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UNIT 5 COOLING SYSTEMS OF IC ENGINESCooling Systemsof IC EnginesStructure5.1IntroductionObjectives5.2Air Cooling System5.3Water Cooling System5.3.1Components of Water Cooling System5.3.2Advantages of Water Cooling System5.4Summary5.5Key Words5.6Answers to SAQs5.1 INTRODUCTIONWe know that in case of Internal Combustion engines, combustion of air and fuel takesplace inside the engine cylinder and hot gases are generated. The temperature of gaseswill be around 2300-2500 C. This is a very high temperature and may result into burningof 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 workmost efficiently. Too much cooling is also not desirable since it reduces the thermalefficiency. So, the object of cooling system is to keep the engine running at its mostefficient operating temperature.It is to be noted that the engine is quite inefficient when it is cold and hence the coolingsystem is designed in such a way that it prevents cooling when the engine is warming upand 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.ObjectivesAfter 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.5.2 AIR COOLING SYSTEMThere are mainly two types of cooling systems :(a)Air cooled system, and(b)Water cooled system.61
Applied ThermalEngineeringAir Cooled SystemAir cooled system is generally used in small engines say up to 15-20 kW and inaero 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 beconducted to the fins and when the air flows over the fins, heat will be dissipatedto 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.FinCylinderFigure 5.1 : Cylinder with FinsAdvantages of Air Cooled SystemFollowing 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 casethere 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 itmay 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 areexposed to air directly.5.3 WATER COOLING SYSTEM62In 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 ofcombustion. This hot water will then be cooling in the radiator partially by a fan andpartially by the flow developed by the forward motion of the vehicle. The cooled wateris again recirculated through the water jackets.
Types of Water Cooling SystemCooling Systemsof IC EnginesThere are two types of water cooling system :Thermo Siphon SystemIn 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 requiredbut water is circulated because of density difference only.RadiatorEngineFigure 5.2 : Thermo Siphon System of CoolingPump Circulation SystemIn this system circulation of water is obtained by a pump. This pump isdriven by means of engine output shaft through V-belts.EngineFigure 5.3 : Pump Circulation System5.3.1 Components of Water Cooling SystemThermostatEngineRadiatorPumpFigure 5.4 : Water Cooling System using Thermostat ValveFiller capThermostat valveHouse pipeUppertankFanWater jackets around the cylindersCylindersBy passpipeRadiatortubesLowertankWater pumpDrain tapFigure 5.5 : Water Cooling System of a 4-cylinder Engine63
Applied ThermalEngineeringWater cooling system mainly consists of :(a)Radiator,(b)Thermostat valve,(c)Water pump,(d)Fan,(e)Water Jackets, and(f)Antifreeze mixtures.RadiatorIt mainly consists of an upper tank and lower tank and between them is a core. Theupper tank is connected to the water outlets from the engines jackets by a hosepipe and the lover tank is connect to the jacket inlet through water pump by meansof 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 bythe fan which blows air and partially by the air flow developed by the forwardmotion of the vehicle.As shown through water passages and air passages, wafer and air will be flowingfor cooling purpose.It is to be noted that radiators are generally made out of copper and brass and theirjoints are made by ssagesTubular radiator sectionsTubular radiator ssagesFigure 5.6 : Types of Cores Circullar(a) TabullarradiatorRadiator Sectionsand (b) Circullar Radiator SectionssectionsCircullar radiator sectionsThermostat ValveIt is a valve which prevents flow of water from the engine to radiator, so thatengine readily reaches to its maximum efficient operating temperature. Afterattaining maximum efficient operating temperature, it automatically beginsfunctioning. Generally, it prevents the water below 70 C.64
Cooling Systemsof IC EnginesHoseButterfly valveLinkBronze bellowscontracted whenalcohol is in liquidstateFigure 5.7 : Thermostat ValveFigure 5.7 shows the Bellow type thermostat valve which is generally used.It contains a bronze bellow containing liquid alcohol. Bellow is connected to thebutterfly valve disc through the link.When the temperature of water increases, the liquid alcohol evaporates and thebellow expands and in turn opens the butterfly valve, and allows hot water to theradiator, where it is cooled.Water PumpIt is used to pump the circulating water. Impeller type pump will be mounted at thefront end.Pump consists of an impeller mounted on a shaft and enclosed in the pump casing.The pump casing has inlet and outlet openings.The pump is driven by means of engine output shaft only through belts. When it isdriven water will be pumped.Water inletRubberthrowerImpellorWataersealShaftWater outletFigure 5.8 : Water PumpFanIt is driven by the engine output shaft through same belt that drives the pump. It isprovided behind the radiator and it blows air over the radiator for cooling purpose.65
Applied ThermalEngineeringWater JacketsCooling water jackets are provided around the cylinder, cylinder head, valve seatsand any hot parts which are to be cooled. Heat generated in the engine cylinder,conducted through the cylinder walls to the jackets. The water flowing through thejackets absorbs this heat and gets hot. This hot water will then be cooled in theradiator (Referred Figure 5.9).Valve partsSpark plugCylindr headCylindr wallsWater jacketsWaterflowparts CylinderheadgasketCylindr blockFigure 5.9 : Water JacketsAntifreeze MixtureIn western countries if the water used in the radiator freezes because of coldclimates, then ice formed has more volume and produces cracks in the cylinderblocks, pipes, and radiator. So, to prevent freezing antifreeze mixtures or solutionsare 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 asantifreeze 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.5.3.2 Advantages and Disadvantages of Water Cooling SystemAdvantages66(a)Uniform cooling of cylinder, cylinder head and valves.(b)Specific fuel consumption of engine improves by using water coolingsystem.
(c)If we employ water cooling system, then engine need not be provided at thefront end of moving vehicle.(d)Engine is less noisy as compared with air cooled engines, as it has water fordamping noise.Cooling Systemsof IC EnginesDisadvantages(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 ofengine.(d)The water cooling system is costlier as it has more number of parts. Also itrequires more maintenance and care for its parts.SAQ 1(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?5.4 SUMMARYMost internal combustion engines are fluid cooled using either air (a gaseous fluid) or aliquid coolant run through a heat exchanger (radiator) cooled by air. In air coolingsystem, heat is carried away by the air flowing over and around the cylinder. Here finsare cast on the cylinder head and cylinder barrel which provide additional conductiveand radiating surface. In water-cooling system of cooling engines, the cylinder walls andheads are provided with jacket through which the cooling liquid can circulate.5.5 KEY WORDSCooling System: A cooling system in an internal combustion enginethat is used to maintain the various enginecomponents at temperatures conductive to longlife and proper functioning.Air Cooling System: In this system, heat is carried away by the airflowing over and around the cylinder.Water Cooling System: In this system, the cylinder walls and heads areprovided with jacket through which the coolingliquid can circulate.67
Applied ThermalEngineering5.6 ANSWERS TO SAQsRefer the preceding text for all the Answers to SAQs.68
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. 5.5 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
