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1 Lubrication system
Lubrication
Lubrication is an art of admitting a lubricant (oil, grease, etc.) between two surfaces that are in contact and in relative motion. The purpose of lubrication in engine is to perform one or several of the following function:-
1) To reduce friction and wear between the moving parts and thereby the energy loss and to increase the life of engine.
2) To provide selling action e.g. the lubrication oil helps the piston rings to maintain an effective seal against the high pressure gasses in the cylinder from leaking out into the crankcase.
3) To cool the surface by carrying away the heat generated in engine components.
4) To clean the surface by washing away carbon and the metal particles caused by wear.
Of all these function, the first function is considered to be the most important one. In internal combustion engines, the problem of lubrication become more difficult because of the high temperature experienced during the combustion process and by the wide range of temperature encounter throughout the cycle. So the energy losses from the friction between different components of the engine can be minimized by providing proper lubrication.
1.2) Lubrication of engine component
In the reciprocating engine there are many surfaces in the contact with each other and therefore they should be lubricated to reduce friction. The principal friction surfaces requiring lubrication in an internal combustion engine are :-
1. Piston and cylinder
2. Crankshaft and their bearings
3. Crank pin and their bearing
4. Wristpin and their bearing
5. Valve gear
1.3) Type of Lubrication system
The function of lubrication system is to provide sufficient quantity of cool, filtered oil to give positive and adequate lubrication to all the moving parts of an engine. The various systems used for internal combustion engine may be classified as:-
1) Mist lubrication system
2) Wet sump lubrication system
3) Dry sump lubrication system
1.3.1) Mist lubrication system
This system is used where crankcase lubrication is not suitable. In two stroke engine, as the charge is compressed in the crankcase, it is not possible to have the lubrication oil in the sump. Hence mist lubrication is used in practice. In such engine, the lubrication oil is mixed with the fuel, the usual ratio being 3% to 6%. The oil and fuel mixture is inducted through the carburetor. The fuel is vaporized and the oil in the form of mist goes via the crankcase into the cylinder. The oil which strikes the crankcase walls lubricates the main and connecting rod bearings and the rest of oil lubricate the piston, piston rings and the cylinder.
The advantage of this system is its simplicity and low cost as it does not require an oil pump, filter, etc. however there are certain disadvantage which are enumerated are following:
1) It cause heavy exhaust stroke due to burning of lubricating oil partially or fully and also forms deposit on piston crown and exhaust port which are affect engine efficiency.
2) Since the oil come in close contact with acidic vapor produced during the combustion process get contaminant and may result in the corrosion of bearing surfaces.
3) This system call for a thorough mixing if effective lubrication. This requires either separate mixing prior to use or use of some additive to give the oil good mixing characteristics.
4) During closed throttle operation as in the case of vehicle moving down the hill, the engine will suffer from insufficient lubrication as the supply of fuel is less. This is an important limitation of system.
1.3.2) Wet sump lubrication system
In the wet sump lubrication system, the bottom of the crankcase contains an oil pan or sump from which the lubricating oil is pumped to various engine components by a pump. After lubrication these parts, the oil flow back to the sump by gravity. Again it is picked by a pump and recirculated through the engine lubricating system. There are three varieties in the wet sump lubricating system. They are:
1) The splash system
2) The splash and pressure system
3) The pressure feed system
1.3.2.) 1- Splash system
This type of lubricating system is used in light duty engine. The lubricating oil is discharge into the bottom of the engine crankcase and maintained at a predetermined level. The oil is drawn by the pump and delivered through a distributing pipe extending the length if the crankcase into the splash trough located under the big end of all the connecting rods. These troughs were provided with overflows and oil in the trough are therefore kept at a constant level. A splasher or dipper is provided under each connecting rod cap which dips into the oil in the trough at every revolution of the crankshaft and the oil is splashed all over the interior of crankcase, into the pistons and onto the exposed portion of cylinder walls. The oil dripping from the cylinder is collected in the sump where it is cooled by the air flowing around. The cooled oil is then recirculated