UC Irvine

This research explores the effects of adding water vapor to fuel for a diffusion flame. Inert gases have been used in the dilution of combustion commonly to reduce emissions. Water is a unique diluent because it provides important radical species influencing the flame, particularly with cooling or destabilizing effects when the enthalpy of the diluted fuel is reduced. The objective of this research is to study the behavior of a methane diffusion flame with various amounts of water vapor added to the fuel using a coflow burner and to compare the flame behavior with various percentages of water vapor added into the fuel. The present work continues previous studies on water-diluted flame behavior and explores the effect of elevated pressures. The simulation research uses PeleLM code for computing combustion behavior when water is added to diffusion flames. Besides various water content in atmospheric conditions, the flame was also simulated to pressures of 1.4, 5.7, and 11.1 atm. The results extracted and analyzed include temperature profiles and various species mole fractions such as CO2, CO, OH, H, O, and H2O. The overall flame images show that the flame base is lifted at higher water content conditions from the tip of the burner. At 0.65 mole water content and 11.1 atm, the flame base is observed anchoring back to the tip of the burner. When increasing the pressure, the flame, in general, becomes thinner and more compact, which means the reaction zone is reduced. The results show more drastic changes of flame appearance at elevated pressures when beyond 5.7 atm, and the water addition into the flame reduces the CO concentration. The computed H and O atoms are at superequilibrium for about two to three times (more than the equilibrium) at lower pressure conditions and around five times at higher water concentrations. OH remains near the equilibrium for all the pressure and water conditions.