Effect of fuel temperature on flame characteristics of supersonic turbulent combustion

Abstract

A comprehensive numerical study is undertaken to investigate the dynamics of hydrogen-air supersonic turbulent flames in a shear coaxial configuration. The effects of fuel temperature on the flow and flame characteristics are examined systematically. The numerical methodology is based on a hybrid RANS/LES model for compressible, multi-species flows with finite-rate chemical reactions. Results from simulations employing different levels of grid resolution and numerical schemes are compared and validated against experimental data. The importance of adequate grid resolution and high-order numerical schemes to achieve high-fidelity prediction of fine-scale flow features is underscored. In particular, the multi-dimensional high-order oMLP scheme shows remarkable pre-diction capabilities without incurring excessive computational cost. The lifted turbulent flame characteristics with combustion occurring mostly in a premixed mode downstream after turbulent mixing in the shear layer are identified and elaborated. A parametric study is subsequently performed to investigate the effect of fuel tem-perature. It is found that the combustion regime changes from partially-premixed to non-premixed mode as the fuel temperature is increased. The flame width and combustion efficiency increase with increasing fuel tem-perature, due to the enhancement of mixing following the reduced convective Mach number. The most promi-nent effect of fuel temperature is the reduction of flame length, a crucial factor for the design of supersonic combustors.