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A cycle-by-cycle analysis of HC emissions from each cylinder of a four-stroke V-6, 3.3 L production engine was made during cold start. The HC emissions were measured in the exhaust port using a high frequency flame ionization detector (FID). The effect of the initial startup position of the piston and valves in the cycle on combustion and HC emissions from each cylinder was examined. The mass of fuel injected, burned and emitted was calculated for each cycle. The equivalence ratio of the charge in the firing cycles was determined. The analysis covered the first 120 cycles and included the effect of engine transients on HC emissions.

While Variable Valve Timing (VVT) holds the potential to alleviate some of the compromises normally associated with engine operation over broad speed and load ranges, generalizing its benefits in a quantitative manner is difficult. Details of base engine design and the means of VVT execution and engine duty cycle play major roles in determining the outcome of such an application. With the profusion of VVT means available, the matter of selecting an appropriate system for a given engine and duty cycle is difficult particularly when there is a host of competing features and technologies. This treatment of VVT is based on assessments of compromises associated with static valve timing and provides a framework for considering VVT as an engine performance option. Extensive use is made of pressure and geometric data, and several generalizations are made relative to strategies for incorporating common VVT systems.