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I.C. ENGINES LECTURE NO: 14 (5 May 2014). Engine Heat Combustion can reach 4500ºF (2500ºC) This is hot enough to melt metal parts The cooling system removes.

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Presentation on theme: "I.C. ENGINES LECTURE NO: 14 (5 May 2014). Engine Heat Combustion can reach 4500ºF (2500ºC) This is hot enough to melt metal parts The cooling system removes."— Presentation transcript:

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/m 2 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 Iron400˚C Al300 ˚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 Conduction Convection Radiation

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 Components: water pump radiator hoses radiator fan thermostat

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

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

33 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 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 Radiator Hoses Two basic types of radiator hoses

39 Hose Clamps Three basic types of hose clamps

40 Radiator Transfers coolant heat to the outside air

41 Radiator Types DownflowCrossflow

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 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 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 Thermostat A temperature-sensitive valve

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

72 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 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 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


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