ICCT study concludes there are no technical barriers to use of higher blends of ethanol
Tue 04 February 2014
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The International Council on Clean Transportation (ICCT) has released a paper assessing the technical barriers to the use of higher blends of ethanol. Broadly, the study concludes that technical barriers do not prevent the use of higher blends of ethanol, and slow international uptake of blends such as E15 and E85 is due to other factors, including high cost, legal and warranty issues, and consumer awareness and acceptance.
The paper was commissioned by the Bipartisan Policy Center (BPC) as part of a yearlong effort aimed at fostering “constructive dialogue and action” on reforming the US Renewable Fuel Standard.
The ICCT team only examined technical barriers to the consumption of blends of ethanol above 10%: the effect of higher ethanol blends on passenger vehicles and smaller engines and the impact on infrastructure. The study does not address non-technical barriers to the use of higher blends (e.g., car warranties, cost, food-versus-fuels arguments).
The primary technical concerns with using intermediate-level blends of ethanol in the vehicle fleet include:
• Fuel economy. Ethanol has about one-third lower energy density than gasoline; accordingly, cars drive fewer miles per gallon when operating on ethanol blends compared with unblended gasoline. Fuel tanks could be made larger in new vehicles partially to address this problem, but there is no way directly to modify the fuel to offset the lower energy density of ethanol compared with gasoline.
The Environmental Protection Agency (EPA) has investigated the potential that cars running on E30 could be more efficient on an energy basis if their engines are designed for that fuel mix. Higher ethanol blending raises the octane rating, and provides much higher evaporative cooling of the intake charge. These effects can allow the engine to operate more efficiently by enabling an increased compression ratio and higher levels of turbocharger boost with smaller engines. Operators of such cars would have to exercise caution as misfueling on lower ethanol blends could lead to engine knocking or greatly reduced performance.
Tailpipe emissions of CO2 from the combustion of ethanol and gasoline are similar on an energy basis—i.e. using ethanol does not affect a vehicle’s tailpipe CO2 emissions per mile driven.
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