Critical observations on the modeling of nonreacting and reacting diesel sprays

Abstract

This paper begins by discussing the structure of nonreacting and reacting diesel sprays. After a general discussion of approaches to model nonreacting diesel sprays, results from some recent work employing the Reynolds-averaged Navier–Stokes equations to model the nonreacting spray are presented. It is shown through detailed comparison with measured results that, under conventional high-pressure, high-temperature chamber and high-pressure injection conditions, the vaporizing diesel spray behaves like a gas jet and can be modeled as such without noticeable loss of accuracy in reproducing the structure of the spray. Moving on to consider a reacting diesel spray, turbulence–chemistry interaction models for the reacting spray are reviewed. Challenges in determining the suitability of one model over another, based on information available in the literature, are highlighted. The Reynolds-averaged Navier–Stokes simulation results of reacting diesel sprays in which an unsteady-flamelet-generated manifold model is employed for turbulence–chemistry interactions are discussed in detail. It is shown that the model, like others reported in the literature, can predict the ignition delay and the flame lift-off heights with reasonable accuracy. The model has also been extended to compute the concentrations of soot and nitrogen oxides in reacting diesel sprays. Nitrogen oxides are modeled using the mechanism from GRI-Mech 3.0 and soot is modeled using a kinetic mechanism coupled with a tracer particle approach to estimate the residence times within the jet. As part of this review, other recent studies on modeling pollutants in the reacting diesel spray are also reviewed in this work. Finally, recent studies employing large-eddy simulations of diesel sprays are reviewed. Initial simulations of the reacting diesel spray using a large-eddy simulation approach coupled with an unsteady-flamelet-generated manifold model are presented. The paper closes with a summary and suggestions for further work in modeling diesel sprays.