The new report represents an extension of a 2011 scoping study that investigated how gasoline containing 20% ethanol by volume (E20) might affect wetted automotive fuel system components such as pumps, dampers, level senders, and injectors. That scoping project (CRC Project No. AVFL-15) was used to identify areas where further testing should be performed.

Background. Increasing the ethanol concentration in motor gasoline has been suggested as a way to meet Renewable Fuel Standard 2 (RFS2) requirements. The US Environmental Protection Agency (EPA) has approved waivers for selling fuel containing up to 15% ethanol (E15) in model year 2001 and newer light-duty vehicles. (Earlier post.)

Various philosophical and technical grounds for support or opposition to this change have been offered, and an increasing amount of data is emerging on the impact of higher ethanol content in gasoline. While the studies published to date provide some perspective on the positive and negative impacts of E20 (where the subscript designates the percent by volume ethanol blended with unleaded gasoline) and E15, there has been little independent reproduction of published results, and gaps in the published literature remain as well.

The durability of wetted fuel system parts was probed in the Coordinating Research Council (CRC) Report Number 662. The screening study documented in that report covered a spectrum of fuel system components exposed to E20; individual components were tested in addition to full fuel systems. That work concludes that E20 fuels do negatively impact a subset of fuel-wetted parts, while other fuel-wetted parts showed no effect in screening. However, all the conclusions in [that study] are based on single or in some cases duplicate tests of a particular component/fuel interaction. A failure in a single test raises concern that vehicles in the field will at some point begin to experience similar failures.

As a rule of thumb, original equipment manufacturers (OEMs) expect part failures to occur at less than one per thousand vehicles, so a part failure in a single test is highly worrisome. Nonetheless it is possible that such a failure is a random event that results from the chance influence of an uncontrolled variable in the experiment. Furthermore, a single point test cannot give a quantitative indication of the expected frequency of occurrence, only that the data suggests (but does not prove) that the observed event is fairly likely.

—“Durability Of Fuel Pumps And Fuel Level Senders In Neat And Aggressive E15”

The new study. The primary test fuels for the new study were E15 and an aggressive blend of E15 (E15a). E15a represents the worst-case blends of gasoline and 15 volume percent ethanol that might be found in the field. E10 and E0 test fuels were also incorporated into this study in a second phase as reference points to assess the relative performance of the E15 and E15a test blends.

Automobile manufacturers developed a candidate list of vehicles for testing. Based on manufacturer suggestions, 15 designs from different manufacturers spanning the 1996 to 2009 model years were used. The study estimates that the design selections from the original scoping study represented at least 37 million vehicles with components and systems similar in construction and materials. Based on the scoping study, several fuel pumps and fuel level senders were selected for testing in the current work. The subset of parts used in the current work represents approximately 29 million 2001-2007 vehicles.

The protocols for testing fuel pumps and senders—fuel pump endurance aging, soak durability, and tear down analyses; fuel level sender resistance and full sweep aging—followed the procedures used in the original scoping study. The testing procedures were based on existing SAE and USCAR protocols which are used in the automotive industry to predict new product life.

Among the findings:

• The pump soak test could discriminate the interaction of fuel pumps with test fuel. Some pump design-fuel combinations had no deviations in performance while other pump design-fuel combinations led to pump failures. One fuel pump model, currently in use in the field, seized in almost every replicate of the pump soak test when either neat or aggressive E15 was used as test fuel, but pumps of this model did not fail on any replicate of the same test when either E0 or E10 was used as test fuel.

• here are pump designs (currently in use in the field) that did not seize in the fuel pump soak test, but did exhibit statistically significant flow loss when tested with neat or aggressive E15.

• The pump endurance test could sort fuel pumps by their interaction with test fuel; some pump design-fuel combinations had no deviations in performance while other pump design-fuel combinations led to pump failure. One fuel pump model, currently in use in the field, seized in almost every replicate of the pump endurance test when either neat or aggressive E15 was used as test fuel, but did not fail on any replicate of the same test when E0 was used as test fuel. Another design of pump, currently in use in the field, was not impacted by mid-blend ethanol in the endurance test.

• Exposure to E15 or aggressive E15 caused dimensional changes in all impellers. Depending on pump model, the standard deviation of thickness was approximately 2 to 27 times greater in E15 than in E0 at the end of the soak test.

• The tests showed issues with the performance of the fuel level senders when tested with the E15 and E15a blends. Both the E15a and E15 blends had three instances of significant signal defects. The significant signal defects experienced (consumer observable resistance spikes) could potentially cause interference with proper OBDII function. While not consistent and not found in all samples tested, the results indicate some effect of the E15 and E15a blends on sender operation.

Resources

• CRC Report No. 664 Durability Of Fuel Pumps And Fuel Level Senders In Neat And Aggressive E15