Impact of Intake Oxygen Enrichment on Oxidative Reactivity and Properties of Diesel Soot

Abstract

Oxygen addition to a four-cylinder turbo-charged common rail diesel engine was carried out by intake oxygen enrichment and by fuel oxygenation in order to study the effect of additional oxygen on oxidative reactivity and properties of diesel soot at low and high loads. The analyses of heat release rates and cylinder temperatures indicate that the effect of oxygen enrichment is more appreciable at high load than at low load. Correspondingly, there are more noticeable changes in crystalline structure and oxidative reactivity of soot from high load than of soot from low load. However, the surface O content on the soot does not show a consistent trend at low and high loads with oxygen enrichment. In addition, soot generated from high load with intake oxygen enrichment is observed to contain some metallic species, whereas soot from low load has little or no metallic species, which is attributed to the oxidation of lubricating oil by a synergistic effect of high oxygen concentration and high temperature. There might be an effect of the soot crystalline structure on soot oxidative reactivity, but the major influence on the reactivity is shown to be closely related to the amounts of metallic species present in soot due to the catalytic role of metallic species in soot oxidation.