Numerical Study of the Influence of Turbulence-Chemistry Interaction on URANS Simulations of Diesel Spray Flame Structures

Abstract

The present work performs unsteady Reynolds-averaged Navier-Stokes simulations to study the effect of turbulence-chemistry interaction (TCI) on diesel spray flames. Three nozzle diameters (d(0)) of 100, 180, and 363 mu m are considered in the present study. The Eulerian stochastic fields (ESF) method (with the TCI effect) and well-stirred reactor (WSR) model (without the TCI effect) are considered in the present work. The model evaluation is carried out for ambient gas densities (rho(am)) of 30.0 and 58.5 kg/m(3). The ESF method is demonstrated to be able to reproduce the ignition delay time (IDT) and lift-off length (LOL) with an improved accuracy than that from the WSR method. Furthermore, TCI has relatively more influence on LOL than on IDT. A normalized LOL (LOL*) is introduced, which considers the effect of d(0), and its subsequent effect on the fuel-richness in the rich premixed core region is analyzed. The RO2 distribution is less influenced by the TCI effect as ambient density increases. The ESF model generally predicts a longer and wider CH2O distribution. The difference in the spatial distribution of CH2O between the ESF and WSR model diminishes as d(0) increases. At rho(am) = 30.0 kg/m(3), the ESF method results in a broader region of OH with lower peak OH values than in the WSR case. However, at rho(am) = 58.5 kg/m(3), the variation of the peak OH value is less susceptible to the increase in d(0) and the presence of the TCI model. Furthermore, the influence of TCI on the total OH mass decreases as d(0) increases. The total NOx mass qualitatively follows the same trend as the total OH mass. This present work clearly shows that the influence of TCI on the global spray and combustion characteristics becomes less prominent when d(0) increases.