Effects of gas preheat temperature on soot formation in co-flow methane and ethylene diffusion flames

Abstract

This study reports the effects of gas preheat temperature on soot formation in a series of methane (CH4), ethylene (C2H4) and nitrogen-diluted C2H4 co-flow diffusion flames with a constant mass flow rate of carbon element. The flames were established in a Santoro-type burner and the temperatures of co-flow air and fuel were varied simultaneously from 293 K to 723 K. Planar distributions of soot volume fraction and soot temperature were measured using laser-induced incandescence and two-color pyrometry based on incandescence, respectively. The results show that the preheat temperature of gases has no significant effect on the shape of the CH4 and nitrogen-diluted C2H4 flames, but significantly influences that of the C2H4 flames with high soot loadings. With an increase in gas preheat temperature, both soot formation and oxidation are enhanced and soot loading increases for all flames. The magnitude of enhancement correlates with the soot loading, while the effect is more significant in the flames with lower soot loading. Soot temperature in the CH4 and nitrogen-diluted C2H4 flames also increases but is not as much as the change in the gas preheat temperature. However, for the C2H4 flames, an inverse tend is found in the central region of the flames, i.e., that lower soot temperatures are found in the flame with the higher gas preheat temperature.