Modulation of droplet trajectory using oscillating electric fields

The use of sinusoidal electric forces to modulate the location of charged fuel droplets in a channel flow configuration is studied as a potential technology to achieve control over fuel-air mixing. Trajectories of a single non-evaporating droplet are first investigated using both an analytical solution based on a linearised drag model and results obtained with a non-linear model for the drag force. Non-dimensional quantities are also introduced to generalise the problem and provide useful information for technology development. Then, the effects of oscillating electric fields on the dispersion and stratification of fuel vapour are investigated using large-eddy simulations. Kerosene is used as fuel, which is relevant for aviation applications. Results show that oscillating electric fields perpendicular to the bulk flow can significantly enhance the spreading of both droplets and fuel vapour, an effect that is more evident with decreasing angular frequency of the oscillation and decreasing flow bulk velocity. The effects of oscillating electric forces on the spreading of droplets become negligible above a given threshold of the angular frequency of the oscillations. Non-dimensional analysis shows that this threshold depends on both the intensity of the electric force and the gas-phase properties, in particular the dynamic viscosity. The distribution of droplets in the channel is characterised by regions of preferential concentration, where fuel vapour mass fraction tends to be higher. Results also demonstrate that the time-averaged local fuel-air mixing is significantly affected by the period of oscillations, evaporation timescale and residence time in the channel. The present investigation further supports the proposal of using electric forces to improve fuel-air mixing in liquid-fuelled combustors, opening up new possibilities for fuel-preparation systems based on electrohydrodynamics. • Modulation of the trajectory of charged fuel droplets using time-varying electric fields is proposed to achieve control over the fuel-air mixing. • A non-dimensional analytical solution is introduced to describe the trajectory of non-evaporating droplets. • The effect of angular frequency of the electric field oscillation on both droplets and fuel vapour dispersion is investigated. • Improved mixing in a confined region can be achieved for relatively low frequency of oscillations and low flow bulk velocity.