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
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
Other benefits due to ethanol in your car are technical in nature, but
may be summarized as follows:
- Cleans engine over time, especially harmful combustion chamber
- Improved front end volatility for better cold start and improved
operation (driveability and distillation curve effects).
- Dissolves any fuel line and fuel tank water, which are sources of
corrosion, and eliminates them out the exhaust.
- 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.
Discuss in our Forums
See what other readers are saying about this article!
Click here to read & post comments.