Adiabatic laminar burning velocities and NO generation paths of NH3/H2 premixed flames

Abstract

NH3/H2 is an important hydrogen fuel without carbon emissions. In order to know the fundamental flame characteristics of NH3/H2, the adiabatic laminar burning velocity (SL,0) and overall activation energy (Ea) were measured simultaneously by the flat flame method. Four combustion mechanisms were evaluated to clarify the NO generation paths. It was found that SL,0 shows a monotonic nonlinear increase from 10.69 cm/s to 39.99 cm/s with the increasing of equivalent ratio (Φ = 0.6–1.0) and hydrogen mixing ratio (0.2–0.5 vol%). The four mechanisms have a good prediction for SL,0, but an unsatisfactory prediction for Ea. Among them, S-Mech has the best prediction for SL,0 and Ea. Detailed kinetic analysis shows that NNH-reaction (R700, R795, and R801 in S-Mech) simultaneously play an important role in SL,0 and NO generation. Under lean conditions, NO generation is mainly related to H2NO →OH HNO →HO2 NO, and NO reduction is mainly from NO converted to NNH, which is related to NHi generated by NH3 dehydrogenation. This work identified critical reactions of NO generation and systematically explained the path tendency of NH3 combustion at lean conditions.