The Turbocharged GDI – The Competitor to the Diesel Engine?

Authors

Dr. G. K. Fraidl, Dr. P. Kapus, Dr. W. Piock, AVL List GmbH, Graz

Year

2005

Print Info

Fortschritt-Berichte VDI, Reihe 12, Nr. 595

Summary

The combination of direct injection and turbocharging is not only the main reason for the success of the Diesel engine, but also basis for efficient fuel economy concepts with the gasoline engine. Even under the restriction to proven technologies like homogeneous GDI, double continuously variable cam phaser and single scroll turbocharger with fixed geometry, a highly cost effective fuel economy concept was created that offers similar CO2 emissions like the Diesel engine combined with better vehicle performance and significantly lower production cost. Besides the improvement of part load efficiency based on the combination of double cam phaser, high charge motion level and direct injection, shifting of engine operation towards higher engine loads is the basis not only for lower fuel consumption in the NEDC-test, but also for improved real world fuel economy. The best trade-off between fuel economy and vehicle dynamics, especially take off, is offered by a significantly longer drive ratio and only moderate downsizing. For a sufficient customer acceptance of long drive ratios not only the steady state and transient torque behaviour at low engine speeds was significantly improved, but also the nominal speed was shifted towards lower numbers offering constant power over a wide speed range. Due to the shifting of engine operation towards higher engine loads, the efficiency improvement within this load range becomes essential. Whereas most of the established fuel economy technologies for Gasoline engines are not very effective at high loads, with the selected base configuration a relatively simple external cooled EGR offers additional fuel economy benefits up to 4 % at high loads. The fuel economy concept presented is not targeted towards gaining maximum possible efficiency improvement just combining various expensive technologies, but is clearly focussed on a most cost effective volume engine, that becomes a real alternative to the Diesel engine with respect to CO2 emission and fun to drive, however, at significantly lower production cost.

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