Nitrogen in gasoline: Does it cause pollution?

Some oil companies are adding nitrogen to their gasoline. But does it cause pollution as well as boost performance a bit?

Taylor Weidman/The Christian Science Monitor
A customer at a Shell station in Boston, Mass. Shell uses nitrogen enriched gasoline to help keep engine parts clean.

Q: Since nitrogen oxide compounds are components of smog and are common water pollutants, does nitrogen-enriched gasoline create additional pollution?

Rick Oestrike, Poughkeepsie, N.Y.

A: It might seem as if adding nitrogen to gasoline is all the rage among oil companies today, but the idea has been around for years. The US Environmental Protection Agency (EPA) requires that automotive fuels sold in the United States contain detergents to help scrub away pollution before it goes out the vehicle’s tailpipe. Some manufacturers have found that adding nitrogen to the detergent helps keep an engine cleaner by reducing the carbon buildup in the gas tank that can in turn “gunk up” the engine and lower performance.

The nitrogen itself also has a direct cleaning effect, breaking down carbon deposits that can harden on an engine’s moving parts. “If too much collects, this gunk can negatively affect engine performance, causing your car to burn more oil, overheat, and burn gasoline less efficiently,” reports John Fuller on the How Stuff Works website.

Valves inside an engine are designed to let in a specific amount of air and fuel, he adds. When that process is slowed by carbon buildup, a car won’t perform up to its potential.

But while nitrogen-enriched gasoline may provide a slight bump in engine performance, some worry about adding to cars’ already substantial pollution load, especially nitrogen oxide (NOx), which contributes to smog, acid rain, and other environmental problems.

André L. Boehman, a Penn State University engineering and fuel science professor, says that the addition of more nitrogen to the fuel mix “generally will increase NOx emissions.” Professor Boehman would like to see more research done so we can know for sure if (and how much) additional NOx pollution is caused by the use of nitrogen-enriched gasoline.

Shell Oil, which last spring launched its own form of nitrogen-enriched gasoline now for sale in all three grades of gasoline the company sells at its US service stations, denies that the additional nitrogen has any substantive impact on pollution levels. “Most nitrogen in vehicular NOx emissions does not come from gasoline,” the company told The New York Times. “The nitrogen is primarily from the incoming air that mixes with gasoline inside an engine. NOx is produced when the nitrogen from the air reacts with oxygen under high engine temperature and pressure conditions.”

Boehman concedes that “the detergent additive may have such beneficial effects on engine operation, fuel system performance, and other related features of engine system operation that they outweigh the adverse effect” of increased NOx emissions. “For instance, if improved detergency helps to increase fuel efficiency so that you burn less fuel, you may slightly increase the NOx emissions rate per gram of fuel burned, but end up with lower NOx because you burned fewer grams of fuel.”

That said, some environmentalists believe that it’s a good idea to avoid putting nitrogen in your fuel unless you’re sure the gains will outweigh the detriments. And until researchers know more, drivers might want to focus instead on minimizing their vehicles’ overall gasoline consumption and fuel efficiency – and on substituting other cleaner forms of transportation (walking, cycling, mass transit) whenever possible.

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