Summary and Outlook
The ignition characteristics of methane/air and hydrogen/air mixtures using a hot turbulent jet generated by pre-chamber combustion were studied from a fundamental point of view. The existence of two different ignition mechanisms, namely, jet ignition and flame ignition, was found. Jet ignition produced a jet of hot combustion products (which means the pre-chamber flame is quenched when passing through the orifice); flame ignition produced a jet of wrinkled turbulent flames (the composition of the jet is incomplete combustion products containing flames). As the orifice diameter increased, the ignition mechanism switched to flame ignition, from jet ignition. With the increase in pressure, flame ignition became more prevalent. The ignition took place on the side surface of the hot jet during the jet deceleration process for both mixtures. A critical global Damköhler number, Dacrit, defined as the limiting parameter that separated ignition from no ignition, was found to be 140 for methane/air and 40 for hydrogen/air. All possible ignition outcomes were compared on the turbulent combustion regime diagram. Nearly all no-ignition cases fell into the broken reaction zone, and jet and flame ignition cases mostly fell within the thin reaction zones.