An experimental and numerical study of the effects of reactant temperatures on soot formation in a coflow diffusion ethylene flame

The effects of elevated reactant temperatures on soot formation in a laminar coflow ethylene flame were experimentally and numerically investigated. Ethylene flames at the reference reactant temperatures (both air and fuel), Tr, of 300K (LT), 473K (MT), 673K (HT), and 713K (UHT) were established. In the experiment, soot volume fractions (fv), primary particle diameters (dp), and soot (flame) temperatures (TF) were measured. The flames were also simulated by the CoFlame code with the Conjugate Heat Transfer (CHT) condition. The experimental results show that elevating Tr positively affects soot formation. The increase in the maximum fv is greater on the wing pathline (∼1.9 times) than on the centerline (∼1.2 times) when the adiabatic flame temperature increases by ∼100K. An analysis of the experimental and numerical data suggests that soot formation is promoted by enhanced soot surface growth. The numerical simulation reveals that PAH (polycyclic aromatic hydrocarbon) adsorption, which is a function of PAH concentration, becomes important at high Tr as its mass contribution increases from ∼50% to ∼70%. This may be attributed to early fuel pyrolysis within the fuel tube.