Figure 9 Typical injection rate shaping (4 kHz fluctuation, Average injection rate 4 g/s)
Figure 9 shows a typical example of fuel injection rate shaping with periodical fluctuation of injection rate, average injection rate of 4 g/s, frequency of 4 kHz and fluctuation amplitude of 2 g/s. The injection nozzle used in these experiments was a single hole type one with a hole diameter of 0.28 mm and L/D of 4. The injection pressure was 30 MPa and the fuel was injected under atmospheric conditions.
The effects of the amplitude of fluctuation on the maximum spray width at two frequencies, 1 kHz and 2.4 kHz, are shown in Fig.10. As shown in this graph, the spray width increases with the amplitude of fluctuation, resulting in the widely dispersed spray. However, since the degree of the effect changes with the frequency, we need to explore the effects of the frequency in the future study.
Figure 11 shows the high speed cross-sectional images of sprays with and without fluctuation. In order to visualize the cross-section of spray, the spray was illuminated by a light sheet of Ar laser and photographed with ICCD camera. In the case of the spray with 6.8 kHz fluctuation, Fig.11 (b), three images were captured within one period of fluctuation. As shown in Fig.11 (b), in spite of the small amplitude of fluctuation, 0.5 g/s in this case, it seems like a pulsating spray that a large cloud of droplets was ejected periodically. Though the dense and long liquid core apparently exists at the quasi-steady spray as shown in Fig.11 (a), the liquid core becomes shorter at the spray with fluctuation. These widely dispersed spray and shortened liquid core have possibilities of favorable effects on spray combustion, which has to be clarified by future study.
