City Research Online

Abstract

Two 3-D six-hole transparent enlarged model injector have been manufactured with full optical access; both were 15 times larger than the real size, but one had a length-to-diameter ratio twice as the second one. The working fluid was water and aqueous solutions of glycerol circulating through the nozzle injector under steadystate flow conditions at different flow rates, pressures and needle lift positions. Real-time in-nozzle flow visualisations were obtained using a high speed video recorder which allowed determination of in-nozzle flow patterns, in particular, formation, dynamics and the development of cavitation. Simultaneous imaging of the flow inside the nozzle injector showed that reducing the needle lift would suppress the cavitation intensity in both models especially during early stage of cavitation causing a delay on its onset from a CN≈1.1 at full lift to CN=1.9 at 25% of the full. The main noticeable effect of L/D was found to be at the exit of the nozzles where different types of in-nozzle flow would be experienced due to different length of the nozzles with larger L/D having a more developed and stable cavitating flow and is expected to affect spray outside the nozzles. The effect of viscosity was only evident during early stage of cavitation with a delay on the onset of the cavitation and a less intense cavitation with blends at higher viscosities. The results also showed that an increase in temperature had the effect of enhancing cavitation due to lower viscosity and weaker molecular bounding.

Publication Type:	Book Section
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Engineering

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