Enhancing Ammonia Combustion Using Pre-Chamber Turbulent Jet Combined with Various Ignition Strategies

Abstract

In this study, new combustion strategies are proposed to enhance ammonia combustion, and the enhancement is examined through combustion vessel experiments. Specifically, a pre-chamber with single narrow orifice is employed to produce a flameless strong turbulent jet to increase the turbulence intensity of main-chamber mixture. Subsequently, various ignition strategies are used to ignite the mixture in the downstream of the jet, including conventional plug spark ignition, microwave-assisted ignition and turbulent jet ignition (TJI). In the case of TJI, the second pre-chamber producing a jet flame to ignite the mixture, which is referred to as the turbulence-enhanced TJI strategy in this study. Stoichiometric ammonia/‘air’ mixtures were employed in the experiments, with initial pressures of 5 and 8 bar and an initial temperature of 393 K. The results show all three combustion strategies improve ammonia combustion, and the enhancing effects are greatly influenced by the time intervals between the two ignition events. It is found that spark ignition during flameless jet ejection causes extinction of the ignition kernel because of the strong turbulence. Conversely, both microwave-assisted ignition and turbulent jet ignition can achieve stable ignition during flameless jet ejection duration, presenting more significant enhancing effects. Overall, the turbulence-enhanced TJI strategy exhibits the most significant enhancing effects on ammonia combustion, with the combustion duration decreased by 77.6% maximum while maintaining higher combustion efficiency compared to laminar spherical flame propagation. Additionally, significant enhancing effects persist with increasing pressure. The experimental results indicate that turbulence-enhanced TJI is a promising strategy to enhance ammonia engine combustion.

Keywords: Ammonia, pre-chamber, constant-volume combustion vessel, Turbulent jet ignition, microwave assisted ignition