An experimental study of turbulent lifted flames at elevated pressures

Studying the lift-off behavior of non-premixed jet flames is important to understanding the flame stabilization mechanisms in practical systems, including gas flares and combustors, and to improving the safety of pressurized fuel tanks in case of fuel leaks. This is typically done with the canonical configuration of an axisymmetric fuel jet issuing into a quiescent or co-flowing oxidizer and abundant data are available in the literature. However, most of these data were collected at normal or sub-atmospheric pressure and little data are available at elevated pressure and high Reynolds numbers, conditions relevant to practical configurations. The present study fills this gap by reporting lift-off height measurements of methane and ethane non-premixed jet flames for pressures up to 7 bar and Re = 57,500 in the presence of an air co-flow. Data are interpreted using Kalghatgi's model for the dimensionless lift-off height, which was previously proven successful for sub-atmospheric to normal pressures, as well as elevated pressure but only for low turbulent Reynolds numbers and propane. In this contribution, Kalghatgi's model has been shown to accurately predict the slope of the lift-off height vs. jet velocity curves at elevated pressure and large Reynolds number for methane and ethane. A new term, a function of the stoichiometric mixture fraction, the laminar burning velocity, and a turbulent Schmidt number, is also introduced to extend the predictive capabilities of Kalghatgi's model to configurations featuring a co-flow.