Soot and nitric oxide modeling in reacting diesel jets with an unsteady flamelet progress variable model

Abstract

In this work, computations of soot and nitric oxide in reacting diesel jets are carried out for a wide range of conditions by employing a Reynolds-averaged Navier–Stokes model in which an unsteady flamelet progress variable submodel is employed to represent turbulence–chemistry interactions. The computations are carried out in a constant-volume chamber. Soot kinetics are represented using a chemical mechanism that models the growth of soot precursors starting from a single aromatic ring by hydrogen abstraction and carbon (acetylene) addition, and nitric oxide is modeled using the kinetics from a submechanism of GRI-Mech 3.0. Tracer particles are used to track the residence time of the injected mass in the jet. For the soot and nitric oxide computations, this residence time is used to track the progression of the soot and nitric oxide reactions in time. The computational conditions selected reflect the changes in the injection pressure, the chamber temperature, the oxygen concentration and density, and the orifice diameter. Comparisons with the measured soot concentrations are shown when the measured results are available. Furthermore, the dependence of the soot and nitric oxide formed in the jet on the flame lift-off height is examined. Analysis of the entrained mass upstream of the lift-off height confirms that this correlation arises from the variation in the entrained oxygen.