Water-in-diesel emulsion and microemulsion fuels -The effect of water on emission levels

Licentiate thesis, 2008

Water-in-diesel emulsions are known as environmentally favourable alternatives to conventional diesel fuel. Introducing water into the combustion results in reduced emissions of the health hazardous components nitrogen oxide (NOx) and particulate matter (PM). The concept of using emulsions is advantageous as it is easy to replace regular diesel. In this thesis combustion of water-in-diesel emulsion and microemulsion fuels is investigated with respect to emission levels and the result is compared with that of regular diesel. An emission study in a heavy-duty diesel engine revealed a large difference in soot emissions between the emulsion and microemulsion fuels on the one hand and regular diesel on the other hand. Regarding NOx emissions the engine combustion study showed only small differences between the fuels. The reasons for the effect of water on emissions are discussed. In addition, the water drop sizes in the two types of fuels have been determined from diffusion coefficient data measured by nuclear magnetic resonance (NMR) diffusometry. A more in-depth study of water-in-diesel microemulsions, with the same surfactants as in the emission study, was performed in order to identify the microemulsion region of the system when varying the composition and temperature. The choice of surfactants was limited to nonionics, in order not to introduce any elements in the fuel that can give negative impact during combustion. The chosen surfactant combination, an alcohol ethoxylate and a sugar ester of fatty acid, resulted in a rather narrow microemulsion region, which increased in size with increasing surfactant concentration. The microstructure of the microemulsions was investigated by NMR diffusometry and revealed the presence of spherical water domains in diesel.