Fluid Dynamic Study of Unthrottled Part Load SI Engine Operations with Asymmetric Valve Lifts 2009-24-0017
This paper describes how a fully three-dimensional CFD model was used to investigate the turbulence generation mechanisms of an unthrottled 4 valve SI engine operating with different intake valve lift strategies (symmetric and asymmetric). In the context of Early Intake Valve Closure (EIVC) strategies, the aim of the work is to highlight the potentialities to increase turbulence levels also at light load using asynchronous intake valve lift, thus promoting both tumble and swirl motions.
Six simulations are presented, four at low engine speed (2500 rpm) and two at high speed (6000 rpm, that serve as reference), concerning an SI engine at full and light load, with symmetric and asymmetric intake lifts. One of these simulations was executed in standard throttling conditions.
The CFD transient simulations involved three strokes of the engine: exhaust, intake and compression up to combustion TDC. 1D data are used for boundary and initial conditions. Experimental steady state flow test data are also used for a preliminary assessment of the CFD model capability.
It is shown that, at equal engine load achieved with EIVC strategies, the case with a single valve lift yields higher turbulence intensities than dual symmetric lifts.