Design and experimental characterization of electrostatically assisted automotive fuel injectors.

摘要

With current automotive fuel injector designs, fuel mass and momentum cannot be independently controlled during engine operation. By introducing electrostatic charge to the fuel as it is injected, a means of altering the injector spray pattern without changing the mass injected is available. A commercially available automotive fuel injector was modified to apply electrostatic charge to the fuel spray. The resulting electrostatically charged sprays were compared to non-charged sprays from the same injector using a Mie scattering technique to image the spray, Fraunhofer diffraction to measure droplet size, and particle image velocimetry to measure droplet velocities. Results showed application of charge results in increased spray penetration during early injection, increased droplet axial velocities, and reduced spray-to-spray variations in droplet size. Measurements of the charge transferred by a spray indicated relatively weak electrostatically induced forces relative to inertial forces, but showed that conductivity enhancers or alcohol blended fuels can substantially increase charge transfer. The effect of charge on the combustion process was investigated by capturing high speed video of charged and non-charged droplets composed of blends of ethanol and isooctane. Substantial changes in droplet morphology depending on the polarity of the charge applied were found. In addition, to test charged sprays in a practical combustion system, an engine test cell was constructed using a spark ignition engine typical of current designs for automotive use. Findings indicate that application of charge to the injector can increase peak cylinder pressure and reduce unburned hydrocarbon emissions a small amount with the trade off of a slight increase in emissions of oxides of nitrogen.