CHARACTERISTICS OF ADHESION DIESEL FUEL ON AN IMPINGEMENT DISK WALL. PART 3: AMBIENT PRESSURE EFFECT

Wall impingement of fuel spray is known as the main contributor to DI diesel engines with small combustion cavities. Recently, high boost intake air charging has been adopted in the diesel engine for higher power and better performance including low emissions. Consequently, the compressed air density in the cylinder is becoming high, and it seems that this high density surrounding air has a greater effect on the impingement behavior of fuel sprays. Therefore, under high gas density conditions, precise investigation of impingement fuel sprays is needed. In this paper, the effect of ambient pressure and injection pressure on the adhered fuel mass of normal impingement diesel sprays was investigated experimentally. Nonevaporated diesel spray was injected into a high-pressure vessel, and the spray impinged to a flat wall was placed in the vessel. The ambient pressure in the vessel was set from 0.1 to 4 MPa. The mass of the disk with adhered fuel was measured using an electronic balance, and the fuel mass adhered on its surface was evaluated. As a result, it was found that the adhered mass ratio decreased with an increase of ambient pressures from 0.1 to 1 MPa. However, at ambient pressure over 1.0 MPa, the adhered mass ratio became almost constant for a condition of 30 mm impingement distance but it still decreased under longer impingement distances such as 90 mm. Under long impingement distances, adhered fuel mass in high ambient pressure conditions such as 4 MPa was half of that under 1 MPa conditions. Moreover, the height of the impingement spray changed in various ways under various ambient pressures. It had partial correlation with adhered mass ratio. The result also shows that adhered mass was greatly affected by the Weber number which was obtained with impingement velocity and the Sauter mean diameter of the spray. Finally, the jet number was introduced to summarize the effects of ambient pressure and impingement Weber number on adhered mass ratio.