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• Cylinder wall is usually kept below 200°C.• To prevent high thermal stresses caused due to high temperature.• High cylinder head temperature may cause pre-ignition in SI engine.• Spark plug and valve must be cool to avoid knock and pre-ignition.
• The cooling system serves to remove heat from the hot engine components and maintain normal temperature condition of the running engine.• There are mainly two types of cooling system air cooling system liquid cooling system
• Air cooled system is generally used in small engines say up to 15-25kw and in aero planes engines.• In this system fins and extended surfaces are provided on the cylinder walls , cylinder head , etc.• Heat generated due to the combustion engine cylinder will be conducted to the fins and when the air flows over the fins ,heat will be dissipated to air.
Amount of heat dissipated to air depends upon Amount of air flowing through the fins. Fins surface area Thermal conductivity of metal used for fins.
Air cooling system
In this method, cooling water jackets are providedaround the cylinder, cylinder head, etc. The water whencirculated through the jackets, it absorbs heat ofcombustion. This hot water will then be cooling in theradiator partially by a fan andpartially by the flow developed by the forward motion ofthe vehicle. The cooled water is again recirculatedthrough the water jackets.
• Radiator & pressure cap• Cooling fan• Water pump• Water jackets• Thermostat• Hoses• Coolant
• 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.• 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.
• It is to be noted that radiators are generally made out of copper and brass and their joints are made by soldering.
• Serves the purpose of maintaining the cooling system pressure at a definite level during engine operation and equalizing it with atomspheric pressure when the engine is cooled off.
• Driven by the engine and draws air though the radiator to cool the coolant.• Power is ab-sorbed from the engine even when it is not required.• Most cooling system use some type of cooling fan. There are 3 types of fan. • Electric fan • Clutch type fan • Flex fan
• It is used to pump the circulating water.Impeller type pump will be mounted at the front 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 is driven water will be pumped
• Passageways through which water circulates through the block.
• The thermostats main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. At low temperatures, the outlet to the radiator is completely blocked -- all of the coolant is recirculated back through the engine.• Once the temperature of the coolant rises to between 180 and 195 F (82 - 91 C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200 to 218 F (93 - 103 C), the thermostat is open all the way.
• Coolant is a mixture of antifreeze and water. Antifreeze lowers the freezing point and raises the boiling point.• 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 have any harmful effect on any part ofcooling system.(d) It should be cheap and easily available.Examples : Glycerin along with water, Ethylene Glycol , Asolution of alcohol and water. etc.
• Starting of the engine will be difficult at low temperatures.• Reduced evaporation of the fuel at low temperatures.• Lower average combustion gas temperature and pressure reducing specific power and efficiency.• Higher friction due to higher viscosity of lubricating oil at lower temperatures.