Development Of A Modified Joback-Reid Group Contribution Method To Predict The Sooting Tendency Of Oxygenated Fuels

Several studies have shown that oxygenated fuels significantly reduce soot emissions in combustion systems. Thus, it is important to understand the role a molecule plays in soot formation. In this paper, smoke point measurements were performed to assess the sooting tendency of different compounds. Threshold sooting index (TSI) values were derived and used to establish a soot rating scale. Furthermore, a TSI prediction model based on a modified Joback-Reid (JR) group contribution method (GCM) was developed. The TSI experimental determination showed that (1) a saturated carbon exhibited the highest soot suppression potential among the hydrocarbon functional groups; (2) at comparable carbon content, aromatics had the highest TSIs followed by cyclic hydrocarbons, iso-alkanes, and n-alkanes; and (3) among the oxygenated functional groups, the aldehyde group generally had the highest tendency to reduce soot followed by ketone, hydroxyl, and ether. A soot reduction was induced by the oxygenated additives mainly owing to a dilution effect exerted by the hydrocarbon functional groups on the aromatic content of the surrogate diesel blend. The reduction increased with the amount of the additive fuel and diminished with an increasing carbon unsaturation level. The substitution effect introduced by the oxygen functional groups had a secondary role and featured a larger impact when an oxygen atom was included in paraffinic structures. Among furanics, the number and position of double carbon to carbon bonds in the ring affected the soot formation tendency. The modified JR GCM allowed predicting TSIs with a high confidence level for both hydrocarbons and oxygenated functional groups. It featured a higher prediction accuracy and a lower model complexity than other models found in the previous literature. This was achieved by introducing ad hoc descriptors for unsaturated compounds, describing conjugation, double carbon to carbon bond frequency, and allylic groups. The oxygen to carbon bond type demonstrated a significant role in soot suppression of oxygen-centered functional groups.