Effect of pressure on the characteristics of lifted flames

Abstract

The effects of pressure on the characteristics of lifted flames in a coflow with propane fuel were investigated experimentally in a pressure chamber. Changing the pressure influenced the density, reaction kinetics, and flame propagation speed. The pressure range tested was P = 0.5–5.5 atm. As the fuel jet velocity increased, a nozzle-attached flame transitioned to a lifted flame before blowout occurred. Depending on pressure, the onset conditions of liftoff and blowout occurred in the laminar, transition, or turbulent regimes. When P < 1.6 atm, the flame was lifted and had a tribrachial edge structure in the laminar regime, and the liftoff height (HL) increased with increasing pressure. Both the liftoff and blowout velocities decreased with decreasing pressure, and they merged at 0.5 atm. A correlation was derived in terms of the Schmidt number (Sc) and the Reynolds number (Re): Pn/2(HLPn/2)(Sc−1)/(2Sc−1)∝Re. The reattachment velocity in the laminar and transition regimes linearly decreased with pressure. The liftoff height had two local minimum points at given Reynolds number in the transition regime, and then increased linearly in the turbulent regime.