Numerical Estimation of Asymmetry of In-Cylinder Flow in a Light Duty Direct Injection Engine with Re-Entrant Piston Bowl

摘要

Partially premixed combustion (PPC) can be applied to decrease emissions and increase fuel efficiency in direct injection, compression ignition (DICI) combustion engines. PPC is strongly influenced by the mixing of fuel and oxidizer, which for a given fuel is controlled mainly by (a) the fuel injection, (b) the in-cylinder flow, and (c) the geometry and dynamics of the engine. As the injection timings can vary over a wide range in PPC combustion, detailed knowledge of the in-cylinder flow over the whole intake and compression strokes can improve our understanding of PPC combustion. In computational fluid dynamics (CFD) the in-cylinder flow is sometimes simplified and modeled as a solid-body rotation profile at some time prior to injection to produce a realistic flow field at the moment of injection. In real engines, the in-cylinder flow motion is governed by the intake manifold, the valve motion, and the engine geometry. The deviation of the real in-cylinder flow from a solid body rotation flow field varies with different piston positions. This paper reports on an CFD study of the formation and development of a real engine in-cylinder flow field in an optical light duty PPC engine from the opening of the intake valve at -360 CAD ATDC up to 20 CAD ATDC in a motored case (without fuel injection). The focus is put on the analysis of the temporal and spatial development of the swirl flow motion. The resulting flow field of the simulation is compared with the results from CFD simulation of an initial axially symmetric (sector-mesh) flow in the cylinder. The adequateness of sector type mesh including solid-body rotation assumption as an initial flow is analyzed.