The 7000-strong Stagecoach UK bus fleet is now using nanoparticles of the Envirox oxidation catalyst as a fuel additive.
Envirox is based on a well-established oxidation catalyst but has now been formulated for use in diesel fuel at just five parts per billion without any need to modify the engine. The result is a cleaner and more complete combustion, which the company claims produces an up to 12% fuel saving as well as reducing carbon deposits in the engine and lowering emissions.
The fuel-borne catalyst is composed of particles of cerium oxide 10 nm across, a material commonly used in conventional catalytic converters to clean up vehicle exhausts. Cerium oxide catalyses the conversion of carbon monoxide and hydrocarbon gases to carbon dioxide and water. It also reduces nitrogen oxides.
Researchers have attempted to formulate the compound as a fuel additive before but have generally failed to improve on fuel efficiency or cut emissions. Cerulean believe they have circumvented the problems with their nanoscale approach because at this size, the catalyst remains evenly suspended in the liquid fuel.
Stagecoach intends to try the product in up to 1000 of its buses across the UK. According to Chief Executive Brian Souter, “We believe this new product has huge potential and we are delighted to once again be leading the way in the UK bus industry in developing new ideas.”
Cerulean International Ltd is a subsidiary of Oxonica Ltd an Oxford University spin-out company. Oxonica’s Christopher Harris recently patented an improvement to the Envirox system that uses an organic solvent system to comminute, or coat the nanoparticles with an organic anhydride or acid, an ester, or a Lewis base. This coating is intended to help the particles disperse still more evenly in diesel fuel.
The permutations for nanoparticles additives are not to merely coating cerium oxide. In the initial nanoparticle patent, Gareth Wakefield describes how the particles might also be doped with a divalent or trivalent metal or metalloid. Doping might improve the properties further, although Stagecoach will be trialling only the undoped version.
The original version of this article by David Bradley originally appeared in The Alchemist in October 2003.