Oil-in-water emulsified fuels, such as the
Orimulsion system and
bitumen emulsions, are examples of water-continuous systems. These emulsions are often considered high internal phase emulsions (HIPE) because the continuous phase makes up about 30% of the fuel composition, whereas the dispersed phase is usually the minor component. Emulsions of heavy crude oils and bitumen are easier to pump than their original forms, which typically require heating or dilution with light oils like
kerosene to facilitate handling. Emulsions of residual fuels, including heavy fuel oils used in industrial applications, can also be created to reduce the reliance on
cutter fluids and improve combustion emissions from lower-quality fuels. Water-in-oil emulsified fuels, such as diesel and biodiesel-water emulsions, are widely used in Europe, with standards established by the CEN workshop (CWA 15145:2004). These emulsions usually contain between 5% and 30% water by mass. Water-in-diesel emulsions can serve as alternative fuels, offering lower emissions and improved brake
thermal efficiency. Since 2006, Nonox Ltd. has offered on-demand water-in-fuel emulsions for heavy fuel oil (HFO) and diesel, used in shipping and stationary boilers. This approach, known as Emulsion to Combustion (E2C), allows for mixing without chemical surfactants, the adjustment of the water-to-fuel ratio based on load, and prevents separation during storage. This system has demonstrated reductions in soot emissions of up to 90% and
NOx emissions by 40%, while also delivering
fuel savings depending on baseline efficiency. Microemulsions of fuels have been prepared using specific types of surfactants, which differentiate them from other commercial emulsion fuels. These microemulsions are often utilized in contexts where safety (e.g., fire prevention;) or enhanced commercial returns (e.g., improved oil recovery using surfactant flooding;) justify the additional costs. ==Theory==