Combustion characteristics of non-premixed CH4/CO2 jet flames in coflow air at normal and elevated temperatures

Abstract

Experimental study on the combustion characteristics of CH4/CO2 non-premixed jet flames in a coflow air at normal and elevated temperatures was conducted for the development of biogas-fueled regenerative burner. The CH4/N2 non-premixed jet flame was also investigated for comparison. The laminar flame height, lift-off height and blow-out limit were obtained and compared. The experimental results show that the laminar flame height of CH4/CO2 flame is lower than that of CH4/N2 flame in the same condition. The reason was clarified by theoretical analysis and two-dimensional numerical computation. For the turbulent flame, the CO2 dilution in the fuel steam leads to a higher liftoff height and a lower blowout limit. The fuel velocity range of stable lifted flame and the blowout limit are significantly increased at elevated air temperature. The premixed flame model was employed to analyze the liftoff heights and blowout velocities. The non-dimensional liftoff height increases linearly versus the non-dimensional fuel jet velocity. And linear relationship between non-dimensional blowout velocity and Reynolds number was obtained. The influences of laminar flame speed, fuel kinematic viscosity and the density ratio of fuel to coflow air on liftoff height and blowout limit were investigated by using the premixed flame model and sensitivity analysis.