Cycle-resolved Computations of Compressible Vortical Flow in Cylinders of Engines

Abstract

Cycle-by-cycle differences of the flow in engine cylinders, that is, the cyclic variations, are analyzed in a fine grid system of about 1,000,000 grid points. A computational method without grid motions is employed on the basis of the multi-level formulation. We apply this method to a square-piston engine. First, we can see that the computational results obtained in an engine cycle agree well with the experiments using freon as the working fluid under the condition with a Mach number in excess of 0.5. Drastic transition to turbulence near TDC is also grasped by the computations and experiments. Next, the calculations are performed during three continuous cycles of the engine. The flow structure around the center of engine cylinder, that is, around the ignition point, varies cycle by cycle. The present cyclic variations of flow field may lead to combustion instability. It should be stressed that the present method clarifies the cyclic variations, although a lot of researches have been devoted for ensemble-averaged computations.