Flow and Mixture Distribution in a High-Speed Five-Valve Direct Injected Gasoline Engine

Abstract

The in-cylinder flow, spray dynamics, air-spray interaction, and fuel vapour distribution have been characterized in a motorcycle five-valve gasoline engine in terms of their effect on performance and emissions. A five-valve single-cylinder optical engine was employed which operated at speeds up to 3000 r/min in the close spacing configuration, with an early induction injection strategy using a centrally mounted swirl pressure atomizer. Particle image velocimetry, spray imaging in a spray chamber and in the engine, and planar laser-induced fluorescence revealed the importance of a strong and ordered in-cylinder flow for the efficient distribution of the liquid fuel throughout the cylinder volume and its complete evaporation prior to combustion, especially in the relatively low speed regime investigated. Furthermore, in the absence of a large-scale vortex structure during compression, incomplete mixing may still occur, resulting in mixture inhomogeneities and flow instability. Consequently, in contrast to port fuel injected engines, where good mixing could be achieved at high revolution rates, even with an unstructured flow, in direct injection engines an ordered flow structure is a prerequisite for efficient combustion and low exhaust emissions.