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Intake volumetric efficiency (VE) of a spark-ignition engine varies with valve timings, engine speeds, and manifold air loads. The existing approaches to reveal the underlying effects of these VE factors on instant valve flows remain complicated and expensive. In an effort to develop an applicable approach to analyze the detail valve flows, a naturally aspirated production engine with dual independent VVT was dynamometer-tested with fast in-cylinder pressure measurements and slow manifold pressure measurements. Both intake and exhaust valve flow was then reproduced using a new model, DQS model, in crank-angle resolution (CAR). One new flow mechanism, the flow wave subsidence, has been revealed to be one of the major drives of VE changes. We propose a dynamic quasi-steady (DQS) flow model to reproduce the valve flow profile from the measured pressure data. The DQS model features two manifold dynamics and a delay in the use of in-cylinder pressure measurements.

A strategy to facilitate the mixture preparation process in PFI engines is to delay the Intake Valve Opening (IVO) by shifting the cam phasing so that the cylinder pressure is sub-atmospheric when the valve opens. The physics of the effect are discussed in terms of the pressure differential between the manifold and the cylinder, and the resulting flow and charge temperature history. The effect was evaluated by measuring the equivalence ratio of the trapped charge and the exhaust HC emissions in the first cycle of cranking in a 2.4L engine. When the IVO timing was changed from 18° BTDC to 21° ATDC, the in-cylinder fuel equivalence ratio increased by approximately 10%. This increase was attributed mainly to the enrichment of the charge by displacing the leaner mixture at the top of the cylinder in the period between BDC and IVC. The exhaust HC, however, increased by 40%. No conclusive explanation was established for this increase in HC emissions.