This paper deals with improvements of power and exhaust gas emissions in a passenger car diesel engine by Premixed Compression Ignition (PCI) combustion and two stage super charging. A low compression ratio type piston was used to assure suitable ignition delay which sufficient air was introduced into the spray plume to suppress NOx and smoke formation. As a result, PCI combustion successfully controls NOx and smoke emissions simultaneously at low loads. At high loads in which it is difficult to utilize PCI combustion, combustion which combined high boost pressure by two stage super charging and high EGR rate, favorably reduce NOx emission with no degradation in smoke emission and torque. In addition, the low compression ratio led to higher specific power, because it suppressed the peak pressure.
