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An experimental and analytical study was conducted to investigate the effects of load control with port throttling on stability and fuel consumption at idle. With port throttling, the pressure in the intake port increases during the valve-closed period due to flow past the throttle. If the pressure in the port recovers to ambient before the valve overlap period, back flow into the intake system from the cylinder is eliminated. This allows increased valve overlap to be used without increasing the residual mass fraction in the cylinder. Results showed that, with high valve overlap and port throttling, idle stability and fuel consumption can be maintained at values associated with low overlap in a conventionally throttled engine. However, implementation of this concept in production is regarded to require precision-fit and balanced port throttles, an external vacuum pump for vacuum systems support, and revision of the PCV system.

A PROCO Flow Simulation (PFSIM) model has been developed to calculate the angular velocity (swirl) and radial velocity (squish) as a function of crank angle for the four strokes of the motored engine cycle. In addition, the PFSIM model calculates the time dependent cylinder pressure, temperature and mass. The model accepts the following swirl-related parameters as input: dimensionless angular momentum and mass flow coefficients for a specific intake and exhaust system configuration. These parameters determine the intake-generated swirl which is computed from the angular momentum flux entering the cylinder during the induction process. An angular momentum flux swirl meter was used to obtain the required input data for three different intake port configurations, and calculations of the bulk cylinder flow were carried out with PFSIM for each intake port configuration.