A Comparative Study on Influence of EIVC and LIVC on Fuel Economy of a TGDI Engine Part II: Influences of Intake Event and Intake Valve Closing Timing on the Cylinder Charge Motion

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. Simulation results indicate that for all three load points, although the engine with LIVC may have a weaker charge motion in the intake stroke than that with EIVC, turbulence intensity for the charge motion in the engine with LIVC becomes greater in the compression stroke than that with EIVC. The higher the load, the greater the difference in turbulence intensities at the end of the compression stroke between the two engines. Simulation results provide an explanation to the observed phenomenon that combustion durations for the engine with LIVC were much shorter than those for the engine with EIVC under the same engine load.