Effects of Swirl and Tumble on In-Cylinder Fuel Distribution in a Central Injected DISI Engine

The effect of the in-cylinder bulk flow on fuel distributions in the cylinder of a motored direct-injection S.I. engine was measured. Five different bulk flows were induced through combinations of shrouded and unshrouded valves, and port deactivation: stock, high tumble, reverse tumble, swirl, and swirl/tumble. Planar Mie scattering was used to observe the fuel spray movement in the centerline plane of a transparent cylinder engine. A fiber optic instrumented spark plug was used to measure the resulting cycle-resolved equivalence ratio in the vicinity of the spark plug. The four-valve engine had the injector located on the cylinder axis; the fiber optic probe was located between the intake valves. Injection timings of 90, 180, and 270 degrees after TDC were examined. Measurements were made at 750 and 1500 rpm with certification gasoline at open throttle conditions.

From the images it was found that the type and strength of the bulk flow greatly affected the spray behavior. Except for late injection, tumble tended to concentrate the fuel spray near the piston toward the exhaust side of the cylinder, while reverse tumble concentrated the fuel near the piston on the intake side. Strong swirl tended to concentrate the fuel spray along the cylinder axis and seemed to inhibit its radial outward diffusion. This conclusion was supported by the fiber optic probe measurements that showed significantly lower fuel concentrations near the spark plug with swirl, well into the compression stroke. It was also found that strong bulk flows can persist well into the compression stroke; movement of the spray by tumble and reverse tumble can be seen even at the late injection timing of 270 degrees. At TDC of compression, the pure tumble flow generated the highest fuel concentrations in the vicinity of the spark plug at both engine speeds and all injection timings. The swirl and swirl-tumble flows produced the lowest fuel concentrations near TDC; stock and reverse-tumble flows resulted in intermediate concentrations.