Numerical Simulation Of Combustion Characteristics Of Ammonia/Methane Mixed Flame At High Temperature And Pressure

Energy is an important material guarantee for the development of national economy,and the exploration of energy determines the future development fate of the country.Ammonia（NH₃）,as a carbon-free fuel,has attracted much attention from researchers recently.Although ammonia fuel faces challenges such as low flammability and high NOx emissions,mixing methane with ammonia can effectively improve the low flammability of ammonia fuel and maintain low carbon emissions.The research on combustion characteristics of ammonia/methane mixture fuel can provide basic theoretical support for the popularization and application of ammonia mixture fuel.It is promising to study laminar combustion velocity and other combustion characteristics of ammonia/methane fuels under high temperature and high pressure conditions because high temperature and high pressure are related to the application conditions of current industrial combustion equipment.Therefore,the combustion characteristics of ammonia/methane laminar premixed flame were numerically simulated in this thesis,and the influences of different working conditions（such as air preheating temperature,pressure and ammonia content）on flame structure,combustion stability and pollutant emission characteristics were explored.In order to enhance the combustion stability of ammonia/methane flame and reduce NO emission,three-dimensional simulation is also carried out for LUCY combustion chamber to explore the influence of temperature rise and pressurization on the velocity field,temperature field and NO emission of ammonia/methane fuel in LUCY combustion chamber.Based on CFD software Chemkin,the oxidation chemical properties of ammonia/methane laminar PREMIX flame were analyzed using the one-dimensional free propagation Premix model,and then three-dimensional numerical simulation was carried out based on Fluent turbulence model and combustion model.The simplified chemical reaction mechanism proposed by Okafor is coupled with the EDC combustion model to deal with the turbulent chemical interaction.The results show that:（1）the LBV of ammonia/methane flame increases with the increase of temperature,and decreases with the increase of pressure.The increase of pressure will lead to a significantly shorter ignition delay,increasing the risk of spontaneous combustion in the premixed combustor.H+O₂<=>O+OH continuously generates high energy radicals O and OH in the reaction process,which is an important reaction to promote the formation of OH radicals.With the increase of preheating temperature,the promoting effect of this reaction on OH formation was gradually weakened.When the pressure increases,the promoting effect of this reaction on OH formation becomes stronger.NO matter increasing the preheating temperature or pressure,the two important paths leading to NO generation or consumption have not changed.However,the increase of preheating temperature and pressure leads to the increase of reaction rate of global reaction path.（2）In order to solve the problem of excessive emission of major pollutants,it is better to use ammonia methane mixed fuel on the condition of 0.6<Φ<0.8 under the condition of F-class gas turbine.Under high temperature and high pressure（T=723K,p=16.5atm）,the most important reaction of NO formation is H+NO+M<=>HNO+M.The most important reaction leading to CO consumption is OH+CO<=>H+CO₂.（3）When the pressure is constant,the large vortex region decreases with the increase of air preheating temperature.When the temperature is constant,the whole vortex region increases with the increase of pressure.The combustion chamber temperature increases with the increase of preheating temperature and pressure.But under different preheating temperature,the temperature curve of outletline is not the same.The emission of NO and N₂O in the export area is very low.The high NO emission zone is usually found at the end of the oxidizer jet or in the space between the wall,which is almost identical to the high temperature zone.The maximum emission values of NO and N₂O in the combustion chamber increase with the increase of pressure and preheating temperature.However,NO emission at the outlet decreases first and then increases with the increase of pressure.In addition,NO emission at the outlet of ammonia/methane fuel increases with the increase of preheating temperature under any pressure.In conclusion,this study will enrich the ammonia combustion database and provide new guidance for the design and development of low-carbon and efficient ammonia fuel gas turbines.