SLOW-COMBUSTION OF N-HEPTANE, ISOOCTANE AND A TOLUENE/N-HEPTANE MIXTURE

The oxidation of n-heptane, iso-octane and a toluene/n-heptane mixture was studied in a jet-stirred flow reactor operating under pressure at stoichiometric feed ratio in the low-temperature range. In particular, the transition from slow-combustion to a higher reactivity condition was examined by analyzing the composition of the reaction products as the residence time was increased. It was found that high-octane-number fuels, such as iso-octane and toluene, have a high tendency to add O2 keeping intact the original fuel structure forming 2,2,4,4-tetramethyltetrahydrofuran and benzaldehyde, respectively. Conversely, n-heptane has a high tendency to fragment in olefins and light oxygenated species already in slow-combustion. The different tendency to form oxygenated fuel-skeleton retaining species could be responsible for their different reactivity and consequently autoignition tendency.