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Combustion and pollutant formation in a new recently introduced Common-Rail DI Diesel engine concept with roof-shaped combustion chamber and tumble charge motion are numerically investigated using the Representative Interactive Flamelet concept (RIF). A reference case with a cup shaped piston bowl for full load operating conditions is considered in detail. In addition to the reference case, three more cases are investigated with a variation of start of injection (SOI). A surrogate fuel consisting of n-decane (70% liquid volume fraction) and α-methylnaphthalene (30% liquid volume fraction) is used in the simulation. The underlying complete reaction mechanism comprises 506 elementary reactions and 118 chemical species. Special emphasis is put on pollutant formation, in particular on the formation of NOx, where a new technique based on a three-dimensional transport equation within the flamelet framework is applied.

Representative Interactive Flamelets (RIF) have proven successful in predicting Diesel engine combustion. The RIF concept is based on the assumption that chemistry is fast compared to the smallest turbulent time scales, associated with the turnover time of a Kolmogorov eddy. The assumption of fast chemistry may become questionable with respect to the prediction of pollutant formation; the formation of NOx, for example, is a rather slow process. For this reason, three different approaches to account for NOx emissions within the flamelet approach are presented and discussed in this study. This includes taking the pollutant mass fractions directly from the flamelet equations, a technique based on a three-dimensional transport equation as well as the extended Zeldovich mechanism. Combustion and pollutant emissions in a Common-Rail DI Diesel engine are numerically investigated using the RIF concept. Special emphasis is put on NOx emissions.