Numerical study on the combustion and emission characteristics of premixed NH3/H2 jet flame
The utilization of fossil fuels has propelled the advancement of human society;however,it has also caused global climate change,posing a threat to the survival and development of humanity.In this context,ammonia and hydrogen,as zero-carbon fu-els,have attracted much attention.However,their combustion utilization faces numerous challenges.MILD combustion is a new combus-tion technology that may achieve clean and efficient combustion of NH3/H2 blended fuel,but research in this area is currently very limit-ed.The combustion and emission characteristics of a premixed NH3/H2 jet flame was thoroughly investigated by numerical simulation.Spe-cially,the hydrogen proportion(X(H2)F)and jet equivalence ratio(ΦJ)were varied,and a detailed analysis on temperature rise,reac-tion zone size,lift-off height,radical concentrations,and NOx emissions was conducted.Results indicate that the addition of a small amount of H2 significantly enhances the stability of ammonia flame,lowers the auto-ignition temperature,and eliminates flame lift phe-nomenon.Moreover,an increase in X(H2)F elevates the combustion temperature,accelerates the production of H,O,and OH radicals,thereby leading to a transition in the combustion regime from MILD to high-temperature combustion.Under fuel-rich conditions and low X(H2)F,significant amounts of NH3 decompose into H2 prior to main combustion reactions,resulting in high combustion temperatures.As for NOx emissions,N2O and NO are the dominant sources,while NO2 is negligible.Generally,the emissions of N2O and NO first increase and then decrease with increasing XH2,F.Moreover,when X(H2)F is low,the peak concentrations and emissions of N2O and NO are com-parable.However,as X(H2)F increases,the temperature rises,leading to the decomposition of N2O,with NO becoming the primary source of NOx emissions.Furthermore,under fuel-rich conditions,the combustion temperature,OH concentration,and the entrainment of jet to the coflow O2 collectively influence the NOx emission.
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