What is "white diesel"?

White diesel is the trade name of a fuel for diesel engines mostly used in public transport.
It is a stabilized emulsion of water in diesel, that is a mix in which the water, in the form of very fine particles, is uniformly distributed within the diesel giving it a ‘whiteish' appearance. The stabilization is achieved by using particular tensio-active substances that allow the emulsion to remain unaltered for a sufficiently long period of time (several months).

The recent interest in these emulsions as an alternative to diesel in a number of sectors is the result of the capacity of the water, once inside the combustion chamber, to reduce some of the toxic emissions such as sulphur oxide and particles.