Microemulsions are alternatives to emulsions as a means to
incorporate water in a fuel. The terms “microemulsion” and
“emulsion” seem to imply that such systems are very similar,
differing just in the size of the dispersed component, but that is
not the case. There are several fundamental differences between
a microemulsion and an emulsion and the most important characteristics
of the two types of systems are summarized in Fig. 6
[50].
Microemulsion-based fuel formulations date back to 1976
when Gillberg and Friberg published a paper on the use of waterin-
diesel microemulsions as fuel [51]. Since microemulsions
consist of much smaller domain sizes than emulsions, one may
anticipate that they are superior to emulsions with regard to the
atomization process but there are indications that the opposite
holds true. As mentioned above, Qingguo and Gollahalli have
reported that macroemulsions, i.e., normal emulsions, produced
smaller drops in the flame than microemulsions [37]. In the
experiments they used 10% water in so-called Jet-A fuel in both
types of formulations. The general characteristics of emulsions
Fig. 6.