Bioalcohol Electrosprays for Practical Propulsion Systems

Electrosprays of ethanol, 1-propanol and 1-butanol were studied experimentally at flow rates ranging from 5 to 25 mL/h, and voltages ranging from 3 to 6 kV, spraying along and against the direction of gravity. To study the general spray phenomenology and to provide measurements of the size and velocity of droplets, high-speed movies were taken of the light scattered by the spray from a planar laser sheet. Four modes of spraying were obtained when spraying along the direction of gravity. However, when spraying against the direction of gravity, another five modes were observed. The values of the measured velocities corresponded to low Reynolds numbers and low Nusselt numbers but high convective heat transfer coefficients. Electrical conductivity played a major role in bioalcohol electrospraying, but viscosity had a negligible effect. The possibility of coupling electrostatic spraying with combustion was established experimentally by performing burning experiments at 4 kV and 10 mL/h. Two distinct modes of flame were observed when burning the electrosprays, first a large diffusion flame and then a flat flame near the ground plate. The group combustion number calculation showed that the flame burned in a group combustion mode.