Soot Kinetic Modeling and Empirical Validation on Smokeless Diesel Combustion with Oxygenated Fuels

This paper provides new insights on the mechanism of the smokeless diesel combustion with oxygenated fuels, based on a combination of soot kinetic modeling and optical diagnostics. The chemical effects of fuel compositions, including aromatics - paraffins blend, neat oxygenated fuels and oxygenate additives, on sooting equivalence ratio ‘ϕ’ - temperature ‘T’ dependence were numerically examined using a detailed soot kinetic model. To better understand the physical factors affecting soot formation in oxygenated fuel sprays, the effects of injection pressure and ambient gas temperature on the flame lift-off length and relative soot concentration in oxygenated fuel jets were experimentally investigated.

The computational results show that the leaner mixture side of soot formation peninsula on the ϕ - T map, rather than the lower temperature one, should be utilized to suppress the formation of PAHs and ultra-fine particles together with the large reduction in particulate mass. Especially for highly oxygenated fuels, the smokeless ϕ - T region on the leaner mixture side of soot formation peninsula can be enlarged effectively due to the notable reduction in production of PAHs. Furthermore, the experimental results show that oxygenated fuel jets lead to shorter lift-off length but leaner mixture formation at lift-off location than those in diesel fuel jets. The oxygen entrainment estimates coupled with relative soot concentration measurements show a remarkable difference in the average equivalence ratio at the lift-off location leading to no significant soot level between diesel fuel and highly oxygenated fuel.