Calculations Of Knock Suppression In Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection

Published: February 2006

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Calculations are described of knock suppression using direct ethanol injection in spark ignition gasoline/ethanol engines. The calculations show that evaporative cooling from direct ethanol injection, coupled with the high octane rating of ethanol, can be highly effective in inhibiting knock, thereby allowing use of small turbocharged engines with substantially increased efficiency. The calculations indicate that the enhanced knock suppression can allow for more than a factor of two increase in manifold pressure relative to conventional, naturally aspirated engines while also allowing for increased compression ratio. This increased pressure could enable substantial engine downsizing resulting in a part-load efficiency increase of 30% relative to conventional port fueled injected engine operation. Less than one gallon of ethanol for twenty gallons of gasoline could be sufficient to allow this engine downsizing and efficiency increase. Direct ethanol injection could provide a new opportunity to use ethanol more effectively to both displace gasoline and, more importantly, to increase gasoline utilization efficiency.

MITEI Authors

Leslie Bromberg Principal Research Engineer and Group Leader

Plasma Science and Fusion Center

Daniel Cohn Research Scientist

MIT Energy Initiative

John Heywood Professor

Mechanical Engineering; MIT Joint Program on the Science and Policy of Global Change