Ford, GM and AVL researchers argue match-blending a flawed approach to evaluate ethanol-gasoline blends (corrected)

6 November 2014

(Earlier version attributed the final quote to the research team. Our apologies for the error.)

In a newly published SAE paper, a team from Ford, General Motors and AVL argues that the exclusive use of a match blending approach to prepare ethanol-gasoline blends for regulatory emissions testing “has fundamental flaws”.

This echoes the recent criticism by the Urban Air Initiative (UAI) and the Energy Future Coalition (EFC) that the latest version of the US Environmental Protection Agency’s (EPA) MOtor Vehicle Emission Simulator (MOVES) modeling system for estimating emissions from mobile sources is “seriously flawed” with respect to its reliance on match blending. (Earlier post.)

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Ethanol blends are created in two ways: by adding more ethanol to a product approved for commercial use, such as E10 (“splash blending”); or by adjusting the gasoline blendstock first to match certain selected parameters (“match blending”).

In their paper, the researchers from Ford, GM and AVL note that:

Modification of gasoline blendstock composition in preparing ethanol-gasoline blends has a significant impact on vehicle exhaust emissions. In “splash” blending the blendstock is fixed, ethanol-gasoline blend compositions are clearly defined, and effects on emissions are relatively straightforward to interpret. In “match” blending the blendstock composition is modified for each ethanol-gasoline blend to match one or more fuel properties. The effects on emissions depend on which fuel properties are matched and what modifications are made, making trends difficult to interpret.

The distillation profile of gasolines without ethanol is a smooth, roughly linear relationship of temperature vs. percent fuel distilled. The use of three points on the curve (T10, T50, and T90, defined as the 10%v, 50%v, and 90%v evaporated temperatures) has been sufficient to define their volatility-related behavior in engines, the researchers note. These parameters are commonly “matched” in studies intended to evaluate fuel composition effects on emissions.

For ethanol-gasoline blends, higher boiling-point hydrocarbons must be added to match T50 and T90 with fuels having less ethanol. However, as a result, they note:

The degradation of emissions which can result is primarily due to the added hydrocarbons, but has often been incorrectly attributed to the ethanol. Studies to evaluate the effects of ethanol should be conducted by adjusting the blendstock only as necessary to satisfy ASTM D4814 requirements. Blending ethanol at up to 30%v with an E10 blendstock should generally require only minimal changes in composition to meet ASTM D4814.

Steven VanderGriend, Urban Air Initiative Technical Director, said that the new paper can serve as an important tool to correct the MOVES (Motor Vehicle Emissions Simulator) model that EPA requires states to use when estimating air quality impacts of motor fuels.

As an independent source, the auto industry experts who were involved in this study are validating the concerns we have had for quite some time now. In fact we are very excited with regard to the conclusion they reached that studies to evaluate the effects of ethanol should be conducted by adjusting the blendstock only as necessary to satisfy ASTM requirements. Blending ethanol at up to 30% volume with an E10 blendstock should generally require no change in composition to meet ASTM D4814.

Resources

• Anderson, J., Wallington, T., Stein, R., and Studzinski, W. (2014) “Issues with T50 and T90 as Match Criteria for Ethanol-Gasoline Blends,” SAE Int. J. Fuels Lubr. 7(3) doi: 10.4271/2014-01-9080