Heat transfer during laminar flame quenching: Effect of fuels

Abstract

Propagation of a laminar flame in a constant volume combustion chamber is associated with wall-quenching heat transfer. The unsteady heat transfer has been determined from measurements that were made in the closed chamber. The experiments were performed at pressures near atmospheric for methane-air, ethyleneair and propane-air mixtures over the range of equivalence ratios from 0.8 to 1.2 A substantially universal relation between the normalized wall heat flux and the normalized time is obtained. The normalizing factor for the heat flux is the rate of heat liberation in the flame prior to quenching, πuSu(−ΔHc per unit of mass of mixture), and the normalizing factor for the time is the thermal diffusivity divided by the square of the flame speed, αu/Su2. The peak value of the wall heat flux is one third of the value used for scaling. Calculations were also made using a finite difference method and an integral method. Two step chemical kinetics was used in the finite difference calculations while a greatly simplified ignition temperature approach was employed in the integral method. The results from the finite difference calculation were in good agreement with the experimental data. In the integral method, choosing a single value for the ignition temperature (equal to the unburned gas temperature plus three-tenths of the adiabatic temperature increase due to combustion) for all three fuels also yielded good agreement with the experimental data.