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COOLING SYSTEM IN AUTOMOBILES

 Reasons to provide cooling system in engine:

  • The even expansion of piston in the cylinder may result in seizure of the piston.
  • High temperatures reduce strength of piston and cylinder liner.
  • Overheated cylinder may lead to pre-ignition of charge, in case of SI engine.
  • Physical and chemical changes may occur in lubricating oil which may case sticking of piston rings and excessive wear of cylinder.
  • If the cylinder head temperature is high the volumetric efficiency and power output of engine reduces.

Over cooling :

  • Starting of engine becomes difficult.
  • Engine life is reduced due to corrosion.
  • Some of the heat which could be used to expand the gases will be lost.
  • The fuel will not vaporize properly and some of the gases produced by combustion will condense on the cylinder walls.
  • Inadequate lubrication of the engine, due to oil not being warm enough to flow freely.

 Methods of Cooling:

There are mainly following two methods/System of Cooling 

  • Air Cooling
  • Water/Liquid Cooling

Air Cooling System:

  • The heat, which is conducted to the outer parts of the engine, is radiated and conducted away by the stream of air, which is obtained from the atmosphere.
  • In order to have efficient cooling by means of air, providing fins around the cylinder and cylinder head increases the contact area.
  • The fins are metallic ridges, which are formed during the casting of the cylinder and cylinder head.
The amount of heat carried off by the air-cooling depends upon the following factors: 

    • The total area of the fin surfaces, 
    • The velocity and amount of the cooling air 
    • The temperature of the fins and of the cooling air. 

  • Air-cooling is mostly tractors of less horsepower, motorcycles, scooters, small cars and small aircraft engines where the forward motion of the machine gives good velocity to cool the engine.

Advantages Air Cooling System: 

  • Its design of air-cooled engine is simple.
  • It is lighter in weight than water-cooled engines due to the absence of water jackets, radiator, circulating pump and the weight of the cooling water.
  • It is cheaper to manufacture.
  • It needs less care and maintenance.
  • This system of cooling is particularly advantageous where there are extreme climatic conditions in the arctic or where there is scarcity of water as in deserts.
  • No risk of damage from frost, such as cracking of cylinder jackets or radiator water tubes.

Water Cooling System:

Water cooling system serves two purposes in the working of an engine: 

  • It takes away the excessive heat generated in the engine and saves it from over heating.
  • It keeps the engine at working temperature for efficient and economical working.

Methods/types are used to circulating water around the cylinder and cylinder head are: 

  • Thermo-syphon Cooling.
  • Force or pump cooling.
  • Cooling with thermostatic regulator.
  • Pressurized water cooling.
  • Evaporative cooling.

Components of Water Cooling System: 

Parts of liquid cooling system

  • Radiator & pressure cap 
  • Cooling fan
  • Water pump 
  • Water jackets
  • Thermostat 
  • Connecting Hoses 
  • Coolant

Radiator

  • 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 hose pipe 
  • The lower tank is connect to the jacket inlet through water pump by means of hose 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.

Radiator Pressure cap:

  • Serves the purpose of maintaining the cooling system pressure at a definite level during engine operation and equalizing it with atmospheric pressure when the engine is cooled off.

Fan:

  • The fan is generally mounted on the water pump pulley, although on some engines it is attached directly to the crankshaft. • It serves two purposes in the cooling system of a engine.

  • It draws atmospheric air through the radiator and thus increases the efficiency of the radiator in cooling hot water.
  • It throws fresh air over the outer surface of the engine, which takes away the heat conducted by the engine parts and thus increases the efficiency of the entire cooling system.

Water pump: 

  •  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. The pump casing has inlet and outlet openings.
  • The pump is driven by means of engine output shaft only through belts. When it is driven water will be pumped.

Water Jackets:  

• Passageways through which water circulates through the block.

Thermostat : 

  • The thermo-static device which prevents the water jacket from circulating through the radiator for cooling until its temperature has reached to a value suitable for efficient engine operation.
  • The thermostat's main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. 

  • At low temperatures, the outlet to the radiator is completely blocked and all of the coolant is recirculate back through the engine. 
  • Once the temperature of the coolant rises to between180 and 195 F (82 - 91 °C), the thermostat starts to open, allowing fluid to flow through the radiator. 
  • By the time the coolant reaches 200 to 218 F (93 - 103 °C), the thermostat is open all the way.

Coolants : 

  • Anti freeze mixture or solutions are added to water in extreme winter seasons to lower its freezing temperature below the danger point.
  • Commonly used anti-freeze materials are:

    • Denatured alcohol 
    • Wood Alcohol
    • Glycerin
    • Kerosene
    • Sugar solution
    • Ethylene Glycol and propylene Glycol


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