Computed no emission characteristics of CH₄/NH₃ and H₂/NH₃ opposed-jet diffusion flames

The combustion and NO emission of CH₄/NH₃ and H₂/NH₃ blended fuels as alternative energy sources were studied. By using the configuration of opposed-jet diffusion flames, the effects of ammonia concentrations on the flame structures, chemical reaction and NO formations of CH₄ and H₂ were investigated and compared. The numerical model consists of a revised OPPDIF program and narrowband radiation model with detailed chemical kinetics. The analyses of the H₂ diffusion flames showed that the NO formation is dominated by the thermal-NO due to high flame temperature. While for CH₄ diffusion flames, the variations of the NO emission and flame temperature with strain rates are similar only when the strain rate is above 100 s^-1. A great amount of NO are generated by prompt-NO through CH₃, CH₂ and CH radicals, and only small amount of NO are from thermal route. Since the H₂ flame has a higher temperature, the NO production rate is higher than the CH₄ flame. For the studies of H₂/NH₃ and CH₄/NH₃ blended fuels, the maximum flame temperatures decrease with the increase of the NH₃ concentrations, but the net production rates of NO increase with NH₃ addition. The NO formation route is mainly due to the fuel-NO which comes from chemical reactions of NH₃.