Experimental investigation on soot formation and characteristics of ethylene flames: Scale effects

Abstract

Understanding the mechanism of scale effect was of great significance for both fundamental theory and actual combustion regulation. Using five combustors of different diameters (4, 6, 7, 8, and 10 mm), this study experimentally investigated the impact of scale effect on soot formation and combustion characteristics using optical and sampling diagnostic methods. For the optical results of two-color pyrometry, the scale effect exerted a non-monotonic effect on flame temperature. The flame temperature increased firstly with the enlargement of the combustor diameter from 4 to 7 mm, but it decreased rapidly when the combustor diameter continued to increase from 7 to 10 mm. However, the soot concentration increased at first and then remained constant approximately with the enlargement of combustor diameter, which exhibited a different tendency from flame temperature. For the sampling results of TEM and TGA, fringe tortuosity and oxidation rate of soot decreased with the combustor diameter enlargement, indicating the higher soot carbonization degree from the larger scale. Furthermore, for the result of exhaust gas analysis, the C2H4 concentration decreased first and then increased with the enlargement of combustor diameter, which also proved that the scale effect exerted a non-monotonic effect on the combustion process.