Feasibility of using negative pressure for jet injection applications

We report on an experimental study of high-speed micro-scale liquid jets ejected into low-pressure environments, which has applications for the use of negative pressure modules in jet injector systems. The jets were impulsively started by the action of a stiff spring-piston and ejected through a narrow orifice, D₀ ~ 100 μm, into partial vacuums ranging from atmospheric pressure down to −80 kPa. We find that due to the high exit velocity, v_j ~ 100 m/s, the main jet stream is largely unaffected, but we reveal some fascinating fine features during the start-up phase, largely due to the presence of a small liquid volume pulled through the orifice prior to actuating the jet. In particular, as the pressure decreases, the start-up time increases and the initial spray becomes more pronounced. However, the primary outcome of this feasibility study is that use of negative pressures is viable for jet injector applications, and we hypothesize an optimal range of working pressures and configurations.