A comparison study on the combustion and sooting characteristics of base engine oil and n-dodecane in laminar diffusion flames

Abstract

With the introduction of more strict emission legislations and advanced engine technologies, the contribution of engine oil to soot emissions from engines becomes more and more significant. In order to understand the sooting tendency of engine oil, experiments and chemical kinetic analysis were performed on a laminar diffusion flame of the base engine oil, together with a similar n-dodecane flame for comparison. Distributions of polycyclic aromatic hydrocarbon (PAH) and soot in the flames were measured using the method of laser-induced fluorescence and two-color planar laser induced incandescence respectively in the two flames. A reduced n-dodecane-PAH mechanism was adopted to simulate the PAHs’ formations in the n-dodecane flame with the laminarSMOKE code. To simulate the four-ring aromatic species (A4), a precursor of soot in simulations, in the base engine oil flame, the reaction rate of a formation reaction of the A4 species, A2R5 + C4H2 => A4, was enhanced by 3.6 times to better predict the PAH formation process of base oil. With this modification, the n-dodecane-PAH mechanism can well predict the A4 species in the base engine oil flames. Based on the experimental measurements and numerical simulations, the laminar diffusion flames of n-dodecane and base engine oil were analyzed and compared.