New fuel polymer can cut pollution

Polyisobutylene is a polymer which, when added to petrol, can produce a 70% decrease in emissions of carbon monoxide, unburned hydrocarbons, and nitrogen oxides, says Paul Waters, a scientific advisor to General Technology Applications in Gainsville, the company that developed the additive. The polymer also produces a 10% increase in horsepower, and a 20% increase in fuel efficiency.

When fuel without the additive is sprayed into an engine’s combustion chamber, smaller hydrocarbons separate immediately from the larger ones, explained Waters, vaporising more rapidly and concentrating near the spark plug at ignition. Larger hydrocarbon molecules tend to form liquid films in the induction channel prior to the cylinder, and on the cylinder walls. The result is that the smaller molecules burn too quickly, causing an early high temperature spike which generates oxides of nitrogen, and often the larger molecules remain unburned. This situation also causes knock, poor effective pressure, and particulates.

To increase the amount of oxygen available for combustion, oxygenates such as MTBE are commonly added to gasoline. However, recent concern about the use of MTBE has been raised amid mounting evidence of groundwater contamination.

Rather than boosting the oxygen content, polyisobutylene changes the physical properties of the fuel. Once in the cylinder of an internal combustion engine, the additive acts as a deterrent to the formation of mist, reducing the separation of larger and smaller hydrocarbon molecules. This means that fuel burns more evenly and at a lower temperature, harvesting more energy and leaving fewer unburned hydrocarbons.

In two-cycle engines, the polymer significantly reduces raw-gas emissions, as well as noise.

The polymer can be used in all engines, from small two-cycle motors to large diesels, says Waters. Field tests are being conducted in California, Maryland and Wisconsin, as well as in China, Japan and Ireland.