Page 53 - Piston Engine-Based Power Plants

Spark Ignition Engines 45

or more often partly burnt, oil in the exhaust of the engine. For this
reason small two-stroke engines have relatively high levels of certain
emissions.

POWER APPLICATIONS FOR SPARK IGNITION ENGINES

Spark ignition engines can be used in a range of power generation
applications. Small engines, based on automotive engines, are pro-
duced in large numbers and are relatively cheap to buy and reliable
but are inefficient and have relatively short lives. These engines are
most often used for standby and backup duties where the engine will
supply power if the grid supply fails. Under these circumstances neither
efficiency nor lifetime is likely to be of primary importance since the
engines are not required to be in service either very often or for very
long. System sizes can range from a few kW up to 100 kW though
most are smaller than this.

For more mainstream power generation applications, much larger
engines, in the 250 kW to 10 MW range are available, many designed
to burn natural gas. These engines are designed to longer lives, lower
maintenance costs and to achieve high efficiency. Consequently they
are also much more expensive. The largest of these engines can be
highly efficient, some offering up to 49% efficiency for conversion of
natural gas into electricity. These engines can be used for distributed
generation, for local combined heat and power and in some cases for
grid support. Gas engines can also be adapted to burn landfill gas and
biogas. Some can also be adapted to burn ‘furnace gas’, usually a mix-
ture of hydrogen and carbon monoxide, produced during smelting of
metals.