Sooting Behavior of Gaseous Hydrocarbon Diffusion Flames and the Influence of Additives

Abstract

Abstract The sooting behavior of laminar diffusion flames were altered by addition of diluents to the fuel flow. Fuel additives which decrease the sooting tendency had an effectiveness in order of their molar specific heat capacity; helium exhibited some exaggerated trends, probably due to its high thermal diffusivity. The effect of water vapor, carbon dioxide and sulphur dioxide in reducing the tendency to soot was purely thermal with no observable chemical interaction. Trace amounts of oxidizers and halogenated compounds increased the sooting tendency substantially. Results from tests with blended fuels and fuel-hydrogen nitrogen mixtures in which the C/H ratio and temperature were controlled revealed that C/H ratio was not a dominant parameter in the sooting tendency. These results and temperature measurements provided evidence that the sooting behavior of a diffusion flame is controlled by the initial fuel pyrolysis which is dominated by the flame temperature and the field it causes. Since accurate calculations of flame temperature in diffusion flames are difficult to make, we offer the heat production rate and heat capacity of the system as the most practical means of correlating the data. Fuel structure was the other major parameter determining the propensity to soot and it was shown that undercontrolled temperature conditions, butadiene has a far greater tendency to soot than acetylene. Overall these diffusion flame experiments have shown as well that for circular ports the sooting height, as a special case of the flame height, is strictly proportional to the volumetric fuel flow rate.