Better than Hybrids

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The system would use relatively little ethanol, about 1 gallon per 20 gallons of gasoline, so Cohn estimates the separate ethanol tank would have to be refilled about as often as an oil change. Furthermore, since it would require relatively minor modifications to existing technologies, Cohn says the design could be in production vehicles as soon as 2011 -- with the help of a recent collaboration between their startup, Ethanol Boosting Systems (EBS), Cambridge, MA, and Ford Motor Company, Dearborn, MI.

The MIT researchers estimate their engine would add only $500-1000 to the cost of a vehicle, which includes the added costs of the high-end turbocharger, a direct-injection system, and a stronger, smaller engine. This modest premium compares favorably to that of hybrid cars. According to a review in Consumer Reports (April 2006), some hybrid vehicles failed to pay for themselves over the course of five years, even when factoring in federal tax credits and gas prices that rise to $4 a gallon. In contrast, Cohn says, their engine would pay for itself in two to three years.*

This modest premium compares favorably to that of hybrid cars. According to a review in Consumer Reports (April 2006), some hybrid vehicles failed to pay for themselves over the course of five years, even when factoring in federal tax credits and gas prices that rise to $4 a gallon. In contrast, Cohn says, their engine would pay for itself in two to three years.

The new engine should be 30 percent more efficient than conventional engines, based on a computer model the researchers say accurately reproduces the behavior of internal-combustion gasoline engines. In comparison, a Toyota Prius gets about 30-35 percent better fuel economy than a comparable vehicle, according to tests by Consumer Reports. In the same review, the magazine showed a $5,700 price premium for the Toyota Prius over a conventional vehicle.

Rodney Tabaczynski, former director of powertrain research at Ford (who is not involved with EBS), says the ethanol "will definitely help the octane problem" and existing electronic controls and feedback systems should make the controlled injection feasible.

The challenges EBS is likely to encounter he says, have more to do with logistics -- two fuel tanks in a vehicle can be hard to implement, and there's the challenge of making sure ethanol is available at the corner gas station. Also, the engine will need a system that ensures it isn't damaged if the driver forgets to fill the ethanol tank.

Tabaczynski also cautions that real fuel savings will depend on an individual's driving habits. As with hybrids, cars with these engines will get their best mileage when driven in a city, not at 70-75 miles per hour on the highway with the throttle wide open.

*Correction: The original version of this story quoted Consumer Reports as saying no hybrid made up for its cost premium over five years. CR has corrected that statement: two hybrids, the Toyota Prius and Honda Civic Hybrid save about $400 and $300, respectively, they say, albeit only after a sizable tax credit.