at relief pressures as low as approximately 2 MPa - well below the permissible pipeline pressure in most countries. Despite this, there remains a lack of consensus regarding the mechanism of spontaneous ignition from high-pressure hydrogen leakage, and current research in this area is deemed insufficient. This study aims to analyze and discuss the presumed mechanisms of spontaneous ignition comparatively, review the progress in the study of spontaneous ignition of hydrogen in high-pressure leakage based on diffusion ignition theory, and statistically compare and discuss the influences of significant factors existing in pipelines (e.g., macro size factors and internal structure) and/or pipe failures (e.g., rupture factors) on spontaneous ignition. It is hoped that this article will provide scholars involved in the development of hydrogen energy and the theories of spontaneous combustion with a systematic understanding of these phenomena.

Ultra-lean hydrogen-air flames initiated by a hot surface

The benefits of using hydrogen as a fuel for rocket engines dictate the necessity of a deep understanding of possible scenarios of hydrogen ignition and subsequent combustion. Safety requirements on launch sites and hydrogen transportation and storage facilities should be elaborated based on a thorough investigation of hydrogen flame development. The paper aims to provide a detailed numerical analysis of the hot wall ignition of hydrogen-air mixtures with compositions near low flammability limits. It is shown that the development of ultra-lean flames initiated by a hot spot on the solid wall possesses several features compared to ultra-lean flames ignited by a point energy source. Three modes of flame development are observed: stable flame column with bow-shaped flame structure on top, individual flame kernel, and unstable flame column with multiple kernels generation. Effects of mixture composition, along with the impact of hot spot size, are analyzed. Column tip acceleration mechanism is determined. All of the combustion modes obtained are grouped in the diagram, providing information on the limits of various combustion modes depending on the mixture concentration and hot spot size.

An review of research on liquid hydrogen leakage: regarding China’s hydrogen refueling stations

Hydrogen is regarded as the premier energy source for future sustainability and renewability. However, its distinct physicochemical properties render it prone to explosions in the event of a leak. Therefore, there is a need for more comprehensive research dealing with hydrogen leakage, explosion scenarios, and risk assessment. This paper provides an overview of the current hydrogen policies adopted in China. It reviews the processes of hydrogen refueling station construction and the thermophysical mechanisms of liquid hydrogen leakage. In this regard, the effects of various factors, including leakage rate, leakage time, leakage hole size, wind direction and speed, and building location, on the hydrogen leakage rate are analyzed and evaluated. Additionally, the impacts of different factors on hydrogen explosion overpressure are reported, including hydrogen concentration, wind speed, obstacles, and ignition position, in addition to the current applications of quantitative risk assessment methods in hydrogen refueling stations. Finally, the limitations of current research on liquid hydrogen leakage and explosion accidents are highlighted, along with the shortcomings of current risk assessment methods for liquid hydrogen refueling stations.

Experimental Study on the Influence of Ignition Position on the Overpressure of Hydrogen Jet Flame.

The accidental leakage of hydrogen poses a significant barrier to the widespread adoption and development of hydrogen energy due to the potential risks of fire, explosion, and jet fire hazards. Experimental investigations have been conducted on the process of jet fires formed by igniting hydrogen jet streams after accidental releases in scenarios such as high-pressure hydrogen gas storage tanks and hydrogen transmission pipelines. These experiments utilized a release pipe with a diameter of 10 mm and a length of 0.75 m, along with three pressure sensors, to study the influence of release pressure and ignition position on jet flame overpressure and flame propagation. Extensive tests at 1.5 MPa yielded a hydrogen flammability map containing two nonflammable zones and one flammable zone, along with a graph illustrating the relationship between overpressure and ignition points. Furthermore, experiments conducted at ignition positions of 0.05, 0.5 and 1.0 m under release pressures ranging from 6 to 10 MPa revealed that release pressure had no significant effect, while ignition position notably influenced the waveform and peak of the shockwave. Additionally, a peak shockwave reaching 30 kPa was observed at the downstream of the pipe outlet when ignited at 0.05 m, far exceeding the threshold of 24 kPa associated with fatalities. This research aims to provide valuable insights for safety design and protection distance considerations in scenarios involving hydrogen release and ignition.

Experimental investigation on the development characteristics of high-pressure hydrogen jet flame under different ignition conditions

With the rapid development and application of hydrogen in the chemical and energy industry, the safety of hydrogen industrial facilities has been widely concerned. In this study, the safety of hydrogen accidently released from a high-pressure tube storage system (tube diameter:10 mm, storage tank volume:4 L) was explored experimentally. The combustion behavior of the transient hydrogen jet and explosion overpressure under self-ignition and electric spark induction were investigated. Besides, the explosion overpressure and jet flame evolution laws of the hydrogen cloud induced by the release of unsteady turbulent hydrogen jets into the open environment were analyzed. The results revealed that the peak value of hydrogen self-ignition explosion overpressure was higher than that of electric spark ignition overpressure. Compared with spark ignition, hydrogen self-ignition flame structures can be maintained for longer time. However, spark ignition at low release pressures was more likely to cause hydrogen ignition and explosion compared to self-ignition. Finally, the combustion behavior and potential hazards of the ignited free transient hydrogen jet under different ignition modes were analyzed. This study can provide a reference for the prevention and control of hydrogen explosion accidents in practice.

Numerical investigation of hydrogen ignition induced by unsteady flow phenomena

The purpose of the present study is to evaluate the possibility of using a gas dynamic heater as an igniter of the combustible gas mixtures. The impacts of some operating and geometrical parameters on average temperature of the gas dynamic heater are investigated by numerical simulation of axisymmetric turbulent flow in the resonance tube. The operating gas of the heater is air which is completely decoupled from the ignition chamber. The combustible mixtures under consideration is stoichiometric hydrogen-oxygen at atmospheric pressure, in which the ignition is studied solving the governing equations for one dimensional reacting flow using detailed chemistry. The finite volume method is used in the presently developed flow solver for numerical simulations. The results show that despite highly fluctuating temperature of the end wall of the resonance tube as a hot surface, it can provide proper condition for gas mixture ignition in the chamber, by adjusting an inlet pressure and geometry of the gas dynamic heater. The end wall average temperature depends on the nozzle inlet pressure and convergence angle of the resonance tube, and the results demonstrate that the characteristics of temperature time history of repeating cycles are so effective on ignition process.

Effects of Various Compression Ratios on a Direct Injection Spark Ignition Hydrogen-Fueled Engine in a Single-Cylinder Engine

AbstractThe effects of compression ratio and injection timing on a direct injection spark ignition hydrogen engine under various excessive air ratios were analyzed using a 0.4-L single-cylinder engine in this study. The engine speed was set to 1500 rpm, and the excessive air ratio was changed by controlling the amount of injected hydrogen under wide-open throttle conditions. The compression ratio was changed from 10, 12, and 14 and the injection timing was varied from BTDC 200, 160, 120°CA. The results revealed that for a compression ratio 14 at a rich limit, late injection timing reduced knocking incidence by taking advantage of stratified mixtures combustion and increased indicated thermal efficiency by reducing combustion loss while producing lower NOx emissions. For compression ratio 14 at an excessive air ratio of 2.2, late injection timing increased indicated thermal efficiency by reducing both combustion and heat losses, achieving the higher indicated thermal efficiency of 42.3%. Although NOx emissions increased with the injection timing retardation, NOx emissions decreased to under 1 g/kWh under excessive air ratios above 2.5 conditions at all injection timings.

Experimental study of the hydrogen leakage and ignition in a ventilated room

Experimental study of the hydrogen leakage and ignition in a ventilated room

A detailed kinetic submechanism for OH[formula omitted] chemiluminescence in hydrogen combustion revisited. Part 2

In this series of two papers, we present a novel physically sound kinetic submechanism aimed at modeling the formation and decay of chemiluminescent (electronically excited) OH∗ molecules in the ignition and combustion of hydrogen and hydrogen-based mixtures over a wide range of temperatures and pressures. The present Part describes the construction of this detailed reaction submechanism based on the groundwork and findings of the preceding paper. In so doing, we relied both on critical evaluation of known and at times conflicting experimental and theoretical data on the elementary reaction kinetics of OH∗ and on our quantum chemical calculations and rate constant estimates for the key processes. The kinetic model under development was validated against the representative dataset of the observed OH(A2Σ+→X2Π) chemiluminescent emission accompanying the high-temperature (post-shock) oxidation of various H2-containing mixtures. To improve its performance against the collected OH∗ emission data, the rate constants of some reactive and quenching processes, to which the OH∗ kinetics is the most sensitive and for which there is a particular uncertainty, were jointly varied within the limits imposed by theoretical considerations and/or the scatter in the available experimental evidence. Thus, by refining the rate constants of these elementary processes, we obtained a reasonable reaction submechanism for OH∗ that describes the known experimental data better than previous models.Novelty and significance statement Although ultraviolet OH∗ chemiluminescence as an optical signature of the combustion process and the underlying chemistry is known to provide unique capabilities for combustion diagnostics, the development of the detailed reaction mechanisms intended for quantitative interpretation of the OH∗ emission measurements has now almost stagnated. Indeed, existing kinetic models contain a discouragingly small number of elementary processes and, apparently, do not account for the full variety of possible reaction pathways of OH∗ formation and depletion. Therefore, in this serial work, we have intended to revise the current ideas about the kinetics of OH∗ production and consumption during ignition and combustion and focused first on the OH∗ kinetics in a reacting H2/O2/Ar/N2 mixture. The principal outcome of this Part of the series is a new physically based kinetic submechanism aimed at modeling the formation and decay of electronically excited OH∗ molecules in the ignition and combustion of hydrogen and hydrogen-containing mixtures. Its incorporation into any conventional kinetic model of hydrogen oxidation enables quantitative interpretation of the OH(A2Σ+−X2Π) chemiluminescent emission observed experimentally in flames and shock-heated reacting flows with an accuracy higher than that of previous analogous mechanisms. No less importantly, the rate constant approximations for a number of individual elementary processes with OH∗, recommended here based on the critical review of literature data and on our quantum chemical calculations, are also of independent interest for the kinetics of electronically excited OH∗ particles. Finally, the OH∗ reaction subset we suggested for hydrogen flames can form the basis of more complex OH∗ chemiluminescence modeling reaction mechanisms for other fuels and fuel compositions.

A detailed kinetic submechanism for OH[formula omitted] chemiluminescence in hydrogen combustion revisited. Part 1

In this series of two papers, we present a novel physically sound kinetic submechanism aimed at modeling the formation and decay of chemiluminescent (electronically excited) OH∗ molecules in the ignition and combustion of hydrogen and hydrogen-based mixtures over a wide range of thermodynamic parameters and mixture compositions. The present part of this series describes the preparatory stages of the work, such as the aggregation of the data set for the OH∗ chemiluminescent emission (including the OH∗ emission profiles obtained in our shock-tube experiments), the choice of the basic kinetic model of hydrogen oxidation, and, importantly, quantum chemical calculations and theoretical estimates for the rate constant of the nonadiabatic preassociation reaction H + O + M ⇆ OH∗ + M, recognized as a major source of excited OH∗ molecules in hydrogen-air flames. These rate constant estimates are carried out in a wide range of temperatures (200–4000 K) and pressures (10−3−100 bar). It is shown that the rate constant of this key reaction exhibits distinct non-Arrhenius temperature behavior and, moreover, has a complex fall-off pressure dependence, with the transition from a third to a second-order, high-pressure regime occurring at pressures about 10 atm. The obtained dependence on temperature and pressure is in excellent agreement with the known experimental data and can be recommended (as part of the appropriate reaction mechanisms) for further kinetic modeling of OH∗ chemiluminescence accompanying the high-temperature oxidation of hydrogen and other fuels.Novelty and Significance StatementAlthough ultraviolet OH∗ chemiluminescence as an optical signature of the combustion process and the underlying chemistry is known to provide unique capabilities for combustion diagnostics, the development of the detailed reaction mechanisms intended for quantitative interpretation of the OH∗ emission measurements has now almost stagnated. Indeed, existing kinetic models contain a discouragingly small number of elementary processes and, apparently, do not account for the full variety of possible reaction pathways of OH∗ formation and depletion. Therefore, in this serial work, we have revised the current ideas about the kinetics of OH∗ production and consumption during ignition and combustion and focused first on the OH∗ kinetics in a reacting H2/O2/Ar/N2 mixture. The fundamentally significant and novel results of this Part of the present series are (i) the rate constant of the nonadiabatic preassociation reaction H + O + M ⇆ OH∗ + M (the primary source of OH∗ in hydrogen combustion), theoretically obtained for the first time as a function of temperature and pressure, and (ii) the OH∗ emission profiles obtained in our shock-tube experiments. The other aspects described here, such as the aggregation of the literature-based data set for the post-shock OH∗ chemiluminescent emission and the choice of the basic kinetic model of hydrogen oxidation, are also of interest and relevance.

Prognozowanie procesu emisji wodoru z obudowy turbogeneratora z powstawaniem palnych mieszanin wodorowo-powietrznych i spalaniem pochodni

Predicting the process of hydrogen emission from the turbogenerator housing with the formation of flammable hydrogen-air mixtures and flare combustion The operation of turbogenerators of nuclear and thermal power plants is accompanied by the release of heat, which contributes to the heating of generator components and can lead to an emergency situation (fire). Since As turbogenerators operate for long periods of time, the process of continuous cooling of generator equipment plays an important role, as its overheating can lead to emergency chain reactions, fires, explosions, etc. Analysis of statistical data on the occurrence of emergency situations (fires) related to hydrogen leaks from process equipment indicates insufficient operational qualifications of operational personnel, poor quality of equipment repair, errors of repair personnel and their violation of technical requirements for repairing equipment and their systems, design defects in equipment and systems that ensure its operation. It has been established that the causes of emergency situations are: hydrogen leakage due to leaks in equipment, spontaneous ignition of hydrogen, the presence of air space in turbogenerator equipment, violation of technological regulations, contamination of hydrogen with moisture and pollution, unhermetization of the generator body. Modeling of the hydrogen combustion process during its release from the casing of a turbine-generator was carried out using the example of a power plant engine room. The study showed that the longest hydrogen combustion time will occur when hydrogen is released through holes with geometric size d0 in the range of 0.05--0.1 m (50--100 mm). At larger values of the geometric size of the hole d0 > 0.1 m, the hydrogen burning time is insignificant, and at values of d0 < 0.005 m, the length of the flame burner L does not exceed 1.15 m. The results of the study confirm that hydrogen flame torch combustion can occur as a result of turbogenerator failure. The calculations established the need for fire protection of the supporting metal structures of the engine room to ensure a fire resistance limit of at least 45 minutes under the hydrocarbon curve.

Chemical Kinetic Analysis of High-Pressure Hydrogen Ignition and Combustion toward Green Aviation

In the framework of the “Multidisciplinary Optimization and Regulations for Low-boom and Environmentally Sustainable Supersonic aviation” project, pursued by a consortium of European government and academic institutions, coordinated by Politecnico di Torino under the European Commission Horizon 2020 financial support, the Italian Aerospace Research Centre is computationally investigating the high-pressure hydrogen/air kinetic combustion in the operative conditions typically encountered in supersonic aeronautic ramjet engines. This task is being carried out starting from the zero-dimensional and one-dimensional chemical kinetic assessment of the complex and strongly pressure-sensitive ignition behavior and flame propagation characteristics of hydrogen combustion through the validation against experimental shock tube and laminar flame speed measurements. The 0D results indicate that the kinetic mechanism by Politecnico di Milano and the scheme formulated by Kéromnès et al. provide the best matching with the experimental ignition delay time measurements carried out in high-pressure shock tube strongly argon-diluted reaction conditions. Otherwise, the best behavior in terms of laminar flame propagation is achieved by the Mueller scheme, while the other investigated kinetic mechanisms fail to predict the flame speeds at elevated pressures. This confirms the non-linear and intensive pressure-sensitive behavior of hydrogen combustion especially in the critical high-pressure and low-temperature region which is hard to be described by a single all-encompassing chemical model.

Numerical study on the effects of the obstacle shapes on the spontaneous ignition of high-pressure hydrogen in a tube

It is necessary to investigate the impact of different obstacle shapes on high-pressure hydrogen spontaneous ignition due to the role obstacles play in promoting its generation. This paper first carried out model validation and found that the simulation could accurately reproduce the position and time of the initial flame detection, flame evolution, and pressure in the triangular-shaped obstacle tube as observed in the experiments. Subsequently, simulations were employed to explore the impact of three different obstacle shapes (triangular-shaped, arc-shaped, and square-shaped) on spontaneous ignition with the tube. The variation in obstacle shapes affects the initial flame detection position and the length of the flame, while it has minimal impact on the spontaneous ignition time. The square-shaped obstacles result in the closest initial flame detection position point to the burst disk and the longest flame in the tube, followed by the arc-shaped obstacles, and finally the triangular-shaped obstacles.

Effects of cryogenic temperature on turbulent premixed hydrogen/air flames

As a carbon-free fuel, hydrogen (H2) is of increasing importance in the development of low-emission engines. Due to a low volumetric energy density, H2 is preferably stored at cryogenic temperatures (Tu≤100 K). In this context, it is indispensable to investigate the combustion behavior of hydrogen at such low temperatures. Although some studies focused on the ignition and detonation of hydrogen, investigations about premixed H2/air flame propagation interacting with turbulence at cryogenic temperatures are rather scarce. In this work, stoichiometric turbulent premixed H2/air flames are studied at cryogenic temperature (Tu=100K) and normal temperature (Tu=300K), using three-dimensional direct numerical simulations with detailed chemistry and transport. It is found that at cryogenic temperature, dimensionless turbulent flame speed and flame surface area increase significantly due to Darrieus–Landau instability (DLI) induced by a large expansion ratio. Since the effective Lewis numbers of the two cases are close to unity, the diffusive-thermal instability (DTI) is negligible in the cases. Furthermore, it is found that there are substantial differences in the peaks of HO2 and H2O2 mass fractions between the two cases, probably due to smaller local flame curvatures at cryogenic temperature. Moreover, the results indicate that the flame response to stretch is not sensitive to the change of the initial temperature. A larger fractal inner cutoff scale is found at Tu=100K, suggesting that the flame exhibits more large-scale flame wrinkling than that at Tu=300K due to the impact of DLI. All these facts lead to the conclusion that cryogenic temperature can significantly promote large-scale flame wrinkling, increase turbulent flame speed and flame surface area, and affect intermediate species distribution. This suggests that combustion of cryogenic H2 may have a high risk of flashback.

Real gas effects on the dynamics of a reactive diffusion layer: Application to the study of spontaneous ignition limit of pressurized hydrogen jet

The spontaneous ignition of hydrogen accidentally released from pressurized equipment poses safety risk to the utilization of hydrogen as an energy carrier. This work aims at studying the pressure and temperature dependent real gas effects, resulting from the high-pressure conditions in the storage facility, on the spontaneous ignition. Numerical simulations were performed based on a one-dimensional diffusion layer ignition model applied to the head of the hydrogen jet into air. The real gas effects were considered in the equation of state, thermodynamics, transport properties, and mass action law. The critical pressure of spontaneous ignition was determined for both unconfined releases through round holes and confined releases through extension tubes. The results demonstrate satisfactory agreement with experimental data. In unconfined releases, real gas effects lead to higher critical pressures. The relative difference was 10% for a 0.6 mm hole and increased drastically as the hole size was decreased. In confined releases, the critical pressure was relatively low and the real gas effects were negligible. The real gas effects manifest mainly through the equation of state and thermodynamics. The density and frozen sound speed of hydrogen are under-predicted and over-predicted by the ideal gas model, respectively. This delays the volumetric expansion competing with the heat release process, and thus results in easier ignition for ideal gas than for real gas. The present results demonstrate that real gas effects should at least be considered in the equation of state and thermodynamic functions for accurate simulation of highly pressurized hydrogen injection.

Study on lean combustion of ammonia-hydrogen mixtures in a pre-chamber engine

Ammonia holds promise for achieving zero carbon emissions from internal combustion engines. The pre-chamber turbulent jet ignition, characterized by multipoint distributed ignition and rapid combustion, could be applied to ammonia combustion to extend combustion limits and stability. This study investigates the impacts of hydrogen energy fraction (Hfrac), equivalence ratio, and ignition timing on the combustion and emission characteristics of ammonia-hydrogen mixture at lean combustion conditions in a pre-chamber (PC) marine engine by CFD Simulation. In H2-fuel active PC mode, increasing the hydrogen content or achieving stoichiometric combustion within the PC will shorten the cold jet phase and accelerate the formation of a more intense hot jet. As the Hfrac and the equivalence ratio in the main-chamber increase, the combustion pressure, temperature, and heat release rate (HRR) rise, while the combustion duration shortens due to enhanced reactivity, potentially leading to end gas auto-ignition and knock due to lower auto-ignition energy of the mixture. NO primarily forms near the flame front, and both NO concentration and the generation area increase with an increase in hydrogen content and equivalence ratio. Fuel-NO is likely to be the dominant factor in NO generation with lean combustion conditions. N2O, as a product of NH3 low-temperature combustion, is mainly concentrated near the flame front. An increase in unburned NH3 emissions corresponds to an increase in N2O emissions. Delaying the ignition timing to reduce NOx emissions is primarily achieved by controlling NO emissions, even though there is a slight increase in N2O.