Development of a predictive method to analyze the effect of “new” gases on soot formation based on Laser-Induced Incandescence measurements

We have developed a method for characterizing sooting tendencies for gases. To develop the method, soot volume fractions were measured using laser-induced incandescence (LII) in rich-premixed Bunsen-type flames with varying fuel compositions of C2H6, C3H8, C4H10, N2, CO2 and H2 in CH4. Upon the addition of higher hydrocarbons to methane the sooting tendency was observed to increase, for the inert gases the sooting tendency decreased. A correlation was found between an equivalent propane fraction representation of the composition of higher alkanes and the actual soot fractions for the binary hydrocarbon mixtures. The addition of hydrogen either increases or decreases the soot fraction depending on the rest of the fuel composition. This behavior for hydrogen is at present poorly understood. All measurements were used as input for an analysis to yield a regression equation for comparison of gases based on their sooting tendency at equivalence ratios where soot formation, deposition and emission may occur in end-use appliances. Comparison of the experimental results with predictions using the regression equation shows that the method can rank gases based on their sooting tendencies with reasonable accuracy.