42287-G9
Experimental Investigation of the Effect of Electrostatic Fields on Electrically Charged Sprays of Liquid Fuels at Elevated Pressure and Temperature
Electrostatic fields were shown to affect combustion, especially of relatively high conductivity fuels such as the recently emerging bio-fuels, such as ethanol and the recently emerging butanol. Specifically two lines of experimental work were pursued: On the one hand the combustion of suspended, single droplets of ethanol and ethanol-gasoline blends was studied and it was shown that flame structure could be drastically altered by the application of appropriate electrostatic fields. On the other hand, the injection of diesel/ ethanol blends from practical injectors was studied and it was shown that ethanol content can drastically increase mixture conductivity and therefore allow for the effect of electrostatic field on the spay to be enhanced.
Specific achievements up-to-date
Establishment of electrostatic effects on droplet combustion. Experimental findings were provided on the effect of electrostatically charging the fuel on single-burning droplet combustion in normal gravity. It was established that significant modification of the flame morphology and the droplet burning time can be achieved, solely on account of the droplet charge, without the application of external electric fields. Negative charging of the droplets of mixtures of isooctane with either ethanol or a commercially available anti-static additive generated intense motion of the flame and abbreviated for certain blend compositions the droplet burning time by as much as 40%. Positive charging of the droplet generated almost spherical flames, because electrostatic attraction towards the droplet countered the effect of buoyancy. By comparing combustion of droplets of the same conductivity but different composition, coupling of electrostatics with combustion chemistry was established.
Ethanol-diesel electrostatically assisted sprays. An experimental investigation of electrosprays of ethanol-diesel blends and electrostatically assisted injection of ethanol and ethanol-isooctane blends was performed in order to investigate the potential of novel injection techniques for ethanol-containing fuels. An exponential dependence of liquid fuel conductivity on ethanol content was established. Simple, fundamental electrosprays of ethanol-diesel blends containing 5-15% ethanol exhibited micro-dripping atomization and produced sprays that approached the monodispersity that has been observed for pure ethanol sprays operating in the cone-jet mode. Experiments were also performed with ethanol and ethanol-isooctane blends on a commercially available swirl-type fuel injector that was modified with a conductive cap in order to electrostatically charge the fuel emerging from it. Electrostatically charged ethanol sprays penetrated in the ambient gas significantly less at the early stage of injection, especially for lower injection pressures. Additionally, the angle formed by the hollow cone of spray was larger for the charged sprays. Such effects are expectedly diminishing with decreasing alcohol content.
Butanol electrosprays. The possibility of producing butanol efficiently with the use of fermentation processes has been recently demonstrated. This could potentially lead to the production from renewable sources of a fuel that has energy density significantly increased with respect to the currently widely used ethanol. We provided preliminary experimental results on the structure of butanol electrosprays with a particular emphasis on the determination of the dependence of droplet size on mass flow rate and applied electric field. In parallel, a comparison was provided with the electrosprays of low conductivity fuels for which data are available from previous published studies. These preliminary results showed significant differences from low-conductivity fuel electrosprays that practically produced monodisperse aerosols. This is a strong indication that the “cone jet” mode that has been used extensively with hydrocarbon electrosprays may not be sustainable for butanol sprays. The results were rationalized in terms of an experimental study of the dependence of butanol conductivity on applied voltage.
Broader impact of the performed research
The performed research has characterized thoroughly electrostatics as a potential tool for automotive injection and combustion. This is particularly true for the emerging field of bio-fuels some of which (e.g. ethanol, butanol) are particularly appropriate for electrostatically assisted atomization. Three graduate student were educated in this technology (M.S. Agathou, E.K. Anderson, and D.S. Elegant), one of whom was supported with PRF funds. (E.K. Anderson) The PI and his students co-authored 7 journal and 6 conference papers on the subject of the project. Three undergraduate students (S.Gast, A. Black, and Jeremy Koch) were involved in the project through independent studies that were supervised by the PI. Messrs Gast and Black were supported by a SUMR supplement initially designed for Mr. Gast’s support. His commitment left resources for the support of a second student also eligible under the SUMR criteria. The fruitful collaboration with a group in the University of
