MIT engine boosts mileage by 30 percent
Precisely timed blast of ethanol eliminates knocks in experimental engine that would add only $1,000 to cost of car.
The engine, which is only about half the size of a conventional gas engine, could be on the market in about five years and could add about $1,000 to the cost of a car. That's less than the $3,000 to $5,000 added by a hybrid engine. Thus, consumers will recover the cost more quickly (because the engine uses less gas) and get about the same mileage as a hybrid.
If all of today's engines had the technology, MIT estimates, it could cut U.S. auto fuel consumption from 140 billion gallons to 110 billion gallons annually.
The ethanol injection suppresses the spontaneous combustion inside the cylinder. Spontaneous combustion creates an aggravating knocking sound, but with the knock eliminated, engine manufacturers can then adopt two design conventions common in diesel engines. With one, the engine can be highly turbocharged, which means that more air and fuel can be squeezed into the chamber.
Also, the engine can be designed with a higher compression ratio (the ratio between the compression chamber before and after compression). This allows the gas to expand more, releasing more energy.
With more gas working more efficiently in the chamber, mileage goes up about 30 percent. Leslie Bromberg and Daniel Cohn, at MIT's Plasma Science and Fusion Center, and John Heywood, director of the Sloan Automotive Lab and professor of mechanical engineering, have run simulations, and Ford is testing the concept with Ethanol Boosting Systems, the company formed by the three.
Gasoline and the ethanol would be kept in separate tanks.
"To actually affect oil consumption, we need to have people want to buy our engine, so our work also emphasizes keeping down the added cost and minimizing any inconvenience to the driver," said Cohn in a prepared statement.