Droplet evaporation modeling of electrified fatty acid methyl esters

Abstract

The influence of electric charge on the evaporation characteristics of fatty acid methyl ester fuels from short to long carbon chain length is simulated using a validated evaporation model. A fuel droplet is assumed to undergo electrostatic fragmentation or fission in a manner which results in a large ‘residual’ droplet and a number of other smaller ‘sibling’ droplets, as has been experimentally observed in previous work. Droplet evaporation simulations are performed both for a non-reacting case and for a case where the sibling droplets burn at the adiabatic flame temperature. The simulations are complemented with measurements of biodiesel spray current taken from a charge injection atomizer, so as to enable use of experimentally measured charge as an initial condition in the simulation. Charge advantageously influences the evaporation time, particularly under the assumption that generated sibling droplets undergo combustion. The influence of charge, droplet Reynolds number and the physical properties of the methyl esters are examined, demonstrating similar overall behaviour among fuels, however showing that time histories are grouped by carbon chain length. The experimental data indicates that specific charge is a key driver behind reducing evaporation time as Reynolds number increases. However, the relationship between charge influence vs. Reynolds number diminishes in situations where sibling droplets burn. This contribution sheds light on the influence of electric charge on the vaporization of biodiesel fuels, and provides useful data which can guide future interpretation of charge influence on vaporization in reacting and non-reacting environments.