The following is an excerpt from Sustainable Ethanol: Biofuels, Biorefineries, Cellulosic Biomass, Flex-Fuel Vehicles, and Sustainable Farming for Energy Independence
Improving Fuel Economy on Ethanol
One criticism of ethanol is that it replaces only a small portion of our gasoline use. But this is a poor reason to abandon ethanol. It would make no more sense than abandoning wind power because it can’t supply all our electricity. It is, however, a reason to work on conservation and energy efficiency just as intently as production. We use more energy than necessary, primarily because petroleum has historically been inexpensive. As cheap oil becomes scarce, we must find ways to curtail our use of transportation fuels.
Some ethanol critics cite its poor fuel economy compared to gasoline. Actually, ethanol can be an ally in energy conservation and better fuel economy. Preliminary studies show E10 already achieves better fuel economy than ethanol-free gasoline in some vehicles. E85 exhibits reduced fuel economy in today’s flex fuel vehicles, but critics often fail to acknowledge this situation can improve. Manufacturers could optimize vehicles for better fuel economy on E10 and E85. This would reduce our cost per mile driven. It would also improve ethanol’s energy balance, in turn benefiting our environment, energy security, and trade balance.
Ethanol’s energy density is low compared to gasoline, but energy density is not the only property affecting fuel economy. We must also consider how efficiently a vehicle uses energy. No technology is capable of converting 100% of available energy into useful work. Energy is lost to friction and heat. But vehicles optimized for ethanol are able to direct a greater percentage of available energy toward turning the wheels, offsetting lower energy content. This is possible thanks to ethanol’s high octane rating and other beneficial combustion properties. Ethanol optimization technologies already exist. Full implementation of these technologies could yield huge benefits through better fuel economy.
In these times of high fuel prices, we often hear of potential solutions such as hybrid vehicles, biofuels, hydrogen, and fuel cells. We need to resist the temptation to see these as competing alternatives. It is tantalizing to think some single “silver bullet” technology will solve all our energy problems. Realistically speaking, if we reject every energy alternative that can’t single-handedly replace oil, we will have nothing left. We need many different alternative fuels and most importantly, we need to combine fuels and technologies for maximum efficiency. Biofuels such as ethanol can be a valuable component of a highly efficient transportation system.
Fuel Economy on E10
E10 (10% denatured ethanol and 80% gasoline) works in nearly all gasoline-burning vehicles. In Chapter 5, we introduced two studies indicating little or no reduction in fuel economy on average for E10 as compared to ethanol-free gasoline.[i] The lower BTU content of E10 does not necessarily lead to worse fuel economy. Some cars achieved significantly better fuel economy on E10. Considering most North American ethanol use is currently in the form of E10, its favorable fuel economy redounds to the benefit of ethanol’s overall energy balance and cost effectiveness in our transportation system. Can fuel economy on E10 be improved still more? In both the EPA and American Coalition for Ethanol studies, fuel economy varied considerably among different car models. Some variability would be expected with real world conditions and among different drivers. These studies, however, were done under controlled conditions, indicating some real differences in the efficiency with which different vehicles burn E10.
Simply making E10 performance data available for new and used cars would allow motorists to make buying decisions based on E10 fuel economy. For used cars, the data might not be consistent because differing levels of engine deposits or other use factors might make a difference, but some trend lines might appear even there. New car performance on E10 should be more consistent and measurable.
See chapter 6 of Sustainable Ethanol for these additional topics:
Improving Flex-Fuel Vehicles
Ethanol and Hybrid Electric Vehicles
Ethanol Boosting with Direct Injection
Ethanol, Hydrogen, and Fuel Cells
Figure 6-1. Change in Fuel Economy Using E10 Relative to Ethanol-free Gasoline
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[i]. KT Knapp, FD Stump, & SB Tejada, “The Effect of Fuel on the Emissions of Vehicles over a Wide Range of Temperatures,” Journal of the Air & Waste Management Association 43 (July 1998); American Coalition for Ethanol, Fuel Economy Study, 2005, http://www.ethanol.org/documents/ACEFuelEconomyStudy.pdf.