The National Renewable Energy Laboratory (NREL) has carefully completed reviewing 43 studies on the effects of E15 on engine durability, emissions, and other factors and issued a report finding that the available literature did not show meaningful differences between E15 and E10 in any performance category. In specifically evaluating the Coordinating Research Councils (CRC) controversial engine durability study, NREL found the conclusion that engines will experience mechanical engine failure when operating on E15 is not supported by the data. The NREL report identified numerous flaws with the CRC engine durability study, including:
- Failure to use E10 as a control fuel. Engines that failed on E20 or E15 were subsequently tested on E0, but not on E10 (despite the fact that E10 is the predominant in-use fuel today). This approach presumes that failures were related to ethanol content, rather than any number of other factors that could have caused the failure.
- One of the engines that failed on E15 also failed the test on E0. Quite obviously, ethanol content had nothing to do with the failure for this engine. Yet, CRC discarded the data from this vehicle for the studys statistical analysis.
- Cherry-picked engine sample. Despite the fact that most modern engines employ technologies that improve valve and valve set performance, CRC chose engines that do not use these technologies and, thus, were most likely to have valve problems. According to NREL, the vehicles chosen included several engines already known to have durability issues, including one that was subject to a recall involving valve problems when running on E0 and E10.
- Lack of transparency in test cycle schematic. According to NREL, [t]he durability test cycle schematic published in CRCs report does not contain enough detail to allow it to be independently reproduced.
- Test cycles maximum speed limit increased likelihood of valve damage. The CRC test cycle enforced a low maximum engine speed, which had the effect of increasing the likelihood of valve damage, because low speed operation may decrease valve rotation rates
- Faulty leakdown failure criteria. Most of the failures on E15 and E20 were related to engines that did not pass an arbitrary cylinder leakdown test. While other tests in the CRC study used established standards from OEMs and EPA, the leakdown test utilized arbitrary criteria with no scientific basis. According to NREL, CRC selected a 10% leakdown failure limit, more restrictive (50% below) than that of the lowest value specified by OEMs for engines in the study.
- Incorrect use of leakage tester tool. The manufacturer of the leakage tester used states that no cylinder will maintain 0% leakage and that this tool is best used to compare a suspect cylinder to a known good cylinder on the same engine. However, the CRC test used the tool to measure leakage compared to an arbitrary failure criterion of 10%.
- Inappropriate statistical analysis. The CRC study used assumed values (i.e., dummy data) for vehicles that were not actually tested. These dummy values demonstrated consistent bias in relation to the question that the analysis was intended to determine.