Influence of Wall Properties on the Characteristics of a Gasoline Spray After Wall Impingement 2004-01-1951
Interest in spray-wall interactions has grown because of the development of direct-injection stratified-charge (DISC) spark ignition (SI) engines. In this type of engine, impingement of the spray on the piston wall often leads to high emissions of unburned hydrocarbons and soot. These emissions have proven to be one of the major drawbacks of the DISC SI engine, so it is important to obtain detailed knowledge about the different processes involved in spray impingement and their effects.
In this study, the size and velocity of droplets reflected from a wall were characterized by Phase Doppler Anemometry (PDA). The impinging spray was also visualized using an AVL VisioScope. The experiments were carried out on a real gasoline spray impinging on a wall under simulated engine conditions in a spray chamber. A sensitivity analysis was carried out to investigate the influence of different wall properties and wall temperature, on the impingement and secondary atomization processes. The influence of bulk air properties and impingement angles were also investigated.
From the visual investigation it was discovered that most of the reflected drops were transported away from the impingement point by a wall jet just above the wall. Very few drops bounced away from the wall with a large reflection angle. There were no visual changes when wall temperature and surface roughness were changed. The PDA-measurements detected a shift in the drop size distribution of the secondary reflected spray towards smaller diameters compared to the incoming spray, but the influence of wall properties was weak. A tendency was also found for the secondary break-up at the wall to decline as the surrounding pressure was increased.