Effects of N2 dilution on NH3/H2/air combustion using turbulent jet ignition.

To achieve sustainable transportation, ammonia (NH 3) and hydrogen (H 2) 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 NH 3 /H 2 /air adopting TJI, and the effect of nitrogen (N 2) dilution on factors such as ignition mechanism and flame propagation process was analyzed. The results indicate that N 2 dilution worsens the combustion of NH 3 /H 2 /air. When the H 2 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. • Effects of N 2 dilution on NH 3 /H 2 /air combustion with TJI is studied. • H 2 -assisted TJI reduces the sensitivity of ignition performance to dilution. • High-speed jet suppresses flame propagation near the orifice in active TJI mode. • Scavenging can improve the flammability limit for N 2 diluted NH 3 /H 2. • Weak flame may occur in the early combustion for low reactivity mixture. [ABSTRACT FROM AUTHOR]