A study on measuring ammonia-hydrogen IDTs and constructing an ammonia-hydrogen combustion mechanism at engine-relevant thermodynamic and fuel concentration conditions

To avoid increasing the dilution gas to achieve higher temperatures for rapid compression machines (RCM) at the end of compression, this study introduced an oil-bath heating system designed to precisely improve the initial temperature of the mixture, thereby enabling ammonia-hydrogen ignition at practical fuel concentrations for internal combustion engines (ICEs). Using this oil-bath heated RCM, the ignition delay times (IDTs) of ammoniahydrogen under conditions relevant to ICEs were measured. The ammonia-hydrogen combustion mechanism proposed by Stagni et al. (10.1016/j.proci.2022.08.024) was then validated against these measured IDTs and subsequently optimized. Guided by a comprehensive review of the existing literature on ammonia-hydrogen chemistry, the optimization involved updating 42 reaction rate coefficients and adding 9 new reactions. The optimized mechanism, comprising 31 species and 214 reactions, demonstrated accurate predictions of ignition delay time, laminar flame speed, and species mole fractions across a wide range of experimental setups and conditions for ammonia-hydrogen, confirming the mechanism's robust performance and its suitability for highprecision simulations in ammonia-hydrogen ICE applications.