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The increasing cost of gasoline, and the new laws requiring
alternative fuels have turned the attention of car and truck
designers to substitutes. Chief among alternative fuels is alcohol.
Considerable research has been done, and is still carried out, for
alcohol in spark ignition engines. Alcohol fuels were used
extensively in Germany during WWII, and alcohol blends are used in
many vehicles at the present time.
Methanol and ethanol are the forms of alcohol receiving the most
attention. Both are made from non-petroleum products. Methanol can be
produced from coal, and ethanol can be made from farm products such
as sugar cane, corn, and potatoes. Both alcohols have a higher octane
number than gasoline. High heat of vaporization, however, indicates
that the use of alcohol could give harder starting problems than
gasoline, which means a need for a larger fuel tank and larger jet
sizes in the carburetor. It requires less air for combustion, though,
which compensates for the high calorific values. In proportion, this
could result in practically the same air-fuel ratio for all three.
Experimental tests have shown that alcohol-fueled spark ignition
engines can produce as much or slightly higher power than gasoline.
Alcohol fuels have a higher self-ignition temperature than gasoline,
which rates them better from a safety standpoint, but this same
quality bars them from use in a diesel engine which depends on the
heat of compression to ignite the fuel. At the present time, only
ethanol can be blended in small concentrations (10%%) with gasoline.
Because of the high octane rating, alcohols can be used in relatively
high compression ratios, and experiments indicate that emissions from
engines fueled by alcohol would require the use of exhaust gas
recirculation controls.
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