An Assessment and Comparison of De-Throttling Approaches and Technologies for Further Reductions in Fuel Consumption in a Modern GDI Engine

The paper outlines the fuel consumption benefits available from de-throttling technologies that can help to bring gasoline engine efficiency on a par with that of diesel engines. The paper shows the relative efficiency improvements offered by a fully-variable intake valve lift system in conjunction with wide-range cam phasers, which also incorporate the facility to provide zero valve lift to enable cylinder deactivation. Testbed results recorded with a prototype concept engine show the degree to which early intake valve closing, valve overlap and cylinder deactivation can work together, and the limitations of this synergy at different operating conditions. The paper demonstrates the potential of a production-feasible 2.0 litre Central GDI engine to deliver in excess of 105kW/litre, and yet to achieve less than 300g/kW.h BSFC at 2000/2.0bar BMEP with λ=1.0 fueling - an efficiency value which is competitive with diesel engine efficiencies, whilst offering the cleaner combustion, and simpler, more robust aftertreatment processes inherently afforded with positive ignition gasoline engines, utilizing pre-mixed flame stoichiometric combustion.