Thermal effect and oxygen-enriched effect of N₂O decomposition on soot formation in ethylene diffusion flames

This study experimentally investigated the effect of nitrous oxide (N₂O) decomposition on soot formation in N₂O/ethylene diffusion flames. The effect of N₂O decomposition on the soot formation mechanism was examined in three oxidation cases (Cases Case I–III). In Case I, N₂O was used as the oxidant; in Case II, an oxygen-enriched N₂/O₂ mixture (67 % N₂ + 33 % O₂) was used as the oxidant; and in Case III, standard air (79 % N₂ + 21 % O₂) was used as the oxidant. A triple-port burner was used to generate diffusion flames with various R (ratio of the oxidizer flow velocity to the fuel flow velocity) values (R = 0–6). The soot concentration was measured through laser-induced incandescence, and the soot temperature was determined using two-color pyrometry. The measured soot temperatures increased significantly due to the thermal effect in the upstream position of the N₂O/C₂H₄ flames. The oxygen-enrichment effect on soot formation increased gradually from 10 % to 60 % as R increased from 0.5 to 6. The integration of the soot concentration along the flame length revealed that the soot formation rate and soot oxidation rate might rebalance under the N₂O decomposition effect.