Interactions of Multi-hole DI Sprays with Charge Motion and their Implications to Flexible Valve-trained Engine Performance

Advanced valvetrain coupled with Direct Injection (DI) provides an opportunity to simultaneous reduction of fuel consumption and emissions. Because of their robustness and cost performance, multi-hole injectors are being adopted as gasoline DI fuel injectors. Ethanol and ethanol-gasoline blends synergistically improve the performance of a turbo-charged DI gasoline engine, especially in down-sized, down-sped and variable-valvetrain engine architecture. This paper presents Mie-scattering spray imaging results taken with an Optical Accessible Engine (OAE). OAE offers dynamic and realistic in-cylinder charge motion with direct imaging capability, and the interaction with the ethanol spray with the intake air is studied. Two types of cams which are designed for Early Intake Valve Close (EIVC) and Later Intake Valve Close (LIVC) are tested, and the effect of variable valve profile and deactivation of one of the intake valves are discussed. Multi-dimensional Computation Fluid Dynamics (CFD) results for predicting DI multi-hole ethanol spray behaviors are presented as well. The effects of injection timing on the bulk flow motion and fuel-air mixing, in terms of tumble and swirl ratios, turbulence, and fuel wall film behaviors are discussed. Combined with metal engine test results which run with gasoline, the important mechanisms for reducing fuel consumption and emissions in a SIDI, variable-valve actuated engine are demonstrated.