Flame-Flow Interaction in Premixed Turbulent Flames During Transient Head-On Quenching

Abstract

This paper reports on experimental investigations of turbulent flame-wall interaction (FWI) during transient head-on quenching (HOQ) of premixed flames. The entire process, including flame-wall approach and flame quenching, was analyzed using high repetition rate particle image velocimetry (PIV) and simultaneous flame front tracking based on laser-induced fluorescence (LIF) of the OH molecule. The influence of convection upon flame structures and flow fields was analyzed qualitatively and quantitatively for the fuels methane (CH4) and ethylene (C2H4) at ϕ = 1. For this transient FWI, flames were initialized by laser spark ignition 5 mm above the burner nozzle. Subsequently, flames propagated against a steel wall, located 32 mm above the burner nozzle, where they were eventually quenched in the HOQ regime due to enthalpy losses. Twenty ignition events were recorded and analyzed for each fuel. Quenching distances were 179 μm for CH4 and 159 μm for C2H4, which lead by nondimensionalization with flame thickness to Peclet numbers of 3.1 and 5.5, respectively. Flame wrinkling and fresh gas velocity fluctuations proved flame and flow laminarization during wall approach. Velocity fluctuations cause flame wrinkling, which is higher for CH4 than C2H4 despite lower velocity fluctuations. Lewis number effects explained this phenomenon. Results from flame propagation showed that convection dominates propagation far from the wall and differences in flame propagation are related to the different laminar flame speeds of the fuels. Close to the wall flames of both fuels propagate similarly, but experimental results clearly indicate a decrease in intrinsic flame speed. In general, the experimental results are in good agreement with other experimental studies and several numerical studies, which are mainly based on direct numerical simulations.