Abstract
In recent diesel engines, interference between a diesel spray flame and a cavity wall in a combustion chamber cannot be avoided by downsizing of the engine and increasing injection pressure. Therefore, part of heat generated by diesel combustion is lost to the wall. Reduction of its heat loss is an important technical issue for further improvement of thermal efficiency of the engine. The heat transfer between the flame and the wall depends on flow characteristics of the impingement spray flame near the wall. Therefore, it is important to understand flow structure of impingement diesel flame near the wall.By using a common rail direct fuel injection system, the spray impinged on the flat plate placed in the constant volume vessel under high temperature and pressure conditions. Tomographic images of impingement evaporated diesel spray were captured by a high speed camera. Ignition of the fuel was prevented by filling the vessel with N2 gas. 5%wt of silicon oil was mixed with diesel fuel as tracer particles for visualization of the evaporated diesel spray. The velocity distribution inside the spray near the wall was measured by using time-resolved PIV. The height distribution of the dimensionless velocity near the wall was evaluated and compared with the dimensionless velocity distribution in the velocity boundary layer on a wall placed in the uniform flow. As a result, it was found that the velocity distribution of the post-impingement evaporated spray showed a tendency similar to that of the turbulent boundary layer on a wall.
