Effects of heat release and fuel type on highly turbulent premixed jet flames

Abstract

An experimental study on the fuel type and attendant heat release effects on piloted turbulent premixed jet flames was carried out. The investigation focused on four fuels, namely methane, ethylene, n-heptane, and toluene, five lean to stoichiometric equivalence ratios, and two jet Reynolds numbers. The average flame height and the global turbulent consumption speed were scaled against the laminar flame speed, the maximum heat release rate, and the laminar flame thickness for all fuels and conditions. Results showed that for the different fuel types and for the lower equivalence ratios, the average flame height does not scale well with any of the aforementioned parameters, while the global consumption speed was determined to scale well with laminar flame speed and maximum heat release rate. The thickness of the shear layer was also characterized through detailed particle image velocimetry measurements and was found to decrease with increasing heat release when the jet diameter is used to scale the axial distance. However, when a density-based momentum diameter is used as the scaling parameter of the axial distance, the effect of heat release is suppressed. Additionally, the growth rates of the shear layer thickness could not be scaled between the different fuels using either the laminar flame speed or the maximum heat release rate. Finally, the turbulent kinetic energy and turbulent shear stress development in the shear layer was determined also to be different between the fuels despite keeping either the laminar flame speed or maximum heat release rate constant, with methane flames most notably showing a sharper decay in intensity with axial distance. The fuel effects on the turbulent kinetic energy and the turbulent shear stress were more pronounced at the higher Reynolds number conditions.