Dynamics of electrically charged transient evaporating sprays

Abstract

SUMMARYThe evolution of an evaporating spray plume typical of those under consideration for use in direct injection spark ignition (DISI) engines, for early and late fuel injection strategies is investigated. Here the effect of electric charge, present on individual drops, upon the spray dispersal and evaporation rate is investigated with the aim of optimizing these parameters with respect to typical engine timescales and injection strategy. The predictions suggest that applying electric charge to drops in sprays injected early into the intake stroke does not have a beneficial effect. The spray evaporation rate is not significantly enhanced, and the long time interval between fuel injection and ignition actually promotes spray wall deposition. Conversely, applying electric charge to sprays injected late encourages secondary atomization and the increase in surface area greatly improves the evaporation rate. This is also true at higher engine speeds, corresponding to a much reduced time between fuel injection and ignition. Therefore it is suggested that the selective use of electric charge is viable way of tuning the spray character without effecting fuel metering when moving from an early to a late injection strategy in DISI engines when variable loads are required.

Investigation on Electrostatical Breakup of Bio-Oil Droplets

“…In an ideal situation, when η Rayleigh limit coefficients, so found in our work, the Rayleigh limit coefficient η is equal to 0.592. This value of η is in agreement with the data given by Shrimpton who pointed out that these individually charged droplets usually break up at between 70% and 80% of the Rayleigh limit value, while the charged droplets within a spray plume can break up at 55% value of this limit [12]. …”

“…In fact, some literature has pointed out these individually charged droplets usually break up at a sub-Rayleigh limit [12,21], so the Rayleigh instability could be revised as the following equation:…”

“…In the past 30 years, fuel electrostatic atomization technologies have been developed for diesel, hydrocarbons, and ethanol [8][9][10][11][12][13]. Several researchers have extensively designed and tested several kinds of atomizers to comprehend the effects of parameters such as the nozzle geometry, electrode style, location relative to the grounded surface, orifice size, fuel viscosity, and other physical properties on the specific charge of the resulting spray [8,9,[14][15][16][17].…”

Modeling dielectric charged drop break up using an energy conservation method

“…Electrostatic atomization forms a number of fine, charged droplets [2] which disperse more readily than their uncharged counterparts [3], and may be directed by electric fields [4]. Such droplets are particularly well suited to coating applications such as painting, printing and crop spraying [5] as well more exotic applications such as combustion [6].…”

“…Many authors (e.g. [11]) have examined the dynamics of drop break up with much success, but to develop a sub-model for use in computational charged spray models [3] this approach is far too expensive in terms of computer resources. Roth and Kelly [12] proposed a model based simply upon mass, charge and energy conservation between initial and final energy states using the following assumptions:-We develop this model, only retaining assumptions (iii) and (iv) using the following energy conservation law, (1) Equation (1) states that the pre-break up drop surface (W S ) and electrostatic (W e ) energy is equivalent to the post break up surface and electrostatic energies of a residual drop (subscript 1) and n siblings (subscript 2), together with the stored energy due to the proximity of the charged products at break up.…”