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07-6 2. FUNCTIONS OF LUBRICATION 1) Lubrication It creates a viscous barrier between moving parts that reduces friction, which means less heat and longer life for those parts. As a lubricant, oil must maintain a protective film to prevent metal-to-metal contact. It must be fluid enough to allow easy starting and to circulate quickly through the engine, yet remain thick enough at higher operating temperatures and speeds to provide adequate lubrication. 2) Cooling Combustion heat and friction energy must be removed from the engine in order to prevent its overheating. Most of heat energy is taken by the engine oil. Clean oil passages, proper viscosity and low contamination provide sufficient flow rate of the engine oil and effective cooling. 3) Sealing It helps to seal the space between the pistons and the cylinder walls so that compression is more effective and power is not lost during combustion. 4) Anti-corrosion As a corrosion inhibitor, oil coats internal engine parts to prevent surface rust on the inside of the engine which can be caused by blow-by products and water formed in combustion. It must also be capable of neutralizing the acids that are formed by combustion blow-by and oil oxidation at high temperatures. 5) Cleaning The small particles of dirt or other contaminants are suspended in oil and carried away to be filtered out. As a detergent, engine oil must be able to gather and suspend dirt and other contaminants until the oil can leave them as it passes through the filter and returns to the internal engine environment. |