Fuel-Spray/Charge-Motion Interaction within the Cylinder of a Direct-Injected, 4-Valve, SI Engine

The mixture preparation process was investigated in a direct-injected, 4-valve, SI engine under motored conditions. The interaction between the high-pressure fuel jet and the intake air-flow was observed. Laser-sheet droplet imaging was used to visualize the in-cylinder droplet distributions, and a single-component LDV system was used to measure in-cylinder velocities. The fuel spray was visualized with the engine motored at 1500 and 750 rpm, and with the engine stopped. It was observed that the shape of the fuel spray was distorted by the in-cylinder air motion generated by the intake air flow, and that this effect became more pronounced with increasing engine speed. Velocity measurements were made at five locations on the symmetry plane of the cylinder, with the engine motored at 750 rpm. Comparison of these measurements with, and without, injection revealed that the in-cylinder charge motion was significantly altered by the injection event. After injection, droplets were preferentially transported towards the exhaust side of the cylinder, rather than towards the intake side. This study suggests that the fuel-spray and in-cylinder charge motion are coupled and that it is not possible to accurately model one in the absence of the other.