Influence of porous walls on flame acceleration and flame front perturbations in methane-air and acetylene-air mixtures

Abstract

The patterns of flame front propagation in methane-air and acetylene-air gas mixtures in a half-open channel with a porous inner coating were studied. Polyurethane with open pores was used as a porous coating on the upper and lower internal walls of the channel. The molar excess of methane in the mixture was 0.8 and 1.0, and the molar excess of acetylene in the mixture was 0.6, 0.8 and 1.0. Pore sizes ranged from 0.3 mm to 2.5 mm. Using shadow photographs, the sizes of disturbances λ1 and λ2 generated at the flame front were determined. The sizes were divided into two groups, λ1 ~ 5–20 mm and λ2 ~ 1–6 mm. A comparison of the disturbances with the estimated values of the Darrieus-Landau instability was carried out. The flame front velocities were determined depending on the composition of the mixture and the pore size of the coating: 5–100 m/s for methane-air mixtures and 10–1200 m/s for acetylene-air mixtures. An estimate of the Reynolds numbers in a channel with smooth walls and a porous coating was carried out. Based on the readings of the piezoelectric pressure sensors, the pressures generated by the accelerating flame front were determined: 0.7–7 kPa for methane-air mixtures and 0.007–1.5 MPa for acetylene-air mixtures.