Hot surface ignition delay time of ammonia-hydrogen-methane mixtures

Abstract

In this research, the effects of adding hydrogen and ammonia to the stoichiometric methane-air mixture, as well as adding ammonia to the stoichiometric hydrogen-air mixture, on ignition delay time changes near a hot surface at two constant temperatures (1400 K and 1600 K) are numerically investigated using a detailed mechanism. The hydrogen-to-methane effectiveness limit (HMEL) is defined in this paper, indicating the point at which the beneficial effect of hydrogen on reducing ignition delay time is reversed, resulting in longer ignition delay times compared to the original mixture, stoichiometric methane-air. Additionally, the hydrogen-to-methane optimal range (HMOR) represents the optimal hydrogen addition range to the stoichiometric methane-air mixture that achieves the lowest ignition delay times. An unpredictable jump in ignition delay time is observed in the methane-hydrogen-air mixture at a hot surface temperature of 1600 K when approximately 14.5 % hydrogen is added. Additionally, adding more than 16 % hydrogen results in longer ignition delay times at higher hot surface temperatures. Conversely, the ignition delay time increases with addition of ammonia in both methane and hydrogen mixtures. Furthermore, it is concluded that adding more than 23–25 % ammonia to the stoichiometric hydrogen-air mixture renders it non-ignitable by a hot surface at 1600 K. This study highlights the impact of hydrogen and ammonia addition on ignition delay time, offering valuable insights for practical applications and providing a foundation for further research on the combustion characteristics of fuels, particularly ammonia and hydrogen.