Page 87 - The phenomenal demographic and technological changes in the 21st century

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6. Які марки автобензинів Вам f) Automobile gasoline includes the A-76, A-

відомі? 80, А-92, А-95, А-98 gasoline grades.

TEXT B

BUTANE AS AN OCTANE ENHANCER

1. One of the most important octane enhancers is butane. Butane vaporizing

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at about 31 C at normal atmospheric pressure is dissolved easily in gasoline and
has an octane rating of about 92. Blending it into gasoline not only raises the

gasoline octane but also enables refineries to improve their profit margins since it

costs a lot less to make than other gasoline components.

2. Butane is a highly volatile substance. You see the wavy-looking air when

you put gas in your car. It is mostly escaping butane - a good reason for not

smoking at gas stations.

3. Some volatility is necessary for gasoline. A motor fuel has to evaporate

before it can be burned in an engine. The fuel going into engine cylinders is a

vapour not a liquid. Once a car is up and running vaporizing the gasoline is easy:

the engine heat takes care of it. But starting a cold engine, especially on a cold day

requires a fuel vaporizing very readily all by itself.

4. Too much volatility causes problems, however. On a hot day (or on a cold

day in a hot engine) excessively volatile fuels can cause a condition called vapour

lock. This occurs when evaporated fuel stymies the fuel pump, which can pump

only liquids, and brings everything to a halt. Excessive volatility can also cause

starting and restarting problems. As a result, gasoline makers sell different blends

in different geographic regions at different times of the year. Some producers alter

their blends to compensate for changes in the weather.

5. Highly volatile fuels also cause greater air pollution. All cars leak fuel

vapours, even when they are not in use. The vapours seeping out of carburettors,

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