Experimental and modeling study of chemical-kinetics mechanisms for H2–NH3–air mixtures in laminar premixed jet flames

Abstract

A combined experimental and modeling study of laminar flame speeds for premixed H2–NH3–air jet flames is performed for 0–80% NH3 in H2 by energy and for equivalence ratios from 0.5 (fuel lean) to 1.1 (fuel rich). Experimental flame speeds in the jet flame configuration compare well with previous data from freely propagating spherical flames after corrections for heat losses. These data are then used to validate flame-speed predictions using CHEMKIN software over a wide range of conditions and to evaluate the performance of the GRI-Mech3.0, Tian and Konnov detailed chemical kinetic mechanisms. It is found that these mechanisms perform well for H2–air combustion but begin to deviate substantially (by ∼2×) from each other with the addition of NH3. Differences in flame speeds and associated radical species concentrations (H, O, and OH) are found to be largest for higher levels of NH3 (50% by energy and greater) and with increasing equivalence ratio. A sensitivity analysis reveals that OH is the key radical leading to NH3 decomposition and is a likely source of deviation between model predictions. The experimental data show that the Tian and Konnov mechanisms are the most capable of accurately predicting reductions in flame speed as much as 90–95% with NH3 addition, although the accuracy of each mechanism differs with the level of NH3 within the mixture.