Figure 11. Mass of Entrainment air of the free spray

Figure 12. Mass of entrainment air of the spray impinging at

L_w = 10 mm

Figure 13. Mass of entrainment air of the spray impinging at

L_w = 30 mm

Figure 14. Mass of entrainment air of the spray impinging at

L_w = 50 mm

　

Moreover, comparing with previous data in Figs. 5, 6 and 7, spray tip penetration of impingement spray became surely shorter as wall distance decreasing. However as shown in Figs. 8, 9 and 10, the spray volumes increased with the wall distance decreasing.

　

3.3 Entrainment air

Next, we inquired into entrained air mass so as to know practical utilization of surrounding air after impingement. The results are shown in the following four figures(Fig.11 - Fig.14). The entrained air mass was calculated as follows.

m_ent = p_aV_a (4)

Where, p_a was the density of ambient gas, V_a under each experimental condition. Mass of entrainment air of the free spray under injection period of 2.8 ms is shown in Fig.11. In this figure, the sprays injected into ambient pressure of 0.5 MPa and 1.0 MPa were lost sight after 1.0 ms and 1.6 ms, respectively. The reason was that the sprays under these pressures increased rapidly, and then, the spray tips went over the view field of pressure vessel. This tendency appeared in Figs. 12-14. However we could grasp the increasing tendency of entrained air as time elapsed. In figure 11, the entrainment air at 1 ms from injection start was about 40 mg. At that time, the fuel mass injected from nozzle was about 10 mg as shown in Fig.2. Therefore, air-fuel rate became 4, which seemed very dense spray. Then, the dense spray had air-fuel rate of 9.25 at 2 ms from injection start. Finally, the value of air-fuel rate became 15.45 at 2.8 ms in which the injection period was finished. Figure 12 shows the mass of entrainment air of L_w = 10 mm impingement sprays under injection period of 2.8 ms. The entrainment air mass at 1 ms from injection start was 140 mg, so the air-fuel rate became 14 that was much higher than the free spray. Furthermore, the value of air-fuel rate around 2 ms from injection start became more than 20. Comparing with Fig.11, the entrainment air increased much higher in the condition of L_w = 10 mm than other conditions tested.

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