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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 energyof fuel to power.

Not all of the fuel energy isconverted 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 toexcessive 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 andcast iron alloys, steel and

non-metallic materials.

The physical properties of

these alloys determines the

physical characteristics ofthe 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/corrosionDifficulty machining

Relative poor heat conductivity.

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Engine Construction-cont.

Desirable properties of castaluminum:

1. High strength to weight

ratio.

2. Lower production cost

3. Excellent heat dissipation

Undesirable properties of castaluminum:

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 conductand 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:

1. Conduction

2. Convection

3. 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 excessheat in the combustion chamber

moves through the cylinder walls

by conduction.

The heat transfers from the

engine parts to the air at theexterior 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 fromthe 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 airthrough the radiator.

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Lubrication System

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Introduction

The lubrication system

provides oil to appropriateareas 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 aspecific orifice at a specifiedtemperature, atmospheric

pressure, and time period. Multi-viscosity oils are

popular because they offerlow viscosity characteristicsin low temperatures and highviscosity 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 enginesdesigned to meet 2002 exhaust

standards.

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Lubrication Systems

Small engines use one ofthree lubrication systems.

Splash

Pressure filtration

Pressure