Burning characteristics of ethanol droplet suspended on NiCr wire with applied AC electric field

Abstract

The effect of applied AC electric field on the burning behavior of ethanol droplets suspended on a NiCr wire (0.5 mm in diameter) was investigated by varying the AC frequency fAC (10–1000 Hz) and voltage VAC (1–7 kV). In the baseline case without applying electric field, internal recirculation was developed by heat transfer through the wire to the droplet due to Marangoni convection, enhancing the evaporation rate. Depending on VAC and fAC, three regimes can be identified: vertical oscillation of the droplet due to the combined effects of vertical electrostatic and ielectrophoretic forces (Regime I), combined oscillation and dripping, leading to electrospray of fine droplets from the surface by electrostatic force (Regime II); flame extinction due to substantial fuel loss via electrospray (Regime III). Ethanol droplets exhibited distinct dynamic behaviors from previously studied burning n-decane droplets, primarily due to the differences in fuel permittivity (affecting dielectrophoretic force) and electric conductivity (influencing dielectric relaxation frequency), both of which were not considered previously. Force-based scaling analysis revealed differences in oscillation amplitude and droplet response, and captured the onset conditions for dripping and extinction with fAC,cr ∼ V− p AC, in good agreement with experiments. The normalized droplet lifetime correlated strongly with key physical parameters, including the radial electric field gradient, AC frequency, and flame width and height.