Influence of signal properties on electrohydrodynamic primary break-up of thin sheets of dielectric liquid

Abstract

In industrial air blast atomizers, the fuel is injected at low pressure through an annular slot. This produces a tubular sheet of fuel which is disintegrated into droplets by two coflowing airstreams. Unfortunately, a high air velocity is needed in order to obtain a fine atomization. This is the main drawback of air blast atomizer. With an air velocity below 30m.s-1 the atomization is too weak for fuel ignition. This problem could be encountered in relight ignition at high altitude, where the pressure and the temperature are very low. When the air velocity is below 10m/s the sheet of fuel is not sprayed anymore. This paper is an experimental study of the primary break-up induced by an ElectroHydroDynamic actuator. Experiments have been performed on thin sheet of commercial diesel oil without active surface agent. The flow rate and the liquid sheet thickness are similar to the ones used in turbo engines. In the present work, the sheet of fuel is directly destabilized and disintegrated by an electrohydrodynamic actuator. Atomization is only due to electrical forces and the air velocity is equal to zero. As there is no coflowing airstreams and as the fuel is injected at low pressure, the liquid sheet is stable when the EHD actuator is turned off. Investigations on the primary break-up characteristics have been made with a high speed camera on the break-up length and on the spray cone angle, for various signal frequencies and amplitudes. The liquid velocity ranges from 0.6 to 2 m.s-1 In industrial atomizers, the fuel is injected through an annular slit. Such device produces a thin turbular sheet of fuel. This shape is very efficient for atomization but difficult to investigate. More than a decade of studies in atomization process has proved that mechanism of disintegration are similar on cylindrical and planar thin sheet of liquid. Fig.1 shows a schematic diagram of the experimental setup. The fuel is pumped from a tank to the injector. The flow rate is controlled by .