I.C. ENGINES
LECTURE NO: 14
(5 May 2014)
Engine Heat
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Combustion can reach 4500ºF (2500ºC)
This is hot enough to melt metal parts
The cooling system removes excess heat
Importance of Heat Transfer
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Peak burn gas temperature leads to heat fluxes to
the chamber walls as high as 10 M/m2
During other part of the operating cycle heat flux is
essentially zero
Flux varies with location
High heat flux zone – thermal stresses are more results in Fatigue cracking
Temp should be less then
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Cast Iron
Al
400˚C
300 ˚C
Importance of Heat Transfer
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Gas side surface of the cylinder wall must be below
180˚C to prevent deterioration of lubrication oil
Spark plug and valves must be cool to avoid
Knocking and pre ignition problems
Heat Transfer Affects
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Engine Performance
Efficiency
Emission
Modes Heat Transfer
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Conduction
Convection
Radiation
Conduction
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Conduction
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Cylinder head
Cylinder walls
Pistons
Through pistons rings
Engine block
Manifolds
Convection
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Through fluid in motion
Between fluid and solid surface in relative motion
Heat is transferred by FORCE CONVECTION between
the in- cylinder gases and the
 Cylinder head
 Valves
 Cylinder Walls
 Piston during induction
 Compression process
 Expansion process
 Exhaust process
Convection
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Radiation
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Overall Heat Transfer Process
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Maintain Operating
Temperature
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180ºF to 210ºF (80ºC to 100ºC)
Ensures that clearances are correct
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when an engine warms
temperature, parts expand
to
operating
Ensures proper combustion, minimum
emissions, and maximum performance
Reach Operating Temperature
Quickly
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This minimizes several conditions:
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poor combustion (poor fuel vaporization)
part wear
oil contamination
reduced fuel economy
increased emissions
Heater Operation
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The cooling system circulates coolant to
the vehicle’s heater
Engine heat is used to warm the
passenger compartment
Cooling System
Cooling System Operation
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The water pump forces coolant through
the engine water jackets
The pump is belt or gear driven off the
crankshaft
Cold Engine Operation
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The thermostat is closed
The coolant circulates inside the engine
The engine warms quickly
Hot Engine Operation
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At operating temperature, the thermostat
opens
Heated coolant then flows through the
radiator
Excess heat is transferred from the coolant
to the air flowing through the radiator
Cooling System Types
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Two common types:
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air cooling
liquid cooling
Air Cooling Systems
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Large cylinder cooling fins and outside
air remove excess heat
The cooling fins increase the surface
area of the metal around the cylinder
This allows enough heat to transfer to
the outside air
Plastic or metal shrouds direct air over
the cylinder fins
Liquid Cooling Systems
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Circulate coolant through the water
jackets
Combustion heat is transferred to the
coolant
The cooling system carries it out of the
engine
Liquid Cooling Advantages
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Precise temperature control
Less temperature variation
Reduced emissions
Improved heater operation
Air Cooling versus Liquid
Cooling
Liquid Cooling
Heat is transferred to cylinder wall and then
into the coolant, where it is carried away
Conventional Coolant Flow
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Hot coolant flows from the cylinder
head to the radiator
After being cooled in the radiator, the
coolant flows back into the engine block
Reverse Flow Cooling
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Cool coolant enters the head and hot
coolant exits the block to return to the
radiator
Helps keep a more uniform temperature
throughout the engine
Found on high-performance engines
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Components:
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water pump
radiator hoses
radiator
fan
thermostat
Water Pump
A ribbed belt powers this pump
Crank
pulley
Impeller
Ribbed
belt
Water
pump
pulley
Impeller Pump
Coolant is thrown outward by centrifugal
force, producing suction in the center of
the pump housing
Water Pump Cutaway
Seal leakage will drip from the vent hole
Coolant Flow
Coolant Flow (Conventional)
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Coolant flows out of the radiator,
through the lower hose, into the pump
It then flows through the pump, around
the cylinders, through the heads, up
through the thermostat, and back into
the radiator
Hoses
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Radiator hoses
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carry coolant between the engine water
jackets and the radiator
the lower hose is exposed to water pump
suction, so a spring may needed to prevent
collapse
Heater hoses
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carry hot coolant to the heater core
smaller diameter than radiator hoses
Radiator and Heater Hoses
Radiator Hoses
Two basic types of radiator hoses
Hose Clamps
Three basic types of hose clamps
Radiator
Transfers coolant heat to the outside air
Radiator Types
Downflow
Crossflow
Transmission Oil Cooler
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Often placed in the radiator on cars
with automatic transmissions
Prevents the transmission fluid from
overheating
Transmission Oil Cooler
Small tank inside one
of the
radiator tanks
Oil Cooler System
Radiator and A/C Condenser
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The condenser is usually mounted in
front of the radiator
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in this arrangement, heat from the
condenser flows through the radiator,
reducing efficiency
Side-by-side mounting is sometimes
used
Radiator and A/C Condenser
This vehicle has
side-by-side
mounting
Radiator Cap
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Seals the radiator
Pressurizes the system
Relieves excess pressure
Allows coolant flow between
radiator and the coolant reservoir
the
Radiator Cap
Radiator Cap Pressure Valve
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Spring-loaded disk
Normally, water boils at 212ºF (100ºC)
For each pound of pressure increase, the
boiling point goes up about 3ºF (1.7ºC)
Typical pressure:
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12–16 psi (83–110 kPa)
raises
the
boiling
250–260ºF (121–127ºC)
point
to
Radiator Cap
Vacuum Valve
Opens to allow flow back into the radiator
when the coolant temperature drops
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Closed cooling system
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uses an expansion tank
overflow tube is routed into reservoir tank
Open cooling system
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allows excess coolant to leak onto the
ground
Pressure Cap Operation
Hot engine
Pressure Cap Operation
Cold engine
Cooling System Fans
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Pull air through the core of the radiator
Increase the volume of air flowing
through the radiator
Driven by fan belt or electric motor
Flex Fan
High engine speed causes the blades to
flex, reducing the blowing action
Fluid Coupling Fan Clutch
Filled with
silicone-based oil
The clutch slips at
higher rpm
Thermostatic Fan Clutch
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Bimetal spring controls clutching action
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cold—clutch slips
hot—clutch locks
Electric Cooling Fans
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An electric motor and a thermostatic
switch provide cooling
Common
on
transverse-mounted
engines
Save energy and increase cooling
efficiency
Fans only function when needed
Electric Fan Operation
Cold engine
Electric Fan Operation
Hot engine
PCM-Controlled Fans
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When cold, the ECM does not energize
the fan relays
After warm-up, the ECM feeds current
to the fan relay coils, closing the relay
contacts
High current flows to fans
ElectronicControlled Fans
Radiator Shroud
Ensures that the fan
pulls air through
the radiator core
Thermostat
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Senses the coolant temperature and
controls coolant flow through the
radiator
Reduces coolant flow in a cold
engine
Increases coolant flow in a hot
engine
Thermostat
A temperature-sensitive valve
Thermostat Operation
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Cold engine
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wax-filled pellet has contracted
spring holds valve closed
Hot engine
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when heated, pellet expands
spring tension is overcome
valve opens
Thermostat Operation
A. Cold engine
B. Hot engine
Thermostat Operation
Cold engine
Thermostat Operation
Hot engine
Bypass Valve
Permits coolant
circulation through the
engine when the
thermostat
is closed
Bypass Thermostat
Blocks off the bypass at operating
temperature
Impeller
Flow to
radiator
Water pump
drive pulley
Water pump
housing
Bypass
spring
Bypass
flow
Thermostat
Main
spring
Main flow
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Two common types:
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temperature warning light
engine temperature gauge
Temperature Warning Light
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When the coolant becomes too hot, a
temperature sending unit (switch) in
the block closes, completing a light
circuit
The warning light glows
Warning Light Circuit
Engine Temperature Gauge
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Shows the exact operating temperature
Components:
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gauge
variable resistance sending unit
Engine Temperature Gauge
Operation
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When cold, the sending unit has a high
resistance
Current flow through the gauge is low
The gauge reads cold
When hot, the sending unit resistance
lowers
Current flow through the gauge
increases, the needle deflects to the
right
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Composed of ethylene glycol mixed
with water
Prevents winter freeze-up
Prevents rust and corrosion
Lubricates the water pump
Cools the engine
Corrosion Protection
Protected with Water only
antifreeze
Antifreeze/Water Mixture
50% ANTIFREEZE
50% WATER
Lowers the coolant freezing point
to about –34 ºF (–37 ºC)
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Aids engine starting in cold weather
120-volt heating element mounted in
the block water jacket
Common on diesel engines
Block Heater Installation
Engine and Cooling System
Engine and Cooling System