Lubricating Systems

The lubrication system is subdivided mainly into three groups.

1. Charge Lubrication System. This is the most simplest method of lubrication and does not require oil-filter and oil pump. In this system, the lubricating oil is pre-mixed with the petrol therefore the fuel carries the lubricating oil in the cylinder which helps for lubricating the piston and cylinder. Most of the oil burns with the fuel due to high temperature and burnt oil is carried wi:h the exhaust gases. The lubricating oil cannot be recovered in this system.

This type of lubrication is generally used for two stroke spark ignition engines of scooter and motor cycle. The quantity of lubricating oil mixed with the petrol is 3 to 6% of petrol.

The advantages of this system are listed below

I. It does not require seperate lubricating system so it is most economical.

2. There is no risk of failure of lubrication system.

3. The lubricating oil supplied is regulated at various loads and speeds by the increased fuel flow.

The carbon deposits due to the burning of the oil on the spark plug and on other pirts and non-recover of the oil used are the main disadvantages of this system.

2. Wet Sump Lubrication System. This system employes a large capacity oil sump at the base of crank case and oil is passed to the different parts with the help of pressure pump. The oil returns back to the sump after serving the purpose. The oil under-pressure is circulated generally through the different parts. This system is further subdivided into splash lubrication and pressure lubrication.

3. Dry Sump Lubrication System. In this system, the oil from the sump is carried to a separate storage tank outside the engine cylinder block. The oil from the sump is pumped through filter into the storage tank with the help of a pump. The oil from the storage tank is further pumped by the another pump to the cylinder through oil cooler. This is generally used for high capacity engines. The pressure of the oil used in this system lies between 3 to 8 bar.

Desirable Properties of a Lubricant

The lubricant used must have some properties for the 3uccessful performance of the engine. The properties required for a good lubricant used in I.C. engine are listed below.

1. Viscosity. It is a measure of fluid resistance to flow and the unit used for the viscosity of the oil is poise. This property is most important property of lubricating oil because it determines how efficiently the oil film separates the moving surfaces from each other and prevents them rubbing directly on each other.

The value of the viscosity of lubricant used should lie within a certain range because lower viscosity will cause seizing of the rubbing surfaces therefore viscosity of the lubricant should be selected in such a way that it should not go down below a certain minimum value at the highest temperature at which the parts are likely to operate. The higher viscosity than this will be always safe but it gives higher coefficient of friction which causes greater power loss.

Flash Point: Flash point of the lubricant is the temperature at which it forms vapours and produces combustible mixture with air. The high flash point is always desirable because low flash point will allow the lubricating oil to burn and deposit the carbon on the different moving parts. The minimum flash point of lubricating oil used in I.C. engine varies from 200 to 250°C.

Pour Point. Pour point of the lubricating oil is the temperature below which oil will cease to flow in the pipe line under controlled test conditions. Low pour points are always recommended as its flow will start even when the engine is started in cold weather.

Carbon Residue. The carbon percentage in lubricating oil should be as minimum as possible because its burning forms the carbon deposits on piston head, piston rings and combustion chamber walls and increases the running action.

Neutralisation:. volume expansion  The lubricating oil should be neither acidic nor alkaline otherwise it will have corrosive action on the parts of the engine. The acidity of the oil is generally given by noting the neu'ralization number of an oil. The neutralization numbers of different lubricating oils are given in different codes.

LUBRICATION OF I.C. ENGINES

Requirements of Lubrication

Almost all machine parts of an I.C. engine have relative motion and rub against each other. The lubrication is required to reduce the rubbing action and increase the life of the engine. The purpose of lubrication in I.C. engine is generally two fold. It reduces the rubbing action between different machine parts having relative motion with each other and to carry out part of the heat generated inside the cylinder. The engine parts which are generally lubricated are listed below :

1. Cylinder and piston.

2. Main bearings

3. Big end and small-end bearings of the connecting rod.

4. Gears carrying the motion from one shaft to another shaft.

There are many other minor parts which also require lubrication as rocker arm, camshaft drive and so on.

The lubrication system is considered one of the most important systems to increase the life and for smooth working of the engine.

CLASSIFICATION OF I.C. ENGINES

The internal combustion engines are classified according to .

1. Cycle of operation. They are divided into the following group.

(a) Two-stroke engines. In two-stroke engines, there is one power stroke in every two strokes or one rotation of the crankshaft.

(b) Four-stroke engines. In four-stroke engines, there is one power srrolte in every four strokes or one during two rotations of the crankshaft,

2. Cycle of operation. They are divided into the following groups :

(a) Otto-cycle. (b) Diesel cycle. (c) Dual cycle.

The operations of these cycles are discussed in the previous chapter

3. The fuel used. On this basis they are classified as :

(a) Petrol engines. (b) Diesel engines or heavy oil engines. (c) Gas engines.

4. The method of ignition. On this basis, they are divided into the two following classes.

(a) Spark ignition engines. (S.I. engines) and (b) Compression ignition engines. (C.I. engines).

5. The method of cooling. On this basis they are classified into two groups.

(a) Air-cooled engines. (b) Water-cooled engines.

6. The method of governing

(a) Quantity governing. (b) Quality governing. (c) Hit and Miss-governing.

7. The use of engines. The following is the classification on this basis :

(a) Stationary engines. (b) Automobile engines or engines for road vehicles.

(c) Marine engines. (6) Aero-engines. (e) Locomotive engines.

8. The arrangement of the cylinders. They can be classified as given below :

(a) Inline engine. All the cylinders are arranged in a line and the power is taken from a single crankshaft.

This arrangement is used in automobiles.

(b) V-type. It is a combination-of two inline engines set at an 'angle. The angle of V may vary from

30" to 75".

The length of the crankshaft of V-type engine is half of the crankshaft used for inline engine. This type is also used in automobiles.

(c) Opposed piston engine. The pistons reciprocate in a common cylinder having common combustion chamber at the centre. Opposed piston type is used in small air crafts and in some diesel installations.

(d) Radial engines. All the cylinders are set along the radius of a circle. The connecting rods point towards the centre of the circle. The connecting rods of all the pistons work on a single crank pin which rotates around the centre of the circle. The radial engine occupies little floor space and simplifies the balancing problems. This type was popular in aircrafts.

(e) Rotary engine. The engine consists of three-sided convex-type piston rotating in a cylinder. This type of engine is known as 'Wankel' engine. It is of high speed-type, light in weight and works on spark ignition system.

Internal Combustion Engine(IC Engine)

Any machine which derives heat energy from the combustion of fuel and coverts part of this energy into mechanical work is known as a heat engine. Heat engines are mainly divided into two groups, viz., external combustion engine and internal combustion engine.

In the case of external combustion engines, the combustion of fuel takes place outside the cylinder as in the case of steam engines. The other examples of external combustion engines are hot air engine, steam turbines and closed cycle gas turbines. In external combustion engines, first the heat of combustion is transferred to the working fluid outside the cylinder and then the fluid is expanded to develop the power.

The other types of engines, which are extensively used in practice, are internal combustion engines.

In internal combustion engines, the combustion of fuel in the presence of air takes place inside the cylinder and products of combustion directly act on piston to develop the power. The internal combustion engines are further classified as petrol engines, diesel engines and gas engines according to the type of fuel used.

These are commonly used for road vehicles, locomotives and several industrial applications. The maximum capacity of these engines is limited.

The internal combustion engines offer some special advantages over external combustion engines in smaller power ranges.

1. The thermal efficiency is high.

2. 'The horse power developed per unit weight of engine is high.

3. Starting is easy and quick.

4. It offers greater mechanical simplicity.

5. It requires less space.

6. The capital cost is low.