This thesis focuses on the effect of initial ambient turbulence on the spray characteristics of fuel injected into a constant volume. The investigation is performed experimentally and computationally. The spray axial penetration length and radial penetration width, area and velocity are used as key parameters to characterise the spray in the experimental work together with vapour fuel mass fraction, mean droplet diameters and number of droplets in the computational work. In the experimental study, the liquid fuel (iso-octane) is injected, using a high pressure swirl atomiser, into ambient nitrogen with different prescribed nearly isotropic turbulence levels, characterised by the root mean square (RMS) turbulence velocity. Mie scattering laser sheet and Schlieren techniques are combined with a high speed camera to capture images of the vapour and liquid phases simultaneously as a function of injection pressure and ambient turbulence. These indicate that the latter has a significant influence on tip penetration length, penetration width, cross sectional area and velocity. Increased initial ambient turbulence levels lead to reductions in the penetration length in the axial direction and increases in the penetration width in the radial direction; it is also shown to improve fuel evaporation and mixing. In the computational investigation, the commercial Computational Fluid Dynamics code Fluent is used to explore the effect of the RMS turbulence velocity in a constant volume vessel on the spray characteristics of liquid fuel injected into it. The theoretical results are compared with corresponding experimental data obtained for the case of iso- octane fuel injected into nitrogen; the main features of sprays are successfully predicted. The results show how increased ambient turbulence level in the gas into which fuel is injected influences spray atomisation, break-up and evaporation and leads to reduced vapour penetration length and sauter mean droplet diameter, together with increasing vapour penetration width and number of fuel droplets. Additionally, the effect of injection pressure, ambient density and ambient temperature on spray characteristics is investigated at quiescent and turbulent ambient conditions; in which case increasing the injection pressure leads to increases in both the penetration length and the number of droplets, and a corresponding reduction in the sauter mean diameter.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:582124 |
| Date | January 2012 |
| Creators | Mohamed, Ibrahim Elsayed Elbadawy Ahmed |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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