Large eddy simulation of motored engine

Large Eddy Simulation (LES) with Smagorinsky model is sued to simulate the induction-compression processes of a motored engine within a cycle. A diesel engine constructed with swirl-generating port and dish-type combustion chamber is used as the model engine. For high Reynolds number flow, the wall-function fitted to generalized curvilinear coordinate is proposed in this paper in order to overcome the over-fine grids arrangement near wall region. In order to restrain the non-physical pressure oscillation, which is the fatal drawback in co-located grids layout used in the present study, the odd-even pressure coupling mode is developed. LES results are compared with PIV experiment. The most important result is that the curves of swirl number and turbulence intensity against crank angle are obtained. Swirl velocity is formed by tangent designed port, but is strengthened by the impingement of discharge onto piston surface. The deceleration of piston transfers downward moment into swirl moment. Swirl number reaches its peak value at 120°CA and maintains 2/3 of this peak value to TDC of compression stroke. Turbulence intensity from angle- averaged field is intensified by moving piston and intake-valve, but is decayed by viscous dissipation. At the end of compression stroke, turbulence intensity is only remained at 1/10 of the value in induction process. So the squish flow generation by combustion bowl is expected for waking up turbulence of in-closed flow.