Abstract
HCCI engines have been widely investigated over the past few years because of their high efficiency potential with low NO_x emission, but they have some problems which prevent their current commercialization. Beside problems with the control of ignition timing and low specific power output, they show increased HC and CO emissions. Although these emissions could be aftertreated with oxidation catalyst, a better solution would be to decrease the amount of emissions from the cylinder. By lowering emissions of HC and CO from the engine cylinder the combustion efficiency will be increased and by that the overall efficiency of the engine will also be increased. Some previous studies have shown that significant sources of HC and CO emissions are crevices and boundary layers near cylinder walls. In order to further investigate their influence on these emissions and possible solutions for lowering them, a computational analysis of the influence of crevice volume and cylinder wall temperature will be done. For this analysis, a, newly developed HCCI multi zone computational model will be used. The model incorporates a crevice, boundary layers, and centre zones, and uses detailed chemical kinetics in order to predict the heat released from combustion, and also to calculate the actual amount of HC and CO compounds. The model also incorporates mass transfer between zones in order to maintain the boundary layer thickness, and also the heat transfer between zones and between boundary layer zones and cylinder walls. A high pressure cycle multi zone model is integrated into the cycle simulation code which calculates processes during gas exchange. In this manner, the initial conditions at the start of a high pressure cycle are calculated, and not predicted. In order to have temperature inhomogeneity at the start of the high pressure cycle, a model of temperature distribution between zones has also been developed.
