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Ethanol - The cast of players

The cast of players

The cast of players

Oxygenates such as MTBE and ethanol originally were used in gasoline as anti-knock compounds to replace lead when it was banned from that use. More recently, their increased use has been in response to EPA requirements for gasoline with higher oxygen content, which results in more complete fuel combustion and lower exhaust emissions. Currently, oxygenates are used only in gasoline, though there is no reason they couldn’t be mandated for diesel in the future.

Read the other story in this package: Ethanol - Is ethanol hurting your fuel system?

MTBE, or methyl tertiary butyl ether, is an efficient oxygenate that by 1998 was allowed to be blended with gasoline in strengths of up to 15 percent by volume. It was the popular choice because it had no effect on vehicle performance and was compatible with existing fuel systems and delivery methods. It is a clear liquid that blends well with both gasoline and water, and is classified as a potential human carcinogen by the EPA and the State of California. It is a particularly dangerous contaminant because it has a long life, is not absorbed by soils, and travels quite rapidly for long distances in ground water and aquifers.

Ethanol, or ethyl alcohol, is distilled from fermented corn or other plant life. It is the alcohol that is found in alcoholic beverages, is non-toxic to humans in small amounts, and is biodegradable. (When used industrially, it is denatured to make it toxic and unfit for human consumption.) While it is an effective oxygenate, it has a number of drawbacks when used alone as a fuel or when blended with gasoline.

It has an affinity for water that can result in the problems discussed in the main story, such as the growth of bacteria in the bottom of fuel tanks, and which also makes it difficult to transport by pipeline. Its energy content is about 30 percent lower than gasoline, so performance and fuel economy can suffer slightly when it is blended with gasoline. It is more volatile than gasoline and can evaporate more easily, so the effective life of the blend is shorter.

It doesn’t blend easily with gasoline, so it must be mixed just before it is loaded into a tanker for delivery. Improper mixing can result in stratification in the tanker that will allow the delivery pump to pick up concentrated ethanol, which can damage engines and fuel systems.

The EPA currently limits the levels of ethanol as an oxygenate to 10 percent to keep from voiding manufacturer warranties on engines and fuel systems. That also is a level that seems to be tolerated by microprocessor-controlled engine management systems without modification.