Impacts of oxygenated compounds concentration on sooting propensities and soot oxidative reactivity: Application to Diesel and Biodiesel surrogates

Abstract

The aim of this paper is to evaluate the effect of oxygenated compounds concentration on sooting propensities of surrogate Diesel and Biodiesel, and to investigate the oxidative reactivity of soot obtained by combustion of these surrogates using an atmospheric axis-symmetric co-flow diffusion flame burner. For this end, concentrations from 3 to 30% (in mole%) of methyl decanoate (MD) are added to a surrogate Diesel made up of a binary mixture of 70% of n-decane and 30% of α-methylnaphthalene (α-MN). The sooting propensities of these mixtures are here measured in terms of Yield Sooting Indices (YSIs) in methane diffusion flames doped with 35,000ppm vapors of tested surrogate. Data of soot volume fraction were extracted using light extinction method (LEM). Additionally, soot generated from the combustion of the model Diesel and Biodiesel fuels was then collected, sampled and characterized using physico-chemical techniques. Addition of MD was found to reduce sooting tendencies. This decrease is more pronounced when the concentration of oxygenate additives increases. On the other side, the oxidative reactivity of soot generated from the diffusion flame burner was found to decrease by increasing Biodiesel percentage. Furthermore, soot generated from the combustion of surrogate Diesel and Biodiesel showed different behaviors. Biodiesel-derived soots were smaller and less reactive than Diesel-derived soots. These last displayed less ordered graphite-like structures and higher amorphous carbon concentration.