Transcript Cooling and Lubrication Systems Chapter 8

Cooling and Lubrication Systems
Chapter 8
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Cooling Systems
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Introduction
• Internal combustion engines
use heat to convert the energy
of fuel to power.
• Not all of the fuel energy is
converted to power.
• Excess heat must be removed
from the engine.
• In engines, heat is moved to
the atmosphere by fluids-water and air.
• If excess heat is not removed,
engine components fail due to
excessive temperature.
• Engine temperature is not
consistent throughout the
cycle.
• Heat moves from areas of
high temperature to areas of
low temperature.
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Engine Construction
• Engine components are
constructed of aluminum and
cast iron alloys, steel and
non-metallic materials.
• The physical properties of
these alloys determines the
physical characteristics of
the engine components.
Undesirable properties of cast
iron:
Desirable cast iron properties.
– Greater density
– Structural integrity when
mechanically or thermally
stressed.
– Porous surface--improved
lubrication.
– Graphite enhanced lubrication.
– Less dimensional changes when
heated.
 Increased weight
 Propensity for oxidation/corrosion
 Difficulty machining
 Relative poor heat conductivity.
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Engine Construction-cont.
Desirable properties of cast
aluminum:
1. High strength to weight
ratio.
2. Lower production cost
3. Excellent heat dissipation
Undesirable properties of cast
aluminum:
1. Higher raw material costs
2. Less resistant to wear.
3. Greater thermal expansion
Aluminum is the material of choice for modern small gas engines.
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Cooling Terms
• Thermal Conductivity
– Ability of a material to conduct
and transfer heat
• Thermal expansion
– Expansion of a material when
it is heated.
• Thermal growth
Three means of heat transfer:
1. Conduction
2. Convection
3. Radiation
– Increase in size caused by
heating.
– When cooled does not return
to normal size.
• Thermal distortion
– Asymmetrical or nonlinear
thermal expansion.
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Heat Movement
• Conduction
– Movement of heat through materials.
• Convection
– Movement of heat by fluids.
• Radiation
– Heat movement by transfer from one body to another.
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Two Cooling Systems
• Small engines use two cooling systems;
– Air
– Liquid
• Both systems have two common features.
– Heat is transferred from the combustion chamber to
the crankcase by the oil.
– A large portion of the excess heat is removed with
the exhaust gases.
• The difference is in the medium used to move
the heat from the engine to the atmosphere.
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Air Cooled Heat
Movement
• In air cooled engines the excess
heat in the combustion chamber
moves through the cylinder walls
by conduction.
• The heat transfers from the
engine parts to the air at the
exterior surfaces and into the
atmosphere by convection.
• The air fins increase the surface
area between the engine and the
air--increasing heat transfer.
• The heart of the system is the fins on the flywheel which pumps
the air around the engine.
• The air flow is directed by the air shrouds.
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Water Cooled Heat
Movement
• Water cooled engines transfer the excess heat from
the combustion chamber through the cylinder walls
by conduction.
• Water flowing past the exterior cylinder walls absorbs
the heat and transfers it to the radiator.
• Air flowing through the radiator absorbs the heat and
transfers it to the atmosphere.
• The system relies on a water pump to circulate the
water through the system and a fan to move air
through the radiator.
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Lubrication System
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Introduction
• The lubrication system
provides oil to appropriate
areas of the engine to
maintain a film of oil to
separate bearing surfaces.
• Oil also transfers combustion
heat to the crankcase.
• An important characteristic of
oil is the viscosity.
• Viscosity is the internal
resistance to flow of a fluid.
• The SAE rates the viscosity
of oils.
• Low viscosity means a high
volume of oil flows through a
specific orifice at a specified
temperature, atmospheric
pressure, and time period.
• Multi-viscosity oils are
popular because they offer
low viscosity characteristics
in low temperatures and high
viscosity characteristics with
higher temperatures.
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Oil Standards
• Service Categories-Gasoline Engines
– SA, SB, SC, SD, SE,
SF, SG, SH are
obsolete.
– SJ: 2001 and older
automotive engines.
– SL: All automotive
engines manufactured
after July 2001.
•
Service Categories--Diesel Engines
– CA, CB, CD, CE are obsolete.
– CF: Off road, indirect-injected
manufactured after 1994 and with fuels
over 0.5% sulfur.
– CF-2: Severe duty, two cycle engines.
– CF-4: High speed, four cycle engines.
– CG-4: Severe duty, high speed, four
stroke, with fuels less than 0.5% sulfur.
– CH-4: High speed, four stroke engines
designed to meet 1998 exhaust
standards.
– CI-4: High speed, four stroke engines
designed to meet 2002 exhaust
standards.
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Lubrication Systems
• Small engines use one of
three lubrication systems.
– Splash
– Pressure filtration
– Pressure
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