Don’t Save Energy, Save Exergy! The Enemy of Progress a/k/a Waste Heat
by Jim Lane (Biofuels Digest) … One of the most important efforts to reduce waste heat is in transportation engines. … In transportation engine efficiency, there’s nothing more ambitious on the agenda than the US effort to raise corporate averaged fuel economy (CAFE) standards. The US set a goal of 35.5 miles per gallon for 2016 (up from 25 mpg), and 54.5 miles per gallon for cars and light-duty trucks by 2025, in an agreement with 13 major automakers.
One of the most important opportunities to increase fuel efficiency is in increasing engine compression ratios. Under high compression, more energy becomes exergy — that is, the engine is more efficient, more fuel produces work instead of waste heat.
As J Szybist et al observed in a paper for the Society of Automotive Engineers, “ethanol offers significant potential for increasing the compression ratio of SI engines resulting from its high octane number and high latent heat of vaporization.” Interestingly, they also observed that “high compression ratios can increase the efficiency of ethanol fuel blends, and as a result, the fuel economy penalty associated with the lower energy content of E85 can be reduced by about twenty percent.”
Or, as Costa and Sodr´found in this study, “Higher compression ratios improved engine performance for both fuels throughout all the speed range investigated, with major effects being observed when hydrous ethanol was used.”
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When you think exergy, instead of energy — you bring engine design and community design into the picture, and that’s a really good thing. READ MORE / MORE (8 Slide Guide) Abstract (Society of Automotive Engineers) Abstract (Applied Thermal Engineering)
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