Emulsified Fuels are emulsionscomposed of water and a combustible liquid, either oil or a fuel. Emulsions are a particular example of a dispersion comprising a continuous and a dispersed phase. Most commonly used emulsion fuel is water-in-diesel emulsion. In the case of emulsions both phases are the immiscible liquids, oil and water. Emulsion fuels can be either a microemulsion or an ordinary emulsion. The essential differences between the two are stability and particle size distribution. Microemulsions are isotropic whereas macroemulsions are prone to settling and changes in particle size over time. Both use surfactants and can be either water-in-oil, or oil-in-water or bicontinuous.
Applications
Water continuous emulsified fuels are exemplified by the Orimulsion system and bitumen emulsions. These are often described as a high internal phase emulsions because the continuous phase is around 30% of the composition of the fuel it is more usual for the dispersed phase to be the minor component. Water continuous emulsions of very heavy crudes, bitumen are easier to pump than the original fuel, which would require considerable heating and / or dilution with a distilled product in order to make them easy to handle. Water continuous emulsions of residual fuel, heavy fuel oilsetc. which have a calorific value and are used in industrial applications can also be converted to emulsified fuels, thus reducing the need to use cutter fluids and improving the combustion emissions associated with the inferior fuels. Oil continuous emulsified fuels are exemplified by diesel and water emulsions. These emulsified fuels were recognized in Europe and CEN workshop standard was established. Other types of fuels have been emulsified contain between 5 and 30% water in the overall fuel emulsion. Water-in-diesel fuel emulsion could be used as an alternative fuel for low emissions and high brake thermal efficiency. Microemulsions of fuels have also been prepared. The type of surfactants and quantities required to make these emulsion fuels sets them apart from other commercial emulsion fuels. These are considered where safety issues or commercial return justify the extra costs.
Theory
The main advantages to using emulsified fuels instead of the fuel itself are environmental and economic benefits. Addition of water to the diesel process decreases combustion temperatures and lowers NOx emissions. A paper compares water injection and emulsified fuels into diesel engines and discusses the emissions and mechanisms involved. It concludes that emulsified fuels are singularly effective in simultaneously reducing NOx and PM emissions. Another paper has examined the effects of EGR and Emulsion Fuels.
