Cooling and Lubrication Systems Chapter 8

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Cooling and Lubrication SystemsChapter 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.

• 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.

• Undesirable properties of cast iron
• Increased weight
• Propensity for oxidation/corrosion
• Difficulty machining
• Relative poor heat conductivity.

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Engine Construction-cont.

• Desirable properties of cast aluminum
• High strength to weight ratio.
• Lower production cost
• Excellent heat dissipation

• Undesirable properties of cast aluminum
• Higher raw material costs
• Less resistant to wear.
• 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
• Increase in size caused by heating.
• When cooled does not return to normal size.
• Thermal distortion
• Asymmetrical or nonlinear thermal expansion.

• Three means of heat transfer
• Conduction
• Convection
• Radiation

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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