1. I.C. ENGINES
LECTURE NO: 14
(5 May 2014)

2. Engine Heat Combustion can reach 4500ºF (2500ºC)
This is hot enough to melt metal parts
The cooling system removes excess heat

3. Importance of Heat Transfer
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
Cast Iron 400˚C
Al 300 ˚C

4. Importance of Heat Transfer
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

5. Heat Transfer Affects
Engine Performance
Efficiency
Emission

6. Modes Heat Transfer
Conduction
Convection
Radiation

7. Thermal Dynamics
Convection
Radiation
Conduction

8. Heat Transfer Only 1/3 of heat produced in an engine is actually used.
Where does the remainder go?
What are some “very good” and “good” heat conductors?
What is ambient air temperature?
Thermal Dynamics in relation to material’s surface condition.
Thermal Dynamics in relation to color.

9. Conduction

10. Conduction Cylinder head Cylinder walls Pistons Through pistons rings
Engine block
Manifolds

11. Convection 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

12. Convection

13. Radiation

14. Overall Heat Transfer Process

15. Maintain Operating Temperature
180ºF to 210ºF (80ºC to 100ºC)
Ensures that clearances are correct
when an engine warms to operating temperature, parts expand
Ensures proper combustion, minimum emissions, and maximum performance

16. Reach Operating Temperature Quickly
This minimizes several conditions:
poor combustion (poor fuel vaporization)
part wear
oil contamination
reduced fuel economy
increased emissions

17. Heater Operation
The cooling system circulates coolant to the vehicle’s heater
Engine heat is used to warm the passenger compartment

18. Cooling System

19. Cooling System Operation
The water pump forces coolant through the engine water jackets
The pump is belt or gear driven off the crankshaft

20. Cold Engine Operation The thermostat is closed
The coolant circulates inside the engine
The engine warms quickly

21. Hot Engine Operation 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

22. Cooling System Types
Two common types:
air cooling
liquid cooling

23. Air Cooling Systems
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

24. Liquid Cooling Systems
Circulate coolant through the water jackets
Combustion heat is transferred to the coolant
The cooling system carries it out of the engine

25. Liquid Cooling Advantages
Precise temperature control
Less temperature variation
Reduced emissions
Improved heater operation

26. Air Cooling versus Liquid Cooling

27. Liquid Cooling
Heat is transferred to cylinder wall and then into the coolant, where it is carried away

28. Conventional Coolant Flow
Hot coolant flows from the cylinder head to the radiator
After being cooled in the radiator, the coolant flows back into the engine block

29. Reverse Flow Cooling
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

30. Basic Cooling System Components: water pump radiator hoses radiator
fan
thermostat

31. A ribbed belt powers this pump
Water Pump
A ribbed belt powers this pump
Crank pulley
Impeller
Ribbed belt
Water pump pulley

32. Impeller Pump
Coolant is thrown outward by centrifugal force, producing suction in the center of the pump housing

33. Seal leakage will drip from the vent hole
Water Pump Cutaway
Seal leakage will drip from the vent hole

34. Coolant Flow

35. Coolant Flow (Conventional)
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

36. Hoses Radiator hoses Heater hoses
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
carry hot coolant to the heater core
smaller diameter than radiator hoses

37. Radiator and Heater Hoses

38. Two basic types of radiator hoses

39. Three basic types of hose clamps

40. Transfers coolant heat to the outside air
Radiator
Transfers coolant heat to the outside air

41. Radiator Types
Downflow
Crossflow

42. Transmission Oil Cooler
Often placed in the radiator on cars with automatic transmissions
Prevents the transmission fluid from overheating

43. Transmission Oil Cooler
Small tank inside one of the radiator tanks

44. Oil Cooler System

45. Radiator and A/C Condenser
The condenser is usually mounted in front of the radiator
in this arrangement, heat from the condenser flows through the radiator, reducing efficiency
Side-by-side mounting is sometimes used

46. Radiator and A/C Condenser
This vehicle has side-by-side mounting

47. Radiator Cap Seals the radiator Pressurizes the system
Relieves excess pressure
Allows coolant flow between the radiator and the coolant reservoir

48. Radiator Cap

49. Radiator Cap Pressure Valve
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:
12–16 psi (83–110 kPa)
raises the boiling point to 250–260ºF (121–127ºC)

50. Radiator Cap Vacuum Valve
Opens to allow flow back into the radiator when the coolant temperature drops

51. Closed and Open Cooling Systems Closed cooling system
uses an expansion tank
overflow tube is routed into reservoir tank
Open cooling system
allows excess coolant to leak onto the ground

52. Pressure Cap Operation
Hot engine

53. Pressure Cap Operation
Cold engine

54. Cooling System Fans Pull air through the core of the radiator
Increase the volume of air flowing through the radiator
Driven by fan belt or electric motor

55. Flex Fan
High engine speed causes the blades to flex, reducing the blowing action

56. Fluid Coupling Fan Clutch
Filled with silicone-based oil
The clutch slips at higher rpm

57. Thermostatic Fan Clutch
Bimetal spring controls clutching action
cold—clutch slips
hot—clutch locks

58. Electric Cooling Fans
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

59. Electric Fan Operation
Cold engine

60. Electric Fan Operation
Hot engine

61. PCM-Controlled Fans
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

62. Electronic-Controlled Fans

63. Ensures that the fan pulls air through the radiator core
Radiator Shroud
Ensures that the fan pulls air through the radiator core

64. Thermostat
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

65. A temperature-sensitive valve
Thermostat
A temperature-sensitive valve

66. Thermostat Operation Cold engine Hot engine
wax-filled pellet has contracted
spring holds valve closed
Hot engine
when heated, pellet expands
spring tension is overcome
valve opens

67. Thermostat Operation
A. Cold engine
B. Hot engine

68. Thermostat Operation
Cold engine

69. Thermostat Operation
Hot engine

70. Bypass Valve
Permits coolant circulation through the engine when the thermostat is closed

71. Blocks off the bypass at operating temperature
Bypass Thermostat
Blocks off the bypass at operating temperature
Impeller
Flow to radiator
Water pump drive pulley
Bypass spring
Water pump housing
Bypass flow
Thermostat
Main spring
Main flow

72. Cooling System Instrumentation Two common types:
temperature warning light
engine temperature gauge

73. Temperature Warning Light
When the coolant becomes too hot, a temperature sending unit (switch) in the block closes, completing a light circuit
The warning light glows

74. Warning Light Circuit

75. Engine Temperature Gauge
Shows the exact operating temperature
Components:
gauge
variable resistance sending unit

76. Engine Temperature Gauge Operation
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

77. Antifreeze Composed of ethylene glycol mixed with water
Prevents winter freeze-up
Prevents rust and corrosion
Lubricates the water pump
Cools the engine

78. Corrosion Protection
Protected with antifreeze
Water only

79. Antifreeze/Water Mixture
Lowers the coolant freezing point to about –34 ºF (–37 ºC)

80. Block Heater Aids engine starting in cold weather
120-volt heating element mounted in the block water jacket
Common on diesel engines

81. Block Heater Installation

82. Engine and Cooling System

83. Engine and Cooling System