ME390 Automotive Mechanics 2. Engine Cooling Systems

Topics Covered Need for cooling Types Air cooling Liquid cooling

Need for Engine cooling High temperatures reached during combustion (2000 – 2500oC in CI engines) Over heating of parts result in engine breakdown

Need for Engine cooling Effects of inadequate cooling Evaporation of lubricating oil Setting up of thermal stresses Sticking of piston rings in the cylinder due to carbonization of the oil Burning of piston crown Burning and warping of exhaust valves Reduction in volumetric efficiency i.e. reduced weight of charge retained in the cylinder

Need for Engine cooling Result of excessive cooling Reduction in thermal efficiency Increased corrosion Reduced mechanical efficiency Improper vaporization of fuel. Optimum cooling is required for most effective operation of the engine. Hence the cooling system removes excess heat from the engine to avoid over heating and subsequent problems associated with it.

Types of cooling Direct or Air cooling Indirect or liquid cooling

Air cooling Large quantity of air is circulated around the hot engine components Air flows either due to vehicle movement or due to fan or blower in case where the engine is enclosed. Air flows through the spaces between fins provided around the cylinder and cylinder head. Fins around the cylinder and cylinder head facilitates air cooling

Air cooling Blower cooling of an opposed engine (VW beetle)

Air cooling Factors that determine heat dissipating capacity in air cooling Fin shape, size and spacing Velocity and amount of air flowing over the fins Temperature of the cylinder, fins and cooling air

Air cooling Merits Demerits Less complex design Less engine weight Cheaper to manufacture Compact No risk of coolant frost Easier engine maintenance Demerits Greater mechanical noise Not suitable for multi-cylinder engine

Liquid cooling Most widely used owing to better heat transfer. Coolants used Water Ethylene glycol Preston Glycerine Water is most widely used due to its easy availability and high heat transfer capacity.

Liquid cooling Parts of liquid cooling system (pump circulation system) Water jackets Water pump Thermostat Radiator Fan

Liquid cooling Water Jackets Cooling water jackets are provided around the cylinder, cylinder head, valve seats and 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 the jackets absorbs this heat and gets hot. This hot water will then be cooled in the radiator

Liquid cooling Water Pump It is used to pump the circulating water. Impeller type pump will be mounted at the front end. The pump is driven by means of engine output shaft only through belts. When it is driven water will be pumped.

Liquid cooling Thermostat valve It controls the flow of coolant to the engine. It is a valve which prevents flow of water from the engine to radiator, so that engine readily reaches to its maximum efficient operating temperature. After attaining maximum efficient operating temperature, it automatically begins functioning. Generally, it prevents the water below 70°C. It contains a bronze bellow containing liquid alcohol. Bellow is connected to the butterfly valve disc through the link. When the temperature of water increases, the liquid alcohol evaporates and the bellow expands and in turn opens the butterfly valve, and allows hot water to the radiator, where it is cooled.

Liquid cooling Radiator 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.

Liquid cooling Fan It is driven by the engine output shaft through same belt that drives the pump. It is provided behind the radiator and it blows air over the radiator for cooling purpose.

Liquid cooling (Pump circulation system)

Liquid cooling (Pump circulation system)

Liquid cooling Thermo syphon system Water jackets in Cylinder block and Cylinder head Radiator Hot water moving up to radiator top header Cold water moving to fill the coolant space Fan Thermo syphon system Works on the principle of natural convection Coolant is at rest when the engine is cold During engine operation the coolant gets heated and moves up to top header of the radiator Cold water from lower part of radiator flows and fills up the coolant space in cylinder head and cylinder block Hot water flows down through the radiator and gets cooled by air flow

Liquid cooling Thermo syphon system For successful operation the pipes should be free/clear and large. Jackets should be placed as low as possible compared to the radiator Requires large radiator, large amount of water. Excessive temperature difference is necessary for proper circulation Prevents the engine from running too cold Simple in construction and operation

Liquid cooling Problems Air in the cooling system Freezing of the coolant Deposit formation in the cooling system