A Study on Charge Motion Requirements for a Class-Leading GTDI Engine

Paper #:
  • 2017-24-0065

  • 2017-09-04
An integral part of combustion system development for previous NA gasoline engines was the optimization of charge motion towards the best compromise in terms of full load performance, part load stability, emissions and, last but not least, fuel economy. This situation might have changed with the introduction of GTDI engines. While it is generally accepted that an increased charge motion level improves the mixture preparation of a direct injection gasoline engine, the tradeoff in terms of performance seems to become less dominant as the boosting systems of modern engines are typically sound enough to compensate the flow losses generated by the more restrictive ports. Certainly the increased boost level does not come for free. Increased charge motion generates higher pumping- and wall heat losses. Hence it is questionable and engine dependent, whether more charge motion is always better. Besides from the above mentioned tradeoff between pumping / wall heat losses and burn rate, emissions etc. another aspect is the optimum charge motion level for best knock performance at high load. A high charge motion level leads to a faster combustion and by that the knock critical endgas areas are burned faster. On the other hand the faster burn rate leads to increased pressure in the endgas area which then reduces the self-ignition time of the unburnt mass. Hence the optimum charge motion level to suppress knock is a parameter which needs to be tuned carefully. To understand the influence of charge motion level on fuel consumption, stability, emissions and performance, the very successful Ford 1.0l 3-cylinder Ecoboost® engine, which is available as gasoline engine in many Ford vehicles worldwide, has been modified, such that different tumble levels could be realized. Furthermore the intake side valvetrain system has been modified in a way that different opening timings of the both intake valves of one cylinder could be selected. By this measure both, the swirl level and the intake event could be varied. With the above mentioned engine hardware modifications this study investigates the influence of charge motion on important combustion characteristics. To improve the understanding of the dyno based results 1D and 3D simulations have been conducted. The results obtained during this project will be discussed in depth in this paper.
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