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rocket engines, each of which are internal combustion engines on the same principle as
previously described. Firearms are also a form of internal combustion engine. [1][2]
Internal combustion engines are quite different from external combustion engines, such as steam
or Stirling engines, in which the energy is delivered to a working fluid not consisting of, mixed
with, or contaminated by combustion products. Working fluids can be air, hot water, pressurized
water or even liquid sodium, heated in a boiler. ICEs are usually powered by energy-dense fuels
such as gasoline or diesel, liquids derived from fossil fuels. While there are many stationary
applications, most ICEs are used in mobile applications and are the dominant power supply for
vehicles such as cars, aircraft, and boats.
Typically an ICE is fed with fossil fuels like natural gas or petroleum products such as gasoline,
diesel fuel or fuel oil. There's a growing usage of renewable fuels like biodiesel for compression
ignition engines and bioethanol or methanol for spark ignition engines. Hydrogen is sometimes
used, and can be made from either fossil fuels or renewable energy.

Figure 1. Diagram of a cylinder as found in 4-stroke gasoline engines.

2. 1. Four Stroke Engines
A four-stroke engine (also known as four cycle) is an internal combustion engine in which the
piston completes four separate strokes while turning a crankshaft. A stroke refers to the full

GiDB|DERGi Sayı 5, 2016