Electric field-influencing combustion behaviors of droplets of ethanol, biodiesel and diesel

Abstract

The droplet combustion in an electric field is fundamental for the electrospray combustion. In this paper, experimental research was done to investigate the effect of the vertical electric field on the combustion behaviors (including the flame and droplet characteristics) of droplets of ethanol, biodiesel and diesel. The outcomes demonstrated that the flame morphology was controlled by the competition between the electric field force and natural buoyancy. As the electric field strength (E) increased, the upward flame (0 ≤ E < 100 kV/m), quasi-spherical flame (E ≈ 100 kV/m) and downward flame (100 < E ≤ 200 kV/m) successively emerged. This expressed as a decrease in upper flame heights and an increase in bottom flame heights. The fuel order of the flame height variation extent was ethanol < biodiesel < diesel. An increase before 100 kV/m and a decrease after 100 kV/m for the flame width existed, whose value variations were similar in all droplets. These differences in flame size had a direct impact on the magnitude of flame fronts, which in turn determined the area where the fuel vapor and oxygen reacted. Therefore, the combustion duration of the biodiesel and diesel droplets increased before 100 kV/m and decreased after 100 kV/m. Due to the downward movement of the electric arc, the combustion duration of the ethanol droplet increased with the electric field strength. The maximum increases in combustion durations of the ethanol, biodiesel and diesel droplets in the electric field could achieve 14.1%, 18.1% and 21.9%, respectively. This work supplies a further understanding of the droplet combustion in electric fields and the electrospray combustion.