Fuel emulsions and microemulsions based on Fischer–Tropsch diesel

Emulsions and microemulsions of water in Fischer–Tropsch (FT) diesel have been investigated regarding microstructure and emissions from combustion. Both the emulsions and the microemulsions were formed with only nonionic surfactants in order not to introduce other elements than C, O and H. The microstructure and the drop dimensions were investigated by means of NMR diffusometry and, for the emulsions, also with light microscopy. The water drop sizes in the emulsions were overestimated by the NMR method compared to the light microscopy. The NMR investigation of the microemulsions indicated that when small amphiphiles were used in the formulation a highly dynamic system formed compared to microemulsions formulated with more traditional surfactants, like sorbitan monooleate and long-chain alcohol ethoxylates. Combustion experiments were performed with emulsions of FT-diesel and of regular diesel and the emissions of nitrogen oxides and soot were monitored and compared with the levels obtained with water-free diesel. The emissions from combustion of FT-diesel in a standard diesel engine gave lower levels of nitrogen oxides and soot compared to regular diesel. Introducing water in the form of an emulsion gave a strong further reduction of the soot level.