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.