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The Gasoline Wars

Oil companies use additive packages to help their fuels stand out from the crowd

by Michael McCoy
April 6, 2009 | A version of this story appeared in Volume 87, Issue 14

Credit: Michael McCoy/C&EN
Shell is making a big splash with its Nitrogen Enriched Gasolines.
Credit: Michael McCoy/C&EN
Shell is making a big splash with its Nitrogen Enriched Gasolines.

CHEVRON WITH TECHRON! BP gasoline with Invigorate! And here's a new one: Nitrogen Enriched Gasolines from Shell!

Fuel additives have some pretty hokey names, but behind them is real chemistry. It's aimed both at problems that lurk under the hoods of today's automobiles and at the wallets of drivers who are asked to pay more for brand-name gasoline.

The latest entry in the additive name game is Shell Oil's line of nitrogen-containing fuels. Shell unveiled its Nitrogen Enriched Gasolines brand last month at gas stations across the U.S. The roll-out comes with ads that feature lab-coated scientists standing in front of a zig-zaggy molecule. They are holding examples of the clean intake valves drivers will enjoy if they use Shell gasolines blended with a new nitrogen-containing detergent compound.

With the new additive, Shell joins BP, which has been rolling out its Invigorate additive formula at U.S. gas stations for the past several months. The granddaddy of fuel additives is Techron, a 30-year-old Chevron brand that was broadened to Texaco fuels after the two firms merged in 2001. It will get a marketing push this spring.

Of the three marketing approaches, Shell's evokes chemistry most vividly. Jens Mueller-Belau, the firm's fuels portfolio and category manager in North America, says this is no mistake. "We did a lot of research with consumers on whether we should brand it with a name that doesn't mean anything, or describe the concept," he says. " 'Nitrogen-enriched' instantly resonated."

According to a press release accompanying Shell's launch, "Nitrogen is a key element of the active cleaning molecule in the new fuel." The release explains that nitrogen makes the additive more stable at the higher temperatures common in modern automobile engines.

Shell won't say much more about the molecule. When pressed, Jim Macias, technology manager for Shell fuels, will disclose only that the detergent molecules added to fuels typically have an oligomeric backbone and polar functionality. "There's a lot of thinking about nitrogen—strategic placement in the molecule and optimizing the amount," he says.

Although the molecule in the enriched Shell fuels may be new, it turns out that almost all detergent additives contain nitrogen—and have for a long time.

In the 1960s and early 1970s, low-molecular-weight amines were used to control carburetor deposits, according to Thomas Zahalka, technology manager for gasoline additives at Afton Chemical, a leading fuel additives manufacturer. Although these amines were effective in the relatively cool region around the carburetor, Zahalka says, they were not stable on the hotter surfaces of the fuel intake valves.

Hardier polybutene amine detergents arrived in the early 1970s. In 1980, Chevron patented a next-generation cleaning approach based on polyether amines (PEAs). Even though the patent has since run out, Peter Fuentes-Afflick, a senior scientist at Chevron's research center in Richmond, Calif., says no other major gasoline marketer uses PEAs.

This is to Chevron's advantage, Fuentes-Afflick claims, since PEAs clean better than the polybutene amines and so-called polybutene Mannichs that he says most competitors employ. Competing technologies clean valves and injectors well, he says, but tend to contribute to deposits in the engine's combustion chamber. "Because of the backbone of our chemistry, it exothermically breaks down in the combustion chamber," he says.

REGARDLESS of the chemistry, oil companies brand additive packages to distinguish their fuels from each other and from nonbranded gas that typically sells for less. Although the Environmental Protection Agency requires all fuel marketers to include an additive package, Shell's Mueller-Belau points out that almost half of them are adding it at levels that are at or near EPA's minimum standard.

In fact, detergent levels dropped far enough earlier this decade that in 2004, automakers BMW, General Motors, Honda, and Toyota got together to create a standard for gasoline detergents called Top Tier. Marketers seeking to qualify their fuels as Top Tier Detergent Gasoline must pass tests for intake valve cleanliness, fuel injector fouling, and the like. Chevron and Shell are on the list, but other big brands like BP and Exxon are not.

Afton's Zahalka explains that detergents are the workhorse of an additive package that also includes carrier fluids, solvents, and corrosion inhibitors. The carrier fluids are thermally stable polymeric compounds that provide a liquid medium in which the detergents can remove carbon deposits from engine surfaces.

Like the surfactants found in laundry detergents, fuel detergents contain both hydrophobic and hydrophilic domains. "But unlike typical surfactants, which come in many chemical flavors such as cationic, anionic, zwitterionic, and nonionic, only 'basic nitrogen' can function in the very severe environment found in the intake system of an engine," Zahalka says. "These detergents are unlike anything seen in the world of aqueous surfactants."

Besides competitive pressures, one of the reasons the big gasoline companies are emphasizing additives these days is the arrival of new direct fuel-injection engines. According to the automotive consulting firm CSM, direct-injection engines are expected to represent 20% of the world's new passenger car market this year, rising to 50% by 2014.

In conventional engines, the fuel injectors are behind the air intake valves, whereas in direct-injection engines they are down in the hot combustion chamber itself. The result is a more efficient combustion process that yields greater power, greater fuel efficiency, or some of both.

Gasoline marketers like to point out that these gains come at a cost. Shell's Mueller-Belau explains that the fuels in such engines labor under double the temperature and hundreds of times the pressure they do in conventional fuel-injected engines. The upshot is increased risk of carbon deposit buildup. Macias, "his team, and our partners looked for detergents that can hold up under these conditions," he says.

Likewise, at Chevron, Fuentes-Afflick argues that because more of the action in cars with direct-injection engines is taking place in the combustion chamber, Techron is especially beneficial for them.

Oil company claims aside, are additive-enhanced fuels worth it? Carlton H. Jewitt, head of Jewitt & Associates, thinks so. Before retiring 10 years ago and starting his own consulting firm, Jewitt was manager of fuels technical service at Ashland Oil. His job was to evaluate and test additives and issue recommendations to management.

According to Jewitt, modern, computer-controlled engines demand a good deposit-fighting additive. "As new engine technology develops in an effort to squeeze more harmful emissions out of the tailpipe, it's all that much more important that these engines are kept clean," he says.

Like the chemical and oil companies in the business, Jewitt is mum about the exact chemistry of fuel additives, but he does note the wide range of options—some that are more effective than others. And although he won't name names, Jewitt makes a telling remark about his own fuel-buying practices. "I and my wife limit our vehicles to certain brands of gasoline," he says.


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