Browse Publications Technical Papers 2010-32-0067

Optical Characterization of PFI Gasoline Sprays: Effect of Injection Pressure 2010-32-0067

In the present study, PFI injectors which are suitable for small engines were characterized to study the effect of pressure on various spray parameters. Two plate-type PFI injectors were studied: one with two orifices, and the other with four orifices. The nozzle orifice sizes were determined by microscopy. The fuel quantity injected at pressures of 200 kPa, 500 kPa and 800 kPa, were measured by collecting the fuel, for injection pulses of different durations.
The spray structure of the PFI sprays was determined by shadowgraphy. A single pulsed Nd:YAG laser in conjunction with fluorescent diffuser optics was used as the light source for shadowgraphy. Backlit images of the spray were obtained at various times after the start of injection using a CCD camera. This was done for sprays at different pressures, and different pulse durations. The spray angle, and spray tip penetration were determined from the processed shadowgraphy images. The backlit images also showed insights into the development of the spray. It was observed that coalescence occurs, with liquid from the orifices merging early on to form a single core.
Droplet sizes were determined at various times after the start of injection. Shadowgraphy on small regions of the spray (~ 1.4 mm x 2.5 mm) was performed with backlighting with a pulsed laser and dye plates, and a long focal length microscope attached to a CCD camera. The droplet size distributions and variation of Sauter mean diameter (SMD) with time were determined at different pressures and spray durations. The SMDs were found to reduce significantly when the pressure was changed from 200 kPa to 800 kPa, with values dropping from around 140-180 micron to around 80-100 micron. The 4-hole injector was found to give smaller droplet sizes than the two-hole injector at the same injection pressures.


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