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.

FLUID MECHANICS

Fundamental Concepts:

·         Mechanics : Deals with action of forces on bodies at rest or in motion.

·         State of rest and Motion: They are relative and depend on the frame of reference.  If the position with reference to frame of reference is fixed with time, then the body is said to be in a state of rest.  Otherwise, it is said to be in a state of motion.

·         Scalar and heater quantities: Quantities which require only magnitude to represent them are called scalar quantities.  Quantities which acquire magnitudes and direction to represent them are called vector quantities.

Eg: Mass, time internal, Distance traveled à Scalars

            Weight, Displacement, Velocity à Vectors

·         Velocity and Speed: Rate of displacement is called velocity and Rate and distance traveled is called Speed.

Unit: m/s

·         Acceleration: Rate of change of velocity is called acceleration. Negative acceleration is called retardation.

·         Momentum: The capacity of a body to impart motion to other bodies is called momentum.

The momentum of a moving body is measured by the product of mass and velocity the moving body

Momentum = Mass x Velocity

Unit: Kg m/s

·       Newton’s first law of motion: Every body continues to be in its state of rest or uniform motion unless compelled by an external agency.

·       Inertia: It is the inherent property the body to retain its state of rest or uniform motion.

·       Force: It is an external agency which overcomes or tends to overcome the inertia of a body.

·       Newton’s second law of motion: The rate of change of momentum of a body is directly proportional to the magnitudes of the applied force and takes place in the direction of the applied force.

·       Matter: Anything which possess mass and requires space to occupy is called matter.

·       States of matter:

Matter can exist in the following states

¨      Solid state.

¨      Fluid state.

¨      Solid state: In case of solids intermolecular force is very large and hence molecules are not free to move. Solids exhibit definite shape and volume. Solids undergo certain amount of deformation and then attain state of equilibrium when subjected to tensile, compressive and shear forces.

¨      Fluid State: Liquids and gases together are called fluids. Incase of liquids Intermolecular force is comparatively small. Therefore liquids exhibit definite volume. But they assume the shape of the container

            Liquids offer very little resistance against tensile force.  Liquids offer maximum resistance against compressive forces. Therefore, liquids are also called incompressible fluids. Liquids undergo continuous or prolonged angular deformation or shear strain when subjected to tangential force or shear force. This property of the liquid is called flow of liquid. Any substance which exhibits the property of flow is called fluid. Therefore liquids are considered as fluids.

            In case of gases intermolecular force is very small. Therefore the molecules are free to move along any direction. Therefore gases will occupy or assume the shape as well as the volume of the container.

            Gases offer little resistance against compressive forces. Therefore gases are called compressible fluids. When subjected to shear force gases undergo continuous or prolonged angular deformation or shear strain. This property of gas is called flow of gases. Any substance which exhibits the property of flow is called fluid. Therefore gases are considered as fluids. 

Thermodynamics

Thermodynamics deals with heat inter-action and work inter-action with the substances called systems. Work and heat are forms of energy. Transfer of heat or work to a substance brings about certain changes in the substance and whatever change happens is called a process. Thermo means heat. Since work is also a form of energy, thermo is taken to mean heat and work. Dynamics refers to the changes that occur as a result of heat or work transfer.

Biological systems are capable doing work. For example, micro-organism is capable swimming in the body fluid of its host. It needs to do the work. Where does energy for doing this work come from? It is the metabolic activity that converts some form of energy (Nutrition that it takes form host is a form of chemical energy) into work. It is important then to understand how this happens so that we can exploit this to our engineering benefit.

In thermodynamics we have work transfer, heat transfer and then we have a system for interaction which undergoes a process.