knocking in I.C. Engines

 

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Detonation or knocking in I.C. Engines – The loud pulsating noise heard within the engine cylinder of an I.C. engine is known as detonation (also called knocking or inking). It is caused due to the propagation of a high speed pressure wave created by the auto-ignition of end portion of unburnt fuel. The blow of this pressure wave may be of sufficient strength to break the piston. Thus, the detonation is harmful to the engine and must be avoided. The following are certain factors which causes detonation:

1.    The shape of the combustion chamber,

2.    The relative position of the sparking plugs in case of petrol engines,

3.    The chemical nature of the fuel,

4.    The initial temperature and pressure of the fuel, and

5.    The rate of combustion of that portion of the fuel which is the first to ignite. This portion of the fuel in heating up, compresses the remaining unburnt fuel, thus producing the conditions for auto-ignition to occur.

The detonation in petrol engines can be suppressed or reduced by the addition of a small amount of lead ethide or ethyl fluid to the fuel. This is called doping.

The following are the chief effects due to detonation:

1.    A loud pulsating noise which may be accompanied by a vibration of the engine.

2.    An increase in the heat lost to the surface of the combustion chamber.

3.    An increase in carbon deposits.

Fluid coupling and its UN known information

  Fluid coupling and its  UN known information

 

It is a device for transmitting rotation between shafts by means of the acceleration and deceleration of a hydraulic fluid (such as oil). Also known as hydraulic coupling. Structurally, a fluid coupling consists of an impeller on the input or driving shaft and a runner on the output or driven shaft. The two contain the fluid. Impeller and runner are bladed rotors, the impeller acting as a pump and the runner reacting as a turbine. Basically, the impeller accelerates the fluid from near its axis, at which the tangential component of absolute velocity is low, to near its periphery, at which the tangential component of absolute velocity is high. This increase in velocity represents an increase in kinetic energy. The fluid mass emerges at high velocity from the impeller, impinges on the runner blades, gives up its energy, and leaves the runner at low velocity.

Hydraulic fluid couplings transfer rotational force from a transmitting axis to a receiving axis. The coupling consists of two toroids — doughnut-shaped objects — in a sealed container of hydraulic fluid. One toroid is attached to the driving shaft and spins with the rotational force. The spinning toroid moves the hydraulic fluid around the receiving toroid. The movement of the fluid turns the receiving toroid and thus turns the connected shaft.

Although fluid couplings use hydraulic fluid within their construction, the mechanism loses a portion of its force to friction and results in the creation of heat. No fluid coupling can run at 100 percent efficiency. Excessive heat production from poorly maintained couplings can result in damage to the coupling and surrounding systems.

A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives, where variable speed operation and/or controlled start-up without shock loading of the power transmission system is essential.

What become your kid ????

 A company ...

 Announced that it needed people for the job,

 Accordingly_

 A lot of people came to the interview.

 Everyone was seated in a hall ...

 Question papers for all,

 Farewell letter was also given.

 Now the company manager spoke,

 '... there are ten questions in this quiz.'

 'You will be allotted five minutes.

 By then you have to answer these questions. '

 'Qualified persons will be selected and given jobs' ....

 Five minutes started ..

 Everyone wrote fast answer that time is limited.

 When the time is up ...

 The manager who bought the farewell paper for everyone said that you gave less time to each one when buying the farewell and we could not write the answer to all the questions except we were able to answer five questions and seven questions.

 Only two of them gave the blank sheet to the manager that he had not written any reply to.

 after that,

 Said the company manager.

 '' Only two people who did not write the answer sheet are eligible to work in this company.

 Others can go home. "

 The same surprise for everyone,

 Everyone asked the company manager to join one.

 _You say we do not work for answering questions correctly.

 How did you get the job done to only those two who did not answer any questions?

 (This is the question that arises in us at this point. Is there a job for those who have answered and those who have not?)

 To which the manager said,

 "Everybody read that tenth question,"

 Everyone who read it went home without being able to speak,

 This is the tenth question.

 # 10) This means that you do not have to answer any of the above questions.

 This is not something to be laughed at.

 Something we all need to think about,

 Wouldn't you have gotten the job if you had set aside two minutes and read the whole question paper?

 For Thought #:

 Except that in this modern age we have to buy a lot of marks by telling children to read step by step,

 No one thinks our children should grow up good and smart ...

Types of mechanical forces

 

A force exerted on a body can cause a change in either the shape or the motion of the body. The unit of force in SI system is the newton (N) and CGS system is dyne. No solid body is perfectly rigid and when forces are applied to it, changes in dimensions occur. Such changes are not always perceptible to the human eye since they are negligible. For example, the span of a bridge will sag under the weight of a vehicle and a spanner will bend slightly when tightening a nut. It is important for civil engineers and designers to appreciate the effects of forces on materials, together with their mechanical properties of materials.

There are three main types of mechanical forces that can act on a body. They are:

1.      Tensile force

2.      Compressive force and

3.      Shear force

1. Tensile force

Tensile force that tends to stretch a material, as shown in the figure 1 below.

Figure 1: Tensile force

For example,

1.      Rubber bands, when stretched, are in tension.

2.      The rope or cable of a crane carrying a load is in tension.

3.      When a nut is tightened, a bolt is under tension.

A tensile force will increases the length of the material on which it acts.

2. Compressive force

Compressive force that tends to squeeze or crush a material, as shown in the figure below.

For example,

A pillar supporting a bridge is in compression.

1. The sole of a shoe is in compression.
2. The jib of a crane is in compression.
3. A compressive force will decrease the length of the material on which it acts.

3. Shear force

Shear force that tends to slide one face of the material over an adjacent face.

For example,

1. A rivet holding two plates together is in shear if a tensile force is applied between the plates as shown in Figure
2. A guillotine cutting sheet metal, or garden shears, each provide a shear force.
3. A horizontal beam is subject to shear force.
4. Transmission joints on cars are subject to shear forces.

A shear force can cause a material to bend, slide or twist.

What is Cetane Number ???? Awesome information

 What is Cetane Number? How rating of fuels used in C. I. Engines (Compression Ignition Engines) is done using Cetane number and other parameters?

The knocking tendency is also found in compression ignition (C. I.) engines with an effect similar to that of S. I. engines, but it is due to a different phenomenon. The knock in C. I. engines is due to sudden ignition and abnormally rapid combustion of accumulated fuel in the combustion chamber. Such a situation occurs because of an ignition lag in the combustion of the fuel between the time of injection and the actual burning.

The property of ignition lag is generally measured in terms of cetane number. It is defined as the percentage, by volume, of cetane in a mixture of cetane and alpha-methyl-naphthalene that produces the same ignition lag as the fuel being tested, in the same engine and under the same operating conditions. For example, a fuel of cetane number 50 has the same ignition quality as a mixture of 50 percent cetane and 50 percent alpha-methyl-naphthalene.

The cetane which is a straight chain paraffin with good ignition quality is assigned a cetane number of 100 and alpha methyl-naphthalene which is a hydrocarbon with poor ignition quality, is assigned a zero cetane number.

Notes:                                                                             

1.    The knocking in C. I. engines may be controlled by decreasing ignition lag. The shorter the ignition lag, the lesser is the tendency to knock.

2.    The cetane number of diesel oil, generally available, is 40 to 55.

Eating Rice is health

 * Some  doctors have been deceived into believing that eating rice will lead to diabetes. *

* In fact, eating rice will cure diseases *

* What are the benefits of any rice!? *

1. * Black gourd rice *

Rice eaten by kings. Cancer does not come. Insulin secretion.

2. * Groom samba rice *:

Nerve, body strong. Masculinity may.

3. * Poongar rice *:

Is childbirth. Breastfeeding.

4. * Wild rice *:

Corrects diabetes, constipation, cancer.

5. * Conceived rice *:

By the way, things like constipation are okay.

6. * Chronological rice *:

After the Buddha had eaten. Brain, nerve, blood, kidney are OK.

7. * Bamboo rice *:

Arthritis and knee pain are okay.

8. * Sixtieth Curry Rice *:

The bone is right.

9. * Iluppaippusambar rice *:

Good for stroke. Foot pain is OK.

10. * Thangachamba rice *:

The tooth, the heart is strong.

11. * Black rice *:

Restores lost power. Cure deadly diseases.

12. * Garuda samba rice *:

Blood, body and mind are cleansed.

13. * Car Rice *:

Skin disease is OK.

14. * Umbrella Banana Rice *:

The bowel is cleansed.

15. * Kichili Samba Rice *:

High in iron and calcium.

16. * Blue samba rice *:

Anemia will go away.

17. * Cumin samba rice *:

Giving beauty. The resistance might.

18. * Pure Coriander Rice *:

The internal organs are strong.

19. * Pitted rice *:

Breastfeeding.

20. * Salem Sanna Rice *:

Strengthens muscle, nerve, and bone.

21. * Picini rice *:

Menstruation and pelvic pain are okay.

22. * Zucchini Rice *:

Pillow body may be leopard beauty.

23. * Walon Samba Rice *:

Is childbirth. Gather beauty for women and slim down in between. The hips are strong. Men may have sperm power.

24. * Watan Samba Rice *:

Quiet sleep will come

25. * Department *

Gives strength to the body. Increases strength. Strengthens the body.

26. * Until *

Reduce obesity. Prevent constipation. Reduce the amount of sugar

27. * Dye *

Relieves fever and dryness. Eliminates impotence. Controls stomach related diseases.

28. * Horsepower *

Muscles and bones become stronger.

39. * Hand stabbing *

Provides essential nutrients to the body. Prevents cancer. Prevents kidney stones. Helps to reduce body weight.

30. * Red wild rice *

Lowers cholesterol in the blood. Helps to control sugar levels.

31. * Red rice *

Minerals help greatly in the growth of hair, teeth, nails, muscles and bones.

32. * Dwarf rice *

Blood cleanses the body. Skin disease is cured.

Thanks.

Enthalpy

 Enthalpy is the measure of heat energy in the air due to sensible heat or latent heat. Sensible heat is the heat (energy) in the air due to the temperature of the air and the latent heat is the heat (energy) in the air due to the moisture of the air. The sum of the latent energy and the sensible energy is called the air enthalpy. Enthalpy is expressed in Btu per pound of dry air (Btu/lb of dry air) or kilojoules per kilogram (kJ/kg).

Enthalpy is useful in air heating and cooling applications. Air with same amount of energy may either be dry hot air (high sensible heat) or cool moist air (high latent heat)

The enthalpy scale is located above the saturation, upper boundary of the chart. Lines of constant enthalpy run diagonally downward from left to right across the chart; follow almost exactly the line of constant wet bulb temperature.

When a process takes place at constant pressure, the heat absorbed or released is equal to the Enthalpy change. Enthalpy is sometimes known as “heat content”, but “enthalpy” is an interesting and unusual word, so most people like to use it. Etymologically, the word “entropy” is derived from the Greek, meaning “turning” and “enthalpy” is derived from the Greek meaning “warming”. As for pronunciation, Entropy is usually stressed on its first syllable, while enthalpy is usually stressed on the second.

Enthalpy(H) is the sum of the internal energy(U) and the product of pressure(P) and volume(V).

Enthalpy H can be written as,

H = U + pV

Where, H = Enthalpy of the system

U = Internal energy of the system

p = Pressure of the system

V = Volume of the system

Enthalpy is not measured directly, however, the change in enthalpy (ΔH) is measured, which is the heat added or lost by the system. It is entirely dependent on the state functions T, p and U.

Enthalpy can also be written as

ΔH=ΔU+ΔPV

At constant temperature, for the process heat flow(q) is equal to the change in enthalpy, this is represented as

ΔH=q

Enthalpy Units

The Enthalpy is expressed as,

H = Energy/Mass

Any physical quantity can be represented by dimensions. The arbitrary magnitudes allocated to the dimensions are called units. There are two types of dimensions namely primary or fundamental and secondary or derived dimensions.

Primary dimensions are: mass, m; length, L; time, t; temperature, T

Secondary dimensions are the ones that can be derived from primary dimensions such as velocity(m/s2 ), pressure (Pa = kg/m.s2 ).

There are two unit systems currently available SI (International System) and USCS (United States Customary System) or English system. We, however, will use SI units exclusively in this course. The SI units are based on the decimal relationship between units.