Combustion Characteristics of a Methane Jet Flame in Hot Oxidant Coflow Diluted by H2O versus the Case by N2

This numerical study investigates combustion characteristics of a CH4 jet flame in hot oxidant coflow (JHC) diluted by H2O versus the case by N2. Both MILD oxy–fuel combustion and traditional combustion are generated by varying the coflow oxygen level from 3% to 85% in volume. To distinguish physical and chemical effects of changing the diluent from N2 to H2O, the JHC flame diluted by XH2O (artificial H2O without reactivity) is also simulated. It is demonstrated that both the temperature and the dimension of the JHC flame reduce substantially when changing the diluent from N2 to H2O. Such reductions derive primarily from different fluid properties of N2 and H2O, i.e., H2O has a lower fluid density and a higher thermal capacity. The change from N2 to H2O is also found to have an impact more chemically on formation of the main intermediate species (i.e., H, O, CO, OH) and simultaneously to increase the flame lift-off distance due to longer ignition delay. Hence, the MILD combustion is expected to occur more...