Chemical kinetic analysis on influence of hydrogen enrichment on the combustion characteristics of ammonia air using newly proposed reaction model

In recent years, ammonia has shown great potential for future green fuel. However, ammonia combustion is a challenging task due to its narrow flammability limit, low flame speed, and slow kinetics compared with conventional hydrocarbon fuels. The blending of ammonia with higher reactive fuel such as hydrogen seems a novel alternative to overcome these difficulties. So, a comprehensive study of NH3/H2/air combustion characteristics is necessary. In the literature, numerous ammonia reaction models can be found, but most of them failed to demonstrate good combustion characteristics with NH3/H2/air mixtures. A new NH3/H2/air reaction model is suggested or proposed in the present work by referring to the previously available literature. The newly proposed reaction model consists of 32 species and 259 reactions. Model validation for laminar flame speed and ignition delay time at different operating conditions are performed in this study using the newly proposed reaction mechanism. Also, an extensive chemical kinetic modeling for heat release rate, flame speed and OH sensitivity analysis, reaction pathway analysis, and emission characteristics of NH3/H2/air mixture is studied. The results show that the proposed reaction model closely follows the experimental trends, and lesser inconsistency is observed than the other reaction models compared in this study. All referenced reaction models used in the present work for comparison shows large discrepancies with experimental results of NH3/H2/air combustion, especially more discrepancies are observed at higher hydrogen enrichment conditions. Hydrogen enrichment positively affects the heat release rate intensity and flame speed of NH3/air mixture. Through the addition of hydrogen, the burning velocity of ammonia can be increased up to the level of hydrocarbon fuels, and the combination of ammonia and hydrogen blend can be used as an effective industrial fuel.