Figure 15. The comparison of mass of entrainment air on injection period of 2.8 ms
Figure 16. The comparison of mass of entrainment air on injection period of 1.8 ms
Figure 17. The comparison of mass of entrainment air on injection period of 3.8 ms
It suggested that the free spray had a core region, and a distribution of the droplets in this region was dense, but the dense core region could break up to fine droplets by spray impingement.
The entrained air mass at Lw = 30 mm was plotted against time from injection start. It is shown in Fig.13. The air-fuel rate at 1 ms and 2 ms from injection start was 8.5 and 15.75, respectively. Also, the entrainment air in the figure increased steeper than that of the free spray, but grew up slowly than that of the spray impinging at Lw = 10 mm. Figure 14 shows the entrainment air of the spray impinging at Lw = 50 mm. The air-fuel rate at 1 ms, 2 ms and 2.8 ms from injection start was 5.5, 8.5 and 11.85, respectively. Comparing with Fig.11, the entrainment air of this impingement spray increased slowly than that of the free spray. It was considered that the spray impinging at Lw = 50 mm had no effect on increasing of entrainment air.
In order to study the entrained air mass quantitatively, the increasing tendencies of these four figures on 2.8 ms-sprays were summarized in one figure. The result is shown in Fig.15. Also, for the comparative study, the entrainment air of the free spray is expressed as broken line. As the injection period was short, the break-up length got gradually shorter. However regarding the break-up length, all the free spray had more than 40 mm. So, in the case of Lw = 10 mm and 30 mm which corresponded to the impingement before break-up, the entrained air quantity became twice or more higher than that of the free spray around 1.5 ms from injection start. On the other hand, in the case of Lw = 50 mm, which was recognized to be slightly longer than break-up length, the entrainment air after 1.9 ms from injection start grew less and less with comparison of the free spray, although the entrainment of before 1.9 ms was higher than that of the free spray.
Figure 16 shows the entrainment air on injection period of 1.8 ms. With regard to increasing tendency, this figure is almost similar to Fig.8. Each curve increased slowly in comparison with that of 2.8 ms-spray shown in Fig.15. It seemed that the higher injection rate rise at the early stage resulted in an increase of entrained air. Also, in the sprays of Lw = 10 mm and 30 mm impingements, entrainment air increased steeper than that of the free spray. In the case of Lw = 50 mm, the entrained air increased less than that of the free spray. It seemed that this result was caused by both short injection period and lower injection rate rise at the early stage.
Figure 17 shows the comparison of entrainment air on injection period of 3.8 ms. The increasing rate of entrainment air was the highest in the results obtained under this experimental condition. Also, the spray of Lw = 10 mm and 30 mm impingements had the larger value in comparison with the value of the free spray. In the spray of Lw = 50 mm impingement, the slope of entrainment air increased with that of the free spray. The reason was considered that the 3.8 ms-spray had long injection period.
In figure 15, 16 and 1 7, it meant that increment of spray volume resulted the increment of the entrained air. It was considered that if the injection rates at early stage were the same with each other, the entrainment air after that stage was dependent on injection rate history. Also, this result could be explained by the fact that the liquid column before break-up made a reflecting or roll-up as it impinged on the wall[6]. On the other hand, it seemed that the complete spray after break-up was cohered or stagnated on the vertical wall.
