Figure 8. The comparison of spray volumes at injection period of 1.8 ms
Figure 9. The comparison of spray volumes at injection period of 2.8 ms
Figure 10. The comparison of spray volumes at injection period of 3.8 ms
The impingement times of sprays were changed from 0.097 ms to 0.637 ms according the distances of the wall. In this figure, break-up length of the free spray was about 40 mm. As for the sprays impinging at Lw = 10 mm and 30 mm, wall impingement occurred at before the break-up. On the other hand, the sprays of Lw = 50 mm and 70 mm impinged at after the break-up.
In the cases of Lw = 10 mm and 30 mm, it was confirmed that the volumes of post-impingement sprays increased remarkably than those of free sprays. The spray impingement to the wall of Lw = 10 mm was on-set after 0.097 ms elapsed from injection start. Here, the spray volume did not increase in the instance of impingement. Up to the 0.4 ms elapsed from the injection, the spray volume grew up nearly with the free spray. Then it began to increase more and more as the time elapsed. Also, spray which was impinged at 0.352 ms to the wall of Lw = 30 mm proceeded almost with the free spray until 0.7 ms and then, the volume began to increase more and more as the time elapsed, although the increasing rate of spray volume was lower than that of Lw = 10 mm. In spite of the spray impinging before break-up, its volume did not increase for a short period. At that period, the spray path penetration increased less than that of the free spray as shown in Fig.5, and dense spray seemed to appear at the impingement point. Therefore, it was considered that the impingement spray had stagnated in the short period between the instance of impingement and beginning time of volume increase. As for combustion in small size DI diesel engine, it seemed that this stagnation period caused incomplete combustion or particulate emission.
On the other hand, in the case of Lw = 50 mm, the spray volume after impingement had lower value than that of the free spray. The spray was impinged after 0.637 ms elapsed from injection start, and it had relatively long stagnating or adhering period. After about 1.4 ms elapsed, its volume began to increase, but its rate was lower than that of the free spray.
The volumes of 2.8 ms- and 3.8 ms-sprays under ambient pressure of 1.5 MPa are shown in Figs. 9 and 10. As for the increasing tendencies of sprays impinging at Lw = 10 mm and 30 mm, the 3.8 ms-spray increased steeper than 2.8 ms-spray as the time elapsed. However, comparing with 1.8 ms-spray shown in Fig.8, both 2.8 ms- and 3.8 ms-sprays increased steeper than 1.8 ms-spray. It was considered that spray volume was influenced by both injection rate rise at the early stage and injection rate history. This result appeared in the case of Lw = 50 mm as well. That is to say, the volume of 2.8 ms-spray impinging at Lw = 50 mm began to increase slower than that of free spray. However the volume of 3.8 ms-spray of Lw = 50 mm began to increase steeper than that of the free spray.
In figures 8 and 9, the data of volumes of free sprays tended to be scattered since the injections were finished at 1.8 ms and 2.8 ms, respectively from injection start. In a sense, these scattering data might be represented the irregularity of the spray development[12]. In figure 10, all of the data including the free spray ones rarely scattered. The reason seemed that the 3.8 ms-spray had long injection period with keeping the high injection rate.
From Figures 8, 9 and 10, it was confirmed that the spray volumes after impinging at Lw = 10 mm and 30 mm increased than those of the free spray. Also, as the distance from nozzle tip to the wall became shorter, the spray volume became increasing. With regard to spray volume, it was concluded that the spray impinging to a vertical wall before break-up increased more than the free spray, which meant sufficient utilization in space of combustion chamber.
