Multidimensional simulations of non-reacting and reacting diesel and biodiesel sprays

Abstract

Numerical simulations of non-reacting and reacting diesel and biodiesel sprays in a constant-volume chamber are presented in this paper and some of the results compared to measured data. The conditions of the study include the effects of chamber air dilution with inert gases and varying chamber temperature. n-Heptane is used as the surrogate fuel for diesel fuel and a tri-component fuel mixture consisting of n-heptane, methyl decanoate, and methyl 9-decenoate is used as the surrogate fuel for biodiesel. The computed and measured liquid-phase penetrations in the non-reacting sprays agree within 30% for the range of conditions considered. The vapour penetrations agree within 10%. For the reacting simulations, the turbulence/chemistry interaction is modelled using an unsteady flamelet generated manifold (UFGM) sub-model. As reported in prior work, the UFGM model predicts the flame lift-off height well. The soot model employed is a semi-empirical two-equation model that accounts for nucleation of soot precursors, surface growth via acetylene addition and PAH condensation, coagulation, and oxidation. NO is modelled using the kinetics from a sub-mechanism of GRI-Mech 3.0. The measured trends in soot distribution in the sprays are predicted well although there are significant differences in actual soot volume fractions.