Experimental Investigation on the Gas Jet Behavior for a Hollow Cone Piezoelectric Injector 2014-01-2749
Direct injection of natural gas in engines is considered a promising approach toward reducing engine out emissions and fuel consumption. As a consequence, new gas injection strategies have to be developed for easing direct injection of natural gas and its mixing processes with the surrounding air.
In this study, the behavior of a hollow cone gas jet generated by a piezoelectric injector was experimentally investigated by means of tracer-based planar laser-induced fluorescence (PLIF). Pressurized acetone-doped nitrogen was injected in a constant pressure and temperature measurement chamber with optical access. The jet was imaged at different timings after start of injection and its time evolution was analyzed as a function of injection pressure and needle lift. The acquired PLIF images provide quantitative information about temporal evolution of the transient gas jet in terms of penetration length and jet width, while they qualitatively describe spatial distribution in terms of local gas concentration, estimated average jet concentration and jet volume. For all investigated operating points, the jet evolution followed a different trend than what is documented for circular nozzles. The investigated gas jets were seen to undergo two different stages during the injection: in the early stage, the gas jets showed a hollow cone nature and their cross-sectional area was characterized by two independent layers, which then merged into a single jet, representing the second stage of injection. Furthermore, increased injection pressures and needle lifts led to higher penetration lengths, jet widths, estimated volumes and average jet concentrations due to higher momentum. In particular, this study illustrated that both injection pressure and needle lift have more influence on the jet maximal width than on its penetration length. It was found that higher injection pressures and increased needle lifts lower the collapsing tendency of the gas jet toward the centerline.