Controlled Fuel Economy Test Results
The Auto/Oil Air Quality Improvement Research Program is a cooperative program initiated by three domestic auto companies and fourteen petroleum companies. It primary purpose is to determine how changes in fuels and vehicles might reduce emissions and improve air quality. But, the Auto/Oil program also generates information on fuel economy because measuring fuel economy is a routine part of the Federal Test Procedure emissions test.
Auto/Oil recently reported² on the fuel economy of a fleet of twenty 1989 cars (pairs of ten models). The cars weren't driven on the road. Instead, each car was run through a specified operating cycle while it was mounted on a chassis dynamometer in a temperature-controlled laboratory. The cars were fueled with a variety of conventional gasolines, with some of the same gasolines oxygenated with ethanol, or with similar gasolines oxygenated with MTBE. One analysis of the results compared the fuel economy of the oxygenated gasolines to the conventional gasolines:
| Oxygenate in Gasoline |
Percent Change from Value for Conventional Gasoline |
| Energy Content1 |
Fuel Economy2 |
| 10 Vol % Ethanol |
-3.4 |
-2.6 |
| 15 Vol % MTBE |
-2.2 |
-2.4 |
1 Average for fuels of varying composition.
2 Average fuel economy in mpg for all cars in 1989 test fleet and for fuels of varying composition.
So, changing from conventional to oxygenated fuels did not result in a large, unexpected decrease in fuel economy. The decrease was less than or the same as the decrease in energy content. A decrease in fuel economy of this size would be very difficult for the average driver to detect. For example, it is a change from 23 mpg to 22.4 mpg.
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