Water-in-diesel microemulsions studied by NMR diffusometry

Water-in-diesel microemulsion fuels are attractive in that they are thermodynamically stable and visually similar to regular diesel. This is contrary to water-in-diesel emulsion fuels, which are inherently unstable and have a milk-like appearance. Both emulsion- and microemulsion-based fuels give large reductions in soot emissions in combustion. In this work microemulsions have been formulated with nonionic surfactants and with varying amounts of water and the microemulsion regions have been determined in the temperature interval from 17 to 50°C. The extension of the microemulsion regions has been assessed with amount of surfactant, type of surfactant and temperature as parameters. The internal structure of the microemulsions has been investigated by NMR diffusometry by which the diffusion coefficients of diesel hydrocarbons, water and the surfactants are determined. The diffusometry measurements indicate that the water is present as spherical water domains. They also show that as the amount of water increases, the water domains first swell and then increase in number.