The STD Model I shows the smallest spray angle. This order is the same as that in the needle valve opening process.
5. CONCLUSIONS
Scale model experiments were made of flows in D.I. Diesel nozzles and their effects on spray behaviors. Transparent and ten times scale up model nozzles with various internal geometries were used. High-speed video observation was made of the flows in the sac chamber and the discharge hole of the model nozzles during the needle valve opening and closing processes. The sprays issued from the model nozzles were also observed. Main results are summarized as follows.
(1) The flow pattern in the sac chamber is relatively smooth in the initial stage of needle valve opening. Then the choke flow appears in the sac chamber around the time when the minimum cross sectional area of the flow passage switches from the needle valve seat to the discharge holes. In the latter half stage of needle valve opening, the relatively smooth flow pattern appears again which is similar to that in the steady flow.
(2) The liquid column without the breakup issues in the initial stage of needle valve opening. Then the disturbed spray with a large spray angle follows and passes over the initially issued liquid column. In the latter half of the needle valve opening, the spray angle becomes relatively smaller.
(3) The disturbed flow in the upstream of the discharge hole enhances the spray angle. Locating of the discharge hole from the bottom side to the upper portion of the sac chamber or adopting the VCO Model induce this effect.
(4) For the Mini Sac Model, when the needle lift is small, the spiral air cavities develop from the exit of the discharge hole to the inside of the sac chamber. The spray has a hollow cone structure with fine droplets and a very large spray angle.
(5) For all model nozzles, after the needle valve reaches the full lift, the cavitation films appear in the discharge hole, and repeat developing into the sac chamber, linking to each other, and shrinking in the sac chamber. Such cavitation films behaviors cause the fluctuation of the spray angle.
(6) For all model nozzles, the spray angle in the needle valve opening process increases first, takes a maximum, and then decreases to the value under the steady flow condition. In the needle valve closing process, the spray angle increases from that under the steady flow condition just before the closure of the needle valve, takes a maximum, and then suddenly decreases.
ACKNOWLEDGMENT
The authors would like to express their thanks to Mr. Taku Maeda and Mr. Masahiro Kamikawa, former graduate students in the Spray and Combustion Laboratory, University of Hiroshima, for their efforts in the experiment.
REFERENCES
[1] Hiroyasu, H. and Arai, M., SAE Paper, NO. 900475 (1990).
[2] Hiroyasu, H. et al., Proc. 5th ICLASS (1991), p.275.
[3] Soteriou, C., et al., SAE Paper, No. 950080 (1995).
[4] Chaves, H., et al., SAE Paper, NO. 950290 (1995).
[5] Xu, M. et al., Trans. of JSME, Ser. B, Vol.53, No.491 (1987), p.2214 (in Japanese).
