2. Cooling System
• Engine is the device which converts heat energy
generated from the combustion of fuel into useful
mechanical work. Around 25% of whole heat energy
generated from the fuel is utilized for generating the
desired output.
• The rest of heat is either released in the form of exhaust
gases or is absorbed by the engine itself.
• This absorbed heat by the engine is required to be
dissipated through engine cooling system otherwise
engine will become overheated and result in burning of
lubricant which further causes the engine seizure and
damage to the engine components.
3. • Loss of heat through the cylinder walls/liners :
30%
• - Loss of heat through exhaust gases : 35%
• - Loss of heat in friction : 10%
• Keeping in view the essential requirement of
maintaining optimum operating temperature
of the engine a suitable cooling system is
required. However, the cooling beyond the
desired limit, results into decrease in the
engine efficiency.
4. PURPOSE
• The purpose of cooling system is to maintain
the correct engine operating temperature and
dissipate surplus heat resulting from
combustion of fuel in engine cylinder
• The cooling system of IC engine should
maintain the engine temperature at 71-800C
for petrol engine and 88-900C for diesel
engine
5. Types of Cooling System
• Generally there are two types of cooling
systems used in an engine;
• i) Air cooling system-used for smaller engine
• ii) Water cooling system-used for bigger
engine
6. Air cooling system
• In this type of 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.
• Special baffles/fins are used to direct the air to
reach the desired heated component and to
avoid any hot spot.
• Air cooled engines are comparatively lighter ,
easier to warm up than the water cooled engines.
• Air cooled engines can be used in extreme
weather conditions where water may get freezed.
7. Advantages of Air Cooled Engines
• 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.
9. Water Cooling System
• It 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.
• This cooling system has four types of systems:
– Direct or non-return system,
– Thermo-Siphon system,
– Hopper system and
– Pump/forced circulation system.
10. Open jacket or hopper Method
• In this method a hopper or a jacket is provided
around the engine cylinder in which the
cooling water or coolant is flowing.
• As long as the hopper contains water, the
engine continues to operate satisfactorily.
• The hopper is large enough to run for several
hours without refilling. A drain plug is
provided for draining water. This system is not
common in present days.
11. Thermosiphon
• It consists of a radiator, water jacket, fan, temperature gauge and hose
connections
• The system is based on the principle that heated water which surrounds
the cylinder becomes lighter in weight and it rises up wards in liquid
column.
• Hot water goes to the radiator, where it passes through tubes surrounded
by air. Circulation of water takes place due to the density difference
between the hot water in the engine jacket and cold water in the radiator.
• These two are connected at both sides i.e. at the top and the bottom by
using the hose pipe.
• A fan is driven with the help of a V-belt connected to the crankshaft to
suck air through cells of the radiator unit resulting in cooling.
• The disadvantage of the system is that circulation of water is greatly
reduced by accumulation of scale or foreign matter in the passage and
consequently it causes overheating of the engine.
14. Forced Circulation Water Cooling
System
• In this system centrifugal pump is used to
circulate the water throughout the water jackets
and radiator.
• The water flows from the lower portion of the
radiator to the water jacket of the engine through
the centrifugal pump.
• After the circulation water comes back to the
radiator, it loses its heat by the process of
radiation .
• This system is employed in cars, trucks, tractors,
etc.
15. Parts Cooling System
• The main parts in the water-cooling system are:
• Water pump,
• Fan,
• Radiator and pressure cap,
• Fan belt
• Water jacket,
• Thermostat valve,
• Temperature gauge and
• Hose pipes.
16. Parts
Water Pump
• This is a centrifugal type pump.
• It is centrally mounted at the front of the cylinder block and is
usually driven by means of a belt.
• The bottom of the radiator is connected to the suction side of the
pump. The power is transmitted to the pump spindle from a pulley
mounted at the end of the crankshaft.
• Water pumps are often designed with a by-pass opening, which
permits the circulation of water within the cylinder block and
cylinder head only when the engine is cold and the thermostatic
valve is closed.
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.
17. Radiator
• The purpose of the radiator is to
cool down the water received from
the engine. The radiator consists of
three main parts: (i) upper tank, (ii)
lower tank and (iii) tubes.
• Hot water from the upper tank,
which comes from the engine, flows
downwards through the tubes.
• The heat contained in the hot water
is conducted to the copper fins
provided around the tubes.
• An overflow pipe, connected to the
upper tank, permits excess water or
steam to escape.
18. Thermostat Valve
• Types of thermostat
• It is a kind of check valve, which opens and closes with the
effect of temperature.
• It is fitted in the water outlet of the engine.
• During the warm-up period, the thermostat is closed and the
water pump circulates the water only throughout the
cylinder block and cylinder head.
• When the normal operating temperature is reached, the
thermostat valve opens and allows hot water to flow
towards the radiator.
• Standard thermostats are designed to start opening at 70 to
75°C and they fully open at 82°C.
• High temperature thermostats, with permanent anti-freeze
solutions (Prestine, Zerex, etc.), start opening at 80 to 90°C
and fully open at 92°C.
