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A system for stratifying recycled exhaust gas (EGR) to substantially increase dilution tolerance has been applied to a port injected four-valve gasoline engine. This system, known as Combustion Control through Vortex Stratification (CCVS), has shown greatly improved fuel consumption at a stoichiometric air/fuel ratio. Both burnrate (10-90% burn angle) and HC emissions are almost completely insensitive to EGR up to best economy EGR rate. Cycle to cycle combustion variation is also excellent with a coefficient of variation of IMEP of less than 2% at best economy EGR rate. This paper describes a research programme aimed at gaining a better understanding of the in-cylinder processes in this combustion system.

The paper describes a water analogy rig and its associated instrumentation and data acquisition system, developed to make particle image velocimetry (PIV) measurements of in-cylinder flow during the intake stroke. Methods of producing parameters to describe the flow characteristics of four valve engines with tumbling air motion are evaluated and correlation with combustion performance is examined for two different engines with a total of seven different inlet port designs. Each inlet port configuration was also evaluated by conventional steady flow methods. The results show that the dynamic water flow rig gave improved correlation with combustion data than that obtained with conventional steady flow methods of characterising in-cylinder flow patterns.