Page 21 - Piston Engine-Based Power Plants

14 Piston Engine-Based Power Plants

There are a number of situations in which a specialised source of a
fuel gas encourages the use of a gas engine. The most obvious of these
are landfill waste sites which produce a methane-rich gas by a process
of anaerobic fermentation. This gas can be collected and used to gener-
ate power with a gas engine. Some waste processing plants also carry
out the anaerobic fermentation of biomass waste in order to generate a
gas for burning for heat and power production.
The balance between the use of liquid fuel and gaseous fuel for sta-
tionary power generation is also affected by fuel cost. This is particu-
larly noticeable in a region such as the USA where the availability of
cheaper natural gas as a consequence of shale gas recovery in the
twenty-first century has promoted the use of gas engines for power
generation. At the same time, as already noted, environmental
concerns are reducing the use of diesel fuel.
External combustion engines can exploit almost any heat source so
long as it can provide a sufficiently high temperature. For power gen-
eration, the most widely used external combustion engines are Stirling
engines which can convert solar heat energy into electricity.

GASOLINE (PETROL)
Gasoline in the USA, called petrol in many other parts of the world, is
the main liquid fuel used in spark ignition engines, one of the two
main types of piston engines. The fuel is produced during the refining
of crude oil. The amount of gasoline derived from the oil will depend
on the source and the way the oil is processed. For a typical barrel of
US oil, a 159 litres barrel can deliver up to 72 litres of gasoline. The
latter is a mixture of hydrocarbons with between four and twelve
carbon atoms in each molecule. These include alkanes, alkenes and
cycloalkanes.

An important characteristic of gasoline is its octane rating. This is a
measure of the ability of the fuel to resist spontaneous ignition in the
chamber of the engine before it has been ignited by the spark plug.
The smooth operation of the engine depends on the ignition taking
place in a controlled manner. Spontaneous ignition, often called
‘knocking’, impedes this and if it takes place repeatedly it can damage
an engine.