Computed NO Emission Characteristics of CH_4/NH_3 and H_2/NH_3 Opposed-Jet Diffusion Flames

摘要

The combustion and NO emission of CH_4/NH_3 and H_2/NH_3 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 CH_4 and H_2 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 H_2 diffusion flames showed that the NO formation is dominated by the thermal-NO due to high flame temperature. While for CH_4 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 CH_3, CH_2 and CH radicals, and only small amount of NO are from thermal route. Since the H_2 flame has a higher temperature, the NO production rate is higher than the CH_4 flame. For the studies of H_2/NH_3 and CH_4/NH_3 blended fuels, the maximum flame temperatures decrease with the increase of the NH_3 concentrations, but the net production rates of NO increase with NH_3 addition. The NO formation route is mainly due to the fuel-NO which comes from chemical reactions of NH_3.