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


Lecture 4

July 18th, 2013

Signals and Systems

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• Internal combustion engines

• 2 stroke combustion engines


• Diesel engines

Outline

Signals and Systems

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• 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

Signals and Systems

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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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• 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

Signals and Systems

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• 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

Signals and Systems

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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

Signals and Systems

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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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Fuel and air

mixture entering

cylinder.

Signals and Systems

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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.


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

Signals and Systems

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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

Signals and Systems

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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

Signals and Systems

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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.

Signals and Systems

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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

Signals and Systems

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• 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)

Signals and Systems

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• Intake/compression stroke

• Power stroke

• Oil

• Valves

• http://www.youtube.com/watch?v=w14pTBe5LdA

2 Stroke EnginesRecap

Signals and Systems

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2 Stroke Engines

Signals and Systems

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• Internal combustion engines



• Diesel engines

Outline

Signals and Systems

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• Consists of 6 moving parts

• Crankshaft

• Connecting rods

• Pistons

• Intake valve

• Exhaust valve

• Cams

4 Stroke Engines

Piston

Crankshaft

Connecting Rod

Intake ValveExhaust Valve

Signals and Systems

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• 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

Signals and Systems

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• 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

Signals and Systems

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• Consists of 3 stationary parts

• Crankcase

• Combustion chamber

(cylinder)

• Spark plug

4 Stroke Engines

Combustion Chamber

Crankcase

Spark Plug

Signals and Systems

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• 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

Signals and Systems

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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

Signals and Systems

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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

Signals and Systems

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• 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

Signals and Systems

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• 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

Signals and Systems

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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

Signals and Systems

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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

Signals and Systems

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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

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