Sooting Tendency of a Series of Kerosene Surrogates and Blends Containing Various Additives Considered as Sustainable Alternative Fuels

The present work aims at analyzing the sooting tendency of 32 additives considered as potential alternative transportation fuels including 4 C₂-C₅ alcohols, 4 C₇-C₁₀ esters, 16 C₄-C₇ furans, 6 C₁₀ terpenes, and 2 pyrolysis oils (POs), some of which have seldom (if ever) been studied in the literature. The sooting propensity of each additive, following its mixture with a kerosene surrogate, was characterized using the oxygen extended sooting index (OESI), which is based on the measurement of the smoke point (SP), before being converted into unified index (UI) values for modeling purposes. To that end, a benchmarking analysis of the SP measurement approaches commonly used in the literature was first conducted. The SP of a series of reference fuels from the ASTM D1322 standard were measured using different methods to compare their precision, repeatability, and ease of use. This led to identifying the so-called vision-based algorithm-aided procedure as being the best suited. This method was then selected to test the ability of 8 model fuels to emulate the sooting propensity of a commercial Jet-A. Based on the results obtained, an n-dodecane/isocetane/mesitylene/n-propylbenzene blend was chosen to be mixed with up to 40 vol % of additives. The measured UI showed that each tested fuel, except for one terpene (myrcene), soots less than the kerosene surrogate. Their soot-suppressing effect was found to decrease in the following order: alcohols > esters > furans > terpenes. Measured data, moreover, allowed extending the predictive capability of a group contribution model (GCM) recently developed through the proposal of dedicated submodels integrating 15 sooting propensity factors suitable for predicting the tendency to soot of furans and terpenes. While satisfactorily simulating measured data, the GCM proved to be valuable for identifying the chemical structures influencing soot production. Finally, although POs exhibit low UI, their high water content, among other things, removes them from consideration as attractive additives.