Pressure Effects on Incipiently Sooting Partially Premixed Counterflow Flames of Ethylene

摘要

We studied partially premixed ethylene flames under counterflow conditions at pressures up to 8 bar by adding oxygen to the fuel stream of a diffusion flame to lower the equivalence ratio to 5. Combustion occurred in two stages, with unburnt CO and H_2 in the post-premixed flame region feeding a diffusion flame. Soot formed in the region straddling the gas stagnation plane within the double flame structure. Using gas sampling followed by GC-MS analysis we quantified the profiles of species up to 3-ring aromatics. An eightfold pressure increase lead to an increase in flame sooting tendency, even after the flame peak temperature had been lowered by dilution to keep the soot loading light and compatible with microprobe sampling. Modeling revealed that the increased tendency to soot with pressure is partly due to a reduced back diffusion of oxidizing radicals from the diffusion flame side towards the gas stagnation region. Preliminary experiments are under way to quantify the soot in addition to its precursors.