2. WORKING OF INTERNAL COMBUSTION ENGINE

In the previous lesson, we studied the main components and some basic

parameters of the internal combustion (IC) engine. To understand the working of an engine, we will now take a look at the working principle of these engines which comprises a cycle of 4 operations. We will also study different types of IC engines based on these cycles. Next we will compare the advantages and disadvantages of each type of engine.

It is important that the working principle introduced in this chapter is

understood clearly because every engine follows this cycle, howsoever advanced it may be. Subsequent improvements are modifications in design or material to get the maximum output and decreased pollution levels, but the working principle remains the same.

We will also draw the valve timing diagram (VTD) and port timing diagram

(PTD) and study scavenging. Finally, we will classify IC engines.

2.0 Objectives

After going through this lesson, you will be able to:

i. Describe the 4 operations of an engine cycle ii. Explain the working of 2-stroke and 4-stroke engines used in automobiles. iii. Compare the advantages and disadvantages of 2-stroke and 4-stroke engines iv. Explain the working of petrol and diesel engines used in automobiles. v. Compare the advantages and disadvantages of petrol and diesel engines vi. Classify IC engines

2.1 Introduction

In the previous lesson we gave the definition of an engine as ‘any device used

for converting one form of energy into another, especially for converting other forms of energy into mechanical or kinetic energy’. To convert this energy, the engine has to undergo some basic cycle of operations. We know that heat produces motion. A classic example is that of James Watt designing the steam engine when he watched water boiling in a kettle and the lid dancing over it due to steam. Similar effect is produced in an IC engine but in a much more synchronized manner which are described by the 4 operations of suction, compression, power, and exhaust.

2.2 Working of IC Engine In a practical engine, 4 operations

continuously follow each other during the working of the engine. These 4 operations are – suction of charge into the engine cylinder, compression of charge and its ignition, expansion of gases due to which force is exerted on piston, and removal of burnt gases from the cylinder. All these 4 operations constitute one cycle. We shall now see these operations in detail.

2.2.1 Suction

In the suction process, inlet passage is opened and piston moves from one dead centre to the other dead centre. During this time crank shaft rotates 180 degree and fresh charge enters the engine.

2.2.2 Compression

During the compression process, piston moves upward (in a vertical engine) from bottom dead centre (BDC) to top dead centre (TDC) and the charge present in the cylinder is compressed. Pressure and temperature of charge increase due to compression. Just before the piston reaches TDC i.e. around 20-25 degree of crankshaft rotation before TDC, the fuel is ignited due to which combustion of fuel starts.

2.2.3 Expansion

On account of the combustion of fuel, heat is released because of which gases expand and push the piston down with force. This downward motion of the piston rotates the crank shaft 180 degree. During the expansion stroke we get power from the engine.

2.2.4 Exhaust

Once the energy of fuel is released, the burnt gases need to be expelled from the cylinder. This is done in the exhaust stroke. In this stroke, during the movement of the piston from BDC to TDC the exhaust passage remains open and the gases are removed from the cylinder. This completes one cycle of operations.

Self-Check Questions 1. Name the 4 operations of an IC engine. 2. What are TDC and BDC? 3. When is the fuel ignited?

Fig. 2.1: Engine cycle.

2.3 Types of IC Engines – Two-stroke and Four-stroke

Based on the number of strokes in which the 4 operations get completed

there are two types of engines used in automobiles – two-stroke engines and four-stroke engines.

2.3.1 Two-Stroke Engines

In a two stroke engine suction, compression, power, and exhaust get

completed in two strokes of the piston. The two strokes of piston are called up-stroke and down-stroke. In the meantime, crankshaft executes one rotation. Hence, in every rotation of the crankshaft we get power from the engine.

A 2 stroke engine has openings in the cylinder block called the intake port, the

exhaust port, and the transfer port. These are opened and closed by the movement of the piston. Some engines have a reed valve in the intake port which opens and closes due to crankcase vacuum and pressure.

During the up-stroke, due to increase in volume below the piston, suction is created and fresh charge enters the crankcase. Simultaneously, charge present in the cylinder, which had entered the cylinder in the previous cycle, is compressed. At the proper instant, charge present in the cylinder (above the piston) is ignited and combustion takes place. Air present in the charge supplies the oxygen for combustion of fuel. Hence, in up-stroke suction and compression operations are completed.

Due to combustion of fuel, heat is released and gases expand, pushing the

piston down. During the downward motion of the piston, first the intake port closes by the lower portion of the piston and when the top of the piston uncovers the exhaust port, burnt gases start leaving the cylinder. At the same time, pressure on the fresh charge inducted earlier into the crankcase increases and it moves into the cylinder through the transfer port which has been uncovered by now. Thus in the down-stroke, power and exhaust operations are completed and also the fresh charge is transferred into the cylinder from the crankcase.

Fig. 2.2: Two stroke engine (a) Main parts. (b) Cut section.

Fig. 2.2(b) shows the cut-section model of a Bajaj Super® scooter engine wherein the major components are clearly seen. When we press the kick pedal, drive is transmitted to the piston through the crankshaft. The piston executes the two strokes whereupon under proper conditions of operation the engine fires and gets started. The kick start mechanism helps start the engine which then continues to run on its own power and propels the scooter forward.

2.3.1.1 Advantages of Two-Stroke Engines

A two-stroke engine has some advantages over a four-stroke engine:

• A two-stroke engine is of compact design and light weight.

• It has less number of moving parts and being light weight has a very good power to weight ratio.

• It gives power in every rotation of the crankshaft; hence acceleration of a two-stroke engine is better.

2.3.1.2 Disadvantages of Two-Stroke Engines

• A two-stroke engine gives poor fuel average because some fuel air mixture escapes the cylinder without giving power as the exhaust port and transfer port remain open at the same time in the cycle.

• We cannot keep lubricating oil in the engine and it is therefore mixed with petrol and gets burned in the cylinder along with fuel; hence oil consumption is quite large.

• Since the oil is not very clean burning, it leaves carbon deposits and chokes the engine and silencer and also increases pollution.

• A two-stroke engine has a tendency to overheat because it burns fuel at every alternate stroke of the piston once in a crankshaft rotation; also, its life is less since proper system of lubrication cannot be provided.

Self-Check Questions 4. Name the 2 types of engines based on the cycle of operation 5. In 2-stroke engine, one cycle completes in ____ rotation of the crankshaft 6. Name the 2 strokes of a 2-stroke engine and the operations which take place in

each 7. Name the ports present in a 2-stroke engine 8. Name the valve used in a 2-stroke engine and state how it opens/closes 9. Where does the charge first come in a 2-stroke engine 10. When does the charge enter the cylinder in a 2-stroke engine 11. Why can’t we keep lubricating oil in the crankcase in a 2-stroke engine

2.3.2 Four-Stroke Engines

In a four-stroke engine, the four operations of suction, compression, power, exhaust get completed in four strokes of the piston. During this period, the crank shaft rotates by two rotations i.e. 720O.

A four-stroke engine differs from a two-stroke engine in construction and working. It does have the major components such as the cylinder, piston, connecting rod and crank shaft. But, for intake of charge and expulsion of burnt gases there are two ports in the cylinder head which are opened by mechanically operated valves. The inlet valve is opened at the correct time for intake of fresh charge during the suction stroke and the exhaust valve is opened at the correct instant for expulsion of burnt gases from the cylinder. During the compression and power strokes these valves remain closed. The strokes of piston, opening of valves, ignition of charge are all synchronized with respect to the rotation of the crank shaft.

During the suction stroke, with the inlet valve open, piston moves from the top

dead centre to the bottom dead centre and due to the suction created because of increase in volume, fresh charge enters the engine cylinder. By this time the crank shaft rotates 180°. At the end of suction the inlet valve is closed.

In the compression stroke, the piston

moves from bottom dead centre to top dead centre and due to decrease in volume of charge its pressure and temperature increase. At the proper instant, around 20-25O before the top dead centre, the charge is ignited. The piston continues its movement up to the top dead centre, by which time the charge is completely burnt and gases expand due to heat released. The crank shaft completes one rotation.

The expanding gases cannot leave

the cylinder as the valves are closed and hence exert force on the piston pushing it downward. This is the power stroke. In this stroke we obtain power from the engine to drive the vehicle.

When the charge was ignited and combustion of fuel took place, all energy of

the fuel was released. This was converted into mechanical energy which we obtained from the engine at the crankshaft. Now in order to have the engine continue

Fig. 2.3: Four Stroke Engine (a) Parts (b) Model

Fig. 2.4: Engine strokes.

to run we need to expel these burnt gases from the cylinder. This is done in the exhaust stroke. In this stroke, exhaust valve remains open and the piston moves upward from bottom dead centre to top dead centre, pushing the burnt gases out. At the proper instant, exhaust valve is closed.

This completes one cycle of operations. Repetition of this cycle of operations

is required for continued running of the engine. We shall study the valve operating mechanism and the ignition system of a petrol engine in detail in subsequent lessons.

2.3.2.1 Advantages of Four-Stroke Engines

A four-stroke engine has several advantages over two-stroke engines:

• A four-stroke engine gives better fuel average.

• In this engine lubricating oil is not burned in the cylinder but it is kept in the oil pan and circulated and re-used for thousands of kilometers. Hence oil consumption is less and also pollution is less.

• It does not get overheated easily since heat is released only once in two rotations of the crank.

2.3.2.2 Disadvantages of Four-Stroke Engines

• A four-stroke engine has a greater number of moving parts and its initial cost is higher.

• Power obtained in case of a four-stroke engine on the crankshaft is not as smooth because it gives power only every alternate rotation of the crankshaft.

Self-Check Questions 12. In a 4-stroke engine one cycle of operation completes in ____degree of crank

rotation 13. How does charge enter and gases get expelled in a 4-stroke engine. 14. Lubrication oil expense is greater in __________________ engine.

The following table gives the differences between a 2-stroke and a 4-stroke engine:

S. No. 2-stroke engine 4-stroke engine

1. 1 rev. of crank & 2 strokes of piston complete 1 cycle

2 rev. of crank & 4 strokes of piston complete a cycle.

2. Power stroke in every rev; smoother torque delivery, smaller flywheel required

Power stroke in every alternate rev.; torque delivery not as smooth, larger flywheel required

3. Tends to overheat Less tendency to overheat

4. Ports or openings present in cylinder wall which are opened/closed by moving piston

Ports present in cylinder head are opened/closed by mechanically operated valves

5. Simple in construction & light weight.

Complicated valve operating mechanism present.

6. Less efficient due to improper scavenging and consequent dilution of charge

More efficient.

7. Fuel consumption is more since some charge may escape when inlet & exhaust ports are simultaneously open

More economical as intake & exhaust strokes are separate

8. Lubricating oil is mixed with petrol. Separate filter & pump for lubrication

9. Oil consumption is more. Less oil consumption as it is re-circulated

10. Tendency to carbonizing is more Less tendency to carbonize 11. Can run in any direction i.e.

clockwise/counter-clockwise. Direction of rotation is fixed due to presence of valve operating mechanism

Self-Check Questions 15. Why is torque delivery smoother in a 2-stroke engine? 16. In what proportion is lubrication oil mixed with petrol? Which oil is used? 17. Why does silencer of a 2-stroke engine get choked frequently?

2.4 Types of IC engines – Petrol and Diesel

We have already seen that the internal combustion engines can be classified

into two types – whether the engine is a two-stroke cycle engine or four-stroke cycle engine.

Another criterion for the classification of engines is the fuel that they run on –

petrol or diesel. The engines running on petrol are also called spark ignited engines and those running on diesel are known as compression ignited engines. Petrol engines differ greatly in construction and working from diesel engines and one fuel cannot be used in place of another.

Until now, we have referred to fresh charge being inducted into the engine

cylinder during the suction stroke. This fresh charge is different for petrol and diesel engines. In the case of petrol engine, a mixture of air and petrol formed in the carburetor (in the older type of engines) is inducted into the engine cylinder during the suction stroke. This mixture has sufficient oxygen for complete combustion of fuel. Complete combustion of fuel is important in order that we get good fuel economy and less exhaust pollution. A petrol engine has lesser initial cost, low maintenance cost, is easy to start and has smooth idling i.e. the engine does not shake or vibrate while running. However, it has a high running cost due to the high cost of petrol and lower thermal efficiency due to low compression ratio, making it suitable for light vehicles only.

In a diesel engine, only air is inducted into the engine cylinder during the

suction stroke. This air is taken from the atmosphere and cleaned of dust etc. by the air cleaner. During the compression stroke, the air is very highly compressed, because of which its pressure and temperature increase greatly. Towards the end of compression stroke, diesel in the form of a very fine spray is injected into the hot air. It is pressurized by the Fuel Injection (FI) pump and injected by the Injector. The diesel so injected self-ignites and heat is released, thus expanding the gases and providing power. A diesel engine has low running cost, high thermal efficiency and longer life but has a high initial and maintenance cost. A diesel engine also suffers from late starting, especially in cold weather and is noisy and vibrates and shakes while running.

Self-Check Questions 18. What is the other name of petrol engine? 19. What is the other name of diesel engine? 20. What is the fresh charge in case of petrol engine? 21. What is the fresh charge in case of diesel engine? 22. A mixture of air and diesel is inducted into the engine cylinder in the suction

stroke. State whether True/False.

Petrol and diesel engines can be broadly compared as under: S. No. Petrol engine Diesel engine

1. Works on Otto cycle. Works on Diesel cycle. 2. Spark ignited. Compression ignited. 3. Charge is air and fuel mixture. Charge is air only. 4. Low compression ratio 7:1

to10:1. High compression ratio 18:1 to 22:1 (weight/HP is more as engine is made stronger).

5. Easy starting, smooth idling Difficult starting, rough idling. 6. Light duty, high speed

applications. Heavy duty, low speed application (low speed as combustion is slow).

Fig. 2.5: Distinguishing features (a) Petrol engine. (b) Diesel engine.

7. Quantitative governing. Qualitative governing (mixture strength is varied).

8. Lower thermal efficiency. Higher thermal efficiency. 9. Low initial cost but uneconomic

running. High initial cost but economic running.

10. Low maintenance cost. High maintenance cost. 11. Lighter transmission & smaller

battery required. Heavier transmission & bigger battery required because of greater starting torque.

2.5 Precautions

• Both petrol and diesel are inflammable; hence do not take lighted match, cigarette or any electrical device which may give out a spark near them.

• Both petrol and diesel are lighter than water; hence petrol and diesel fire cannot be doused with water.

• To extinguish petrol or diesel fires, always use sand or dry type fire extinguishers.

Self-Check Questions 23. Compression ratio in case of a petrol engine is between _________ 24. Compression ratio in case of a diesel engine is between _________ 25. Generation of power in petrol engine is varied by varying the quantity of mixture 26. Generation of power in diesel engine is varied by varying the __________ of

mixture or ___________ of fuel 27. Petrol or diesel fire is doused with _______________________

2.6 Timing Diagrams

The opening and closing of valves, the four operations of suction,

compression, expansion, and exhaust and the process of ignition can be shown on a diagram called the valve timing diagram (VTD) in a 4-stroke engine. In a 2-stroke engine it is called port timing diagram (PTD). 2.6.1 Valve Timing Diagram (VTD) 2.6.1.1 VTD for Petrol Engine

Fig. 2.6 shows the theoretical and actual VTD for a 4-stroke petrol engine. As can be seen in Fig. 2.6 (a), valves are shown to open or close and also ignition is shown to take place at dead centres. But in an actual running this is not the case. The valves are opened and closed at points other than at dead centres. The reason for each is given below-

i. IVO α O before TDC (BTDC) so that the inlet valve is fully open when the piston starts its suction stroke.

ii. IVC β O after BDC (ABDC) since when the piston reaches BDC it is seen that

the pressure inside the cylinder is still less than atmospheric so that charge can still be inducted inside the cylinder.

Both these help more charge to enter the cylinder in each cycle.

iii. Ignition starts γ O BTDC and extends upto δ O ATDC so that when the piston

reaches TDC, about half the designed pressure rise due to combustion of fuel has occurred and just 10O ATDC maximum combustion pressure forces the piston down in the power stroke.

iv. EVO θ O BBDC so that the gases which have already spent their energy may start leaving the cylinder by themselves and when the piston starts upward on its exhaust stroke it does not encounter much resistance or back pressure.

v. EVC λ O ATDC since it is seen that when the piston reaches TDC at the end of is exhaust stroke, the pressure inside the cylinder is still greater than atmospheric and if the exhaust valve remains open the gases can leave by their own accord.

iv and v cause exhaust to last for more than 180O which helps scavenge the

cylinder of burnt gases fully. All above help get maximum power and fuel economy form the engine. The

values for each angle are as follows: α = 10 to 30O BTDC, β = 30 to 45O ABDC, γ =

7 to 25O BTDC, δ = 5 to 10O ATDC, θ = 30 to 40O BBDC, and λ = 10 to 15O ATDC. The period (θ + λ ) when both valves are open is called valve overlap. It also helps in scavenging.

Fig. 2.6: VTD for a petrol engine (a) Theoretical. (b) Actual.

2.6.1.2 VTD for Diesel Engine VTD for a 4-stroke diesel engine is shown in Fig. 2.7. The only difference here is that instead of ignition, points of fuel injection start and finish are shown.

Fig. 2.7: Actual VTD for a diesel engine.

2.6.2 Port Timing Diagram The PTD for a 2-stroke petrol engine depicts the points of opening and closing of various ports. You can see that cycle time in terms of rotation of crank angle degrees for suction and exhaust is very much less in a 2-stroke engine than in a 4-stoke engine. Hence scavenging assumes importance in a 2-stroke engine.

Fig. 2.8: Port timing diagram for a petrol engine.

Self-check Questions 28. Give the full forms of BTDC, ABDC, BBDC, ATDC 29. Give the full forms of IVO, EVO, IVC, EVC 30. Give the full forms of IGN, FIS, FIE

2.7 Scavenging

It is the process of removal of burnt gases from the cylinder with the help of fresh charge. If the burnt gases are not removed completely, the fresh charge will get

diluted. Further, since fresh charge is also in vapour formand leave the cylinder with the burnt gases thus resulting in loss of fresh charge.

In the 4-stroke engine scavenging takes place during valve overlap period. In the 2-stroke engine it takes place during the period when bothexhaust ports are open. Scavenging is more important in 2cycle time is less. Methods:

• By using the back of the piston as a scavenge pump

• By using a separate scavenge pump; this method is more suitable for large size engines.

As shown in the Fig. 2.6 the transfer port and exhaust port are situated in front of each other at the lower part of the cylinder. Fresh charge enters the cylinder through the transfer port and is deflected uThus, it pushes the exhaust gases towards the exhaust port to go out.

Self-Check Questions 31. What is meant by scavenging?32. In which engine is scavenging more important? Why?33. How is scavenging done in a 2

2.8 Classification of IC Engines

IC engines can be classified by the following criteria; some of these parameters will be covered in the subsequent courses: 1. Cycle of operation – 2 or 4 stroke reciprocating; rotary2. Cycle of combustion - Otto / Diesel 3. Type of fuel - petrol / gas / heavy oil etc.4. Method of ignition - spark / compression5. Method of cooling - air / water

diluted. Further, since fresh charge is also in vapour form it can mix with burnt gases and leave the cylinder with the burnt gases thus resulting in loss of fresh charge.

stroke engine scavenging takes place during valve overlap period. In stroke engine it takes place during the period when both

exhaust ports are open. Scavenging is more important in 2-stroke engine because

By using the back of the piston as a scavenge pump

By using a separate scavenge pump; this method is more suitable for ze engines.

Fig. 2.9: Cross-flow scavenging.

As shown in the Fig. 2.6 the transfer port and exhaust port are situated in front of each other at the lower part of the cylinder. Fresh charge enters the cylinder through the transfer port and is deflected upwards. Then it comes towards the exhaust port. Thus, it pushes the exhaust gases towards the exhaust port to go out.

What is meant by scavenging? In which engine is scavenging more important? Why? How is scavenging done in a 2-stroke engine?

Classification of IC Engines

IC engines can be classified by the following criteria; some of these parameters will be covered in the subsequent courses:

2 or 4 stroke reciprocating; rotary Otto / Diesel

petrol / gas / heavy oil etc. spark / compression air / water

it can mix with burnt gases and leave the cylinder with the burnt gases thus resulting in loss of fresh charge.

stroke engine scavenging takes place during valve overlap period. In the transfer and

stroke engine because

By using a separate scavenge pump; this method is more suitable for

As shown in the Fig. 2.6 the transfer port and exhaust port are situated in front of each other at the lower part of the cylinder. Fresh charge enters the cylinder through

pwards. Then it comes towards the exhaust port. Thus, it pushes the exhaust gases towards the exhaust port to go out.

IC engines can be classified by the following criteria; some of these parameters will

6. Method of governing - quantitative / qualitative 7. Speed - low / medium / high. 8. Number of cylinders - 1, 2, 3, 4, 6, 8 etc. 9. Cylinder arrangement - horizontal / vertical / Vee / radial 10. Type of valve – poppet / reed / rotary 11. Valve arrangement - I/F/L/T 12. Application – stationary / portable / automobile / marine / aero

Self-Check Questions 34. Name the valves used in 2-stroke engines, if any.

2.9 Assignments

2.9.1 Class Assignment

1. Discuss why the 2-stroke engine does not give double the power of a 4-stroke engine of same capacity even though it has twice the number of power strokes every cycle.

2. Get specifications of some engines used in automobiles. 1. Based on the above data compare the bore, stroke, compression ratio, power,

and torque of engines of same type of vehicles.

2.9.2 Home Assignment

1. Look at some 2-stroke engines and 4-stroke engines and note the differences

you see at the outside. 1. Look at some petrol and diesel engines and note the differences you see at

the outside. 2. See animated engine sites via Google Search.

2.10 Summing Up

All of you see automobiles run on roads. Many of you have a vehicle at home. You might or might not be aware of how it moves. Now after studying this and the next lesson on Working of IC engines you will get a fair idea of what propels the vehicle.

In this lesson we studied the four operations and the working of 2-stroke and

4-stroke engines. In the next lesson we will study the working of petrol and diesel engines.

It is hoped that you enjoyed the lessons on IC engines. It is truly incredible to see how a small piece of equipment releases so much power as to propel something many times its weight at high speeds over long distances and for long periods of time. This is because the engine makes the fuel release its energy in a controlled manner. Just as energy released by the food that we eat helps us carry on our day to

day tasks, so is the case with the engine. IC engine is indeed a marvel of engineering.

2.11 Possible Answers to Self-check Questions

1. suction, compression, expansion, and exhaust 2. TDC- top dead centre: top most position of piston travel; BDC- bottom dead

centre: bottom most position of piston travel 3. some degrees before TDC in the compression stroke 4. 2-stroke engine and 4-stroke engine 5. one 6. up-stroke- suction & compression; down-stroke- expansion & exhaust 7. suction port, transfer port, and exhaust port 8. reed valve opens/closes due to suction/pressure in the crankcase 9. crankcase 10. during the down-stroke through the transfer port 11. the charge travels through the crankcase and will take oil with it to the cylinder 12. 720 13. through mechanically operated valves in the suction and exhaust strokes

respectively 14. 2-stroke engine 15. Because there is a power stroke in every rotation of the crankshaft 16. 2-3% 2T oil 17. Since the oil is not very clean burning, it leaves carbon deposits and chokes

the engine and silencer 18. Spark ignited (SI) engine 19. Compression ignited (CI) engine 20. mixture of petrol and air 21. air only 22. False 23. 7:1 to 10:1 24. 16:1 to 22:1 25. quantity 26. quality, quantity 27. sand, foam 28. Before Top Dead Centre, After Bottom Dead Centre, Before Bottom Dead

Centre, After Top Dead Centre 29. Inlet Valve Opens, Exhaust Valve Opens, Inlet Valve Closes, Exhaust Valve

Closes 30. Ignition, Fuel Injection Starts, Fuel Injection Ends 31. removal of burnt gases from the cylinder with the help of fresh charge 32. scavenging is more important in 2-stroke engine because cycle time is less 33. by compressing the fresh charge with the back of piston so that it move into

the cylinder through transfer port and pushes the burnt gases out 34. reed, rotary

2.12 Terminal Questions

1. Describe the 4 operations of an engine cycle. 2. Explain the working of a 2-stroke engine.

3. Give the advantages and disadvantages of 2-stroke engines. 4. Explain the working of a 4-stroke engine. 5. Give the advantages and disadvantages of 4-stroke engines. 6. Compare and contrast 2-stroke and 4-stroke engines. 7. Describe the working of petrol engine. 8. Describe the working of diesel engine. 9. Compare petrol engine with diesel engine. 10. Draw and explain VTD of a petrol engine. 11. Draw and explain VTD of a diesel engine. 12. Explain why valves are not opened/closed at TDC/BDC 13. Draw the PTD of a petrol engine. 14. Write a note on Scavenging.

2.13 References

1. www.howstuffworks.com 2. Gupta, K. M., 2002. Automobile Engineering, Vol. 1. Umesh Publications,

Delhi.

Suggested Further Reading

1. Nakra, C. P., 2007. Basic Automobile Engineering (English). Reprint. Dhanpat Rai Publishing Co., New Delhi.

2. Chhikara, A., 1999. Automobile Engineering, Vol 1: Engine Systems. Satya Prakashan, New Delhi.

2.15 Glossary

BDC Bottom dead centre: bottom most position of piston travel.

Carburetor Component which mixes correct amounts of air and petrol and supplies the desired quantity of this mixture to the engine.

Charge That which enters the cylinder in the suction stroke.

Compression ignition (CI) engines

Engines in which ignition of fuel takes place due to heat of compressed air e.g. diesel engines.

Four-stroke engine Engine in which the cycle of operations completes in 4 strokes of piston.

Fuel injection (FI) pump High pressure pump which pressurizes diesel for injection.

Idling Minimum engine speed at which it runs smoothly without load.

Injector Component which atomizes and injects diesel in the

engine.

Internal combustion (IC) engine

Engine in which combustion of fuel takes place in the engine cylinder.

PTD Port timing diagram, showing the opening/closing of ports and point of ignition in 2-stroke engines.

Reed valve Strip of thin blade which covers and uncovers the intake port in a 2-stroke engine due to pressure and suction in the crankcase.

Scavenging Removal of burnt gases from the cylinder with the help of fresh charge.

Spark ignition engines Engines in which ignition of fuel takes place due to electric spark e.g. petrol and gas engines.

TDC Top dead centre: top most position of piston travel.

Two-stroke engine Engine in which the cycle of operations completes in 2 strokes of piston.

VTD Valve timing diagram, showing the opening/closing of valves and point of ignition or fuel injection in 4-stroke engines.