Farm Power and Machinery

1. METHODS OF COOLING ENGINE

2. Cooling Methods
 There are two methods of cooling systems used in IC
engines namely Air cooling system and Water
cooling system.
1. Air cooling system
 In this type of cooling system, air is used as a
medium for removing heat from engine to
atmosphere.
 Air cooled engines are those engines, in which heat is
conducted from the working components of the
engine to the atmosphere directly.
 In such engines, cylinders are generally not grouped
in a block.
 Air cooling is usually employed for light vehicles.

3.  Radial ribs or fins are used to increase the external
surface area of the cylinder.
 The length of these fins will be the greatest where
the cylinder is the hottest, particularly near the
cylinder head and will progressively reduce towards
the crank case.
 Air-cooled engines are mounted on motorcycle
frame.
 They are usually exposed to the surrounding
atmosphere.
 They relay on natural air stream.
 Air circulates around the cylinders, head and crank
case during forward movement of the vehicle.

4. Advantages of air cooled engine
 It is simpler in design and construction.
 Water jackets, radiators, water pump, thermostat,
pipes, hoses etc. are eliminated.
 It is more compact.
 Air-cooled engines operate well in both hot and cold
climates.
 Air-cooled engines, rapidly reach their working
temperature from cold.

5.  Air cooling is natural cooling and it is free from
corrosive products.
 This system is more reliable and less maintenance is
required.
 Air-cooled engines can operate at higher working
temperatures than equivalent
 liquid cooled.
 Air cooled engines have no coolant leakage (or)
problems
 It is comparatively lighter in weight.

6. Disadvantages of air cooled engine
 There is uneven cooling of the engine parts.
 Each cylinder has to be cast individually. Fin design
and casting is difficult.
 Used only in small engines provided in brush cutter
and weeder engines, portable engines, lawn mower
engines, etc.,

7. 2. Water cooling system
 In this type of engine water or coolant (heavy water)
is used as a cooling medium.
 These engines are called “water cooled engines”.
 The liquid is circulated around the cylinders by
means of jacket provided, to absorb heat from the
cylinder walls and further the heated water is
conducted through a radiator which helps in cooling
the water.

8. Fig. Flow diagram of cooling liquid in the engine cooling system

9.  There are four common methods of water cooling:
i. Open jacket or hopper method
ii. Thermo syphon method
iii. Forced circulation method
iv. Pressurized cooling

10. i. 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. ii. Thermo syphon method
 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.

12. Fig. Thermo syphon water cooling method

13. iii. Forced Circulation method
 In this method, a water pump is used to force water
from the radiator to the water jacket of the engine.
 After circulating the entire run of water in jacket,
water comes back to the radiator where it loses its
heat by the process of conduction.
 To maintain the correct engine temperature, a
thermostat valve is placed at the outer end of
cylinder head.
 Cooling liquid is by-passed through the water jacket
of the engine until the engine attains the desired
temperature.
 Then thermostat valve opens and by-pass is closed,
allowing the water to go to the radiator.

14. Fig. Forced circulation system

15.  The different parts of the forced circulation method
are explained below:
a. Radiator
 The radiator transfers the heat absorbed by the
water to the surrounding air.
 The radiator is flat and rectangular in shape.
 It consists of tubes which are made of copper or
aluminum alloy.
 These tubes expose large surface area to the air
stream.
 Fins are attached to these tubes.

16. Radiator

17. b. Cooling fan
 A fan is positioned between the radiator and the
engine and is driven by engine crankshaft.
 Fan is to increase the normal air movement across
the radiator core tubes.
 The resultant air movement will provide a
continuous air stream over the tubes and fins to
dissipate the heat from the hot water which is
circulated.

18. Cooling fan

19. C. Thermostat
 The function of the thermostat is to regulate heat
dissipation by controlling the rate of water flow
through the radiator.
 Normally engines are designed to operate most
efficiently over a temperature range between 80ᵒ C
and 100ᵒC.
 Thermostat is placed in the outlet of cooling water
from the engine.
 The thermostat has a valve, which opens only when
the normal operating temperature of about 60ᵒC is
reaches by the water.
 The water flows from engine to upper part of the
radiator through thermostat.

20. Thermostat

21. d. Water Pump
 A centrifugal pump is used to speed up the rate of
water circulation in the cooling system.

22. iv. Pressurized cooling:
 In this type of cooling, the system is made tight
enough to bear the additional pressure.
 A special spring loaded cap for the radiator is
provided to withstand the pressure.
 An overflow pipe is fitted above the spring loaded
part of the cap.
 There is a vacuum relief disc, a spring and the
pressure cap.

23.  When the engine cools, the water level in the
radiator goes down and a vacuum is created.
 The vacuum operates the disc which is pushed down
to save the radiator tubes from collapsing.
 With the increase in pressure, the boiling
temperature of water increases from 100ᵒC to 172ᵒC.
 The higher water temperature gives more efficient
engine performance and is useful at high altitudes.

24. Problem in Cooling system
 In the engines, due to defective cooling system,
several adverse effects are noticed, such as:
1. Overheating
2. Slow warm-up of the engine.
Over heating is mostly due to:
a. Accumulation of rust and scale in the radiator and
water jacket.
b. Defective hose pipe.
c. Defective thermostat.
d. Defective water pump.
e. Loose fan belt.

25. Care and maintenance of cooling system
 Clean and fresh water should be filled in the radiator.
 Salt free water should be used in the radiator as far
as possible for prevention of scale formation.
 In some cold countries, the water in the radiator gets
converted into ice and creates problems in initial
starting of the engine. Hence ethyl alcohol is mixed
with water to avoid ice formation.
 Rotten or soft hose pipe should not be used in the
system.
 Oil and grease should always be kept away from the
belt. Greasy belts should be wiped clean.
 The bearing of the water pump should be lubricated
regularly.

26.  Very hot engines should never be filled with cold
water, to avoid fracture in the cylinder wall and the
cylinder head.
 The cooling system should be cleaned at periodically
to remove rust and scale.
 The radiator cap should not be opened when the
engine is hot.