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In order to improve low speed torques, turbocharged gasoline direct injection (TGDI) engines often employ scavenging with a help of variable valve timing (VVT) controlled by the cam phasers. Scavenging improves the compressor performance at low flows and boosts low-speed-end torques of the engines. Characteristics of the engine combustion in the scavenging zone were studied with a highly-boosted 1.5L TGDI engine experimentally. It was found that the scavenging zone was associated with the highest blowby rates on the engine map. The blowby recirculation was with heavy oil loading, causing considerable hydrocarbon fouling on the intake ports as well as on the stem and the back of the intake valves after the engine was operated in this zone for a certain period of time. The low-speed pre-ignition (LSPI) events observed in the engine tests fell mainly in the scavenging zone.

The present paper is Part II of an investigation on the influences of the late intake valve closing (LIVC) and the early intake valve closing (EIVC) on the engine fuel consumptions at different loads and speeds. The investigation was conducted with two 1.5L turbo-charged gasoline direct injection (TGDI) engines, one with a low-lift intake cam and the other with a high-lift intake cam. The focus of this paper is the cylinder charge motion. Computational fluid dynamic (CFD) analyses were conducted on the characteristics of the cylinder charge motion for the load points 6 bar-bmep / 2000 rpm, 12 bar-bmep / 3000 rpm, and 19 bar-bmep / 1500 rpm, representing naturally aspirated and boost-mode operations without and with scavenging during the valve overlap.