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Ethanol-blended petrol is a great fuel, so what's the fuss?

By William Wells - posted Wednesday, 5 March 2003

The Australian press for the past few months has printed many articles about low-percentage blends of ethanol and petrol. The public has been left with the feeling that something is "wrong" with these fuels, and that the parties promoting ethanol in fuel are trying to foist something on an unsuspecting public that is somehow bad for them.

This article seeks to lay out the truth about ethanol, and as well tell the rest of the story: that it is fuels without ethanol that should give us cause for concern, because of the levels of toxic chemicals that they contain or emit during incomplete combustion.

What is ethanol?

Ethanol is an organic chemical, similar in properties to the hundreds of other components of petroleum-derived gasoline. Yet, there is a big difference: ethanol burns cleaner itself, and also it burns more completely the petrol it is blended into. This is due to the phenomenon of enleanment, possible because the ethanol is already partially oxidised.


Ethanol can be made from fossil fuels such as natural gas liquids or coal, but the source that is most valuable is natural raw materials like sugar cane or grains. This is because the raw material will be remade in exactly the same way during the following crop cycle. This is a result of the action of photosynthesis upon the carbon dioxide released during fermentation at the distillery or combustion in the automobile.

Ethanol and your car.

Engine performance and total emissions are both improved by the addition of ethanol to gasoline. The clean burning nature of ethanol allows you to capture more of the work from the fossil portion of the gasoline, which compensates largely for the lower energy content of ethanol itself. In a 10 per cent blend (E10), all other things being held the same, you might get a zero to 2.7 per cent loss in mileage (kilometres per litre).

Another performance benefit from ethanol is its high octane addition to fuel. Of all the commercially viable octane enhancers possible, nothing delivers more punch than ethanol. The populace still feels the ill effects of the tons of poisonous lead that were spewed into urban environments because of the poor decision to accept lead over ethanol as the octane additive of choice.

Comments have been made in the Australian press that ethanol octane benefits due to an increase in Research number is accomplished at the expense of the Motor number so that the benefit cancels. This is simply untrue. Octane is a measure of the resistance in an engine to damaging knock, which is premature detonation of the fuel before the spark plug fires at the optimal point in the cycle of crankshaft rotation. Research Octane Number is measured under normal driving conditions under light load on a level road. Motor Octane Number is best described as pulling a heavy trailer up a hill; that is, the engine is under considerable load. Like all high octane components added to gasoline, the Research number climbs higher with ethanol addition than the Motor Number, but certainly both values increase.

Other benefits due to ethanol in your car are technical in nature, but may be summarized as follows:

  1. Cleans engine over time, especially harmful combustion chamber deposits.
  2. Improved front end volatility for better cold start and improved operation (driveability and distillation curve effects).
  3. Dissolves any fuel line and fuel tank water, which are sources of corrosion, and eliminates them out the exhaust.
  4. The higher octane of the ethanol blend allows the new cars with higher compression ratio to run without changing refinery operations.

Exhaust versus evaporative emissions.

Adding ethanol to regular unleaded at 10 per cent is an easy way to make unleaded premium, and it extends supplies by 10per cent. Without any modification of the base gasoline, however, the vapour pressure of the fuel will increase slightly, leading to more evaporative, or fugitive, emissions. These are primarily vapours that escape the carbon canister on the automobile, or are forced into the air as the level in a fuel tank rises. They do not include fuel spills, because normally the entire volume of a gasoline spill will evaporate in any case.

The question is whether this greater evaporative mass gives rise to greater pollution potential than the large benefit of exhaust emissions reduction. It is my opinion as a fuel scientist that the nature of the chemical make-up of this new vapour space is less harmful that the unblended, but lower pressure, base gasoline. Ethanol itself, for example, which is now part of the vapour, has a lower ozone-forming potential than olefins and aromatics.

Ethanol and health.

After years of ethanol use in once-polluted major cities in the USA and Brazil, the air is demonstrably cleaner and within federal guidelines for a healthy lifestyle. Not only are toxic species reduced, such as carbon monoxide and aromatics, but also the potential to produce ground level ozone is lower because the elements necessary for its production have been greatly lessened. In particular, high octane benzene, known to cause leukaemia, can be nearly eliminated because ethanol can provide the octane it once did.

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About the Author

Dr. William J. Wells is president of Wells Enterprises International, a Queensland-based consulting and projects company. Dr. Wells has 28 years experience in oxygenated chemicals (the majority in fuel alcohols and ethers) and prior to his move to Australia was Vice President of a company that built a dozen ethanol plants in the USA.

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