Characterization of Multi-hole Spray and Mixing of Ethanol and Gasoline Fuels under DI Engine Conditions

Because of their robustness and cost performance, multi-hole gasoline injectors are being adopted as the direct injection (DI) fuel injector of choice as vehicle manufacturers look for ways to reduce fuel consumption without sacrificing power and emission performance. To realize the full benefits of direct injection, the resulting spray needs to be well targeted, atomized, and appropriately mixed with charge air for the desirable fuel vapor concentration distributions in the combustion chamber. Ethanol and ethanol-gasoline blends synergistically improve the turbo-charged DI gasoline performance, especially in down-sized, down-sped and variable-valve-train engine architecture. This paper presents the spray imaging results from two multi-hole DI gasoline injectors with different design, fueled with pure ethanol (E100) or gasoline (E0), under homogeneous and stratified-charge conditions that represent typical engine operating points. Both high-speed Schlieren and Mie scattering results are presented for tests in pressurized chamber and optical accessible engine. Multidimensional Computation Fluid Dynamics (CFD) model for predicting DI multi-hole ethanol spray behaviors in optical engine is also discussed. The effects of injection timing on the bulk flow motion and fuel-air mixing, in terms of tumble ratios, turbulence, and fuel wall film behaviors are also discussed.