The effect of bowl-in-piston geometry layout on fluid flow pattern

Abstract

In this paper some results concerning the evolution of 3-D fluid flow pattern through all four strokes in combustion chambers with entirely different bowl-inpiston geometry layouts ranging from "omega" to "simple cylinder" were presented. All combustion chambers i. e. those with "omega" bowls, with different profiles, and those with "cylinder" bowls, with different squish area ranging from 44% to 62%, were with flat head, vertical valves, and identical elevation of intake and exhaust ports. A bunch of results emerged by dint of multidimensional modeling of non-reactive fluid flow in arbitrary geometry with moving objects and boundaries. The fluid flow pattern during induction and compression in all cases was extremely complicated and entirely 3-D. It should be noted that significant differences due to geometry of the bowl were encountered only in the vicinity of top dead centre. Namely, in the case of "omega" bowl all three types of organized macro flows were observed while in the case of "cylinder" bowl no circumferential velocity was registered at all. On the contrary, in the case of "cylinder" bowl some interesting results concerning reverse tumble and its center of rotation shifting from exhaust valve zone to intake valve zone during induction stroke and vice-verse from intake valve zone to exhaust valve zone during compression were observed while in the case of "omega" bowl no such a displacement was legible. During expansion the fluid flow pattern is fully controlled by piston motion and during exhaust it is mainly 1-D, except in the close proximity of exhaust valve. For that reason it is not affected by the geometry of the bowl.