Ethanol biofuel could play an important role in reducing petroleum consumption by enabling a substantial increase in the fuel efficiency of gasoline engine vehicles. This ethanol boosted engine concept uses a small amount ethanol to increase the efficiency of use of a much larger amount of gasoline by approximately 30%. Gasoline consumption and the corresponding CO2 emissions would thereby be reduced by approximately 25%. In combination with the additional reduction that results from the substitution of ethanol for gasoline as a fuel, the overall reduction in gasoline consumption and CO2 emissions is greater than 30%. The concept uses appropriately controlled direct injection of ethanol into the engine cylinders. The direct injection provides suppression of engine knock at high pressure. This allows high pressure operation of a much smaller, highly turbocharged engine with the same performance as a larger engine. The engine can also use a higher compression ratio. The engine downsizing and higher compression ratio results in a large increase in fuel efficiency. This approach involves only modest changes to the present gasoline engine systems and fueling infrastructure. The increase in vehicle cost could be modest (approximately $600) and the fuel savings payback time could be approximately 2 years. This leveraged use of ethanol to increase gasoline engine efficiency could substantially increase its energy value and help to alleviate concerns about a low energy output/ input ratio (energy provided by the ethanol/energy needed to produce the ethanol). Thus the ethanol boosting concept can facilitate increased use of biofuel in addition to providing a cost-effective way to increase gasoline engine efficiency.
MITEI Authors
Daniel Cohn
Research Scientist
MIT Energy Initiative
Leslie Bromberg
Research Engineer
Plasma Science and Fusion Center
John Heywood
Professor Emeritus
Department of Mechanical Engineering