Effects of N2 2 dilution on NH3/H2/air 3 /H 2 /air combustion using turbulent jet ignition

To achieve sustainable transportation, ammonia (NH3) and hydrogen (H2) should be applied in internal combustion engines. The adoption of turbulent jet ignition (TJI) can improve ignition and combustion stability. The present study aims to explore the combustion characteristics of NH3/H2/air adopting TJI, and the effect of nitrogen (N2) dilution on factors such as ignition mechanism and flame propagation process was analyzed. The results indicate that N2 dilution worsens the combustion of NH3/H2/air. When the H2 volume fraction is 50%, a dilution ratio of 30% can increase the ignition delay and combustion duration by 3-6 times. With the increase of the dilution ratio, sensitivities of ignition delay and combustion duration to dilution ratio are enhanced in both passive TJI and active TJI modes. Compared to passive TJI, the injection of auxiliary gas in active TJI mode reduces the sensitivity of jet velocity to dilution, which can accelerate the early stage of flame development. However, the high turbulence intensity provided by active TJI makes the ignition position closer to the bottom and causes an extended final stage of combustion. For ultra-low reactivity mixtures, the active TJI with the scavenging system can provide sufficient ignition energy, but ignition occurs after prolonged accumulation of heat and radicals, as well as dissipation of turbulence.