Development of Intake and Exhaust Stroke Flow Simulation in an Engine Cylinder Using CFD Model

The intake and exhaust stroke flow simulation in an engine cylinder illustrates some of the transient, dynamic-mesh features, event handling, moving grids and cell attachment/detachment by setting up and solving a simplified port-valve and piston problem using STAR-CD computational fluid dynamics. The problem is twodimensional and represents a simplified four-stroke engine. The simulation commences at bottom dead centre (BDC) and continues for a time interval corresponding to 720 of crank revolution. Inert scalars with the physical properties of air are used to track the intake and exhaust stream through the exhaust induction strokes in engine cylinder. The flow in engine cylinder is turbulent and driven entirely by the motion of the piston and valves. The port boundary pressures are held constant at ambient condition throughout the simulation. Mesh design in problems with a moving mesh and changing cell connectivity is dominated by the need to keep the dynamic parts of the grid simple so that they can be easily changed during the transient run. The formulation of mesh motion in such problems is divided into two conceptual steps. The first deals with connectivity changed which are defined by PROSTAR events. The second step is to specify the grid vertex positions as function of time by supplying a set of PROSTAR gridmanipulation commands to be executed at each time step. In this model the exhaust valve opens within the first 147 and closes linearly by 282. The intake valve begins to open at 395 and closes by 530. The piston motion is prescribed by setting the standard kinematics parameter for the connecting rod length, the crank radius and the top dead centre position (TDC).

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