Experimental and kinetic analyses on the flame dynamics and stabilization of ammonia/hydrogen-air mixtures in a micro-planar combustor

Abstract

With the combination of experimental and numerical techniques, flame dynamics and stability of ammonia/hydrogen co-firing combustion are unraveled. Five types of fundamental micro-flame structures are, for the first time, experimentally confirmed with varying blending ratios (ε) and equivalence ratios (ϕ), along with a flame stability diagram delineated. It is shown that elevating ε from 30% to 50% extends the blowoff limit by a factor of 2.77 by suppressing or delaying the occurrence of certain flames. This thus leads to a turndown ratio of 15 in ammonia/hydrogen mixtures comparable to those of hydrocarbon fuel-based industrial combustors. To gain insights into the flame stabilization enhancement, further kinetics analyses are conducted with the validated reaction mechanism. The laminar burning velocity of the binary mixture is found to be increased remarkably with increasing ε, which facilitates flame propagation. Kinetics analyses reveal that varying hydrogen content not only enables the production/destruction pathways of major steps to be changed but also leads to the different sensitivity responses of the laminar burning velocity to reaction steps. This is also accompanied by the increase in the reaction rate of the major chain-branching step, thus signifying the importance of the chemical effect for enhanced flame stability. This work sheds light on the fundamental flame dynamic and enhancement mechanisms of ammonia/hydrogen co-firing combustion from macro and molecular perspectives.