Effects of swirl and tumble on mixture preparation during cold start of a gasoline direct-injection engine

The effects of intake-generated swirl and tumble on cold start performance have been investigated in a firing single-cylinder Gasoline Direct-Injection (GDI) engine. The engine utilizes a Ford Zetec cylinder head modified for GDI operation and a fused silica cylinder which provides extensive optical access to the combustion chamber. Uniquely designed port-inserts were positioned in the intake ports to generate enhanced swirling or tumbling motion inside the cylinder. Experiments were conducted using a constant speed (∼ 900 rpm) simulated cold start procedure, where the engine is motored for approximately 40 cycles, after which fuel injection and spark ignition commence and continue for 190 cycles and then the engine is stopped. Measurements were made of the various engine temperatures, engine-out total hydrocarbon emissions, and in-cylinder pressure throughout the test period. The engine combustion quality during cold start was quantified by the amount of accumulated engine-out hydrocarbons over the test period for each flow system. The pre-combustion, in-cylinder fuel distribution was also visualized using two-dimensional laser-induced fluorescence and evaluated in terms of fuel vaporization and fuel-air mixing. The results show that both swirling and tumbling motions enhance fuel vaporization and fuel-air mixing and result in better cold start performance of the GDI engine. Another advantage of utilizing swirling or tumbling motion is that ignition timing can be delayed, due to faster burning, which allows more time for fuel vaporization and fuel-air mixing.