Published: July 25, 2008 03:13 pm            

Ethanol-gas should not cause undue worry

They can be seen across Oklahoma: Conspicuous signs at gasoline stations citing that fuel may contain up to 10 percent ethanol.

“It didn’t take very long for the questions to start after July 1, when gasoline stations in Oklahoma were required to post labels about ethanol content in their fuels,” said Scott Frazier, Oklahoma Cooperative Extension Service energy and manufacturing systems engineer.

Frazier said part of the reason for the questions is that Oklahoma is a relative latecomer to the use of ethanol-gasoline blends. Approximately half the gasoline sold in the United States contains up to 10 percent ethanol.

“Blends vary from low level, about 5 percent ethanol, to high-level blends up to 85 percent ethanol,” he said. “Low-level blends such as E10 are not considered alternative fuels by the U.S. government.

All major U.S. automotive manufacturers warranty all vehicle makes and models produced to use E10 or gasoline.”

The blends used in Oklahoma are almost all of the low-level variety, coming in at 10 percent or less ethanol content. Going hand-in-glove with the use of blends have been worries about decreased fuel economy, where rumor sometimes overshadows fact.

Time to do the math: The British thermal unit or “Btu” refers to a unit of energy. One horsepower is approximately 2,544 Btu per hour.

“Using mathematics relative to energy content per volume and mixing ratios, one comes up with an energy content of 109,300 Btu per gallon for E10,” Frazier said. “This is approximately a 3.3 percent decrease in energy per gallon compared to 100 percent gasoline.”

To put this into perspective, individual gasoline pumps can vary the amount dispensed per gallon by plus or minus 6 cubic inches or approximately 2.6 percent.

“Straight gasoline energy per gallons also can vary at different times of the year and between individual production batches by up to 4.8 percent,” Frazier said. “In fact, there are a number of factors that can affect fuel economy: Temperature, head wind, road conditions, traffic congestion, driving speed, acceleration rate, wheel alignment, tire pressure, running the air conditioner in Oklahoma’s 100-plus degree Fahrenheit days and a host of others.”

The bottom line is that it can be extremely difficult to accurately measure a decrease in fuel economy caused by ethanol when other common factors have the capability to overwhelm the measurements.

“Many of the problems reported with ethanol fuels involve the higher proportion blends such as E85,” Frazier said. “Newer vehicles built after 1995 are built and warranted to operate with E10 and should have minimal fuel-related issues.”

What about older vehicles?

“It’s true that ethanol is more corrosive than straight gasoline for many metals, plastics and rubber,” he said. “Although newer vehicles shouldn’t have a problem, older engines might run a risk of degradation of rubber, cork gaskets and exposed magnesium and aluminum surfaces in the fuel system.”

Ethanol is also an effective solvent. On one hand, this can help remove gum and deposits from fuel systems.

A possible drawback is that dirty fuel systems may begin to precipitate old deposits all at once and clog fuel passages. Ethanol is also hydroscopic, meaning it attracts and mixes with water.

“At lower concentrations of water, the alcohol will mix and remove the water as the fuel is burned,” Frazier said.

“However, if the fuel system has a sealing problem and greater concentrations of water enter the system, various acids can form with the ethanol, which potentially can increase engine wear.”

This can be a problem, especially for engines that sit for periods of time greater than three months.

Frazier said vehicles that are used on a constant basis should experience minimal water contamination problems with E10.

Gasoline blends that contain more than 10 percent ethanol content must be used in “Flex-fuel” vehicles. These engines must have higher compression ratios in order to extract the lower energy content from ethanol in higher blend percentages. In turn, these specially designed engines cannot run straight gasoline at the higher compression ratios.

        

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