Cleaning Up Combustion?

Oxonica cuts diesel consumption but runs into nanotech's environmental quandary.

A University of Oxford spinoff is securing deals in Europe and Asia for a technology that makes better use of today's diesel engines and fuels. Oxonica PLC claims that by facilitating combustion, its nanoparticle fuel additive boosts fuel efficiency an average of 5 percent and cuts soot emissions by as much as 15 percent.

CEO Kevin Matthews says diesel fuel spiked with Oxonica’s nanoparticle catalyst burns longer, boosting fuel efficiency and reducing tailpipe pollution. (Credit: Oxonica)

Last week, Oxonica announced its biggest deal yet: an additives-supply contract with Petrol Ofisi A.S., Turkey's largest fuel distributor, worth $12.7 million this year. The resulting fuel savings could equal 200,000 tons of CO₂ per year, according to Oxonica CEO Kevin Matthews. Ironically, a new set of environmental concerns around nanotechnology represent a serious hurdle to widespread acceptance of Oxonica's technology.

Oxonica's Envirox fuel-efficiency enhancer uses cerium oxide as a catalyst. This metal is one of several used in catalytic converters to reduce the amount of air pollution in engine exhaust. Cerium usually plays a supporting role to platinum, which is a more active catalyst but also more expensive. Fashioning cerium oxide into nanoparticles just 5 to 25 nanometers in diameter has given Oxonica two advantages: it has turned the cheaper metal into a highly active catalyst and produced it in a form that can be blended directly into the fuel.

Size matters, because a catalyst's activity is a function of its surface area, and the total surface area in a mass of particles rises exponentially as the mass of the individual particles decreases. As a result, only a small amount of the product is required; Envirox is blended into diesel fuel at a ratio of just 5 parts per million.

Matthews, an Oxford-trained chemist, says the cerium oxide nanoparticles promote a burn that's more evenly spread and longer lived. In a diesel engine, combustion occurs when the fuel injected into a cylinder is compressed. By spreading out the burn, the fuel-borne catalyst reduces the force exerted at the start of the burn, when the piston is still pushing into the cylinder--a moment when the diesel engine is fighting itself. "What you're getting is a transferal of the burn, so more of it occurs on the positive end of the cycle," says Matthews. Later in the cycle, the particles may make a noncatalytic contribution: by decomposing under the heat and pressure of combustion, the cerium oxide particles release some of their oxygen to feed the flame, combusting residual pockets of fuel.

Scott Anderson, professor of physical and analytical chemistry at the University of Utah, calls Oxonica's fuel-borne catalyst a "workable" idea, based on his own experience testing cerium oxide nanoparticles as catalysts for military jet fuel. "It's well known to be a combustion catalyst. If you put enough of it in, it will certainly increase the combustion rate and that should increase the combustion efficiency," says Anderson.