COOLING SYSTEMS OF IC ENGINES

Introduction:

We know that in case of 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. This is a very high temperature and may result into burning
of oil film between the moving parts and may result into seizing or welding of the same.
So, this temperature must be reduced to about 150-200°C at which the engine will work
most efficiently. Too much cooling is also not desirable since it reduces the thermal
efficiency. So, the object of cooling system is to keep the engine running at its most
efficient operating temperature.
It is to be noted that the engine is quite inefficient when it is cold and hence the cooling
system is designed in such a way that it prevents cooling when the engine is warming up
and till it attains to maximum efficient operating temperature, then it starts cooling.
It is also to be noted that :
(a) About 20-25% of total heat generated is used for producing brake power
   (useful work).
(b) Cooling system is designed to remove 30-35% of total heat.
(c) Remaining heat is lost in friction and carried away by exhaust gases.
Objectives
After studying this unit, you should be able to
• understand the methods of cooling of IC engine,
• explain the air cooling system, and
• know the water cooling system of IC engine.

 AIR COOLING SYSTEM:

 

There are mainly two types of cooling systems :
(a) Air cooled system, and
(b) Water cooled system.
Applied Thermal
Engineering
Air Cooled System
Air cooled system is generally used in small engines say up to 15-20 kW and in
aero plane engines.
In this system 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.
The amount of heat dissipated to air depends upon :
(a) Amount of air flowing through the fins.
(b) Fin surface area.
(c) Thermal conductivity of metal used for fins.
Fin
Cylinder
Figure 5.1 : Cylinder with Fins
Advantages of Air Cooled System
Following are the advantages of air cooled system :
(a) Radiator/pump is absent hence the system is light.
(b) In case of water cooling system there are leakages, but in this case
   there are no leakages.
(c) Coolant and antifreeze solutions are not required.
(d) This system can be used in cold climates, where if water is used it
   may freeze.
Disadvantages of Air Cooled System
(a) Comparatively it is less efficient.
(b) It is used in aero planes and motorcycle engines where the engines are
   exposed to air directly.

 WATER COOLING SYSTEM:

 

In this method, cooling water jackets are provided around the cylinder, cylinder head,
valve seats etc. The water when circulated through the jackets, it absorbs heat of
combustion. 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.
Types of Water Cooling System
Cooling Systems
of IC Engines
There are two types of water cooling system :
Thermo Siphon System
In this system the circulation of water is due to difference in temperature
(i.e. difference in densities) of water. So in this system pump is not required
but water is circulated because of density difference only.

Applied Thermal Engineering:

Water cooling system mainly consists of :
(a) Radiator,
(b) Thermostat valve,
(c) Water pump,
(d) Fan,
(e) Water Jackets, and
(f) Antifreeze mixtures.
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 and the lover tank is connect to the jacket inlet through water pump by means
of hose pipes.
There are 2-types of cores :
(a) Tubular
(b) Cellular as shown.
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.
As shown through water passages and air passages, wafer and air will be flowing
for cooling purpose.
It is to be noted that radiators are generally made out of copper and brass and their
joints are made by soldering.

Thermostat Valve:
It is a valve which prevents flow of water from the engine to radiator, so that
engine readily reaches to its maximum efficient operating temperature. After
attaining maximum efficient operating temperature, it automatically begins
functioning. Generally, it prevents the water below 70°C.


Antifreeze Mixture
In western countries if the water used in the radiator freezes because of cold
climates, then ice formed has more volume and produces cracks in the cylinder
blocks, pipes, and radiator. So, to prevent freezing antifreeze mixtures or solutions
are added in the cooling water.
The ideal antifreeze solutions should have the following properties :
(a) It should dissolve in water easily.
(b) It should not evaporate.
(c) It should not deposit any foreign matter in cooling system.
(d) It should not have any harmful effect on any part of cooling system.
(e) It should be cheap and easily available.
(f) It should not corrode the system.
No single antifreeze satisfies all the requirements. Normally following are used as
antifreeze solutions :
(a) Methyl, ethyl and isopropyl alcohols.
(b) A solution of alcohol and water.
(c) Ethylene Glycol.
(d) A solution of water and Ethylene Glycol.
(e) Glycerin along with water, etc.

 Advantages and Disadvantages of Water Cooling System

Advantages

(a) Uniform cooling of cylinder, cylinder head and valves.
Specific fuel consumption of engine improves by using water cooling
system.
(b) If we employ water cooling system, then engine need not be provided at the
   front end of moving vehicle.
(c) Engine is less noisy as compared with air cooled engines, as it has water for
   damping noise.
Cooling Systems
of IC Engines

Disadvantages

(a) It depends upon the supply of water.
(b) The water pump which circulates water absorbs considerable power.
(c) If the water cooling system fails then it will result in severe damage of
   engine.
(d) The water cooling system is costlier as it has more number of parts. Also it
   requires more maintenance and care for its parts.

SAQ:

(a) Why is cooling necessary for IC engine?
(b) Explain in brief the methods of cooling of IC engine.
(c) Differentiate between air cooling system and water cooling system.
(d) What is the purpose of the fins in an air-cooled system?

 SUMMARY

Most internal combustion engines are fluid cooled using either air (a gaseous fluid) or a
liquid coolant run through a heat exchanger (radiator) cooled by air. In air cooling
system, heat is carried away by the air flowing over and around the cylinder. Here fins
are cast on the cylinder head and cylinder barrel which provide additional conductive
and radiating surface. In water-cooling system of cooling engines, the cylinder walls and
heads are provided with jacket through which the cooling liquid can circulate.

 KEY WORDS

Cooling System : A cooling system in an internal combustion engine
              that is used to maintain the various engine
             components at temperatures conductive to long
            life and proper functioning.
Air Cooling System : In this system, heat is carried away by the air
                  flowing over and around the cylinder.
Water Cooling System : In this system, the cylinder walls and heads are
                    provided with jacket through which the cooling
                   liquid can circulate.