Experimental investigation on combustion characteristics of ammonia/air using turbulent jet ignition with auxiliary oxygen in pre-chamber

Ammonia (NH₃) is a potential alternative fuel for internal combustion engines, but the disadvantages of low combustion intensity and high nitrogen oxides should be addressed to achieve its application. For NH₃ mixture, fuel-rich combustion is a potential method to reduce NOx emissions, and the utilization of turbulent jet ignition (TJI) can enhance its ignition and combustion. Therefore, a strategy of using TJI with assisted oxygen (O₂) injection in the pre-chamber to ignite rich NH₃/air mixtures was proposed in this study. Considering the lack of relevant research, a fundamental investigation was conducted in this work. The results indicate that the provided method can effectively promote the combustion of NH₃/air. The pre-chamber equivalence ratio has no significant effect on the jet strength, but more excess injected O₂ enhances the ignition performance of the unburned mixture in the main chamber. The increase of the main chamber equivalence ratio and the decrease of the orifice diameter will result in a higher jet velocity. The ignition of NH₃/air is the result of turbulence competing with the reactivity of the mixture. Therefore, high jet velocity leads to poor ignition performance due to the low reactivity of NH₃, but appropriate turbulence intensity can promote rapid combustion.