WASHINGTON -- Faced with a crop of lemons -- too much ethanol, a population of cars not tuned to burn it effectively and a driving public leery of the fuel's properties -- the Environmental Protection Agency is proposing to make lemonade.
The effort to untangle itself from this sticky situation is part of a larger proposal by the federal government to make the most sweeping changes in gasoline since lead additives were banned.
Tucked inside the E.P.A.'s March announcement of a plan to cut the amount of sulfur allowed in gasoline was an audacious suggestion that sought to solve all three ethanol challenges at once. The proposal, for a fuel that is 30 percent ethanol, could reduce tailpipe emissions and improve fuel economy -- and even encourage drivers to use more ethanol.
"You make the dog like the dog food," said William H. Woebkenberg, senior engineer for fuels policy in the United States at Mercedes-Benz.
The idea is that while today's typical pump blend -- E10, which is 10 percent ethanol and 90 percent gasoline -- has drawbacks, a blend of 30 percent ethanol and 70 percent gasoline could take advantage of ethanol's strengths. Unlike a flexible-fuel vehicle that can use E85 formulations but offers little financial or performance benefit, an engine tuned specifically for E30 would perform better on that fuel than on the standard E10, creating a market incentive.
The idea has widespread support among technical experts.
It also has another appealing aspect: current ethanol policy is probably unsustainable, because Congress has ordered the oil companies to use ever-larger amounts of ethanol. To comply with the mandate, ethanol levels would have to exceed 10 percent of each gallon of fuel, yet many automakers advise against using higher concentrations unless the car is equipped for it. With a declining demand for gasoline, the problem becomes more acute.
The 30 percent idea is laid out deep in the 938-page text of the proposed Tier 3 rule, which would lower the amount of sulfur in gasoline by two-thirds, to the level required in California. In the proposal, the E.P.A. asked automakers to comment on E30.
Like other efforts to introduce new fuels, it would require big investments at gas stations for blending pumps and storage tanks.
Still, there is a powerful incentive in the E.P.A. plan: offering automakers the option of having their cars certified on E30. Before a new car can be sold in the United States, the company must submit data on the vehicle's pollution output and fuel economy to the E.P.A. Certifying with E30 would call for engines optimized to take advantage of the blend's octane rating of 93 or perhaps higher.
Using high-octane premium-grade gas in an engine that does not require it offers no benefit. But in engines designed to squeeze the fuel-air mixture to very high pressures before igniting it with the spark plug, high-octane fuel burns predictably and can produce more horsepower. (On the other hand, burning low-octane gas in an engine tuned for premium grade can cause erratic combustion, or knocking, and result in severe engine damage.)
Ethanol contains only about two-thirds as much energy as gasoline, gallon for gallon. But if it is burned in engines designed for high cylinder pressures, it will produce competitive horsepower.
In general, the oil companies have opposed using higher concentrations of ethanol. The oil industry is trying to get Congress to change federal rules so they can use less ethanol, not more.
But various engine and fuel experts like the idea, because the E.P.A. is inviting the auto companies to take advantage of the good characteristics of ethanol, including an octane rating that is well over 100.
"That's getting smarter," said Margaret Wooldridge, a professor of mechanical engineering at the University of Michigan. The way ethanol is used now, she said, "if anybody does notice there's any ethanol in the fuel, it's always in a way that is negative."
The trouble with the flexible fuel vehicles on the market now, which can run at blends of up to 85 percent ethanol, is that they are still mostly optimized for gasoline, not ethanol, she said. While there are millions of such vehicles on the road, they run mostly on E10 because that is a better bargain for the driver.
Higher concentrations are no better, and ethanol companies are struggling for acceptance of E15 with drivers, who show little enthusiasm.
"E15 is the answer to the question nobody asked," said Mr. Woebkenberg of Mercedes-Benz. "It is a detriment."
But an E30 blend in an engine designed to use that fuel would be attractive to car buyers, he said, with "ridiculous power and good fuel economy," and owners of those cars would seek out the fuel, unlike owners of flex-fuel cars.
"I hope that the E.P.A. agrees to do it," said C. Boyden Gray, a former aide to President George H. W. Bush who is now a Washington lawyer representing energy clients. In coming years, Mr. Gray and others say, more cars are going to be engineered for high-octane fuel so they can get better fuel economy as automakers move to double economy, and high-octane fuel with 30 percent ethanol is cleaner than blends relying more heavily on gasoline.
But Mr. Gray and other experts said that the E.P.A. would probably have to do more than just give automakers the option to certify vehicles on E30; it would probably have to mandate its availability to give car shoppers confidence that they would be able to refuel such vehicles.
This article originally appeared in The New York Times.