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A variable valve timing mechanism has been applied in a high-speed direct injection diesel engine. The effective compression ratio ( εeff) is lowered by means of late intake valve closing, while keeping the expansion ratio constant. Premixed charge compression ignition (PCCI) combustion, adopting the Miller cycle, was experimentally realized and numerically analysed. Significant improvements in NO x (nitrogen oxides) and soot emissions were achieved for a wide range of engine speeds and loads frequently used in a transient mode test. The operating range of the Miller-PCCI combustion has been expanded up to an indicated mean effective pressure of 1.3 MPa.

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