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This paper presents a new approach of Air Fuel Control (AFR) control strategy based on non-linear dynamics models of the engine air and fuel processes. Higher demands for lower engine exhaust emissions require a more accurate control of the air-fuel ratio during transient operations. A model-based air-fuel ratio control was applied to a production multipoint port injection engine with the initial constraint to keep the original sensors and actuators. The control strategy contains real-time engine models which describe air, fuel and sensors dynamics. In the final step, the control structure was implemented on a production car and evaluated on a chassis dynamometer. Several experiments with different transient conditions have shown reduced air-fuel ratio excursions in magnitude and duration compared to the standard strategy. Moreover, the calibration process was considerably easier than usual and required less testing on the car.

The initial flame kernel behavior in a SI engine was measured by a spark-plug-fiber-optics probe. From these measurements, the flame kernel may be characterized by an expansion speed and a convection velocity. These quantities were correlated with the bum rate on a cycle-to-cycle basis in an engine configurated with quiescent, swirl, and tumble in-cylinder motion. The expansion speed correlates well with the 0-2 percent mass burn duration for all the configurations. The flame convection velocity depends on the in-cylinder motion in the expected manner. There was, however, only a weak correlation between the 10-90 percent burn duration and the initial flame kernel behavior.