Study of solid fuel diffusion flames in a crossflow burner

A small-scale, optically accessible crossflow burner was used to investigate the effects of thermodynamic properties of inert diluent/oxidizer mixtures on solid fuel combustion. Experiments were conducted utilizing three oxidizer mixtures, each comprising O₂ with an inert diluent (60 % by mole) (He, N₂, and Ar). Polymethyl methacrylate (PMMA) was considered in two geometrical configurations, flush and rearward facing step, with two flow conditions for each case based on either constant Reynolds number or constant port velocity (V p ). Optical access facilitated the use of OH* chemiluminescence, OH planar laser induced fluorescence (PLIF), and rainbow schlieren to visualize the flow field. In the flush configuration, under constant V p , the He case demonstrated a laminar reaction zone with unsteadiness increasing according to molecular weight of the mixtures. In the step configuration, a shear layer stabilized reaction zone was observed for all cases except the lowest velocity He mixture, which adhered closer to a diffusion dominated mixing process. Regression rates were obtained and correlated with thermal diffusivities and adiabatic flame temperatures of the diluent mixtures with He producing the highest regression and N 2 the lowest. Between geometrical configurations, N 2 and Ar exhibited no notable difference in regression rate, whereas He mixtures experienced a decrease in the step case due to increased reaction zone standoff from diffusion dominated transport. The results suggest that thermodynamic properties were the dominating influence for regression rates compared to secondary flow field factors such as turbulence .