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While in the U.S. ethanol's efficiency (in low compression engines) is debated, in Sweden, a company making ethanol powered buses (for 18 years) has a new ethanol fueled diesel engine that will cut CO2 emissions vs gasoline 90%.
HOW? Ethanol is a high octane fuel which can be used in high compression applications producing much more power from a given displacement. The result is you can downsize the engine and reduce fuel consumption - and GHG emissions!
New highly efficient diesel-ethanol engine- ready to cut fossil CO2 emissions by 90% (Oct 2007).
Scania has produced ethanol buses for more than 18 years. The technology is mature and viable for intense everyday city service, as verified by fleet operators in several Swedish cities. Time has come for Scania's third ethanol engine generation, which achieves the same efficiency as a conventional diesel engine, while meeting Euro 5 and EEV emission levels.
Scania regards ethanol as the most viable renewable fuel currently available for urban operation, since it can contribute without delay to a sustainable public transport system.
By sustainable public transport Scania means sustainable in an environmental and economical perspective, using fuels that are compatible with current engine technology.
Ethanol is by far the most cost-efficient renewable fuel option on the market today, taking into account factors like availability, infrastructure and access to proven technology. New technologies such as hybrids are around the corner and fuel cells could become viable in ten years’ time, but there is no reason to wait.
The transition to renewable fuels can start NOW using existing technology. --------------------------------------------------------------------------------------------------------------------------------------------------------------------
Actually, you don't have to go to diesel engines to get the fuel efficiency benefits of ethanol. JUst use turbo-charging (or super-charging) and down-size the engine.
Three MIT scientists have designed an engine which uses Direct injection of ethanol with turbo-=charging to get 30% BETTER mpg than the typical low compression internal combustion engine runnning on gas(http://www.psfc.mit.edu/library1/catalog/reports/2000/06ja/06ja016/06ja016_full.pdf">MIT paper). The engine costs about $1,000 - $1,500 more to build and uses 5% ethanol and 95% gasoline. Ethanol is a high octane fuel (115 vs high test gas 92-93) so you can use turbo-charging to get more power out of a given displacement and downsize the engine thus using less fuel!
Ford is now a co-owner of this engine design and is currently selling it only in the Lincoln MKS. (the engine can operate on gasoline but to get the full benefit of direct injection plus turbo-charging you need to boost it with 5% ethanol - directly injected into the combustion chamber). Ford plans to offer this engine across it's entire line of vehicles in the next few years. (But this is much more likely to happen if we see many more ethanol pumps in gas stations. Ford isn't likely to commit to building lot's of these engines unless people can see a clear benefit to using them .. i.e. wth ethanol boosting).
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