Study Finds Engine Damage Caused by E15 Gas

Boaters who fuel up on the road should monitor ethanol levels closely. Photo/New England Boating

The results of 2 studies released by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy show that using gasoline blended with 15% ethanol in volume (E15) in marine engines can cause significant damage in outboard, sterndrive and inboard engines.

The studies were conducted on engines provided by Volvo Penta and Mercury Marine, with the Energy Department approving the final analysis of the results. The engines tested on gasoline with 0% ethanol blending did not exhibit fuel-related issues.

“A Study of the Effects of Running Gasoline with 15% Ethanol Concentration in Current Production Outboard Four-Stroke Engines and Conventional Two-Stroke Outboard Marine Engines,” conducted by David Hilbert of Mercury Marine, focused on a 9.9-hp carbureted, 2-stroke outboard, a 200-hp EFI 2.5L 2-stroke, a 300-hp 4-stroke supercharged Verado outboard and a 4.3L V6 EFI 4-stroke catalyzed sterndrive. Here are the published results on these engines:

“Results are based on a sample population of one engine per test fuel. As such, these results are not considered statistically significant, but may serve as an indicator of potential issues. More testing would be required to better understand the potential effects of E15.

9.9-hp Carbureted Four-Stroke:

  • The E15 engine exhibited variability of HC emissions at idle during end-of-endurance emissions tests, which was likely caused by lean misfire.
  • Both the E0 control engine and E15 test engine ran leaner at idle and low speed operation at the end of endurance testing compared with operation at the start of the test.
  • The trend of running lean at idle coupled with the additional enleanment from the E15 fuel caused the E15 engine to have poor run quality (intermittent misfire or partial combustion events) when operated on E15 fuel after 300 hours of endurance.
  • CO emissions were reduced when using E15 fuel due to the leaner operation, as expected for this open-loop controlled engine.
  • The E15 engine exhibited reduced hardness on piston surfaces based on post-test teardown analysis.
  • The exhaust gas temperature increased 17°C at wide-open throttle as a result of the leaner operation when using E15 fuel. Higher combustion temperatures may have caused observed piston hardness reductions. Lack of pre-test hardness measurements prevented a conclusive assessment.
  • Several elastomeric components on the E15 engine showed signs of deterioration compared with the E0 engine.
  • Affected components were exposed to E15 fuel for approximately 2 months; signs of deterioration were evident.

300-hp Four-Stroke Supercharged Verado:

  • The E15 engine failed 3 exhaust valves close to the end of the endurance test.
  • Metallurgical analysis showed that the valves developed high cycle fatigue cracks due excessive metal temperatures.
  • The pistons on the E15 engine showed indications of higher operating temperatures compared to the E0 engine’s pistons as evidenced by the visual difference in carbon deposits.
  • The E15 engine generated HC+NOx values in excess of the Family Emissions Limit (FEL) when operated on E15 fuel, but did not exceed that limit when operated on E0 emissions certification fuel.
  • The primary contributor to this increase in exhaust emissions was NOx due to enleanment caused by the oxygenated fuel.
  • CO emissions were reduced when using E15 fuel due to leaner operation, as expected for this open-loop controlled engine.

200-hp EFI 2.5L Two-Stroke:

  • The 200 EFI two-stroke engine showed no signs of exhaust emissions deterioration differences due to the fuel.
  • The E15 fuel caused the engine to run lean resulting in reduced HC and CO emissions. NOx was of little concern on this type of engine since NOx accounted for less than 2% of the total regulated HC+NOx emissions.
  • The E15 engine failed a rod bearing at 256 hours of endurance, which prevented completion of the 300-hour durability test
  • Root cause of the bearing failure was not determined due to progressive damage.
  • More testing would be necessary to understand the effect of ethanol on oil dispersion and lubrication in two-stroke engines where the fuel and oil move through the crankcase together.

4.3L V6 EFI Four-Stroke Catalyzed Sterndrive:

  • Since E15 fuel was readily available in the test facility and an engine equipped with exhaust catalysts was on the dynamometer, emissions tests were conducted on a 4.3L V6 sterndrive engine to better understand the immediate impacts of ethanol on this engine family.
  • At rated speed and load (open-loop fuel control) E15 caused exhaust gas temperatures to increase by 20°C on average and the catalyst temperatures to increase by about 30°C.
  • More rapid aging of the catalyst system occur due to the elevated catalyst temperature when considering the high load duty cycle typically experienced by marine engine applications.

Conclusions and Recommendations:

Several issues were discovered in this study from an exhaust emissions and an engine durability standpoint as a result of running E15 fuel in outboard marine engines. Run-quality concerns were also identified as a result of the lean operation on the carbureted engine.

Additional investigation is necessary to more fully understand the observed effects and to extrapolate them to all types of marine engines over broader operating conditions. Effects on operation at part load, transient acceleration/deceleration, cold start, hot restart, and other driveability-related concerns need to be evaluated. This test program was mainly testing for end-of-life durability failures, which would not likely be the first issues experienced by the end users. A customer would likely be affected by run quality/driveability issues or materials compatibility/corrosion issues before durability issues. The wide range of technology used in marine engines due to the wide range of engine output will complicate this issue.

More testing is needed to understand how ethanol blends affect lubrication systems in two-stroke engines that have fuel and oil moving through the crankcase together. Crankcase oil dispersion is the only mechanism by which two-stroke engines of this architecture provide lubrication at critical interfaces such as bearings and cylinder walls. Ethanol may have an effect on the dispersion or lubricity of the oil.

A better understanding of how long term storage affects ethanol blends in marine fuel systems would require more real- world testing. Marine vessels often go through long periods of storage that could affect the fuel systems given the fact that the ethanol portion can absorb water when exposed, especially in humid areas near saltwater.

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