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Why cooling system required for I.C engines

Description about cooling system, type of cooling systems, description, advantages and disadvantages about  air cooling, liquid cooling, thermo syphon cooling, pump cooling, thermostat cooling, pressurized water cooling, evaporative cooling

  • In I.C engine, during the cycle inside the cylinder the temperature of the gases range approximately between 350 C to 27500 C
  • If external cooling is not provided to the engine, then engine cylinder and piston are exposed to high temperature
  • While increasing the temperature of engine parts cylinder and piston after certain rage about 650 C, metal properties of the engine parts may lose and they tends to expand, size will increase and damage will takes place
  • At this condition lubricating oil will evaporate quickly
  • In spark ignition engine, preignition of the charge will takes place due to engine parts overheat
  • So that due this reasons, cooling system is required for I.C engines
  • Cooling medium is used to remove the heat approximately 25 to 35 percent of total heat supplied in the fuel
  • Lubricating oil is used to remove the heat approximately 3 to 5 percent of total heat supplied in the fuel

Type of cooling system in I.C engines

  • Air cooling
  • Liquid cooling

Air cooling

  • Heat is carried away by the air flowing over and around the engine cylinder
  • Fins are cast on the cylinder head and cylinder barrel
  • Fines are used for additional conductivity and radiating surface and arrangement of the fines are perpendicular to the cylinder surface
  • Air cooling is used in scooters, motorcycles etc.

air-cooling-system




Advantage of air cooling system

  • Engine design is simple and no water cooling is requited
  • No danger of coolant leakage etc.
  • Weight of engine is reduced by using air cooling system, in case of water cooling addition components will required and engine weight will increase
  • Installation of air cooled engines is easier

Disadvantages of air cooling system

  • Output of the air cooled engine is less than output of the liquid cooled engines
  • Cooling is not uniform
  • Maintenance is not easy
  • Smaller useful compression ratio

Liquid cooling

  • Jackets are provide around cylinder wall and head, which is used to circulate the cooling water around the engine parts
  • Cylinder wall heat is transferred to the liquid by convection and conduction
  • Liquid becomes heated in its passage through the jackets and after that it is passed in air cooled radiation system then liquid will get cooled and again circulated to the jacket
  • Heat from the liquid is transfer to atmospheric air by air cooled radiation system

Type of liquid cooling systems

  • Thermo syphon cooling
  • Forced cooling
  • Cooling with thermostatic regulator
  • Pressurized water cooling
  • Evaporative cooling

Thermo syphon cooling

  • This type of cooling system is depends on the principle of water becomes light on heating
  • Arrangement of thermo syphon cooling system as shown in the bellow fig
  • Radiator to is connected to the top of the water jacket by pipe and bottom of the radiator to the bottom of the water jacket
  • Hot water travel from water jacket to upper tank of the radiator and then travel trough radiator to lower tank, in radiator hot water gets cooled by air passes through radiator by fan arrangement and vehicle motion, as shown in the image
  • Thermo syphon cooling is simple and automatic
  • The principle of this cooling system is when cylinder wall is heated then water in the jacket will also heated
  • Hot water gets light weight when compared to the cold water, therefore light water travel to the upper tank of the radiator
  • Cool water in the lower tank is circulate to the water jacket, hot water in the upper tank is circulate to the lower tank trough radiator
  • By the radiator principle hot water will gets cool
  • In this cooling system cooling is depends on the temperature and it is independent of the engine speed

thermo-syphon-cooling-system

Forced cooling

  • In this cooling system pump is used to circulation of water in the water jacket
  • Belt is connected to between pump and engine shaft, when engine stats then pump also start working and circulation of water and cooling will take place
  • Cooling is independent of temperature, for sometimes over cooling will takes place
  • While moving uphill the cooling requirement is increased due to more fuel is burned, the coolant circulation is reduced which may result in over hating the engine
  • The major defect is when engine is stopped then cooling also stopped immediately, but cooling is required until the temperature is get normal value

Thermostat cooling

  • In this cooling system thermostats are used to control the cooling system
  • Arrangement of the thermostat cooling system is as shown in the bellow image
  • Thermostat is consists of bellows which are made of thin copper tube, partially filled with a volatile liquid
  • Initially thermostat valve is closed, when the temperature of the water is increased up to maximum limit, then volatile liquid and bellows in the thermostat will expand
  • So that valve is open, then hot water circulated to the radiator and it gets cool
  • Opening of the valve is takes place until coolant water reached to the normal temperature, which is set the lower temperature limit, then bellows is contract and valve is closed

thermostat-cooling-system

thermostat-close-and-open




Pressured water cooling

  • When the coolant pressure increases then boiling temperature also increase, so that maximum heat transfer is occurred in the radiator due to a larger temperature difference
  • Water pressure is maintained between 1.5 bar to 2.0 bar
  • Vacuum valve is used to avoid formation of vacuum when the water is cooled after engine has stopped

 

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