WASHINGTON, Sept. 29, 2016 - People who own boats, lawnmowers and other seasonal equipment have debated for years, sometimes heatedly, about the engine-impacts of ethanol-blended gasoline.

Specifically, the dispute has centered on the issue of water uptake and “phase separation” in small and off-road engines. Now, a new study released by the Energy Department’s National Renewable Energy Laboratory (NREL) is injecting some much-needed insight into the dispute by indicating that gas becomes stale before water uptake becomes a concern.

Phase separation occurs when an excessive amount of water is introduced into the fuel tank, leading the ethanol and water to mix and sink to the bottom of the tank. The engine cannot operate on the ethanol/water mixture, and the mixture may also cause corrosion of metals in the engine fuel system.

Recreational equipment and lawn and garden equipment – collectively, “non-road equipment” –that may be used seasonally and then stored for many months, is designed to operate on E10, says NREL, but some organizations and owners of non-road equipment have expressed concerns about ethanol blends, and in particular about the potential for E10 blends to take up water from humid air leading to phase separation.

The research found that the petroleum components of ethanol-blended gasoline become degraded and unfit for use in an engine long before the ethanol portion takes up enough water to cause phase separation in the fuel tank. 

“In a small engine fuel tank in a constantly high-temperature, high-humidity environment, it takes three months or longer for E10 and other ethanol blends to take up enough water for phase separation,” says NREL. “This confirms the statement by Mercury Marine that water uptake in E10 blends ‘does not happen at a level or rate that is relevant.’”

“Every manufacturer of small and off-road engines has approved the use of E10 in their equipment for many years,” said Bob Dinneen, president of the Renewable Fuels Association (RFA), who requested the study.

“If owners of this equipment simply follow the manufacturers’ recommendations for fuel, maintenance and winterization, they won’t have any issues at all. But, as this study shows, letting gasoline sit in your tank for extended periods of time is likely to cause some issues – irrespective of whether the gasoline contains ethanol or not.”

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The report also notes that an advantage of ethanol blends is that they actually hold more water in suspension without phase separation than the hydrocarbon components of gasoline, and that more ethanol improves resistance to phase separation. “This is an advantage that can help keep fuel systems ‘dry’ by moving low levels of water out of the system,” the researchers say.

“Simply put, critics who continue to suggest E10 is a problem for small engines and boat motors are all wet. This research from NREL clearly demonstrates once and for all that ethanol actually helps these engines run more efficiently,” Dinneen said.

“It also shows that gasoline goes bad long before the ethanol in the tank could cause any problems due to moisture uptake. This research effectively disproves the half-baked anecdotes and horror stories about E10 and small engines that have been pushed for decades by ill-informed biofuel opponents and snake-oil additive salesmen.”

To read a summary of the study, click here. To read the full study, click here.


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