Engine Cooling Systems

Necessity Of Engine Cooling:

• If there is no engine cooling system in a car, it might reaches higher temperature which can important components burn gasket, delivery lines.
• If no engine cooling system, lubrication oil can change its composition.
• High temperature attainment can reduce the strength of piston, cylinder lining, etc.
• Engine cooling is required to keep the temperature low to increase volumetric efficiency, reduce engine failure.

Demerits Of Over-Cooling:

Disadvantages of over-cooling are:

• Starting of engine becomes difficult.
• Reduction in engine life.
• Inadequate lubrication of engine.
• Improper vaporization of fuel.

Demerits Of Under-Cooling:

Disadvantages of under-cooling are:

• Reduction in life of piston and cylinders due to the attainment of high temperature.
• Under cooled engine lead to pre-ignition of fuel in SI engines.
• Composition of lube oil may change.

Effects of Operating Variables on Engine Heat Transfer:

• Compression Ratio  ↣  if compression ratio is greater than mean total volume of engine is increased which increase the compression and expansion. Due to greater expansion temperature of gas is reduced, thereby decrease in heat transfer happened.
• F/A Ratio  ↣  At 1.2 equivalence ratio, maximum gas temperature reaches and maximum heat rejection occurs.
• Engine Load or Speed  ↣  With the increase in engine speed, the temperature of engine increases which increase the heat rejection.
• Ignition Timing  ↣  When the spark advance is different from the optimum value, the heat rejected is increased.

Cooling Systems:

There are two types of Engine Cooling Systems which are given below:

• Air Cooling System  ↣  Used fins(on the outer surface of engine) on which air strikes and cooling happens. 

• Water/Liquid Cooling System  ↣  Used liquid (mostly water) for cooling.

Water Cooling Systems are further divided into different types which are explained below:

1. Thermosyphon Cooling System:

• Cooling is independent of engine speed.
• The circulation of water starts only after the engine has become hot enough to cause thermosyphon effect.
• Radiator should be above engine for flow of water to be cooled under force of gravity.

2. Forced or Pump Cooling System:

• Water is continuously flow into engine by centrifugal pump operated by engine.
• Thermostat is used to control water temperature.
• If the temperature of water does not cross the pre-determine temperature of thermal expansion of thermostat, the water is continuously flowing through pump into engine.  
• If the temperature of water cross the pre-determine temperature of thermal expansion of thermostat, the water is cooled first by passing it through radiator and then flow into engine by means of pump.

3. Evaporative Cooling System:

• Water from tank is flowed by pump into engine for cooling.
• When water is heated, it is allowed to flow through pipe into radiator where vapors moves up and is cooled (condensed) by flowing water through jackets.
• This system is only for stationary engines.

4. Pressurized Water Cooling System:

•  The rate of heat transfer depends upon the temperature difference between bodies, surface area and conductivity of materials.
• To reduce the size of radiator, the cooling system is sealed from atmosphere and is kept under certain pressure.
• In this case temperature of boiling water increases as the pressure on it is raised.
• This allow the greater heat transfer due to greater temperature difference.

Main Components Of Water Cooling System:

Following are the main components of water cooling system:

1. Water Jackets
2. Water Pump
3. Fan 
4. Thermostat
5. Connecting Hose Pipes
6. Radiator
7. Radiator Cap (Pressurized)

References:

• University notes + my knowledge.
• Videos from YouTube.
• Images from Google Images.
• Book: IC Engines by V Ganesan (4th Edition).
• Class Lectures.