Development of optimised compact chemical kinetic mechanisms to support the transition to net zero

Abstract

Attitudes towards energy sources and any pollutant emissions as a result of their use are rapidly changing in a world seeking to reduce the rate of climate change. Renewable electricity generation is beginning to displace the legacy fossil fuel combustion based devices. However, due to intermittency issues with these renewable sources in the power generation sector and the scale and diversity of the transportation sector, combustion devices will linger in the mix, perhaps even indefinitely through the use of renewable fuels. Therefore, it is paramount that ever more stringent pollutant emission regulations are set and met and in order to achieve this, further understanding and computational modelling capabilities of the fuels to be used is required. In this work, chemical kinetic models are further developed and refined and comprehensive validation used to assess their ability to predict both global (burning velocities, ignition delay times) and detailed (speciation) properties. The fuel components studied in this work include the primary reference fuels, iso-octane and n-heptane, which represent the base level chemicals used to approximate real fuels in both laboratory-based research and computational surrogates. Additionally, with the advent of green hydrogen and its formation into green ammonia the study of fuel alternatives, such as ammonia, and fuel enhancers, such as nitromethane, have been included in this work. The chemical kinetic models are compact to allow for their direct implementation in computing dynamic systems. All mechanisms provide good to excellent agreement with experimental data for burning velocities and ignition delay times, and an assessment of their ability to predict speciation results with key sensitivities and uncertainties is outlined. Finally, these mechanisms have been implemented to consider the key trends at conditions of practical relevance, with a focus on the characteristic timescales within flames.