GTS Dean
Enthusiast
See this article:
E85 vs. Gasoline Comparison Test
It claims about 26.5% worse mileage for E85 (so not quite as bad as 50% worse).
Ethanol has a much higher resistance to knock, which allows more spark advance than gasoline. It also has a lower heat of vaporization - which means that it cools the intake charge more than gas in the liquid to vapor phase change. On a straight-up energy comparison basis, ethanol only has about 65% of the heating value of gasoline. It takes 9 parts air to 1 part ethanol for combustion. It takes 14.7 parts air to 1 part gasoline for combustion.
Ethanol-blended fuels also are granted an exemption from federal motor fuel excise taxes, which means less money from user fees to maintain or expand the nation's road system. All gasoline and gas replacement liquid fuels are taxed at the refinery rack at 18.4 cents/gallon. Ethanol in blended fuels are then eligible to get a rebate from the US Treasury of 45 cents/gal for every gallon of ethanol blended. This amounts to a net 26.6 cent/gallon subsidy to the ethanol industry (read: ArcherDanielsMidland - ADM).
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