A similar amendment, however, was blocked during the Senate floor vote on its energy bill.

At its formation, AllSAFE released a report on the potential impacts of mid-level ethanol blends (fuels with more than 10% ethanol) on the existing pool of engines, vehicles, boats and equipment—i.e, both on-road and off-road applications, from boats and all-terrain vehicles down to leaf blowers and chainsaws.

There are significant known and unknown technical issues associated with changing the US conventional motor gasoline pool to accommodate higher than E10 blends. While some of these may be surmountable with additional research and the resultant use of new materials and engine/equipment designs, these can only be implemented in new equipment and with proper lead time. Important data gaps aside, with present knowledge, it is likely that there will be adverse, large-scale impacts if higher than E10 is required as motor gasoline for the existing fleet of on-road and off-road equipment, particularly the latter. Minimizing these likely adverse impacts on existing equipment and vehicles would require significant and expensive adaptation and mitigation measures.

—Dr. Ranajit Sahu, report author

Some of the changes  in fuel properties due to the addition of ethanol to gasoline the report covers include:

• Change in octane number.

• Change in fuel volatility (as measured through several properties, including vapor pressure,  vapor-liquid ratio, and the temperature-distillation curve). Of the issues caused by fuel volatility, the primary concern that occurs at elevated ambient temperatures is vapor lock, according to Sahu. Vapor lock is a condition where the fuel in the engine’s fuel delivery system vaporizes preventing the required volume of fuel to be delivered. Increasing the ethanol concentration beyond E10 “is likely to increase the likelihood” of vapor lock for open loop fuel control system engines typically used on older vehicles and most off-road engines. “Even in the closed loop engine systems used in some off-road engines and in most late-model vehicles, there remains the likelihood of vapor lock.”

• Change due to the enleanment effect of ethanol. Because ethanol contains oxygen, when blended with gasoline it changes the stoichiometric air-to-fuel ratio of the blend. This is about 14.7 to 1.0 (on weight basis) for gasoline, but 14.0-14.1 to 1.0 for an E10 blend  because oxygen is contained in the ethanol and because some of the hydrocarbons have been displaced. The engine design anticipates that the fuel utilized will match the air-to-fuel ratio characteristics utilized in the engine design and calibration.

  Because ethanol blended fuels require more fuel for the same amount of air to achieve stoichiometric conditions, the fuel system must adapt by introducing more fuel or the desired mixture is not achieved. The effect of this type of fuel change on an engine is called “enleanment.”

  The effect of enleanment depends on engine design and how fuel is metered into the engine.

• Change in the energy density.

• Effect on water solubility and phase separation. In some situations, ethanol/gasoline blends might absorb water vapor from the atmosphere, leading to phase separation. Such problems are of greater concern for engines with open-vented fuel tanks that are operated in humid environments, such as marine engines.

• Effect on material compatibility.

• Effect on emissions.

Sahu notes the number of changes that Brazilian automakers implemented in their vehicles to support the use of higher ethanol blends (E20) to accommodate higher ethanol blends. 

It should be noted at the outset that ASTM has a standard for E85 which covers formulations ranging from E70 to E85. However, there are no standards for mid-level blends between E10- E70. Without standards, these formulations are being made on an ad-hoc basis by users, as needed typically by splash blending denatured ethanol with some type of base gasoline. Therefore, there is no comparability between properties of these mid-level blends made by various users.

...it is important to remember that US emission standards are more stringent than those in Brazil. For US vehicles, manufacturers select oxygen sensors and onboard diagnostic (OBD) systems specifically to cover the expected range of oxygen in the exhaust gas. If the fuel ethanol pushes the exhaust oxygen content outside the range of the oxygen sensor, the vehicle’s OBD system won’t work properly and may erroneously illuminate or fail to illuminate the dashboard warning light.

In addition, manufacturers must calibrate vehicle and product systems to the expected fuel to ensure the proper air-fuel ratio for both emissions and performance purposes. In the US, off-road engines are also regulated for emissions regardless of their size or equipment that they power. Generally, the off-road engines do not utilize oxygen sensors and computer controls to adjust fuel delivery by a closed loop system. In many products, emission compliance has dictated air-to-fuel ratio controls that are a delicate balance between being too rich and, therefore, out of compliance, or too lean, resulting in performance or durability problems.

AllSAFE is made up of the following national associations that represent: (1) consumer and commercial users of ethanol blends and other fuels in their equipment and vehicles; (2) manufacturers of boats, vehicles, engines and equipment; and (3) gasoline retailers that sell gasoline and ethanol-fuel blends, including the existing 10% ethanol blends.

Resources:

• Technical Paper On The Introduction of Greater Than E10-Gasoline Blends (Ranajit Sahu)