A new study by the Department of Energy (DOE) is providing fresh insight into a decades-old debate about the impacts of ethanol-blended gasoline on water uptake and “phase separation” in small and off-road engines.
The study, conducted by DOE’s National Renewable Energy Laboratory (NREL), 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. “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. In other words, gasoline becomes “stale” and unusable before water uptake by the ethanol component becomes a concern.
“Significant gasoline weathering (evaporation of the most volatile components) can occur over one month of storage in a high-temperature, high-humidity environment, with total mass losses as high as 30-70% for certain tanks,” according to the study, which was commissioned by the Renewable Fuels Association (RFA). “This means gasoline weathering, which can have a negative effect on fuel quality, generally occurs well in advance of any issues related to phase separation. The fuel vapor pressure may drop to levels where the fuel is not fit for purpose (engine will be difficult or impossible to start) and there may also be gum formation.”
As part of the study, NREL scientists stored gasoline-ethanol blends ranging from E0 (0% ethanol) to E85 (83% ethanol) in actual lawn mower fuel tanks over several months in a climate-controlled chamber meant to replicate hot, humid environments like Houston and Orlando. The samples were tested at regular intervals for evidence of gasoline weathering and water uptake.
Renewable Fuels Association (RFA) President and CEO Bob Dinneen says the study shows 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,” said Dinneen. “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.”