Experimental investigation on the burning and pulsation characteristics of propane and methane diffusion flames under wind environments

The evolution of flame centerline trajectory and pulsation frequency for diffusion flames under wind environments are thoroughly investigated in this paper. The combustion experiments of two fuels, propane and methane, were carried out under wind velocities of 1.40–3.96 m/s using a 0.1 m*0.1 m gas burner. The experimental results show that the evolution of the flame centerline trajectory mainly depends on wind velocity, however, the flame centerline length is primarily related to the fuel flow rate. The counteracting effect of enhanced air supply and increased momentum leads to a slight change of centerline length with increasing wind velocity. Based on the flame centerline trajectory, the air entrainment length scale ([Formula presented]) is obtained and a dimensionless prediction model for flame centerline length is proposed, [Formula presented]=6.23[Formula presented]. The global pulsation frequency was found to be mainly determined by the downstream fluctuation of diffusion flame although multi-scale vortices were found. The flame pulsation frequency depends on the wind velocity but is irrelevant to the fuel flow rate. By taking the boundary layer thickness as the characteristic length scale, an empirical model was built, St=0.421/Fr^0.52. The model is applicable to predict the pulsation frequency of momentum-dominant diffusion flames under both wind and still environments.