1. Four Stroke Engine
History of the FourStroke
Automobile Engine
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2. Four Stroke Engine
History of the Four-Stroke
Automobile Engine
Perhaps the most well known engine type in the world, the automotive fourstroke engine has become the power plant of choice for today's consumers
due to itsgreater efficiency and cost effectiveness over alternate
reciprocating engines.The story of the internal combustion engine began in
1680 with a Dutch physi-cist, Christian Huygens, who conceptually
designed an engine fueled by gun powder. However, the first internal
combustion engine was actually built by a Sweetish
inventor by the name of Francios Isaac de Rivaz in 1807. Through the
combustionof a hydrogen and oxygen mixture, his engine, with some
difficulty, powered acrudely constructed automobile. As the years went on,
other inventors modified the design to be fueled by anything from gasoline
to coal. The next greatest leap came in 1862 when a French engineer,
Alphonse Beau de Rochas, designed and patented the first four-stroke
engine. In 1864 an Austrian engineer, Siegfried Marcus, build the first gasoline powered vehicle, which was comprised of a cart
and a one cylinder engine. But the biggest break through came in 1876
when Nikolaus August Otto invented the first successful four-stroke engine,
aptly nick-namingthe four-stroke cycle the ”Otto Cycle.” [1] The next great
milestone in the development of the four stroke engine was achieved by
Gottlieb Daimler in 1885, who invented an engine with a vertical positioned
cylinder, fueled by gasoline injected into a cylinder chamber through a
carburetor. The innovations from these important inventors over the years
culminated in Daimler's engine which is commonly referred to as the ”blue
print” to the modern day internal combustion engine. [1] From the inception
of the four-stroke internal combustion engine, many paths have been
explored and followed to create the superior design, especially in the
configuration of the cylinders. In general, there are seven types of
reciprocating engine designs, an engine that employs one or more cylinders
in which a piston(s) reciprocates back and forth. The first of these designs
was the single cylinder engine. After its success, designers began to play
with twin engines, or two cylinder engines which lead to the In-Line
Engine, the V Engine, the Opposed Cylinder Engine, the W engine, the
Opposed Piston Engine, and the Radial Engine. These different setups
where further explored with engines such as the Vauxhall Wyvern and
Velox engines to the Ford V-Four engine, utilizing an even greater numbers
of cylinders than the original twin engines.
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3. Four Stroke Engine
Today's four-stroke engine manufacturer's mainly build In-Line or V
configured engines. Perhaps the most widely recognized engine today is the
Chevrolet Small Block V8 Engine. This engine was made popular through
their depend ability and through hobbyists and the performance market
because of the inter changeability of parts. After 35 years, General Motors
discontinued their infamous engine, replacing it with the new Generation II
engine in 1992. Although Chevroletseemingly has dominated today's after
market industry, other manufacturers have successfully made engines for
their vehicles from the Ford V-Eight, to the Cadillac North Star, to the
Porsche In-Line Six as well as mainly others.
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4. Four Stroke Engine
Basic Components of
Four-Stroke Engines
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5. Four Stroke Engine
Basic Components of Four-Stroke Engines
A. Intake Valve- opens at the proper time to let in air and
fuel.
B. . Valve Cover- Protects the valves and the valve
springs. Keeps dirt out and lubricating oil in.
C. . Intake Port- the passageway in a cylinder head for
the fuel and air to pass through.
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6. Four Stroke Engine
D. Head- a platform containing most of the parts of the
combustion chamber.
E. Coolant- circulating water and antifreeze to keep the
temperature regulated.
F. . Engine Block- cast in one piece. The basis for most
of the parts of the engine.
G. Oil Pan- where the oil is collected and recirculated.
H. Oil Sump- the collected oil primarily for lubricating
the crankshaft and rod bearing
I. Camshaft- a round shaft with lobes, that rotates to
open and close the fuel and exhaust valves.
J. . Exhaust Valve- open at the proper time to release the
exhaust
K. Spark Plug- a device, inserted into the combustion
chamber for firing an electrical spark to ignite air-fuel
mixture
L. Exhaust Port- the passageway in a cylinder head, for
the exhaust to pass through
M. . Piston- the part of the engine that moves up and
down in the cylinder converting the gasoline into
motion
N. Connecting Rod- links the piston to the crankshaft.
O. Rod Bearing- used to reduce friction to the rod and
crankshaft
P. Crankshaft- converts the up and down motion of the
piston into a turning, or rotating motion
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7. Four Stroke Engine
Engine-Operating Cycle
of Most Petrol and Diesel
Engines
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8. Four Stroke Engine
Engine-Operating Cycle of Most Petrol and Diesel
Engines
Each movement of the cylinder up or down the cylinder is one stroke of
the four stroke combustion cycle or Otto cycle. Most modern internal
combustion engines use the four stroke cycle. The four
stroke cycle consists of an induction stroke where air and fuel are taken
into the cylinder as the piston moves downwards, a compression stroke
where the air and fuel are compressed by the upstroke of the cylinder, the
ignition or power stroke where the compressed mixture is ignited and the
expansion forces the cylinder downwards, and an exhaust stroke where the
waste gases are forced out of the
cylinder. The intake and outlet ports open and close to allow air to be drawn
into the cylinder and exhaust gases to be expelled.
During the intake stroke the inlet valve opens at the top of the cylinder, as
the piston moves down air and fuel are drawn into the cylinder. As the
piston reaches its lowest position the inlet valve closes and the piston
travels upwards compressing the air -fuel mixture. As the pi ston reaches its
highest position
at maximum compression a spark ignites the mixture causing a rapid
expansion of gas raising the pressure in the cylinder and forcing the piston
downwards. Once the cylinder has reached its lowest position the outlet
port o pens and as the piston rises up the cylinder the exhaust gases are
forced out. The valves which open and close the port are sprung to make
them naturally close. The valves are opened by a system of rotating cams
and pushrods driven by a camshaft which in t urn is timed and driven from
the crankshaft. The valve timings vary between engines depending on the
setup, generally there is some overlap to speed the flow of gases
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9. Four Stroke Engine
Intake
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10. Four Stroke Engine
Intake
The intake stroke of the combustion cycle is when
the piston travels down the cylinder with the intake port/ports open. A
mixture of air and explosive fuel are drawn into the cylinder, the
proportions of which are called the air -fuel ratio. Both the air-fuel ratio and
the quality of the mixture (dispersion, droplet size etc.) is i mportant for an
efficient combustion process. There are two methods of mixing air and fuel
in a combustion engine, using a carburettor or fuel injection system.
In a carburetted engine, during the intake stroke of the piston a vacuum is
created in the inlet manifold. With a multi cylinder engine the vacuum is
almost constant. The carburettor is located at the top of the manifold and air
is drawn through it by the vacuum created in the manifold. The carburettor
has a small fuel chamber supplied from the fuel tank by a pump, fuel passes
through the carburettor to small fuel jets positioned in the air flow. The flow
of air past the jets creates a pressure difference causing the fuel to be drawn
out. The fuel vaporises in the air flow and passes through the manifold and
into cylinders on their intake stroke. The diagram below shows the basic
operation of a fixed jet carburettor.
Electronic fuel injection systems spray fuel at high pressure either directly
into the combustion chamber or into the intake port of the cylinder during
the intake stroke. Using fuel injection enables improved control over the air
-fuel mixture and reduces the power required to draw fuel from the jets. The
diagram below shows a typical electronic fuel injection system. Diesel
engines typically use direct injection which injects fuel directly into the
combustion chamber during the compression stroke. The intake stroke on a
diesel engine only draws air into the cylinder.
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11. Four Stroke Engine
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12. Four Stroke Engine
Compression
Compressi
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13. Four Stroke Engine
The compression stroke is the upwards movement of the piston in the
cylinder with the valves closed following the intake stroke. This upwards
motion compresses the fuel air mixture inside the combustion chamber
raising the pressure. The difference between the initial volume of the
cylinder and the final volume at the top of the compression stroke is known
as the compression ratio. Typically this is approximately 9:1 in spark
ignition engines and 15:1 for diesel engines. The compression ratio is
particularly important in compression fired engines such as diesel engines.
The fuel - air mix and compression ratio is critical to avoid pre -ignition
which is the abnormal ignition of fuel in the combustion chamber before the
combustion stroke. In diesel engines the fuel is injected under high pressure
towards the top of the compression stroke. The distribution of fuel before
combustion is also of interest because it affects the efficiency of
combustion.
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14. Four Stroke Engine
Combustion
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15. Four Stroke Engine
Combustion
Spark plugs are used to generate the spark which ignites the compressed
fuel and air mixtu re in the spark ignition engine. To generate the spark a
high voltage of around 20,000 Volts is applied. Low voltage current is fed
through the primary winding of an inductor coil generating a magnetic field.
The high voltage is generated when the low volt age supply is interrupted
and the magnetic field breaks down generating a high voltage in the
secondary winding which has a much larger number of coils. The low
voltage supply to the coil is controlled by the distributor which also controls
the spark plug that the high voltage surge is sent to. The distributor timing
is critical and usually is timed mechanically from the engine. The diagram
below shows the typical set - up of an ignition system for a spark ignition
engine. Compression ignition engines such as the diesel engine do not use
spark plugs to ignite the fuel - air mix. When the piston reaches the top of
the compression stroke the temperature and pressure in the combustion
chamber is sufficient to ignite the mixture. Controlled ignition in both spark
ignition and diesel engines is essential for efficient combustion and avoid
uncontrolled combustion effects such as pre- ignition, auto - ignition and
engine knock.
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16. Four Stroke Engine
Exhaust
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17. Four Stroke Engine
Exhaust
Exhaust gases are pushed out of the cylinder by the
upwards motion of the piston following the ignition stroke. The exhaust
gases are passed into the exhaust manifold and channelled into the exhaust
pipe where they are released into the atmosphere. The exhaust system may
contain a smoke box to trap the larger soot particles, it may also be fitted
with a catalytic converter which removes some of the harmful components
from the exhaust gases. On newer cars some of the exhaust gases are
recycled back into the inlet system (typically at the manifold or air filter),
this is known as exhaust gas re - circulation EGR. The efficiency of the
combustion process and the design of the engine determine the exhaust
constituents. Typically exhaust gases contain oxygen, nitrogen, water
vapour, carbon dioxide, carbon monoxide, hydrogen, nitrous oxides,
particulates and unburned hydrocarbons.
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18. Four Stroke Engine
Exhaust and Inlet
Valve Overlap
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19. Four Stroke Engine
Exhaust and Inlet Valve Overlap
Exhaust and inlet valve overlap is the transition
between the exhaust and inlet strokes and is a practical necessity for the
efficient running of any internal combustion engine. Given the constraints
imposed by the operation of mechanical valves and the inertia of the air in
the inlet manifold, it is necessary to begin opening the inlet valve before the
piston reaches Top Dead Centre (TDC) on the exhaust stroke. Likewise, in
order to effectively remove all of the combustion gases, the exhaust valve
remains open until after TDC. Thus, there is a point in each full cycle when
both exhaust and inlet valves are open. The number of degrees over which
this occurs and the proportional split across TDC is very much dependent
on the engine design and the speed at which it operates.
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20. Four Stroke Engine
Four Stroke Petrol
Engine
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21. Four Stroke Engine
The cycle of operation in a four stroke petrol engine is completed
in two revolutions of crank shaft or four strokes of piston. Stroke is
defined as the distance traveled by the piston from one of the dead
centers to the other dead centre. It is also equal to two times the crank
radius. Hence in a four stroke engine work is obtained only during one
stroke out of the four strokes of the piston required to complete one
cycle. This engine works on Otto or constant volume cycle. 1. Suction
stroke: To start with the piston is at or very near T.D.C. and the inlet valve
is open and exhaust valve is closed. As the piston moves from
T.D.C. to B.D.C. rarefaction is formed in the cylinder which causes
the charge to rush in and fill the space vacated by the piston. The
charge consists of a mixture of air and petrol prepared by the
carburetor. The admission of charge inside the engine cylinder
continues until the inlet valve closes at B.D.C. 2. Compression stroke: Both
the valves are closed and the piston moves from B.D.C. to T.D.C. The
charge is compressed up to a compression ratio of 5:1 to 9:1 and pressure
and temperature at the end of compression are about 6 to 12 bar and 250º C
to 300º C respectively. 3. Working, Power or Expansion stroke: When
the piston reaches T.D.C. position, or just at the end of compression
stroke, the charge is ignited by causing an electric spark between the
electrodes of a spark plug, which is located some where in the walls
of cylinder head. During combustion the chemical energy of fuel is released
and there is rise in temperature and pressure of gases. The temperature of
gases increases to about 1800º C to 2000º C and the pressure reaches 30 to
40 bar. Up till now the volume of gases formed however remains almost
constant with both valves closed. Now the combustion products expand
and push the piston down the cylinder. The reciprocating piston motion is
converted into rotary motion of crankshaft by a connecting rod and crank.
During expansion the pressure drops due to increase in the volume of gases
and absorption of heat by cylinder walls. 4. Exhaust stroke: Theoretically
exhaust valve opens at the end of working stroke when the piston is at
B.D.C. position. But actually exhaust valve begins to open when about 85
% of the working stroke is completed. A pressure of 4 to 5 bar at this instant
forces about 60 % of the burnt gases into the exhaust manifold at high
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22. Four Stroke Engine
speed. The remaining burnt gases are cleared off the swept volume when
the piston moves from B.D.C. to T.D.C. During this stroke the pressure
in side the cylinder is slightly above the atmospheric value. Some of
the burnt gases are however left in the clearance space. The exhaust
valve closes shortly after the piston reaches T.D.C. The inlet valve opens
slightly before the end of exhaust stroke and the cycle repeats.
Four Stroke Engine
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23. Four Stroke Engine
Working Of Four Stroke Engine
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24. Four Stroke Engine
Four Stroke Diesel
Engine
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25. Four Stroke Engine
The cycle of operation in a four stroke diesel engine is completed in two
revolutions of crankshaft or four strokes of piston using diesel oil as fuel.
This engine works on diesel cycle. 1. Suction Stroke: Starting of engine
is done by an electric motor or manually. In both cases the energy is
supplied to the engine. In this stroke the inlet valve opens and the outlet
valve remains closed. Piston moves from T.D.C. to B.D.C. and in
this way a vacuum is created in the cylinder. This vacuum is filled
by air alone and piston reaches to B.D.C. 2. Compression Stroke: Both
valves are closed. This time piston moves from B.D.C. to T.D.C. Air is
compressed in this stroke up to a compression ratio of 15:1 to 22:1 and a
very high temperature is produced due to high pressure. The high
temperature is the only cause of combustion of the fuel. The piston takes the
power in this stroke from the flywheel. During this stroke the pressure and
temperature attain a high value of 40 to 60 bar and 600º C to 700º C. 3.
Working Stroke: At the end of compression stroke or when the
piston reaches the T.D.C. position, a fine spray of diesel is injected in the
cylinder through injector. The fuel burns by the heat of compressed air and
due to its burning the power is produced. This power pushes the piston
downward i.e. from T.D.C. to B.D.C. The excess energy of the piston is
stored in the flywheel of the engine, which is further used for the
remaining three strokes of the engine. The reciprocating motion of the
piston is converted into the rotary motion of the crankshaft by
connecting rod and crank. During expansion the pressure drops due to
increase in volume of gases and absorption of heat by cylinder walls. 4.
Exhaust Stroke: The exhaust valve begins to open when about 85%
of the working stroke is completed. The force of piston coming from
B.D.C. to T.D.C. forces the burnt gases into the exhaust manifold. Some
of the gases are forced out due to higher pressure in the cylinder and the
remaining gases are forced out by the piston. Some of the burnt gases are
however left inside the clearance space. The exhaust valve closes shortly
after T.D.C. The inlet valve opens slightly before the end of exhaust
and in this way the cycle repeats.
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26. Four Stroke Engine
Four Stroke Disele Engine
Working Of Four Stroke Disele Engine
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27. Four Stroke Engine
Comparison between
petrol and diesel engine
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28. Four Stroke Engine
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29. Four Stroke Engine
REFERENCES
Googl.com
Wikkiped.com
Mchanicalengineers.com
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