1. Internal Combustion Engines Faculty - Er. Ashis Saxena

2. Index Unit 1 Introduction to I.C Engines Fuels Unit 2 SI Engines Unit 3 CI Engines Unit 4 Engine Cooling Lubrication Supercharging Testing and Performance Unit 5 Compressors

3. Unit - 4 Chapter – 4(a) Engine Cooling

4. Prerequisites of Engine cooling What shall you know before going into details of engine cooling?  In an Internal Combustion engines, combustion of air and fuel takes place inside the engine cylinder and hot gases are generated.  The temperature of gases will be around 2300-2500°C.  About 25-35% of total heat generated is used for producing useful work.  Cooling system is designed to remove 30-35% of total heat.  Remaining heat is lost in friction and carried away by exhaust gases.

5. Is cooling System necessary? The answer to the question above lies in asking another question. What will be the consequences if the engine will run too hot?  Overheated spark plug  Overheated cylinder walls  Pre-ignition  Knock The result of above will be very high pressure rise and possible damage to engine.

6. Is cooling System necessary? The answer to the question above lies in asking another question. What will be the consequences if the engine will run too hot?  Heat Fatigue of components – Burnt Pistons – Burnt Valves

7. Is cooling System necessary? The answer to the question above lies in asking another question. What will be the consequences if the engine will run too hot?  Failure of lubrication system – Chemical & Physical Changes in lubricating Oil – Oil film at cylinder destroyed  Wear & sticking of piston rings  Scoring of cylinder walls  Scoring of piston  Seizure of piston

8. Is cooling System necessary? The answer to the question above lies in asking another question. What will be the consequences if the engine will run too hot?  Warping & fracture of components  Complete engine failure  Complete loss of power

9. Is extra cooling advantageous? What will be the consequences if the engine will run too cold?  Unnecessary Wear  Poor Fuel Economy  Incomplete Combustion  Lower coolant Temperature  More energy transferred out of cylinder  Energy is wasted & not available for work (Power)

10. Is extra cooling advantageous? What will be the consequences if the engine will run too cold?  Promotes corrosive conditions in engine  Water of combustion reacts with sulfur oxides in exhaust  Forms acids  Allows water & sludge to accumulate in crankcase  Reduces the thermal efficiency

11. Characteristics of an efficient Cooling System Following are two main characteristics desired of an efficient cooling system  It should be capable of removing about 30% of heat generated in the combustion chamber while maintaining the optimum temperature of the engine under all operating conditions of the engine.  It should remove heat at a faster rate when engine is hot. However during starting of the engine the cooling should be minimum, so that the working parts of the engine reach their operating temperature in a short time.

12. Types of Cooling Systems There are two types of systems in general for cooling the IC engines AAAAir or direct cooling system. LLLLiquid or indirect cooling system.

13. Air Cooled System  In this system air is used to dissipate heat directly.  Fins or extended surfaces are provided on the cylinder walls, cylinder head, etc.  Heat generated due to combustion in the engine cylinder will be conducted to the fins and when the air flows over the fins, heat will be dissipated to air.  Air cooled system is generally used in small engines (motor cycles, small cars) and in aero plane engines.  More Difficult to control temperature.  Its used in bigger engines is accompanied by a fan to circulate air around engine.

14. Air Cooled System The amount of heat dissipated to air depends upon:  Amount of air flowing through the fins.  Fin surface area.  Thermal conductivity of metal used for fins.

15. Air Cooled System

16. Advantages of Air Cooled System  Absence of water jackets, radiator makes the design simpler and easy maintenance.  Radiator/pump is absent hence the system is light.  In case of water cooling system there are leakages, but in this case there are no leakages.  Coolant and antifreeze solutions are not required.  This system can be used in cold climates, where if water is used it may freeze.  Weight of air cooled engine is less.

17. Disadvantages of Air Cooled System  Can be applied only to small and medium sized engines.  Cooling is not uniform.  Higher working temperatures compared to water-cooling.  Produce more aerodynamic noise  Lower maximum allowable compression ratios.  The fan, if used absorbs as much as 5% of the power developed by the engine.

18. Liquid Cooled System  In this method, cooling water jackets are provided around the cylinder, cylinder head, valve seats etc.  A fluid circulates through pipes and passageways in the engine it absorbs heat, cooling the engine.  This hot water will then be cooling in the radiator partially by a fan and partially by the flow developed by the forward motion of the vehicle.  The cooled water is again recirculated through the water jackets.

19. Liquid Cooled System

20. Types of Liquid Cooling Systems There are following important types of liquid cooling systems: DDDDirect or non-return system. TTTThermo Siphon System. PPPPump Circulation System or Forced circulation system.

21. Direct or non-return system  This system is useful for large installations where plenty of water is available.  The water from a storage tank is directly supplied through an inlet valve to the engine cooling water jacket.  The hot water is not cooled for reuse but simply discharged.

22. Thermo Siphon System  Consider the figure. Heat is supplied to the fluid in the tank A.  Because of the relatively lower density, the hot fluid travels up, its place being taken up by comparatively cold fluid from the tank B through the pipe p 2.  The hot fluid flows through the pipe p 1 to the tank B where it gets cooled.  Thus the fluid circulates through the system in the form of convection currents. Heat Hot

23. Thermo Siphon System  For engine application, tank A represents the engine cylinder jackets while tank B represents a radiator and water acts as the circulating fluid.  The main advantages of the system are its simplicity and automatic circulation of cooling water.  The main limitation of the system is its inability to meet the requirement of large flow rate of water, particularly for high output engines.

24. Pump or Forced Circulation Cooling System  In this system circulation of water is obtained by a pump.  This pump is driven by means of engine output shaft through V- belts.

25. Pump or Forced Circulation Cooling System

26. Forced Circulation System - Components (a) Radiator, (b) Thermostat valve, (c) Water pump, (d) Fan, (e) Water Jackets, and (f) Antifreeze mixtures.

27. Water Cooling System of a 4-cylinder Engine

28. Radiator  A radiator is a type of heat exchanger. It is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan.  The purpose of a radiator is to provide a large amount of cooling surface area so that the water passing downward through it in thin streams is cooled efficiently.  It mainly consists of an upper tank and lower tank and between them is a core.  The upper tank is connected to the water outlets from the engines jackets by a house pipe and the lower tank is connected to the jacket inlet through water pump by means of house pipes.  When the water is flowing down through the radiator core, it is cooled partially by the fan which blows air and partially by the air flow developed by the forward motion of the vehicle.

29. Radiator  The coolant flows through oval-shaped core tubes.  Heat is transferred through the tube wall and soldered joint to fins.  The fins are exposed to airflow, which removes heat from the radiator and carries it away.

30. A radiator may be either a down-flow or a cross-flow type.

32. Thermostat valve  There is a normal operating temperature range between low temperature and high-temperature extremes.  The thermostat controls the minimum normal temperature.  The thermostat is a temperature-controlled valve placed at the engine coolant outlet & it prevents flow of water from the engine to radiator, so that engine readily reaches to its maximum efficient operating temperature.

33. Pump or Forced Circulation Cooling System

34. FIGURE (a) When the engine is cold, the coolant flows through the bypass. (b) When the thermostat opens, the coolant can flow to the radiator. A mechanical link, connected to the heat sensor, opens the thermostat valve. As the thermostat begins to open, it allows some coolant to flow to the radiator, where it is cooled.

35. Water Pump  The water pump (also called a coolant pump) is driven by a belt from the crankshaft or driven by the camshaft.  It is used to pump the circulating water.  Impeller type pump will be mounted at the front end.  Pump consists of an impeller mounted on a shaft and enclosed in the pump casing.

36. Coolant flow through the impeller and scroll of a coolant pump for a V-type engine.

38. Fan  Air is forced across the radiator core by a cooling fan.  It is driven by the engine output shaft through same belt that drives the pump.  It is provided behind the radiator and it blows air over the radiator for cooling purpose.

39. A typical engine-driven cooling fan.

40. A typical electric cooling fan assembly showing the radiator and related components.

41. A typical electric cooling fan assembly after being removed from the vehicle.

42. Coolant/Antifreeze  Coolant is a mixture of antifreeze and water.  Water is able to absorb more heat per gallon than any other liquid coolant.  Under standard conditions, water boils at 212°F (100°C) and freezes at 32°F (0°C).  When water freezes, it increases in volume about 9%.  The expansion of the freezing water can easily crack engine blocks, cylinder heads, and radiators.  All manufacturers recommend the use of ethylene glycol-based antifreeze mixtures for protection against this problem.

43. Coolant/Antifreeze The ideal antifreeze solutions should have the following properties: IIt should dissolve in water easily. IIt should not evaporate. IIt should not deposit any foreign matter in cooling system. IIt should not have any harmful effect on any part of cooling system. IIt should be cheap and easily available. IIt should not corrode the system.

44. No single antifreeze satisfies all the requirements. Normally following are used as antifreeze solutions : MMethyl, ethyl and isopropyl alcohols. AA solution of alcohol and water. EEthylene Glycol. AA solution of water and Ethylene Glycol. GGlycerin along with water, etc.

45. Advantages of Liquid Cooled System  Uniform cooling of cylinder, cylinder head and valves.  Specific fuel consumption of engine improves by using water cooling system.  If we employ water cooling system, then engine need not be provided at the front end of moving vehicle.  Engine is less noisy as compared with air cooled engines, as it has water for damping noise.

46. Disadvantages of Liquid Cooled System  It depends upon the supply of water.  The water pump which circulates water absorbs considerable power.  If the water cooling system fails then it will result in severe damage of engine.  The water cooling system is costlier as it has more number of parts.  It requires more maintenance and care for its parts.