Effect of fuel temperature on flame characteristics of supersonic turbulent combustion

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 prediction 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 temperature. 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 temperature, due to the enhancement of mixing following the reduced convective Mach number. The most prominent effect of fuel temperature is the reduction of flame length, a crucial factor for the design of supersonic combustors.