INTERNAL
COMBUSTION ENGINE
WHAT IS AN INTERNAL COMBUSTION (IC)
ENGINE?
An internal
combustion engine (ICE)
is a heat engine where the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the
working fluid flow circuit. In an internal combustion engine the expansion of
the high-temperature and high-pressure gases produced by combustion apply
direct force to some component of the engine. The
force is applied typically to pistons, turbine blades,
or a nozzle.
This force moves the component over a distance, transforming chemical energy into useful mechanical
energy. The first commercially successful internal combustion engine
was created by Étienne Lenoir around 1859[1] and the first modern internal
combustion engine was created in 1864 by Siegfried Marcus.
The term internal combustion engine usually refers to an engine in which
combustion is intermittent, such as the more familiar four-stroke
and two-stroke piston engines, along with variants,
such as the six-stroke piston engine and the Wankel rotary
engine. A second class of internal combustion engines use continuous
combustion: gas turbines, jet engines and most rocket engines,
each of which are internal combustion engines on the same principle as
previously described.
HOW THEY ARE DIFFERENT FROM EXTERNAL
COMBUSTION ENGINE?
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 for spark ignition engines. Hydrogen is sometimes used, and can be made
from either fossil fuels or renewable energy.
IC ENGINES CAN BE CLASSIFIED AS:-
In terms of number of stroke
i. Two stroke engine- A two-stroke, or two-cycle, engine is a type of internal combustion engine which completes a power cycle with two
strokes (up and down movements) of the piston during only one crankshaft revolution.
This is in contrast to a "four-stroke engine", which requires four
strokes of the piston to complete a power cycle. In a two-stroke engine, the
end of the combustion stroke and the beginning of the compression stroke happen
simultaneously, with the intake and exhaust functions occurring at the same
time.
Two-stroke engines often have a high power-to-weight ratio, usually in a narrow
range of rotational speeds called the "power band". Compared to
four-stroke engines, two-stroke engines have a greatly reduced number of moving
parts, and so can be more compact and significantly lighter.
ii. Four Stroke- A four-stroke
engine (also known as four-cycle) is an internal
combustion (IC) engine in which the piston completes
four separate strokes while turning a crankshaft. A stroke refers to the full
travel of the piston along the cylinder, in either direction. The four separate
strokes are termed:
1.
Induction: This
stroke of the piston begins at Top Dead
Center (T.D.C.) and ends at Bottom
Dead Center (B.D.C.). In this stroke the intake valve must be in the open
position while the piston pulls an air-fuel mixture into the cylinder by
producing vacuum pressure into the cylinder through its downward motion.
2.
Compression: This
stroke begins at B.D.C, or just at the end of the suction stroke, and ends at
T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation
for ignition during the power stroke (below). Both the intake and exhaust
valves are closed during this stage.
3.
Power: This is
the start of the second revolution of the four stroke cycle. At this point the
crankshaft has completed a full 360 degree revolution. While the piston is at
T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is
ignited by a spark plug (in a gasoline engine) or by heat generated by
high compression (diesel engines), forcefully returning the piston to B.D.C.
This stroke produces mechanical work from the engine to turn the crankshaft.
4.
Exhaust: During
the exhaust stroke,
the piston once again returns to T.D.C from B.D.C while the exhaust valve is
open. This action expels the spent air-fuel mixture through the exhaust valve.
iii. Six strokes- The six-stroke
engine is a type of internal combustion engine based on the four-stroke engine, but with additional
complexity intended to make it more efficient and reduce emissions. Two types
of six-stroke engine have been developed since the 1890s:
In the first approach, called the single piston design,
the engine captures the heat lost from the four-stroke Otto cycle or Diesel cycle and uses it to power an additional
power and exhaust stroke of the piston in the same cylinder. Designs use either
steam or air as the working fluid for the additional power stroke. The pistons in this type of six-stroke
engine go up and down three times for each injection of fuel. There are two
power strokes: one with fuel, the other with steam or air.
The second approach, called the opposed piston design,
uses a second opposed piston in each cylinder that moves at half
the cyclical rate of the main piston, thus giving six piston movements per
cycle. Functionally, the second piston replaces the valve mechanism of a
conventional engine but also increases the compression
ratio.
APPLICATION OF INTERNAL COMBUSTION ENGINES:-
i. Internal combustion engines are most
commonly used for mobile propulsion in automobiles, equipment, and other
portable machinery.
ii. In mobile scenarios internal combustion is
advantageous, since it can provide high power to weight ratios together with
excellent fuel energy-density.
iii. These engines have appeared in almost all automobiles, motorcycles, boats, and in a wide variety of aircraft and locomotives. Where very high power is required, such as jet aircraft, helicopters, and large ships, they appear mostly in the form
of turbines.
iv. They are also used for electric generators
and by industry.
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