Water-in-diesel emulsions and related systems

Water-in-diesel emulsions are fuels for regular diesel engines. The advantages of an emulsion fuel are reductions in the emissions of nitrogen oxides and particulate matters, which are both health hazardous, and reduction in fuel consumption due to better burning efficiency. An important aspect is that diesel emulsions can be used without engine modifications. This review presents the influence of water on the emissions and on the combustion efficiency. Whereas there is a decrease in emissions of nitrogen oxides and particulate matters, there is an increase in the emissions of hydrocarbons and carbon monoxide with increasing water content of the emulsion. The combustion efficiency is improved when water is emulsified with diesel. This is a consequence of the microexplosions, which facilitate atomization of the fuel. The review also covers related fuels, such as diesel-in-water-in-diesel emulsions, i.e., double emulsions, water-in-diesel microemulsions, and water-in-vegetable oil emulsions, i.e., biodiesel emulsions. A brief overview of other types of alternative fuels is also included.