ENGINE COOLING SYSTEM.pdf.mechanical engg
- 1. IC Engines Cooling Systems • Combustion of fuel takes place inside the engine cylinder and hot gases are produced • The temperature of gases will be around 2300-2500°C. • This high temperature may result in physical and chemical changes in lubricating oil and may result into wear, sticking of piston rings, scoring of cylinder walls and seizure of piston • Overheated cylinder head result in overheated spark plug electrodes, exhaust valve leading to pre-ignition • Hence, proper cooling is provided and heat transferred to the walls of the cylinder is continuously removed • Cooling system is designed to remove 30-35% of total heat produced by the burning of fuel.
- 2. Variation of gas temperature during a cycle
- 4. Types of Engine cooling systems • Air cooling (or direct cooling) system • Water cooling (or indirect cooling) system
- 5. Air cooling 1. Air is made to flow past the outside cylinder barrel 2. The heat transfer coefficient between cylinder metal and air is low. Hence, heat transfer area is increased by providing fins. 3. Cooling fins are either cast with the cylinder/cylinder head or can be fixed separately 4. The amount of heat dissipated to air depends upon, • Flow rate of air flowing over the fins. • Fin surface area. • Thermal conductivity of fin material • Also called as direct cooling system
- 6. Advantages and limitations of air cooling Advantages of air cooling system 1. Makes engine design simpler 2. Radiator/pump is absent 3. Coolant and antifreeze solutions are not required. 4. In case of water cooling system there are leakages, but in this case there are no leakages. 5. Engine weight is lesser and power to weight ratio is high 6. Easier to install Limitations of air cooling system 1. Only to smaller engines 2. Can be used only in cold climates, where if water is used may freeze. 3. non-uniform cooling 4. Higher cylinder wall temperature 5. If fan is also used, it may absorb nearly 5% of engine power
- 8. Types of water cooling systems • Direct or non-return system • Thermosyphon system • Forced circulation cooling system • Evaporative cooling system • Pressure cooling system
- 9. Thermosyphon system • In 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 required. Hot water/coolant Cold water/coolant
- 10. Forced circulation cooling system (a) Radiator (b) Thermostat valve (c) Water pump (d) Fan (e) Water Jackets (f) Antifreeze mixtures.
- 11. 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 • The lower tank is connect to the engine jacket inlet through water pump by hose pipes. • There are 2-types of cores : (a) Tubular (b) Cellular • When the water is flowing down through the radiator core, it is cooled partially by a fan and partially by the air flow developed by the forward motion of the vehicle. • Radiators are generally made out of copper and brass and their joints are made by soldering.
- 12. Bellow type thermostat valve which is generally used. 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.
- 13. Advantages and Disadvantages of Water Cooling System Advantages 1. Uniform cooling of cylinder, cylinder head and valves. 2. Specific fuel consumption of engine improves by using water cooling system. 3. Engine need not be provided at the front end of moving vehicle. 4. Engine is less noisy, as it has water for damping noise. Disadvantages 1. depends upon the supply of water. 2. The water pump which circulates water absorbs considerable power. 3. If the water cooling system fails then it will result in severe damage of engine. 4. The water cooling system is costlier as it has more number of parts and requires more maintenance