(1-09) Application of Complex Chemistry to Investigate the Combustion Zone Structure of DI Diesel Sprays under Engine-Like Conditions((DE-3)Diesel Engine Combustion 3-Modeling)

The aim of this paper is to study numerically the detailed flame zone structure of DI diesel sprays during combustion at engine-like conditions. To address this issue, the KIVA-3 code was modified to include complex chemical mechanisms. A "subgrid", partially stirred reactor model was applied to handle turbulence-chemistry interaction. Diesel fuel is assumed to be single-component and its oxidation chemistry is represented by the n-heptane kinetics. The chemical mechanism, reduced to a size of 65 species and 273 elementary reactions, retains the important low/intermediate temperature ignition reactions for n-heptane, the low hydrocarbon oxidation chemistry, the formation reactions of polycyclic aromatic hydrocarbons (PAHs) (up to two aromatic rings), and the NOx formation kinetics. Numerical simulation of the transient diesel combustion process at a specific injection condition was performed. The numerical prediction shows that the current approach is capable of capturing the essential features of the diesel process such as auto-ignition and liftoff phenomena. The simulation illustrates that the lifted flame is stabilized as a triple flame. The simulated spatial soot and NO distributions are similar to those described in Dec's "conceptual diesel model". Analysis of the flame zone shows the molecular precursors of soot (e. g. PAHs and acetylene) produced during the rich burning of the sprays contributing to soot formation, whereas NO is formed closer to the oxygen diffusion layer on the lean side of the flame. The simulation was also extended to investigate the effects of charge composition variation on diesel auto-ignition and combustion. The results demonstrate that variation of oxygen molar concentration in the charge can substantially affect the auto-ignition and combustion pattern of diesel sprays.