A promising technique to enhance fuel efficiency of large capacity S.I. engines is the de-activation of some cylinders at partial load, through the cut-out of fuel metering and a specific control of the airflow. Thanks to the ensuing reduction of throttling losses (the active cylinders operate at a much higher load), fuel consumption can be reduced, without any negative perception from the driver. Such a technique has been already applied successfully on some production engines, at the cost of some additional complication on the valve-train system.
The application analyzed in this study is a little bit different, being aimed to reduce both fuel consumption and emissions, with a minimum impact on engine design. Larger fuel savings may be obtained by coupling the cylinder de-activation with VVT.
However, the most important advantage of the modular engine concept proposed in this paper is in terms of emissions: this study demonstrates that the light-off time of the catalysts may be strongly reduced, and a further improvement is obtained by doubling the effective surface of the catalytic bed.
The study has been carried out on a conventional SI 4.2L V8 engine. The first step of the analysis has been the experimental validation of a 1D-CFD model of the engine, achieved with a very good accuracy at both full and partial load. Then, the engine has been simulated on a grid of 15 operating points, representing the usage in the New European Driving cycle. The following configurations have been analyzed and compared to the base engine: 4 active cylinders, 3 active cylinders; 4 active cylinders and optimization of valve timings; 3 active cylinders and optimization of valve timings.
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