Diesel Spray Impingement Behavior and Adhering Fuel on a Recessed Wall

Characteristics of fuel adhering after wall impingement of diesel spray were investigated experimentally. A flat wall, a recessed-wall which has a conical opening at impingement point, and a rugged-wall which has many concentric circular grooves, were used as an impingement wall. Diesel spray was impinged vertically to the wall in a high pressure chamber under a cold state. The spray behavior impinged on each of the three types walls was observed using a drum camera, which allowed high speed photographs. The spray after impingement on the recessed-wall was reflected from the wall with rolling-up motion, while the spray impinging on the flat wall was expanded along the wall surface to the radial direction. So, the recessed-wall might be expected to control the spray attitude in real engines. The spray height on the recessed-wall was higher than that on a flat wall. The amount of fuel stuck on each wall was measured by a precision balance. In order to inquire into the detailed characteristics of adhering fuel, the adhered fuel was measured by means of dividing into two types; the fuel film itself and the sparsely adhered fuel encircling with the film. Adhering fuel ratios on three types walls were calculated, and they were compared each other. In the case of the recessed-wall, the post-impingement spray was reflected toward the direction of the spray axis, and so adhering fuel in the vicinity of the fuel film became decrease. It contributed to decrease of entire adhering fuel mass. As a result, the adhering fuel ratio of the recessed-wall was smaller than that of the flat wall. On the other hand, adhering fuel ratio of the rugged-wall was more than that of the flat wall, because of the grooves' effect.