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The present study uses a numerical model to investigate the effects of flow turbulence on premixed iso-octane HCCI engine combustion. Different levels of in-cylinder turbulence are generated by using different piston geometries, namely a disc-shape versus a square-shape bowl. The numerical model is based on the KIVA code which is modified to use CHEMKIN as the chemistry solver. A detailed reaction mechanism is used to simulate the fuel chemistry. It is found that turbulence has significant effects on HCCI combustion. In the current engine setup, the main effect of turbulence is to affect the wall heat transfer, and hence to change the mixture temperature which, in turn, influences the ignition timing and combustion duration. The model also predicts that the combustion duration in the square bowl case is longer than that in the disc piston case which agrees with the measurements.

A 6-cylinder truck engine was modified to run in HCCI-mode. The aim was to show whether or not it is possible having HCCI run a multi-cylinder engine, to provide brake values of emissions and efficiency and to verify models for engine system simulation. The work proved that it is feasible to use HCCI in multi-cylinder engines with high brake efficiency. Emissions' strong dependence on inlet temperature and octane number was demonstrated. The numerical models simulated the mean effective pressure with high precision, while inlet and exhaust pressures were less accurate, mainly due to the limitations of the turbo maps used.