Air standard cycle

Air standard cycle.

In actual engine, combustion of air-fuel mixture take place inside the cylinder. But to make the analysis simple, we assume that the working fluid is only air. Here we take only air but in actual case it is air+fuel mixture.

Examples: Otto engine, Diesel engine etc.


Assumption in air standard cycle:

1) Air is the working fluid as it makes our analysis simple.

2) Specific heat remains constant. We know that if we increase temperature, specific heat also increases but this changes in specific heat is not significant. So we normally neglect this.

3) All processes are reversible as we are using ideal gas.

Terminologies in IC engine

Various terminologies in IC engine are listed below:

1) Top Dead Center (TDC) : It is the position of the piston farthest from crankshaft.

2) Bottom Dead Center (BDC) : It is the position of the piston nearest from crankshaft.

3) Stroke or Stroke length: The distance traveled by the piston from TDC to BDC is one stroke known stroke length.

4) Swept volume: The volume covered when piston move from BDC to TDC is swept volume.

5) Clearance volume: It is the volume of the cylinder left when the piston is at TDC.

Engine parts

IC Engine parts

The various parts of engine are listed below:

1) Inlet valve & outlet valve for 4 stroke engine whereas Inlet port & outlet port for 2 stroke engine.

2) Spark plug in case of SI (spark ignition engine) & fuel injector in case of CI (compression ignition engine)

3) Cylinder

4) Piston

5) Water jacket for cooling purpose

6) Gudgeon or piston pin

7) Connecting rod

8) Crank rod

9) Engine shaft


Here, cylinder is made of cast iron or alloy steel through casting.

cylinder head is made of cast iron or aluminium alloy through casting & forging.

Piston is made of cast iron or aluminium alloy through casting & forging.

Piston ring is made of silicon cast iron through casting.

Piston pin is made of forged steel through forging.

Connecting rod is made of forged steel through forging.

Crank shaft is made of aluminium steel through forging.

IC engine & EC engine

Lets compare IC engine & EC engine:


1) Efficiency of IC engine is higher as compared to EC engine.

In such type of engine, product of combustion produces power directly. eg. In petrol engine or in diesel engine, we burn mixture of air & fuel due to which huge pressure is generated and it moves the piston directly. So, combustion of air-fuel mixture is directly responsible for the output. Here there is no such system of heat transfer. Here the stroke of the piston produce power. So, as there is no transfer of heat to working fluid, losses will be less compared to EC engine where transfer of heat takes place.


2) Cost of IC engine is low as compared to EC engine.

The component we use in EC engine like compressor, turbine etc. are very costly which make EC engine costly whereas there is no need of such component in IC engine.


3) Working pressure and temperature are high in IC engine as compared to EC engine.


4) IC engine starts instantaneously whereas EC engine takes some time to start.

This you might have experienced in real life, when you start your vehicle, it starts instantaneously but it is not the case in EC engine. Because in EC engine the size of furnace is very large and once all the coal entered in the furnace, we ignite it. Now it takes some time to generate considerable amount of heat. In boiler, liquid will also take some time to convert in vapour. Then it will come to turbine where it starts rotating. So this all processes take time and as result it take some time to start.


5) Power to weight ratio of IC engine is high as compared to EC engine.

In EC engine, very big devices are used like compressor, turbine, boiler etc. The power generation as a result in EC engine is more than IC engine but when we compared the ratio of how much power it is generating to its weight, this ratio is lesser than IC engine.

Heat Engine

What is heat engine?

Heat engine is a device which convert chemical energy of the fuel to heat energy & further convert heat energy to mechanical energy.

This we have experienced in our real life where we fill petrol or diesel in our vehicle & if we start the vehicle, combustion of the fuel takes place. So the chemical energy of the fuel, once burn convert to heat energy and this heat energy is converted to mechanical energy which helps in the movement of the wheels of the vehicle, as a result our vehicle moves.


There are 2 types of heat engine:

1) External combustion engine
2) Internal combustion engine

External combustion engine: In such type of engine, product of combustion transfer heat to working fluid. eg. In power-plant we burn coal in the furnace which gives heat and this heat is transfer to boiler where steam is produce from water due to this heat added from the furnace. Now in power-plant this steam is used as a working fluid.Here steam produce the required output.

Internal combustion engine: In such type of engine, product of combustion produces power directly. eg. In petrol engine or in diesel engine, we burn mixture of air & fuel due to which huge pressure is generated and it moves the piston directly. So, combustion of air-fuel mixture is directly responsible for the output. Here there is no such system of heat transfer. Here the stroke of the piston produce power. 

Engine

What is engine? or what is the use of an engine?

Engine is a device which convert one form of energy to another.

For example, Heat engine is one type of engine which is a device which convert chemical energy of the fuel to the heat energy & further convert this heat energy to mechanical energy.

This we have experienced in our real life where we fill petrol or diesel in our vehicle & if we start the vehicle, combustion of the fuel takes place. So the chemical energy of the fuel, once burn convert to heat energy and this heat energy is converted to mechanical energy which helps in the movement of the wheels of the vehicle, as a result our vehicle moves.

 

Force system

What do we mean by the force system?

When two or more forces act on a body, they are called a force system.

Coplanar forces: The forces whose line of action lie on the same plane are known as coplanar forces.

Concurrent forces: The forces which meet at one point are known as concurrent forces.

Collinear forces: The forces whose line of action lie on the same line are known as collinear forces.

Coplanar concurrent forces: The forces whose line of action lie on the same plane and which meet at one point also are known as coplanar concurrent forces.

Coplanar non-concurrent forces: The forces whose line of action lie on the same plane but does not meet at one point are known as coplanar non-concurrent forces.

Non-coplanar concurrent forces: The forces whose line of action does not lie on the same plane but meet at one point are known as non-coplanar concurrent forces.

Non-coplanar non-concurrent forces: The forces whose line of action does not lie on the same plane and does not meet at one point also are known as non-coplanar non-concurrent forces.

Triangular law and parallelogram law of addition

What is the use of triangular & parallelogram law?

Now, we know that adding scalar quantities is very simple, just we need to add it normally but for vector quantities such as force, we cannot perform addition like this. So, to add the vector quantity we use the triangular law and parallelogram law. 

Remember that this two law can be used only for the addition of 2 force or 2 vector quantity.

Triangular law for addition: 

If two forces acting simultaneously on a body such that they can be represented by two adjacent sides of a triangle taken in same order, then their resultant will be equal to the third closing side of triangle taken in opposite direction or order.

Parallelogram law for addition:

If two vectors are represented by two adjacent sides of parallelogram then the diagonal through intersection represents their resultant.


These are the graphical method to add vector. we can also use analytical method for the addition of vector.

Scalar, vector and tensor quantity

What is scalar quantity, vector quantity & tensor quantity?

To define any scalar quantity we required only magnitude of that quantity. So, those quantity which can be fully defined based on their magnitude only are scalar quantities. eg. Time, volume, speed etc.

To define any vector quantity we required  magnitude as well as direction of that quantity. So, those quantity which can be fully defined based on their magnitude and direction are vector quantities. By knowing only the magnitude of it, it cannot be fully defined. eg. velocity, acceleration etc.

To define a tensor quantity we required magnitude, direction and the area or plane on which it is acting. So those quantity which can be fully defined only by knowing all three of these are tensor quantity. eg. Stress on a material

Dyne

What is dyne?

It is the force required to accelerate a mass of one gram at a rate of one centimeter per second squared.

1 Dyne = 1 g.cm/s^2 = 10^-5 N

Newton

What is newton?

A newton is how much force is required to make a mass of one kilogram accelerate at the rate of one meter per second square.

1N = 10^5 Dyne

1N = 1kg.m/s^2

Force

What is force?

It is the push or pull which create or tends to create motion, destroy motion or tends to destroy motion.

Force is a vector quantity.

Unit of force in SI system is Newton,
Unit of force in CGS system is Dyne.

Note: 1 N = 10^5 Dyne

Engineering Mechanics

Engineering mechanics is sub-divided into two parts:

1) Static
2) Dynamic

Here, statics deals with stationary bodies where as dynamic deals with the body in motion.

Further, dynamic can be subdivided into kinematics and kinetics.

Kinematics deals only with motion of the body and not the forces causing them where as Kinetics deals with both motion of the body and the forces causing them.

Classification of Mechanics

Engineering Mechanic can be classified as:

1) Engineering Mechanics

2) Strength of materials

3) Mechanics of fluids

Engineering mechanics deals with the rigid bodies or external force acting on the body.

Strength of material deals with the deformable bodies or internal forces acting on the bodies.

Mechanics of fluid deals with the compressible and in compressible fluid i.e. gases or liquids.

Deformable body

What do we mean by deformable body?

It is a body in which relative position of particles changes after the application of forces.

Rigid body

What do we mean by rigid body?

It is an ideal body in which relative position of particles remain same even after application of forces.

When force is applied, it only get displaced and not deformed.

Deformation does not take place here in rigid body. i.e. in rigid bodies, only displacement takes place and there is no deformation in the body.

Mechanics

What is Mechanics?

It is the science that deals with the study of forces (internal or external) and their effects on the body.