Combustion Engines 2 - cs.csub.eduhmehr/Summer Program 2014/Combustion... · Signals and Systems 2...
Transcript of Combustion Engines 2 - cs.csub.eduhmehr/Summer Program 2014/Combustion... · Signals and Systems 2...
Signals and Systems
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California State University, Bakersfield
Kristin Koehler
California State University, Bakersfield
Lecture 4
July 18th, 2013
Signals and Systems
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California State University, Bakersfield
• Internal combustion engines
• 2 stroke combustion engines
• 4 stroke combustion engines
• Diesel engines
Outline
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California State University, Bakersfield
• Consists of 3 moving parts
• Crankshaft
• Connecting rods
• Pistons
2 Stroke Engines
Piston
Crankshaft
Connecting Rod
Signals and Systems
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• The crankshaft is that part of the
engine that converts linear
motion into rotary motion.
• The rotary motion created by the
crankshaft is what drives the
rotation of the wheels on a
vehicle.
• Without a crankshaft there would
not be any way to create rotary
motion, hence a vehicle could not
move.
2 Stroke EnginesCrankshaft
Crankshaft
Signals and Systems
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• The connecting rod connects the
crankshaft to the piston.
• It acts as an extender and a hinge
allowing the crankshaft to move in
a circular motion while the piston
moves linearly (up and down).
Connecting Rod
2 Stroke EnginesConnecting Rod
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• Each piston is housed inside its
own cylinder.
• The piston moves vertically
through the cylinder that houses it.
• The motion of the piston through
the cylinder compresses a mixture
of air and fuel which will be
ignited by a spark plug once it has
reached a certain pressure.
Piston
2 Stroke EnginesPiston
Signals and Systems
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• Consist of 7 stationary parts
• Crankcase
• Intake port
• Transfer port
• Exhaust port
• Cooling fins
• Spark plug (glow plug)
• Cylinder head
2 Stroke Engines
Signals and Systems
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• The crankcase is the lower, round
portion of the cylinder.
• The crankcase houses the crank
and the crankshaft.
• There is NOT an oil reservoir in
the bottom of the crankcase as
there is in a four stroke engine.
Crankcase
2 Stroke EnginesCrankcase
Signals and Systems
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• The intake port is the lower of the
two ports that allow substances in
or out of the cylinder.
• It may be located on either side of
the cylinder and is not always on
the same side as the exhaust port.
• The intake port is where the
mixture of fuel, in this case
gasoline mixed with engine oil,
and air are allowed into the
cylinder.
Intake Port
2 Stroke EnginesIntake Port
Signals and Systems
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California State University, Bakersfield
• The transfer port is located on the
opposite side of the cylinder and
crankcase as the intake port.
• It connects the crankcase and the
cylinder creating a passage for the
fuel and air mixture.
• The intake port is where the
mixture of fuel and air passes
through as it enters the cylinder
above the piston where it will be
compressed.
Transfer Port
2 Stroke EnginesTransfer Port
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California State University, Bakersfield
• The cooling fins are located along
the exterior of the cylinder near
the cylinder head.
• They are located on both sides of
the cylinder to increase efficiency.
• The cooling fins are used to draw
heat out of the cylinder and allow
the heat to dissipate into the
surrounding external air to keep
the engine from overheating.
Cooling Fins
2 Stroke EnginesCooling Fins
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• The spark plug is located at the
center of the top of the cylinder.
• The spark plug creates a spark that
will ignite and burn the fuel
creating power and exhaust.
Spark Plug
2 Stroke EnginesSpark Plug
Signals and Systems
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• The cylinder head is located at the
top of the cylinder.
• The cylinder head is simply the
top of the cylinder that encloses
the piston and keeps the fuel
mixture from escaping until it has
been burned and becomes exhaust
which will exit through the
exhaust port.
Cylinder Head
2 Stroke EnginesCylinder Head
Signals and Systems
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• The way a two stroke engine uses oil is slightly different
than that of the more common four stroke engine.
• In a two stroke engine the oil is actually mixed with the
fuel, typically gasoline, and air mixture that gets injected
into the cylinder.
• Because the oil is mixed with this, that means that when
the fuel is ignited so is the oil. Hence, a two stroke
engine intentionally burns oil and only a portion of the
oil is able to be distributed throughout the engine for
lubrication.
2 Stroke EnginesOil
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2 Stroke EnginesOil
Pros Cons
• All parts are well lubricated
• Lubrication is dispersed
throughout entire engine
through the air
• Burning oil does not mean
that something is wrong
• Constantly burning oil
• Exhaust contains more
pollutants
• Exhaust may have a bluish
color to it and/or an odor of
burning oil
Signals and Systems
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• The two stroke engine has been given its name because
when in operation the piston completes two strokes in
one cycle.
• Intake/Compression stroke
• Power stroke
2 Stroke EnginesHow It Works
Signals and Systems
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• The first stroke that takes place in a two stroke engine is
the intake/compression stroke.
• During this stroke, the cylinder is filled with the mixture
of fuel, gasoline and oil, and air as the piston lowers.
• The fuel mixture is initially released into the crankcase
and makes its way into the transfer port.
• As the piston lowers, the pressure in the crankcase
increases which pushes the fuel through the transfer port
into the cylinder.
2 Stroke EnginesIntake/Compression Stroke
Signals and Systems
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2 Stroke EnginesIntake/Compression Stroke
Fuel and air
mixture entering
cylinder.
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• Once the cylinder is filled with fuel, the piston begins to
rise through the cylinder.
• As the piston rises, the pressure inside the cylinder
increases which also causes the temperature inside the
cylinder to rise in a manner proportional to the pressure.
• At this point both intake and compression have been
achieved.
• While the piston is in the upper portion of the cylinder,
the intake port in uncovered allowing fuel and air to enter
the crankcase.
2 Stroke EnginesIntake/Compression Stroke
Signals and Systems
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• Combustion marks the end of the intake/compression
stroke and the beginning of the power stroke.
• Once the piston has risen to top dead center, when the
piston is as high as it can go and the connecting rod is
entirely vertical, the spark plug is activated.
• The activation of the spark plug creates a spark that
ignites the fuel that has been compressed in the cylinder.
2 Stroke EnginesCombustion
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• The power stroke begins as the compressed fuel in the
cylinder is ignited.
• Upon ignition, the burning fuel expands rapidly which
places a downward force on the piston.
• This force pushes the piston back down the chamber,
uncovering the exhaust port and allowing the exhaust to
escape the cylinder.
2 Stroke EnginesPower Stroke
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• The power that pushes the piston down is also what
creates the rotary motion desired when running an
engine.
• As the piston lowers, the fuel is again being pushed
through the transfer port, allowing the two stroke cycle
to begin again.
2 Stroke EnginesPower Stroke
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• The intake port may have a valve contained within in it
that provides better control of fuel release and prevents
backflow of fuel into the carburetor.
• The most common valve types include
• Reed valves
• Rotary valves
2 Stroke EnginesIntake Valves
• Reed valves are made of some type of reed and only
open to allow fuel into the crankcase.
• Rotary valves are connected to the rotary system and
only uncover the intake port when the piston is in the
upper portion of the cylinder.
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• While reed valves can be quite effective they must be
replaced every so often due to the nature of the reed.
• Rotary valves have several advantages over conventional
engine assemblies such as:
• Higher compression ratios and RPMs
• More compact, lighter cylinder head
• Less complex
• Higher reliability at lower cost
2 Stroke EnginesRotary Valves
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California State University, Bakersfield
• Events that take place BELOW the piston:
• Intake
• Pre-compression
• Transfer
2 Stroke Engines
• Events that take place ABOVE the piston:
• Compression
• Combustion
• Scavenging (release of exhaust)
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• Intake/compression stroke
• Power stroke
• Oil
• Valves
• http://www.youtube.com/watch?v=w14pTBe5LdA
2 Stroke EnginesRecap
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California State University, Bakersfield
2 Stroke Engines
Signals and Systems
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California State University, Bakersfield
• Internal combustion engines
• 2 stroke combustion engines
• 4 stroke combustion engines
• Diesel engines
Outline
Signals and Systems
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California State University, Bakersfield
• Consists of 6 moving parts
• Crankshaft
• Connecting rods
• Pistons
• Intake valve
• Exhaust valve
• Cams
4 Stroke Engines
Piston
Crankshaft
Connecting Rod
Intake ValveExhaust Valve
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California State University, Bakersfield
• Review
• Crankshaft – converts linear motion
into rotary motion
• Connecting rod – connects the
crankshaft to the piston (hinge)
• Piston – moves vertically through
cylinder to compress fuel
4 Stroke EnginesMoving Parts
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California State University, Bakersfield
• Intake valve – the intake valve is opened
as the piston lowers through the chamber
on the first stroke to allow fuel to be
sucked into the cylinder
• Exhaust valve – the exhaust valve is
opened as the piston rises through the
cylinder on the fourth stroke of the cycle
to allow the exhaust to be pushed out
• Rocker arms – the rocker arms press
down on the intake/exhaust valves to
open them
4 Stroke EnginesMoving Parts
Intake Valve
Exhaust Valve
Rocker arm
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California State University, Bakersfield
• Consists of 3 stationary parts
• Crankcase
• Combustion chamber
(cylinder)
• Spark plug
4 Stroke Engines
Combustion Chamber
Crankcase
Spark Plug
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California State University, Bakersfield
• Crankcase – like the two
stroke engine, houses the
crankshaft, but in a four stroke
engine it is also where the oil is
located (in an oil sump)
• Combustion chamber – also
known as the cylinder is what
the piston rises and falls in
• Spark Plug – creates the spark
that ignites the fuel
4 Stroke Engines
Combustion Chamber
Crankcase
Spark Plug
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• In a four stoke engine the oil lies in what
is called an oil sump that is at the bottom
of the crankcase.
• The crankshaft is oiled with every
rotation as it passes through the oil sump
at the bottom of the crankcase.
• Thus, burning oil in a four stroke engine
means that something is wrong and
should be fixed immediately.
4 Stroke EnginesOil
Signals and Systems
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• The four stroke engine consists of four strokes in one
cycle of operation.
• Intake stroke
• Compression stroke
• Combustion stroke (power stroke)
• Exhaust stroke
4 Stroke EnginesHow It Works
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• The intake stroke begins when the
piston is at top-dead center (TDC).
• The intake valve opens and because of
the vacuum that is created in the
cylinder, the mixture of fuel and air is
sucked into the cylinder.
• The intake valve is closed and the
stroke is completed once the piston
reaches bottom-dead center (BDC).
4 Stroke EnginesIntake Stroke
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California State University, Bakersfield
• The compression stroke begins when
the piston is at bottom-dead center.
• With both the intake and exhaust
valves closed, the piston rises through
the cylinder, or combustion chamber,
compressing the mixture of fuel and
air.
• The compression stroke finishes once
the piston reaches top-dead center and
the fuel is at maximum pressure.
4 Stroke EnginesCompression Stroke
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California State University, Bakersfield
• The combustion stroke begins when
the piston is at top-dead center.
• With both the intake and exhaust
valves closed, the spark plug is
triggered, producing a spark that
ignites the fuel in the combustion
chamber. Upon ignition, the fuel
rapidly expands and forces the piston
down into the power stroke.
• The combustion/power stroke finishes
once the piston reaches bottom-dead
center.
4 Stroke EnginesCombustion Stroke
Spark
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• The exhaust stroke begins when the
piston is at bottom-dead center.
• The exhaust valve opens at this point
and as the piston rises through the
cylinder the exhaust fumes are forced
out of the chamber through the
exhaust valve.
• The exhaust stroke finishes once the
piston reaches top-dead center.
• This marks the end of one complete
cycle of a four stroke engine.
4 Stroke EnginesExhaust Stroke
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• http://www.bing.com/videos/search?q=how+a+four+s
troke+engine+works&mid=13323A0C326E68570198
13323A0C326E68570198&view=detail&FORM=VIR
E1
• http://science.howstuffworks.com/transport/engines-equipment/two-stroke.htm
4 Stroke EnginesReview and Comparison
Signals and Systems
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4 Stroke Engines
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• http://auto.howstuffworks.com/engine2.htm
• http://www.outboardmotoroilblog.com/wp-
content/uploads/2009/06/four_stroke_cycle_compression.JPG
• http://1.bp.blogspot.com/_fX9doSZqagk/SxO2gZ1CGtI/AAAAAAAABdQ/lir1rsTqUVc/
s1600/6-3-Two-strokeCompressionIgnition.jpg
References