Abstract
Experimental and numerical modeling studies have been performed to investigate the effect of CO
2
dilution on soot formation in ethylene counterflow diffusion flames. Thermal and chemical effects of CO
2
addition on soot growth was numerically identified by using a fictitious CO
2
species, which was treated as inert in terms of chemical reactions. The results showed that CO
2
addition reduces soot formation both thermodynamically and chemically. In terms of chemical effect, the addition of CO
2
decreases soot formation through various pathways, including: (1) reduced soot precursor (PAH) formation leading to lower inception rates and soot number density, which in turn results in lower surface area for soot mass addition; (2) reduced H, CH
3
, and C
3
H
3
concentrations causing lower H abstraction rate and therefore less active site per surface area for soot growth; and (3) reduced C
2
H
2
mole fraction and thus a slower C
2
H
2
mass addition rate. In addition, the sooting limits were also measured for ethylene counterflow flames in both N
2
and CO
2
atmosphere and the results showed that sooting region was significantly reduced in the CO
2
case compared to the N
2
case.