Lesson 5 engine cooling system

ENGINE COOLING SYSTEM f.mf.m f.mf.m




A system, which controls the engine temperature, is known as the engine cooling system.
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NECESSITY OF COOLING SYSTEM f.mf.m f.mf.m f.mf.m




The cooling system is provided in the IC engine for the following reasons:
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i. The temperature of the burning gases in the engine cylinder reaches up to 1500 to 2000°C, which is f. mf.m f. mf.m f.m f.m f. mf.m f.m f.m f.m f.m f.m f.m f. mf.m f .mf. m f.mf .m f .mf. m f.m f.m f.mf. m f.mf .m f .mf. m f.m f.m f.mf .m




above the melting point of the material of the cylinder body and head of the engine. (Platinum, a
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metal which has one of the highest melting points, melts at 1750 °C, iron at 1530°C and aluminium
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at 657°C.) Therefore, if the heat is not dissipated, it would result in the failure of the cylinder
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material. f.mf.m




ii. Due to very high temperatures, the film of the lubricating oil will get oxidized, thus producing carbon f.mf .m f.mf. m f .mf. m f. mf.m f.mf. m f.mf .m f. mf.m f. mf.m f. mf.m f.m f.m f.m f.m f. mf.m f. mf.m f. mf.m f. mf.m f.m f.m




deposits on the surface. This will result in piston seizure.
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iii. Due to overheating, large temperature differences may lead to a distortion of the engine f.mf.m f .mf. m f.mf. m f.m f.m f .mf. m f. mf.m f.mf.m f. mf. m f.mf. m f. mf.m f.m f.m f.mf.m f.mf .m




components due to the thermal stresses set up. This makes it necessary for, the temperature
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variation to be kept to a minimum. f.mf.m f.mf. m f. mf.m f .mf. m f. mf.m f.mf. m f.mf. m




iv. Higher temperatures also lower the volumetric efficiency of the engine. f. mf.m f.mf. m f .mf. m f .mf. m f .mf. m f. mf.m f.mf.m f. mf.m f.m f.m




REQUIREMENTS OF EFFICIENT COOLING SYSTEM f.mf.m f.mf.m f.mf.m f.mf.m




The two main requirements of an efficient cooling system are:
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I. It must be capable of removing only about 30% of the heat generated in the combustion chamber.
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Too much removal of heat lowers the thermal efficiency of the engine.
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II. It should remove heat at a fast rate when the engine is hot. During the starting of the engine, the
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cooling should be very slow so that the different working parts reach their operating temperatures in
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a short time.
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TYPES OF COOLING SYSTEM f.mf.m f.mf.m f.mf.m




There are two types of cooling systems: f.m f.m f .mf. m f.mf. m f.mf .m f. mf. m f.mf .m




i. Air cooling system and f.mf. m f.m f.m f.mf.m




ii. Water-cooling system. f.mf .m




AIR COOLING SYSTEM f.mf.m f.mf.m




This method is used mainly for small single cylinder engines, such as those motorcycles, scooters, small
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cars and small aircraft engines where the forward motion of the machine gives good velocity to cool the
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engine.
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In this type of cooling system (shown in Figure 1), the heat, which is conducted to the outer parts of the
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engine, is radiated and conducted away by the stream of air, which is obtained from the atmosphere.
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Cooling is done by directing a blast of air around the cylinder and cylinder head, both of which are finned.
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The fins are metallic ridges, which are formed during the casting of the cylinder and cylinder head. This
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finning provides a large surface areas through which the heat can spread and from which heat is taken
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away by cooling air. The blast of air is created by fitting a blower fan on the engine flywheel and this is
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1

, f.mf.m encased in a cowling which extends over and around the cylinder. Air is drawn in by the blower and directed
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f.mf.m over the cylinder to cool it.
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Figure 1: Air cooling system f.mf.m f.mf.m f.mf.m f.mf.m




Overheating of this type of engine will take place if the spaces between the fins are allowed to become f.mf .m f.m f.m f .mf. m f .mf. m f .mf. m f. mf.m f .mf. m f .mf. m f. mf.m f.mf. m f. mf.m f.m f.m f.m f.m f. mf.m f.mf .m f.m f.m f .mf. m f .mf. m




choked with dirt. The amount of heat carried off by the air-cooling depends upon the following factors:
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i. The total area of the fin surfaces, f. mf.m f.mf. m f.mf. m f. mf.m f. mf.m f.mf. m




ii. The velocity and amount of the cooling air and f. mf.m f.mf.m f. mf. m f. mf.m f.mf. m f .mf. m f.m f.m f. mf.m




iii. The temperature of the fins and of the cooling air. f. mf.m f.m f.m f .mf. m f .mf. m f.mf. m f. mf.m f.mf .m f.mf. m f. mf.m




Advantages of Air Cooled Engines f .mf.m f.mf .m f.mf.m f.mf.m




Air cooled engines have the following advantages:
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i. Its design of air-cooled engine is simple. f.mf.m f.mf .m f. mf. m f.m f.m f. mf.m f. mf. m




ii. It is lighter in weight than water-cooled engines due to the absence of water jackets, radiator,
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circulating pump and the weight of the cooling water.
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iii. It is cheaper to manufacture. f.mf.m f.mf .m f. mf.m f.mf. m




iv. It needs less care and maintenance. f.mf.m f. mf.m f.mf. m f.mf. m f. mf.m




v. This system of cooling is particularly advantageous where there are extreme climatic conditions in
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the arctic or where there is scarcity of water as in deserts.
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vi. No risk of damage from frost, such as cracking of cylinder jackets or radiator water tubes.
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WATER COOLING SYSTEM f.mf.m f.mf.m




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