INFLUENCE OF SULFUR-DIOXIDE ON SOOT FORMATION IN DIFFUSION FLAMES

An overventilated coflowing axisymmetric laminar ethylene diffusion flame was used to study the influence of sulfur dioxide addition to both the fuel and oxidizer on soot formation. The experiments were designed such that the relative influences of temperature, fuel concentration, and direct chemical interaction can be isolated when sulfur dioxide is added to the fuel side in varying quantities. A quantitative assessment of these three effects was made using an Arrhenius type expression that makes allowance for changes in flame profiles and flame residence times. It was shown that the reduced soot resulting from adding sulfur dioxide to the fuel side is due to a reduction in flame temperature and a reduction in the fuel concentration. No indication of a chemical effect was observed up to 35%-40% sulfur dioxide in ethylene. However, when sulfur dioxide mole fraction exceeds 40%. the effect of the direct chemical interaction becomes important in addition to thermal and dilution effects. The influence of sulfur dioxide on the air side was found to be a purely thermal effect when allowance was made for the altered oxidant concentration.