Combustion Modeling of Diesel Sprays

Several models for ignition, combustion and emission formation under diesel engine conditions for multi-dimensional computational fluid dynamics have been proposed in the past. It has been recognized that the use of a reasonably detailed chemistry model improves the combustion and emission prediction especially under low temperature and high exhaust gas recirculation conditions.

The coupling of the combustion chemistry and the turbulent flow can be achieved with different assumptions. In this paper we investigate a selection of n-heptane spray experiments published by the Engine Combustion Network (ECN spray H) with three different combustion models: well-stirred reactor model, transient interactive flamelet model and progress variable based conditional moment closure. All models cater for the use of detailed chemistry, while the turbulence-chemistry interaction modeling and the ability to consider local effects differ.

The same chemical mechanism is used by all combustion models, which allows a comparison of ignition delay, flame stabilization and flame lift-off length between the experiments and the results from simulations using the different combustion models. The investigated parameters influence the predictions of computational fluid dynamics simulations of diesel engines. This study indicates that the most reasonable behavior with respect to ignition, flame stabilization and flame structure is predicted by the progress variable based conditional moment closure model.