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Comparison of net thermal efficiency and emission in two and four stroke gasoline HCCI engine has been carried out for various valve-timings as negative valve overlap and exhaust valve double opening. The valve timings could easily be converted from a mode to another by configuring schedule of electromagnetic valve-train. Extension of operable torque with high thermal efficiency had been expected in two-stroke HCCI operation, however friction and supercharger loss curtailed about half of the gain in indicated thermal efficiency. In four-stroke operation modes, exhaust valve double opening (‘reinduction’ or ‘rebreathing’) showed the best net thermal efficiency and emission, however the extension of high load limit could not be achieved considerably.

A reduced chemical kinetic model has been developed using temperature history measured by Coherent Anti-Stokes Raman Spectroscopy (CARS) and sensitivity analysis. Predictions of knock occurrence by this model show that the chemical role of residual gas and the intake flow have little effect on the knock occurrence crank angle. Furthermore, the effectiveness of the combustion period and the unburned gas temperature before spark ignition on the torque at trace knock limit (TTKL) has been clarified Under certain conditions, it is shown that the increase in torque, caused by the combustion duration shortened by ∼25%, is negated by the temperature rise of ∼15K before spark ignition.