Experimental and numerical comparison of currently available reaction mechanisms for laminar flame speed in 70/30 (%vol.) NH3/H2 flames

Abstract

To achieve net zero carbon emissions, ammonia is gaining traction as a promising alternative fuel. However, the combustion characteristics of ammonia need further investigation. The current study aims to analyze the laminar flame speed, a fundamental physio-chemical property of any combustible mixture, through experimental measurements and kinetic reaction mechanism analysis. The laminar flame speed of 70/30 (%vol) NH3/H2 at atmospheric pressure and ambient temperature across a wide range of equivalence ratios (0.6–1.4) was studied experimentally and compared to the performance of 36 kinetic reaction mechanisms to appraise their performance concerning laminar flame speed prediction for the measured NH3/H2 mixture. The absolute percentage error (APE) formula has been adopted for preliminary estimation based on the experimental measurements of the present study and numerical data. The study found that Duynslaegher et al. 2012 model shows good performance speed across lean and stoichiometry conditions with an APE value between 0%-6%. The mechanism of Nakamura et al., 2017 and Gotama et al., 2022 demonstrates a good estimation of laminar flame speed under rich conditions. The sensitivity analysis revealed that the reactions H+O2=O+OH, NH2+NH2=N2H2+H2, and OH+H2=H+H2O are the most crucial reaction with considerable effect in promoting the laminar flame speed at all conditions, while the reactions of H+O2(+M)=HO2+M, NH2+H=NH+H2, and NH2+O=HNO+H play an essential role in the retardation of laminar flame speed at all conditions. The effect of the aforementioned reactions varies for the equivalence ratio, mainly due to changes in adiabatic flame temperature.