Page 29 - Piston Engine-Based Power Plants

CHAPTER 3 3

Types of Reciprocating Engine

Reciprocating engines come in many varieties but they share one com-
mon feature, power is produced through a piston moving backwards
and forwards (reciprocating) inside a cylinder. That power is generated
by pressure inside the cylinder and the pressure is normally produced
by the combustion of fuel in air within the cylinder, causing the gas in
the cylinder to heat up and expand. The way in which this combustion
is initiated distinguishes spark ignition from diesel engines, the two
principal varieties of reciprocating engine. There is another type of
engine in which the expansion within the cylinder is generated using
heat from outside the device. The most important of these ‘external’
combustion engines is the Stirling engine. Another variant, the steam
engine, where the hot steam is generated outside the cylinder and
admitted into it through a valve to create the pressure that drives the
engine cycle, will not be considered here.

A piston moving within a cylinder produces a linear power stroke
as the gas within the cylinder expands. How that linear motion is har-
nessed to provide usable power is key to the operation of an engine
of this type. Moreover, the motion of the piston as a result of this
expansion must at some stage be halted and reversed in order that
another cycle can take place. How that stroke is controlled and how
the piston is returned are features which further differentiate engine
types.
The commonest type of piston engine is a rotating crankshaft
engine in which the backwards and forwards motion of the piston is
converted, using levers and bearings, into rotary motion in a shaft.
The mechanical design ensures that the piston must return when it
reaches the end of its power stroke, provided the engine continues to
turn. These engines will usually have a large flywheel attached to one
end of the shaft. This provides rotational inertia that ensures shaft
rotation continues through from one power stroke to another.

Piston Engine-Based Power Plants. DOI: https://doi.org/10.1016/B978-0-12-812904-3.00003-3
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