Effect of Flame-Wall Interaction on Local Heat Release of Methane and DME Combustion in a Side-Wall Quenching Geometry

Abstract

This paper is focused on the characterization of local heat release rate and its correlation with flame structures under atmospheric conditions in a side-wall quenching geometry. The influence of different wall temperatures ranging from 330 K to 670 K is compared for stoichiometric and lean (ϕ = 1.0 and 0.83) methane/air as well as dimethyl ether (DME)/air flames. Simultaneous formaldehyde (CH2O) and hydroxyl radical (OH) planar laser-induced fluorescence (PLIF) is used to determine relative local heat release rates (HRRs). Based on the resulting relative HRR distributions, flame front positions are determined and flame curvatures are evaluated. In the laminar flame configuration, for both fuel types at wall-distances y < 0.08 mm, a steep gradient of CH2O-signal is observed. From ensemble-averaged HRR images, quenching distances are deduced and compared. With increasing wall temperature, quenching distances decrease due to increased laminar flame speeds. Compared to methane/air flames, DME/air flames are quenched at smaller quenching distances which is as well attributed to increased laminar flame speeds. In the turbulent flame configuration, fluctuations prevail in the flame-wall interaction (FWI) zone which is associated with local flame curvature. Comparing the near-wall curvature for different wall temperatures, flame curvature decreases with higher wall temperatures due to the increased viscosity of higher temperatures of near-wall gases. The correlation of HRR, flame curvature and wall-normal distance is further investigated and indicates an influence of Lewis-number effects upon turbulent premixed flames near walls.