THE EFFECTS OF SWIRL AND TUMBLE ON COMBUSTION IN SPARK-IGNITION ENGINES

A review has been made of rotating flow (swirl and tumble) in premixed spark-ignition engines and its effects on turbulence generation and f lame propagation. Rotating flow can significantly increase turbulence intensity during the combustion period. This in turn can lead to a red uced burning period and increased thermal efficiency. Rotating flow, p ossibly in combination with squish, can be particularly important for combustion of lean mixtures or with alternative fuels of low laminar f lame speed. in general, rotating now can substantially increase flame propagation speed, reduce cyclic variations, and expand the lean limit , though excessive rotational motion can have deleterious effects on i nduction system flow resistance and also on heat transfer and thermal efficiency. Much research work has been devoted to swirl (rotational m otion around an axis parallel to the axis of the cylinder), but in rec ent years increasing attention has been paid to tumble (rotational mot ion around an axis perpendicular to the cylinder axis). Swirl and tumb le have distinctive characteristics and can interact differently with piston motion and squish. The optimum rotating now field may be a comb ination of the two kinds of rotational motion. The principal features of the mean velocity and turbulence fields associated with these rotat ional motions are reviewed, as well as the mechanisms for decay, gener ation, transport and enhancement of in-cylinder turbulence. Substantia l advances in experimental method and in numerical simulation are lead ing to better understanding of the effects of swirl and tumble on engi ne performance.