Search Results

Homogeneous Charge Compression Ignition (HCCI) engines have the potential of reducing NOx emissions as compared to conventional Diesel or SI engines. Soot emissions are also very low due to the premixed nature of combustion. However, the unburned hydrocarbon emissions are relatively high and the same holds for CO emissions. The formation of these pollutants, for a given fuel, is strongly affected by the temperature distribution as well as by the charge motion within the engine cylinder. The foregoing physical mechanisms determine the local ignition timing and burning rate of the charge affecting engine efficiency, performance and stability. Obviously the success of any model describing HCCI combustion depends on its ability to describe adequately both the chemistry of combustion and the physical phenomena, i.e. heat and mass transfer within the cylinder charge. In the present study a multi-zone model is developed to describe the heat and mass transfer mechanism within the cylinder.

In the present work, a multi-zone model is presented for the simulation of HCCI engines. This model is an improvement of a previous one developed by the authors. The present model describes the combustion, heat and mass transfer processes for the closed part of the engine cycle, i.e. compression, combustion and expansion. The zones occupy geometrical positions within the engine cylinder and exchange heat and mass throughout the compression and expansion strokes, based on their spatial configuration. Heat exchange is considered between zones and to the cylinder wall. A phenomenological model has been developed to describe mass exchange between zones and the flow of a portion of the in-cylinder mixture in and out of the crevice region. The crevice flow is a new feature and is included in the present model since the crevice regions are considered to contribute to unburned HC emissions. Another new feature is the incorporation of chemical kinetics, based on combustion chemistry reactions.