Sooting characteristics of hydrocarbon compounds and their blends relevant to aviation fuel applications

Abstract

The sooting characteristics of neat hydrocarbon compounds from different molecular classes and their blends that are relevant to aviation fuels were systematically investigated in the present work. Smoke points and maximum soot volume fractions of 10 neat hydrocarbon compounds and 33 binary fuel blends were measured in a standard wick-fed flame burner. The threshold sooting indices of test fuels were derived based on the fuel uptake flow rate with threshold imaging method. At the smoke point conditions, flames of all test fuels were noted to have relatively close maximum soot volume fractions, thereby suggesting that the maximum soot concentration contained by a diffusion flame without escaping smoke is relatively insensitive to the effects of fuel molecular structure. At the constant fuel carbon flow rate conditions, it was found that the soot formation generally follows: naphthalenes > monocyclic aromatics > cycloalkanes >iso-alkanes >n-alkanes. The relationships between soot formation and various sooting tendency indices were further examined. For given constituents, their binary blend result at varying blending ratio showed that the maximum soot volume fraction can be approximately linearly correlated with aromatics content, hydrogen content, hydrogen deficiency, and threshold sooting index; the slope varies with different blends. At a given constant fuel carbon flow rate, the results of all test fuels demonstrated that the reciprocal of smoke point is able to correlate linearly with the maximum soot volume fraction through a single curve. Therefore, the present findings indicated that smoke point is more effective even than threshold sooting index in predicting soot formation in diffusion flames.