Fire Safety Science Digital Archive

In the present analysis an effort has been made to predict the sooting tendency of hydrocarbon fuels, both in premixed and diffusion flames, by using the group additivity approach based on the molecular protons whose absorptions fall within predefined regions of the proton NMR spectra . In order to define these regions so that they may have a physical meaning, more than 200 spectra have been studied. As a measure of the sooting tendency in premixed flames, the equivalence fuel/ oxidizer ratio Sc was selected, which assumes the combustion products to be C and H20. This approach was applied to 69 hydrocarbon fuels (alkanes, alkenes, alkynes and aromatics); the predicted values lie in all cases within ±5% of the measured ones. In the case of diffusion flames, the ratio used for the Threshold Soot Index (TSI) calculation, i.e. molecular weight/maximum smoke-free flame height (MW/h), has been taken as a measure of the sooting tendency. Again a large number of hydrocarbons with great variations in molecular structure was studied and the estimated values fell in most cases within ±5% of the measured ones; much better accuracy was obtained for open chain as opposed to ring hydrocarbons