The temperature dependence of soot formation in laminar coflow aromatic flames

The temperature sensitivity of n-propylbenzene and 1,2,4-trimethylbenzene on soot formation in coflow diffusion flames was assessed. Cases with air temperatures at 300K (LT), 473K (MT), and 673K (HT) were established. Soot volume fractions and primary particle diameters were measured by Laser-induced incandescence. Soot temperatures were measured by rapid thermocouple insertion with correction by backward extrapolation. Soot yield also increased with temperature. Compared to alkanes and alkenes, alkylbenzenes exhibited much lower temperature sensitivity. The model suggested that elevating the reactant temperature did not significantly affect the production of soot precursor PAH in alkylbenzene flames, but altered the buoyancy-induced acceleration, which subsequently determined the time available for soot growth. Soot formation was promoted by extending the available time. To isolate the impact of fuel temperature, a case with heated fuel and unheated air (FHT) was also assessed. It is found that raising the fuel temperature affected soot formation more along the centerline than on the wing. This is suggested to be related to the earlier soot inception for FHT along the centerline.