Cold flow characteristics of a novel bluff body hydrogen burner

The cold flow characteristics of a novel partial premixed bluff body (PPBB) low NO_x burner, capable of operating with hydrogen as well as methane-hydrogen blends, were investigated numerically. The PPBB burner features a frustum shaped conical bluff body generating a flame stabilizing recirculation zone. Fuel is partially premixed via jets in an accelerating cross-flow. Steady-state and transient non-reacting simulations using five different turbulence models, i.e. standard k-ε, realizable k-ε, shear stress transport (SST) k-ω, stress-blended eddy simulation (SBES) and large eddy simulation (LES), were conducted. The simulations were validated against particle image velocimetry (PIV) measurements of an unconfined non-reacting flow. All turbulent models were able to predict the recirculation zone length in good agreement with the experimental data. However, only scale resolving simulations could reproduce velocity magnitudes with sufficient accuracy. Time averaged and instantaneous results from the scale resolving simulation were analysed in order to investigate flow characteristics that are special about the PPBB burner design and of relevance for the combustion process. Two different burner configurations were studied and their effects on the flow field were examined. The recirculation zone volume as well as the entrainment into the wall jet around the bluff body were found to correlate with the elevation of the bluff body relative to the burner throat. Both of these parameters are expected to have a strong impact on the overall NO_x emission, since the near burner region is typically one of the main contributors to the NO_x formation.     

Numerical study of hydrogen‐enriched methane–air combustion under ultra‐lean conditions

The demand for gas turbines that accept a variety of fuels has continuously increased over the last decade. Understanding the effects of varying fuel compositions on combustion characteristics and emissions is critical to designing fuel‐flexible combustors. In this study, the combustion characteristics and emissions of methane and hydrogen‐enriched methane were both experimentally and numerically investigated under ultra‐lean conditions (Ø ≤ 0.5). This study was performed using global mechanisms with a one‐step mechanism by Westbrook and Dryer and a two‐step mechanism with an irreversible and reversible CO/CO₂ step (2sCM1 and 2sCM2). Results show that the 2sCM2 mechanism under‐predicted the temperature, major species, and NO_x by more than 100% under ultra‐lean conditions; thus, we proposed a modified‐2sCM2 mechanism to better simulate the combustion characteristics. The mechanisms of Westbrook, 2sCM1, and modified 2sCM2 predicted the temperature and the CO₂ emission with an average deviation of about 5% from the experimental values. Westbrook and 2sCM1, however, over‐predicted the NO_x emission by approximately 81% and 152%, respectively, as compared with an average under‐prediction of 11% by the modified‐2sCM2 mechanism. The numerical results using the proposed modified‐2sCM2 mechanism shows that the presence of hydrogen in the fuel mixture inhibits the oxidation of methane that led to the formation of unburned hydrocarbons in the flame. We also showed that for any given fuel compositions of H₂/CH₄, there is an optimum equivalence ratio at which the pollutant emissions (CO and NO_x) from the combustor are minimal. Zero CO and 5 ppm NO_x emissions were observed at the optimal equivalence ratio of 0.45 for a fuel mixture containing 30% H₂. The present study provides a basis for ultra‐lean combustion toward achieving zero emissions from a fuel‐flexible combustor. Copyright © 2016 John Wiley & Sons, Ltd.     

Mixing and Recirculation Characteristics of A double COncentric Burner with Bluff—Body

The concentric bluff-body jet burner is widely used in industrial combustion systems. This kind of burner often generates a considerably complex recirculation zone behind the bluff body. As a result, the fuel often remains in the recirculation zone, achieving stability of flame. This study investigates, by means of experiments, the variations of the aerodynamics as the fluid is injected into a combustion chamber through a double concentric burner with a bluff-body. The observation and measurement of the aerodynamics in our experiment are conducted under a cold flow. The controlled parameters in our experiment are: variations in the blockage ratio of the center bluff body, the cone angle of the bluff body, and the velocity ratio (U _s/U_p) of the secondary jet and primary jet; the injection of helium bubbles into the primary and secondary jets to observe the recirculation zone behind the bluff body; using Tufts for observing the characteristics of corner recirculation zone in a combustion chamber, measuring the average velocity of each point within the aerodynamics by the 5-hole pitot tube; measuring the distribution of static pressure of the combustion chamber walls with a static pressure tap.     

Optimization of flame stabilization methods in the premixed microcombustion of hydrogen–air mixture

The premixed combustion of a lean hydrogen–air mixture is analyzed in this study to examine various properties and flame stabilization. A two-dimensional (2D) analysis of a microscale combustor is performed with various shapes of bluff bodies (e.g., circular and triangular). Nine bluff bodies are placed at the entrance of the microscale combustor and solved with 2D governing equations. The analysis is performed with the three velocities of 10, 20, and 30 m/s, but the equivalence ratio is fixed in all cases. The various characteristics of the microscale combustor are studied such as the temperature of the wall, difference in peak temperature, the mean velocity at the outlet, and temperature of the exhaust gases. Flame stabilization depends on various factors such as bluff body shape and size, and the velocity of the fuel–air mixture at the inlet and recirculation zone. In comparison to all bluff body cases, we observe that the wall blade bluff body is the most efficient (low exhaust gas temperature, large recirculation zone, low mean velocity at the outlet of the microcombustor, and high wall temperature) compared with all eight other bluff body cases. Combustion efficiency is directly proportional to the wall temperature, meaning that the microcombustor with wall blade bluff bodies is more efficient with a stabilized flame. The simulation results are compared with published data on an L/D ratio of 15.     

Experimental investigation of producer gas burner for thermal application

This paper deals with the performance evaluation of a premixed-type burner with producer gas, in terms of emission, axial and radial flame temperature. In this study, a burner of 150 kWth capacity was tested on an open core downdraft-type gasifier. The developed burner is a concentric tube-type where the air is supplied through a central tube, which is surrounded by another one. The burner consists of a swirl vane for mixing the air and producer gas, mixing tube and bluff body for flame stabilization. Swirl angle and bluff body diameter were kept constant throughout the study. The burner was evaluated with an open core downdraft-type gasifier. The temperature evaluation and emission testing was done for three flow rates and air–fuel ratio. The study shows low NO _x and CO emission at 125 Nm³ h^?1 when compared with that of 75 and 100 Nm³ h^?1. Maximum flame temperature (753 °C) was recorded at 10 cm axial and 10 mm radial distance.     

Impact of EGR fraction on diesel engine performance considering heat loss and temperature‐dependent properties of the working fluid

Exhaust gas recirculation (EGR) to reduce feed gas NO_x emission is common practice in modern diesel engines. Dilution of the intake air with cooled recirculated exhaust gas limits the production of in‐cylinder NO_x due to a lowering of the adiabatic flame temperature and a reduction in oxygen content of the intake mixture. EGR also reduces the mixture‐averaged ratio of specific heats (γ) of the combustion charge leading to a reduction in the thermodynamic cycle efficiency. This trade‐off between minimizing NO_x production and maximizing cycle efficiency is of critical importance when calibrating EGR control schemes. Modeling tools that allow a quantitative analysis of this trade‐off can be very beneficial in tuning EGR systems over a range of operating conditions. In this study, the systematic development of a model that allows an assessment of the impact of EGR on three parameters, namely (a) the thermodynamic cycle efficiency, (b) the mixture temperatures during the cycle and (c) the mixture‐averaged γ, is presented. This is accomplished through a numerical solution of the energy equation while considering the effects of heat loss and temporally varying mixture‐averaged values of γ. Results for a simple phenomenological model relating fuel‐burn rate with EGR fraction and the impact of EGR fraction on NO_x reduction are also included. Copyright © 2008 John Wiley & Sons, Ltd.     

NOx formation in post-flame gases from syngas/air combustion at atmospheric pressure

Species concentration measurements specifically those associated with nitrogen oxides (NO_x) can act as important validation targets for developing kinetic models to predict NO_x emissions under syngas combustion accurately. In the present study, premixed combustion of syngas/air mixtures, with equivalence ratio (Φ) from 0.5 to 1.0 and H₂/CO ratio from 0.25 to 1.0 was conducted in a McKenna burner operating at atmospheric pressure. Temperature and NO_x concentrations were measured in the post-combustion zone. For a given H₂/CO ratio, increasing the equivalence ratio from lean to stoichiometric resulted in an increase in NO and decrease in NO₂ concentration near the flame. Increasing the H₂/CO ratio led to a decrease in the temperature as well as the NO concentration near the flame. Based on the axial profiles above the burner, NO concentration increases right above the flame while NO₂ concentration decreases through NO₂-NO conversion reactions according to the path flux analysis. In addition, the present experiments were operated in the laminar region where multidimensional transport effects play significant roles. In order to account for the radial and axial diffusive and convective coupling to chemical kinetics in laminar flow, a multidimensional model was developed to simulate the post-combustion species and temperature distribution. The measurements were compared against both multidimensional computational fluid dynamics (CFD) simulations and one-dimensional burner-stabilized flame simulations. The multidimensional model predictions resulted in a better agreement with the measurements, clearly highlighting the effect of multidimensional transport.     

Combustion characteristics of a lean premixed LPG–air combustor

Fuel/air mixing effects in a premixer have been examined to investigate the combustion characteristics, such as the emission of NO_x and CO, under simulated lean premixed gas turbine combustor conditions at normal and elevated pressures of up to 3.5 bar with air preheat temperature of 450 K. The results obtained have been compared with a diffusion flame type gas turbine combustor for emission characteristics. The results show that the NO_x emission is profoundly affected by the mixing between fuel and air in the combustor. NO_x emission is lowered by supplying uniform fuel/air gas mixture to the combustor and the NO_x emission reduces with decrease in residence time of the hot gases in the combustor. The NO_x emission level of the lean premixed combustor is a strong function of equivalence ratio and the dependency is smaller for a traditional diffusion flame combustor under the examined experimental conditions. Furthermore, the recirculation flow, affected by dome angle of combustor, reduces the high temperature reaction zone or hot spot in the combustor, thus reducing the NO_x emission levels.     

Investigation of combustion and emission performance of a micro combustor: Effects of bluff body insertion and oxygen enriched combustion conditions

Major challenges for micro combustors are high heat losses and inappropriate residence time. In this study, it was aimed to eliminate these challenges via placing bluff bodies into the combustion zone and combusting fuel with oxygen enriched air. To this end, micro combustor models with different geometries were constructed and in these models, premixed H₂/air combustion was simulated by using ANSYS/Fluent CFD code to investigate effects of bluff body shape, location and thickness, and low level O₂ enhancement on performance determining parameters such as rate of conversion of fuel to useable heat, temperature uniformity, pollutant emissions etc. To further analyze effects of micro combustor geometry, a perforated plate was also placed into the combustion zone. Thermal performance of the micro combustor with perforated plate insertion in O₂ enriched conditions was found to be highest in terms of increased reaction kinetics and heat transfer characteristics. The trade-offs of respective design are increased NO_x emissions and slightly decreased temperature uniformity.     

Frontiers in combustion techniques and burner designs for emissions control and CO2 capture: A review

The use of fossil fuel is expected to increase significantly by midcentury because of the large rise in the world energy demand despite the effective integration of renewable energies in the energy production sector. This increase, alongside with the development of stricter emission regulations, forced the manufacturers of combustion systems, especially gas turbines, to develop novel combustion techniques for the control of NO_x and CO₂ emissions, the latter being a greenhouse gas responsible for more than 60% to the global warming problem. The present review addresses different burner designs and combustion techniques for clean power production in gas turbines. Combustion and emission characteristics, flame instabilities, and solution techniques are presented, such as lean premixed air‐fuel (LPM) and premixed oxy‐fuel combustion techniques, and the combustor performance is compared for both cases. The fuel flexibility approach is also reviewed, as one of the combustion techniques for controlling emissions and reducing flame instabilities, focusing on the hydrogen‐enrichment and the integrated fuel‐flexible premixed oxy‐combustion approaches. State‐of‐the‐art burner designs for gas turbine combustion applications are reviewed in this study, including stagnation point reverse flow (SPRF) burner, dry low NO_x (DLN) and dry low‐emission (DLE) burners, EnVironmental burners (including EV, AEV, and SEV burners), perforated plate (PP) burner, and micromixer (MM) burner. Special emphasis is made on the MM combustor technology, as one of the most recent advances in gas turbines for stable premixed flame operation with wide turndown and effective control of NO_x emissions. Since the generation of pure oxygen is prerequisite to oxy‐combustion, oxygen‐separation membranes became of immense importance either for air separation for clean oxy‐combustion applications or for conversion/splitting of the effluent CO₂ into useful chemical and energy products. The different carbon‐capture technologies, along with the most recent carbon‐utilization approaches towards CO₂ emissions control, are also reviewed.     

Experimental study of fuel‐lean reburn system for NOX reduction and CO emission in oxygen‐enhanced combustion

A fuel‐lean reburn system is found here to be able to replace a conventional reburning technique in terms of increasing efficiency. In the fuel‐lean reburn system, the amount of injected reburn fuel into the reburning zone is low enough to maintain the overall fuel‐lean condition in the furnace, so that no additional air system is required, and CO emission can be maintained at almost zero level. In this study, an experimental study has been done to examine the reduction characteristics of NO_X in a lab scale combustor (15 kW) with various oxygen‐enhanced combustion conditions. Liquefied Petroleum Gas (LPG) was used as a main fuel and reburn fuel. Finally, the current fuel‐lean reburn system, even with only an amount of reburn fuel of 13% of total heat input, was observed to achieve a maximum of 48% in NO_X reduction. Copyright © 2010 John Wiley & Sons, Ltd.     

Staged combustion properties for pulverized coals at high temperature

Staged combustion properties for pulverized coals have been investigated by using a new-concept drop-tube furnace. Two high-temperature electric furnaces were connected in series. Coal was burnt under fuel-rich conditions in the first furnace, then, staged air was supplied at the connection between the two furnaces. Reaction temperature (1800–2100 K) and time (1–2 s) were similar to those used in actual boilers. When coal was burnt at the same stoichiometric ratio as in actual boilers, similar combustion performance values as for actual boilers were obtained regarding NO_x emission and carbon in ash. The most important factor for low NO_x combustion was to raise the combustion temperature above the present range (1800–2100 K) in the fuel-rich zone. The NO_x emission was significantly increased with decrease of burning temperature in the fuel-rich zone when the temperature was lower than 1800 K. But, NO_x emission was cut to around 100–150 ppm, for sub-bituminous coal and hv-bituminous coal, in the latest commercial plants by forming this high-temperature fuel-rich region in the boilers. If the temperature and stoichiometric ratio could be set to the most suitable conditions, and, burning gas and air were mixed well, it would be possible to lower NO_x emission to 30–60 ppm (6% O₂). The most important NO_x reduction reaction in the fuel-rich zone was the NO_x reduction by hydrocarbons. The hydrocarbon formation rate in the flame was varied with coal properties and combustion conditions. The NO_x was easily reduced when coals which easily formed hydrocarbons were used, or, when burning conditions which easily formed hydrocarbons were chosen. Effects of burning temperature and stoichiometric ratio on NO_x emission were reproduced by the previously proposed reaction model. When solid fuel was used, plant performance values varied with fuel properties. The proposed drop-tube furnace system was also found to be a useful analysis technique to evaluate the difference in combustion performance due to the fuel properties.     

A simplified fuel‐NOx model based on regression analysis

The mechanism of detailed chemical reactions in combustion is very complicated, especially when the formation of a pollutant such as NO_x is considered. Based on regression analysis, a simplified fuel–NO_x model is developed for premixed flame. The new model is available for a wider range of temeperature and fuel–air ratios compared with De Soete's (1975) fuel NO model. The reduction CHi species on NO is considered so that the model can be used in both fuel‐lean and fuel‐rich combustion systems. After a great simulation of a one‐dimensional premixed flame system using Miller and Bowman's (1989, Prog. Energy Combust. Sci., 15, 287) detailed elementary reaction model, the calculation of all the reaction rates is presented based on regression analysis. Copyright © 1999 John Wiley & Sons, Ltd.     

Acoustic excitation effect on NOx reduction and flame stability in a lifted non-premixed turbulent hydrogen jet with coaxial air

The effects of acoustic excitation on the reduction in nitric oxidant (NO_x) emission were experimentally investigated in non-premixed lifted hydrogen jet flames with coaxial air. The purpose of the present work was to analyze the acoustic forcing effect on the flow field, the reaction zone, and NO_x emission, and to study the mechanisms of NO_x reduction and flame stabilization. To analyze of the flow field, a PIV method was used that incorporated two Nd-YAG lasers and a CCD camera. The reaction zone was visualized by taking OH* chemiluminescence images with a 307.1 ± 5 nm narrow band pass filter and an ICCD camera. A flow condition was carefully selected at u_F = 150, 200, 250 m/s and u_A = 12, 16, 20 m/s, which was sustainable for acoustic excitation in a lifted flame region. The frequency was swept from 150 to 1000 Hz in 5 Hz steps. From the measurements of the flow field, the reaction zone, and NO_x emission, we concluded that NO_x emission was reduced and minimized at the resonance frequency. The vortex that was generated by acoustic forcing promoted air entrainment and enhanced the fuel-air mixing rate. This premixing effect resulted in a lower flame temperature, and thus lower NO_x emissions. In addition, the liftoff height periodically fluctuated due to the stretch effect as the vortex interacted with the flame base.     

Numerical study of further NOx emission reduction for coal MILD combustion by combining fuel‐rich/lean technology

This paper numerically examines the feasibility of further reducing NO_x emission from a semi‐industrial scale coal MILD (moderate and intense low‐oxygen dilution) combustion furnace by adopting fuel‐rich/lean technology. The implementation is achieved by separating the original fuel jet into two parallel jets which will be used as rich and lean streams. An effort has been made to develop a 13‐step reaction mechanism and NO_x evolution UDFs (user defined functions) for better understanding the interactions between MILD combustion and fuel‐rich/lean technology. The experiment of the reference case (Combustion and Flame 156.9 (2009): 1771‐1784) is well reproduced by the present numerical simulation, indicating high reliability of developed models. The validity of the further reduction of NO_x emission is assessed by the comparison among inner‐fuel‐rich (IFR), outer‐fuel‐rich (OFR), and reference cases resulting from the adjustment of the fuel supply through the two fuel‐rich/lean jets. The results show that both IFR and OFR configurations succeed in achieving further reduction of NO_x emission as compared with the reference case, which stems from both thermal and fuel paths. Specifically, the decrease of thermal‐NO emission originates from the contraction of high‐temperature regions (>1800 K), where nearly 94% reduction occurs within the temperature range of 1800 K and 1950 K while only 6% within 1950 K and 2030 K despite their high temperature sensitivity. The reduction of the fuel‐NO emission is mainly attributed to the promoted NO reduction on char surface and neutralization with HCN and NH₃. Generally, the NO_x emission can be minimized by enlarging the equivalence ratio difference between rich and lean jets, and the OFR configuration exhibits a higher potential than the IFR counterparts. However, since a relatively high temperature (1623 K) secondary air was used in the experiment, the maximum NO_x reduction potential was limited to only 2.5%.     

Solid fuel burning in steady,strained, premixed flow fields: the graphite/air/methane system

A detailed numerical investigation was conducted on the simultaneous burning of laminar premixed CH₄/air flames and solid graphite in a stagnation flow configuration. The graphite and methane were chosen for this model, given that they are practical fuels and their chemical kinetics are considered as the most reliable ones among solid and hydrocarbon fuels, respectively. The simulation was performed by solving the quasi‐one‐dimensional equations of mass, momentum, energy, and species. The GRI 2.1 scheme was used for the gas‐phase kinetics, while the heterogeneous kinetics were described by a six‐step mechanism including stable and radical species. The effects of the graphite surface temperature, the gas‐phase equivalence ratio, and the aerodynamic strain rate on the graphite burning rate and NO_x production and destruction mechanisms were assessed. Results indicate that as the graphite temperature increases, its burning rate as well as the NO_x concentration increase. Furthermore, it was found that by increasing the strain rate, the graphite burning rate increases as a result of the augmented supply of the gas‐phase reactants towards the surface, while the NO_x concentration decreases as a result of the reduced residence time. The effect of the equivalence ratio on both the graphite burning rate and NO_x concentration was found to be non‐monotonic and strongly dependent on the graphite temperature. Comparisons between results obtained for a graphite and a chemically inert surface revealed that the chemical activity of the graphite surface can result in the reduction of NO through reactions of the CH₃, CH₂, CH, and N radicals with NO. Copyright © 2000 John Wiley & Sons, Ltd.     

The role of heat recirculation and flame stabilization in the formation of NOX in a thermo-photovoltaic micro-combustor step wall

The health and durability of micro thermophotovoltaic systems are contingent upon the level of gaseous emissions of micro combustors regarding their small size, thickness, and compactness. In small combustion devices, the flame stabilization is achieved via conjugated heat transfer from the stabilized flame to the fresh reactant via the step of the micro-combustors. The step could also create a recirculation of products, and a stagnation zone for the fluid, as a result leading to the accumulation of pollutants. In turbulent H₂ flame, the main attention is given to the NO_X as no other noxious emission, especially carbon emission (CO, CO₂, PAH, and VOC), form during the combustion of hydrogen. The existence of NO_X in the presence of water, as in the combustion of hydrogen is prevalent, could lead to corrosion in combustor interior walls and other detrimental impacts for the ecosystem. In the presented work, micro-combustion of H₂ flame in a cylinder with a step is simulated and the formation of nitrogen oxides is analyzed. The influence of different combustor specifications (equivalence ratio, solid materials) NO_X species are discussed and evaluated. Results revealed nitrogen oxides form and accumulate in the vertical step of the microchannel and that the microchannel walls are more prone to the high concentrations of nitrogen oxides. The application of cavity promotes the two-dimensionality of flow, resulting in effective heat transfer from the hot gas to the cavity walls. This not only leads to flame anchoring to the cavity walls but also results in significant NO_X.     

The study of methods of NOx inhibition during fuel combustion at power plants with allowance for the use of hydrogen additions

The paper considers methods of NO_x inhibition by affecting the process of NO_x formation. The dependences for the degree of NO_x concentration reduction while intensifying the flame cooling, during water spray to the furnace, and while using flue gases recirculation as well as during fuel emulsification or nonstoichiometric fuel combustion have been obtained. The obtained formulas include a set of parameters which could affect the final value of NO_x concentration. The effect of a given factor could be evaluated on the basis of these dependencies. The calculated degrees of NO_x inhibition display good agreement with full-scale experimental data. The authors study the effect of NO_x concentration on ignition of the alternative hydrogen fuel during co-combustion in the furnace volume. The analysis of experimental data on hydrogen ignition delay in the presence of nitrogen oxides has been carried out. It is shown that depending on NO_x concentration, minimum ignition delay could occur, i.e. minimum effect of additives on the quality of alternative hydrogen fuel combustion may be allowable.The results of the study could be used for design engineering of power plants with the reduced NO_x environmental effect.     

Multi‐objective optimization of the coal combustion performance with artificial neural networks and genetic algorithms

The present work introduces an approach to predict the nitrogen oxides (NO_x) emissions and carbon burnout characteristics of a large capacity pulverized coal‐fired boiler with an artificial neural network (ANN). The NO_x emissions and carbon burnout characteristics are investigated by parametric field experiments. The effects of over‐fire‐air (OFA) flow rates, coal properties, boiler load, air distribution scheme and nozzle tilt are studied. An ANN is used to model the NO_x emissions characteristics and the carbon burnout characteristics. A genetic algorithm (GA) is employed to perform a multi‐objective search to determine the optimum solution of the ANN model, finding the optimal setpoints, which can suggest operators' correct actions to decrease NO_x emissions and the carbon content in the flyash simultaneously, namely, get a good boiler combustion performance with high boiler efficiency while keeping the NO_x emission concentration meet the requirement. Copyright © 2005 John Wiley & Sons, Ltd.     

Study on using hydrogen and ammonia as fuels: Combustion characteristics and NOx formation

This paper evaluates the potential of hydrogen (H₂) and ammonia (NH₃) as carbon‐free fuels. The combustion characteristics and NO_x formation in the combustion of H₂ and NH₃ at different air‐fuel equivalence ratios and initial H₂ concentrations in the fuel gas were experimentally studied. NH₃ burning velocity improved because of increased amounts of H₂ atom in flame with the addition of H₂. NH₃ burning velocity could be moderately improved and could be applied to the commercial gas engine together with H₂ as fuels. H₂ has an accelerant role in H₂–NH₃–air combustion, whereas NH₃ has a major effect on the maximum burning velocity of H₂–NH₃–air. In addition, fuel‐NO_x has a dominant role and thermal‐NO_x has a negligible role in H₂–NH₃–air combustion. Thermal‐NO_x decreases in H₂–NH₃–air combustion compared with pure H₂–air combustion. NO_x concentration reaches its maximum at stoichiometric combustion. Furthermore, H₂ is detected at an air‐fuel equivalence ratio of 1.00 for the decomposition of NH₃ in flame. Hence, the stoichiometric combustion of H₂ and NH₃ should be carefully considered in the practical utilization of H₂ and NH₃ as fuels. H₂ as fuel for improving burning performance with moderate burning velocity and NO_x emission enables the utilization of H₂ and NH₃ as promising fuels. Copyright © 2014 John Wiley & Sons, Ltd.