MIT researchers are developing a half-sized gasoline engine that performs like a full-sized engine but offers fuel efficiency approaching that of today's hybrid engine system--at a far lower cost. The key is carefully controlled injection of ethanol directly into the engine's cylinders when additional power is required from the engine.
These small engines could be on the market within five years, and consumers should find them appealing: By spending about an extra $1,000 and adding a couple of gallons of ethanol every few months, they will have an engine that can go as much as 30 percent further on a gallon of fuel than an ordinary engine. If all of today's cars had the new engine, current U.S. gasoline consumption of 140 billion gallons per year would drop by more than 30 billion gallons. Moreover, the little engine provides high performance without the use of high-octane gasoline.
When the engine is working hard and knock is likely, a small amount of ethanol is directly injected into the hot combustion chamber, where it quickly vaporizes, cooling the fuel and air and making spontaneous combustion much less likely. According to a simulation developed by Leslie Bromberg, a principal researcher at MIT, with ethanol injection the engine won't knock even when the pressure inside the cylinder is three times higher than that in a conventional SI engine.
With knock essentially eliminated, the researchers could incorporate into their engine two operating techniques that help make today's diesel engines so efficient, but without causing the high emissions levels of diesels.
- First, the engine is highly turbocharged.
- Second, the engine can be designed with a higher compression ratio.
The combined changes could increase the power of a given-sized engine by more than a factor of two. But rather than seeking higher vehicle performance--the trend in recent decades--the researchers shrank their engine to half the size. Using well-established computer models, they determined that their small, turbocharged, high-compression-ratio engine will provide the same peak power as the full-scale SI version but will be 20 to 30 percent more fuel efficient.
The ethanol-boosted engine could provide efficiency gains comparable to those of today's hybrid engine system for less extra investment--about $1,000 as opposed to $3,000 to $5,000. The engine should use less than five gallons of ethanol for every 100 gallons of gasoline, so drivers would need to fill their ethanol tank only every one to three months. And the ethanol could be E85, the ethanol/gasoline mixture now being pushed by federal legislation.
Through their startup company, Ethanol Boosting Systems LLC, the researchers are working with their Ford collaborators on testing and developing this new concept. If all goes as expected, within five years vehicles with the new engine could be on the road, using an alternative fuel to replace a bit of gasoline and make more efficient use of the rest.
MIT's pint-sized car engine promises high efficiency, low cost, Nancy Stauffer, MIT Laboratory for Energy and the Environment, October 25, 2006