A review of 43 studies of the effects of E15 (15% ethanol blends) on Model Year 2001 and newer cars by the National Renewable Energy Laboratory (NREL) found that the studies reviewed showed no meaningful differences between E15 and E10 in any performance category.
The NREL study, commissioned by the Renewable Fuels Association, included 33 unique research studies, as well as 10 related reviews. The study does not address engines that EPA has not approved for use with E15, such as pre-2001 cars, marine, snowmobile, motorcycle, and small non-road engines.
The main conclusions of NREL’s analysis were:
Several of the studies tested relatively large numbers of engines or vehicles, including the Coordinating Research Council’s (CRC) engine durability study (28 engines); the University of Minnesota’s in-use fleet study (80 vehicles); and the US DOE’s catalyst durability study (82 vehicles). The data presented in these studies did not show any evidence of deterioration in engine durability or maintenance issues for E15 (or E20) in comparison to E0 and E10 (when tested).
Materials compatibility testing provides no evidence that 15 vol% ethanol blends will cause increased rates of metal corrosion in comparison to 10% blends. In most cases increasing ethanol content from 10 to 15 vol% had no significant effect on elastomer swell.
For 2001 and newer cars emission studies also show that engine control units are able to adequately compensate for the higher oxygen and lower energy content of E15.
Because of the wide variety of control fluids and unique test protocols, especially for fuel system component, engine, and vehicle durability studies, it is difficult to combine the results into a single analysis. The NREL report distinguishes between test fuels and test fluids. Test fluids, such as those suggested by SAE publication J1681, do not meet fuel quality standards and were not intended for comparison of the effects of different fuels because the effects of the aggressive test fluids relative to commercial fuels are unknown.
The engine performance and durability expectations from the materials compatibility and emission test results were confirmed by studies of fuel system, engine, and whole vehicle durability.
Fuel system and engine durability. The NREL team reviewed 5 studies in this area. Engine and vehicle testing studies included:
CRC engine durability study. This study had concluded that two popular engines used in 2001-2009 model year vehicles experienced mechanical failure when operated on E15. However, the NREL researchers determined, the design and methodology of the study left the results open to a different interpretation than that provided by the study authors because of several factors, including: the leakdown failure criterion is not supported in the scientific or applicable OEM literature; statistical analysis included assumed data for vehicles that had not been tested, and omitted data for a vehicle that was tested; E10 was not used as a control fuel.
The NREL team concluded that when those factors are taken into account, the conclusion that engines will experience mechanical engine failure when operating on E15 is not supported by the data.
Minnesota and DOE tests. Two large scale (of about 80 vehicles each) tests were conducted on whole vehicles (as opposed to engines or fuel system components).
A study by University of Minnesota used E20 as the test fuel and an E0 control followed an in-use fleet of cars for one year. In a second study by US DOE, both E15 and E20 were used as the test fuels with E10 as control for five out of twenty-five 2001 and newer vehicle models. The study utilized mileage accumulation dynamometers to age the vehicles to full useful life.
Neither study found increases in fuel-related maintenance in the vehicles tested. While E10 controls were used for only 25% of the cars tested in the DOE study (with E0 as control for 75%) in the USDOE study, because no fuel related issues were apparent with the E15 and E20 fuels, E10 control testing was not necessary.
Component durability studies examined used aggressive test fluids with poorly understood connection to commercial fuels, the NREL team found.
The Minnesota Center for Automotive Research study examined a selection of components intended to represent a wide range of vehicle and material types and found no additional failures of fuel system components with fuels containing ethanol concentration up to 20 vol%.
A second component durability study conducted by CRC, intended to identify the most sensitive components, located a single pump that failed repeatedly on E15 but not on E10; yet in an earlier phase of this work the same pump model did not fail when tested on aggressive test fluids containing 10 and 20 vol% ethanol. A hypothesis exploring the discrepancy between these results was not discussed, nor was the make and model of the pump revealed, making these results inconclusive and further analysis by others impossible, the NREL team decided.
Materials compatibility. Research reviewed by NREL in this area mostly used ASTM Reference Fuel C as the hydrocarbon control and SAE J1681 Aggressive Ethanol blended with Reference Fuel C at different levels as the test fluids. These formulations were not intended for comparison of the effects of different fuels because the effects of the aggressive test fluids relative to real world fuels are unknown, the NREL researchers said—i.e., a material that fails might prove to have acceptable durability in normal use.
Studies using ethanol concentrations ranging from zero to 100% ethanol suggest that corrosion rates and effects on elastomers often peak at ethanol concentrations somewhere between E10 and E35. The NREL reviewers found:
No corrosion was observed for mild steel, 304 stainless steel, 1100 aluminum, or 201 nickel immersed in Aggressive E10 or Aggressive E17 (a surrogate for E15). A second study found corrosion rates in 16 different metals to be less than 0.0025 mm/yr in Aggressive E10 and Aggressive E20, considered insignificant over a 20 year timeframe.
Terne plate, galvanized steel, phosphor bronze and cartridge brass exhibited slightly higher rates of corrosion in aggressive test fluids, but without significant differences between Aggressive E10 and either Aggressive E17 or Aggressive E20. When using non-aggressive ethanol blends, measured corrosion rates were several orders of magnitude less.
Elastomers and plastics showed some measurable effects from exposure to gasoline hydrocarbons with increasing ethanol content. The largest changes in material properties typically occurred between 0 and 10 vol% ethanol; however, differences between materials were far more significant than differences between fuels. Fluorelastomers (generally approved for FFVs) saw the best retention of baseline properties with all levels of ethanol.
he reported results suggest that elastomers and plastics rejected for material compatibility reasons for use with E15 would likely be considered unacceptable for use with E10, the NREL team found.
Regulated emissions. The NREL team also examined studies conducted on tailpipe emissions; catalyst durability; OBD II failures for lean operation; and evaporative emissions. These studies (with the exception of the analysis of OBDII failures) used test methods that are defined in the regulations and the results have been carefully reviewed by the EPA to ensure that E15 would not adversely affect emissions.
Based on their analysis, the NREL researchers found no discernible relationship between the numbers of malfunction indicator light (MIL) illuminations due to lean diagnostic trouble codes (DTCs) and increasing ethanol content. Overall the tailpipe emissions and OBD II results show that 2001 and newer cars are able to compensate for the increased oxygen content and lower energy content of E15 blends, such that combustion and exhaust temperatures do not change significantly.
The evidence suggests that increases in evaporative emissions between vehicles using E10 and E20 are small or non-existent, NREL concluded. Even after the equivalent of one year of aging, measured evaporative emissions remained below regulated levels.
By critically examining the universe of studies on mid-level ethanol blends, the NREL report brings important context and scientific credibility back to the debate over E15. In addition to providing an appreciation for the entire body of scientific work on E15, the report will undoubtedly assist policymakers and the public in recognizing the substantial body of research that has been conducted on E15 showing no evidence of deterioration in engine durability or maintenance issues.—Bob Dinneen, President and CEO of the Renewable Fuels Association
Robert L. McCormick, Janet Yanowitz, Matthew Ratcliff, Bradley T. Zigler (2013) “Review and Evaluation of Studies on the Use of E15 in Light-Duty Vehicles” Prepared for the Renewable Fuels Association Under Technical Services Agreement No. 13-505