CFD Simulation and Optical Engine Diagnostics of Mixture Formation Processes in DI Gasoline Engine with Flexible Valvetrain

Abstract

The interactions of multi-hole direct injection (DI) gasoline sprays with the charge motion are investigated using computational fluid dynamics simulation and high-speed imaging of sprays inside engines. Advanced flexible valve-train, with valve-deactivation and variable valve-lift, produces very dynamic charge flow motions, with varying tumble and swirl ratios. The resultant turbulent flow interact with off-axis multiple-hole DI injections, has important implications for the engine mixing and resultant combustion performance. The effects of injection timing on the bulk flow motion and fuel-air mixing in an optical accessible engine, in terms of tumble and swirl ratios, turbulence, and fuel wall film behaviors are first discussed for the conventional baseline engine geometry. The early-and latevariable intake valve closing events are then tested in a metal engine. The effects of different valve lifts and valve deactivation on the mixing and combustion are then discussed. Using integral analyses of the simulation results, the mechanisms in reducing fuel consumption and emissions in a variable valve-actuation engine, fuelled by side-mounted multi-hole DI injectors are illustrated. The implications to the engine mixing and the resultant combustion in a metal engine are demonstrated.