Computed NO and soot distribution in turbulent transient jets under diesel conditions

In this work, the NO submechanism from GRIMECH 3.0 and three soot models of increasing levels of complexity are employed to predict NO and soot distribution in transient turbulent diesel jets. The soot models are (a) an empirical model in which soot mass formation rate is related to the pressure, temperature, and fuel concentration; (b) a semi-empirical model in which soot nucleation, coagulation, and surface growth are modeled; and (c) a kinetic model. The first two formation models are coupled with soot oxidation models proposed by Nagle and Strickland-Constable and Fenimore and Jones whereas the third model includes soot oxidation in the reaction kinetics. Effects of soot diffusivity and radiant heat transfer are evaluated. Variables studied include the soot volume fraction and number density. NO is found to be a maximum in the high-temperature region of the jet. The empirical soot model predicts maximum soot concentration along the centerline of the jet upstream of the head vortex at all instants during the injection period. The semi-empirical and the kinetic soot models predict maximum soot concentration in the head vortex region of the jet earlier in its development but a maximum along the centerline upstream of the head vortex later in its development. Radiant heat transfer reduces the formation rates of NO and soot and the oxidation rate of soot but its overall effect may not be significant in diesel jets because the residence timescales in the jet are short relative to the timescales associated with heat-loss effects due to radiation.