Comparative study on soot morphology and nanostructure characteristics of higher alcohol fuels and parent n-alkanes in co-flow diffusion flames

Higher-alcohols, as carbon-neutral energy, are more suitable alternative fuels for engines due to their higher reactivity and energy density. Compared to lower alcohols, higher alcohols exhibit alkane-like reactivity due to hydroxyl groups weakening. This work investigated the soot particle microevolution of n-C5-C8 alcohols and alkanes experimentally and numerically. As carbon chain increases, high-soot region exhibits a transition from flame center to wings, with the transition for alcohols occurring at C5-C6, later than alkanes (C2-C3). Flame height, soot concentration, particle size and nanostructure order all increase for C5-C8 alcohols and n-alkanes with increasing carbon. Moreover, the soot characteristic parameters of alcohols gradually approach those of n-alkanes. As carbon increases from 5 to 8, the particle size difference between alcohols and alkanes decreases from 4.3 nm to 3.2 nm. Kinetic analysis showed that the benzene (A1) yields in n-C5-C8 alcohols and n-alkanes increase with increasing carbon chain, but the A1 concentration of alcohols is smaller than that of n-alkanes, which attributed to the inhibition of C2-C3 intermediates of by alcoholic OH. However, the difference in A1 peak decreases with increasing carbon chain due to the transition from the inhibitory effect to promoting effect of hydroxyl groups on C4 intermediates.