during the 21st century, crude oil and petroleum products will become very
scarce and costly to find and produce. At the same time, there will likely be
an increase in the number of automobiles and other IC engines. Although fuel
economy of engines is greatly improved from the past and will probably continue
to beimproved, numbers alone dictate that there will be a great demand for fuel
in the coming decades. Gasoline will become scarce and costly. Alternate fuel
technology, availability, and use must and will become more common in the
coming decades. Although there have always been some IC engines fuelled with
non-gasoline or diesel oil fuels, their numbers have been relatively small.
Because of the high cost of petroleum products, some third-world countries have
for many years been using manufactured alcohol as their main vehicle fuel. Many
pumping stations on natural gas pipelines use the pipeline gas to fuel the
engines driving the pumps. This solves an otherwise complicated problem of
delivering fuel to the pumping stations, many of which are in very isolated
regions. Some large displacement engines have been manufactured especially for
pipeline work. These consist of a bank of engine cylinders and a bank of
compressor cylinders connected to the same crankshaft and contained in a single
engine block similar to a V-style engine.
are an attractive alternate fuel because they can be obtained from a number of
sources, both natural and manufactured. Methanol (methyl alcohol) and ethanol
(ethyl alcohol) are two kinds of alcohol that seem most promising and have had
the most development as engine fuel.
advantages of alcohol as a fuel include:
1. Can be
obtained from a number of sources, both natural and manufactured.
2. Is high
octane fuel with anti-knock index numbers (octane number on fuel pump) of over
100 High octane numbers result, at least in part, from the high flame speed of
alcohol. Engines using high-octane fuel can run more efficiently by using
higher compression ratios.
less overall emissions when compared with gasoline.
burned, it forms more moles of exhaust, which gives higher pressure and more
power in the expansion stroke.
5. Has high
evaporative cooling (hfg) which
results in a cooler intake process and compression stroke. This raises the
volumetric efficiency of the engine and reduces the required work input in the
sulphur content in the fuel.
disadvantages of alcohol fuels include:
twice as much alcohol as gasoline must be burned to give the same energy input
to the engine. With equal thermal efficiency and similar engine output usage,
twice as much fuel would have to be purchased, and the distance which could be
driven with a given fuel tank volume would be cut in half. The same amount of
automobile use would require twice as much storage capacity in the distribution
system, twice the number of storage facilities, and twice the volumeof storage
at the service station, twice as many tank trucks and pipelines, etc. Even with
the lower energy content of alcohol, engine power for a given displacement
would be about the same. This is because of the lower air-fuel ratio needed by
alcohol. Alcohol contains oxygen and thus requires less air for stoichiometric
combustion. More fuel can be burned with the same amount of air.
aldehydes in the exhaust. If as much alcohol fuel was consumed as gasoline,
aldehyde emissions would be a serious exhaust pollution problem.
is much more corrosive than gasoline on copper, brass, aluminium, rubber, and
many plastics. This puts some restrictions on the design and manufacturing of
engines to be used with this fuel. This should also be considered when alcohol
fuels are used in engine systems designed to be used with gasoline. Fuel lines
and tanks, gaskets, and even metal engine parts can deteriorate with long-term
alcohol use (resulting in cracked fuel lines, the need for special fuel tank,
etc). Methanol is very corrosive on metals.
4. Poor cold
weather starting characteristics due to low vapour pressure and evaporation.
Alcohol-fuelled engines generally have difficulty starting at temperatures
below 10°C. Often a small amount of gasoline is added to alcohol fuel, which
greatly improves cold-weather starting. The need to do this, however, greatly
reduces the attractiveness of any alternate fuel.
ignition characteristics in general.
have almost invisible flames, which are considered dangerous when handling
fuel. Again, a small amount of gasoline removes this danger.
Danger of storage tank flammability due to low
vapor pressure. Air can leak into storage tanks and create a combustible
Low flame temperatures generate less NOx, but the
resulting lower exhaust temperatures take longer to heat the catalytic
converter to an efficient operating temperature.
Many people find the strong odor of alcohol very
offensive. Headaches and dizziness have been experienced when refuelling an
Vapour lock in fuel delivery systems.