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Small GasolineEngines
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Engine
A machine for converting energy
into mechanical force and motion.
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Heat Engine
An engine which uses heat to convert
the chemical energy of a fuel intomechanical force and motion
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Two general categories based on design.
External combustion engine
Internal combustion engine
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Engine SizeLargest:The Wartsila-Sulzer RTA96-C
turbocharged two-stroke diesel engine isthe most powerful and most efficient
prime-mover in the world today.
The cylinder bore is just under
38" and the stroke is just over
98".
Each cylinder displaces
111,143 cubic inches (1,820
liters) and produces 7,780
horsepower.Total displacement comes out to 1,556,002 cubic
inches (25,480 liters) for the fourteen cylinder
version.
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Engine Size--cont.
Smallest:
Not much bigger than a stack ofpennies, the "mini engine" is thefirst engine of its size to deliverpower on a continuous basis.
Currently will produce 2.5 watts
of electricity (0.00335 hp). Uses 1/2 fluid ounce of fuel per
hour
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Small Engine
Industry definition: A small engine is
an internal combustion engine
generally rated up to 25 horsepower.
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Small engines are further classified by
ignition, number of strokes, cylinder design,
shaft orientation and cooling system.
(pg. 2 & 3)
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Ignition
Spark ignition
Compression ignition
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Number of Strokes
Four stroke
Two stroke
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Cylinder Design
Small engines usually have one or two cylinders,
but may have as many as four.
Three Common Cylinder Orientations For
Single Cylinder Engines
Vertical Horizontal
Slanted
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Cylinder Design-cont.
V
Horizontally opposed
In-line
Three common cylinder configuration in multiple cylinder
engines:
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Horizontal
Vertical
Small gas engines use three crankshaft orientations:
Cylinder Design-cont.
Multi-position
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When fuel is oxidized (burned) heat is
produced.
Only approximately 30% of the energy
released is converted into useful work.
The remaining (70%) must be removed fromthe engine to prevent the parts from
melting.
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Excessh
eat is removed by:
Cooling system
Exhaust system
Lubrication system
Radiation
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Additional heat is also generated by
friction between the moving parts.
This heat mustalso be
removed.
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Small Engine Development
(pg 5)Year Engine De signer/developer
1680 Gunpowder Christian Huygens
1698 Sa very Pump Thomas Saverly
1712 NewcomenSteam Thomas Newcomen
1763 Watt Double-actingsteam James Watt
1801 Coalgas/electric ignition E ugeneLebon
1802 High pressuresteam RichardTrevithick
1859 Pre-mixedfuelandair E tienneLenoir
1862 Gasoline Nikolaus Otto
1876 Fourcyclegasoline Nikolaus Otto1892 Diesel RudolfDiesel
1953 Die-cast aluminum B&S
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Energy Conversion Principle
All internal combustion engines exhibit andconvert different forms of energy.
Energy is the resource that provides thecapacity to do work.
The two forms of energy used in engines arepotential and kinetic.
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Potential Energy
Stored energy a body has due to its
position, chemical state, or condition.
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Examples of Potential Energy
Fuels have potentialenergy based on theirchemical state.
A compressed spring
has potential energy due
to its mechanical
condition.
Water behind a dam has
potential energy due to
difference in elevation.
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Kinetic Energy
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FlywheelFlywheelWater falling over a dam.
A speeding automobile
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Internal combustion engines operate utilizing
the principles of nine (9) physical phenomena.
Heat
Chemistry
Temperature
Force
Power
Pressure
LeverTorque
Horsepower
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HeatKinetic energy caused
by atoms and
molecules in motion
within a substance.
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In a small engine, as the air-fuel
charge is compressed, internal energy
increases, producing heat.
When the charge is ignited and the burninggases expand, internal energy decreases and
heat is given up.
Engines use heat in two ways
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Heat Transfer
Heat is always transferred from an object of
higher heat to one with lower heat.
Transfer is by conduction, convection,
and radiation
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Temperature
Temperature
Temperature (oF) is theintensity of heat.
The amount of heat ismeasured in BTUs.
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BritishThermal Unit
(BTU)
The amount ofheat required to
raise thetemperature of
1 pound ofwater1oF.
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Force
A force can result in
pressure, torque or work,
depending on how it is
applied.
Anything that changes or tends to change
the state of rest or motion of a body.
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PRESSURE
The cylinder pressure is not
constant. It is highest rightafter combustion, as much as2,000 psi, and decreases as
the piston moves away fromthe cylinderhead.
P
Ti
A force acting on a unit of area.
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Force
In engines the amount offorce exerted on the top of apiston is determined by the
cylinder pressure during thecombustion process.
r e s s u r e
A r e a
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Torque
A force acting on the
perpendicular radialdistance from a point
of rotation.
To (lb-ft) = Force x Radius
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Lever
A lever is a simple machine thatconsists of a rigid bar, which pivots on
a fulcrum with both resistance andeffort applied.
Applied force
Resultant force
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Power is the rate of doing work
P =WT
P =F x D
T
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Horsepower
1 Hp = 33,000 ft-lb/min
A unit of power developed by James Watt to
provide a basis for comparing the amount of
power produced by horses and other engines.
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ChemistryAll internal combustion
engines utilize some
form of fossil fuel.
A fossil fuel is composed of carbon and hydrogen.
When the hydrocarbon is ignited in the
presence of air, the oxygen causes an
exchange of elements which release heat
energy.
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PERFECTCOMBUSTION
EQUATION
C8H 18 + 121
2O 2 + 47N 2 = 8CO 2 + 9H 2 O + 47N 2 + HEAT
Unfortunately, combustion is not perfect---the result is
many unwanted gasses and compounds.
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The End