Internal Combustion Engines

Yogesh Kumar Department of Mechanical Engineering

Govt. Polytechnic Edu. Society Uttawar(Palwal)

1

Heat engine

Any engine that converts thermal energy to mechanical work output. Examples: steam engine, diesel engine, and gasoline (petrol) engine.

Heat engine can be classified On the basis of how

thermal energy is being delivered to working fluid.

1. Internal Combustion engine ; an engine

combustion of working fluid takes place inside the

engine cylinder. i.e Petrol engine, Diesel engine,

Rocket engine etc.

2. External Combustion engine ; an engine

combustion of working fluid takes place outside

the engine cylinder. i.e Steam engine etc.

Classification of Internal Combustion engine a) On the basis of ignition ; S.I engine, C.I engine

b) On the basis of strokes ; 2-Stroke engine, 4-Stroke engine

c) On the basis of engine design ; Reciprocating engine, Rotary engine(single rotor and multi rotor)

d) On the basis of cylinders ; Single Cylinder engine, Multi cylinder engine

e) On the basis of working cycles ; otto cycle engine, diesel cycle engine, dual cycle engine

f) On the basis of ignition ; Spark ignition(S.I) engine, Compression ignition(C.I) engine

g) On the basis of Valve/ Port design ; Poppet Valve, Rotary Valve, Reed Valve, Piston Controlled Porting

h) On the basis of Valve Location ; The T-head, The L-head, The F-head, The I-head(Over head Valve (OHV), Over

head Cam (OHC))

i) On the basis of Fuel ; Petrol engine, Diesel engine, others(Gasoline, CNG, LPG etc) engine

j) On the basis of Cooling ; Direct Air-cooling, Indirect Air-cooling (Liquid Cooling)

2

Location and functions of various parts of IC engines and materials used for them

S.

No

.

Part Name Material used Manufacturing

Method

Utilization/Location

1 Cylinder Block Ductile (Nodular)

Cast Iron ,30C8 (Low

Carbon Steel)

Casting, Forging

and after that heat

transfer ,

Machining

A container fitted with piston, where the fuel is burnt and

power is produced. cylinder is to guide the piston.

2 Cylinder

Head/Cylinder

Cover

Aluminium alloys Casting The inlet valve, exhaust valve, spark plug, injector etc. are

bolted on the cylinder head. The main function of cylinder

head is to seal the cylinder block and not to permit entry and

exit of gases on cover head valve engine.

3 Piston Aluminum Alloy

4652 because of its

Low Specific Gravity

Casting Piston is used to reciprocate inside the cylinder.

It transmits the energy to crankshaft through connecting rod

4 Piston Rings cast iron of fine grain

and high elastic

material

Pot casting

method

To maintain a pressure tight seal between the piston and

cylinder walls.it transfer the heat from the piston head to

cylinder walls and are fitted in split at one end so they can

expand or slipped over the end of piston.

5 Connecting Rod Low Carbon steel

30C8

Forging and after

that heat heat

treatment

One end(Small) of the connecting rod is connected to piston

through piston pin while the other(Big end) is connected to

crank through crank pin.It transmits the reciprocatory motion

of piston to rotary crank.

6 Crank Shaft 37C15 Alloy Steel Casting The crankshaft of an internal combustion engine receives the

efforts or thrust supplied by piston to the connecting rod and

converts the reciprocating motion of piston into rotary motion

of crankshaft.

7 Crank 37C15 Alloy Steel Casting It is a lever between connecting rod and crank shaft

3

S.

No

.

Part Name Material used Manufacturing

Method

Utilization/Location

8 Fly wheel cast or nodular iron, steel

or aluminum, high-

strength steel or

composites

Casting Fly wheel is a rotating mass used as an energy storing device.

A flywheel is secured on the crankshaft. The main function of flywheel is

to rotate the shaft during preparatory stroke. It also makes crankshaft

rotation more uniform.

9 Crank Case cast iron or cast

aluminium

sand casting The main body of the engine to which the cylinder are attached and which

contains the crankshaft and crankshaft bearing is called crankcase. It

serves as the lubricating system too.

10 Poppet Valves Phosphorus Bronze and

Monel metal

The intake and exhaust valves open at the proper time to let in air and fuel

and to let out exhaust.

11 Spark Plug Electrodes-high

nickel alloys

Insulator-

aluminium oxide ceramic

Shell-steel wire

continuous in-line

assembly process

A sparkplug is to maintain proper gap across which spark is produced by

applying high voltage , to ignite the mixture in the ignition(Combustion)

chamber.

12 Engine Bearing steel-aluminium

composites with

sintered bronze, lead

casting To support the moving parts and reduce the friction and allow parts to

move freely.

13 Carburettor cast iron, zinc and

aluminum

Die casting To atomize and meter the liquid fuel and mix it with the air as it enters the

induction system of the engine and maintaining fuel-air ratio at all

operations.

14 Fuel Atomizer or

Injector

Aluminum, low carbon

steels, hardened steels,

non-ferrous metals

injection

molding process

The fuel injector is only a nozzle and a valve: the power to inject the fuel

comes from a pump or a pressure container farther back in the fuel supply.

15 Manifold Aluminium alloy -Alloy

4600, cast iron

Sand casting To supply the air fuel mixture through intake manifold and collects the

exhaust gases through exhaust manifold from engine cylinder.

16 Gudgeon pin or piston

pin

Plain Carbon steel 10C4 Forging followed by

carburising

It connects the piston to connecting rod. It is made hollow for lightness.

17 Pushrod high-tempered steel or

chrome "molly,

cold forging Pushrod is used when the camshaft is situated at the bottom end of

cylinder. It carries the camshaft motion to the valves which are situated at

the cylinder head. 4

5

IC engine Terminology

Bore (D); The nominal inside diameter of the engine cylinder.

Stroke(L); The maximum distance travelled by the piston from TDC to BDC. It is equal to twice the radius of the crank.

L = 2r

Dead centre; The extreme positions of piston.it is of two types.

i. Top Dead Centre (TDC); The extreme position of the piston at the top of the cylinder of the vertical engine is called top dead centre (TDC), Incase of horizontal engines. It is known as inner dead centre (IDC).

ii. Bottom Dead Centre (BDC); The extreme position of the piston at the bottom of the cylinder of the vertical engine called bottom dead centre (BDC). In case of horizontal engines, it is known as outer dead center (ODC).

Crank throw(r)/ Crank radius; it is central distance between crank pin to center of crank shaft.

6

Compression ratio; Compression ratio is a ratio of the Total volume when the piston is at bottom dead

centre to the Clearance volume when the piston is at top dead centre.

Piston Displacement(Swept Volume) Vs; The volume swept by the piston during one stroke i.e

while moving from TDC to BDC.

The compression ratio varies from 5 : 1 to 10 : 1 for petrol engines and from 12:1 to 22 : 1 for diesel

engines.

Piston Speed;

A = Cross sectional area of the piston in Sq.m,

L = Stroke in m,

D = Cylinder bore i.e., inner diameter of the cylinder in m,

7

Working principle of two stroke and four stroke cycle

2-Stroke cycle; Two stroke cycle perform only two

strokes to complete one cycle. The power is obtained

only once in one revolution of the crankshaft. 2-

Stroke cycle used in two types of engines mentioned

below.

1. 2-Stroke Petrol engine

2. 2-Stroke Diesel engine

4-Stroke cycle; four stroke cycle perform only four

strokes to complete one cycle. The power is obtained

only once in two revolutions of the crankshaft. 4-

Stroke cycle used in two types of engines mentioned

below.

1. 4-Stroke Petrol engine

2. 4-Stroke Diesel engine 8

9

First Stroke (Upward Stroke of the Piston) of 2-Stroke Petrol engine

(a) Compression and Inductance: During the upward movement of the piston from BDC to TDC, both the transfer and exhaust ports are covered by the piston.The petrol air mixture which is already transferred into the engine cylinder is compressed by the moving piston. Thus, the pressure and temperature of the charge increases at the end of compression.The compression process is continued until the piston reaches TDC.At the same time, the inlet port is uncovered by the moving piston and the fresh petrol air mixture enters the crankcase through the inlet port.

(b) Ignition and Inductance: After the piston almost reaches the TDC, the compressed petrol air mixture is ignited by means of an electric spark produced by a spark plug. The admission of fresh charge into the crankcase continues till the piston reaches the TDC.

Second Stroke (Downward Stroke of the Piston) of 2-Stroke Petrol engine

(c) Expansion and Crankcase Compression: The ignited gases expand and forces the piston to move down, thus useful work is obtained. When the piston moves down, the petrol air mixture is partially compressed in the crankcase. Thus compression is known as crankcase compression.

(d) Exhaust and Transfer:

Almost at the end of expansion, the exhaust port is uncovered and the combustion products escape to the

atmosphere. Immediately, the transfer port is also uncovered and the partially compressed air fuel mixture from

the crankcase enters the cylinder through transfer port. The crown of the piston is made of a deflected shape, so the fresh air – petrol mixture entering the cylinder is deflected upward in the cylinder. Thus the escape of fresh charge along with the exhaust gases is reduced.

The cycle of operations are then repeated.

10

11

First Stroke (Upward Stroke of the Piston) of 2-Stroke Diesel(C.I) engine

(a) Compression and Inductance: During the upward movement of the piston from BDC to TDC, both the transfer and exhaust ports are covered by the piston.The air which is already transferred into the engine cylinder is compressed by the moving piston. This increases the pressure and temperature of the air.The compression process is continued until the piston reaches TDC. At the same time, the inlet port is uncovered by the moving piston and the fresh air enters the crankcase through the inlet port.

(b) Injection and Inductance: After the piston almost reaches the TDC, the fuel (diesel) is injected through the fuel injector in the cylinder.The combustion of fresh fuel injected into the cylinder takes place due to the high temperature already developed in the cylinder during compression of the air.The admission of fresh air into the crankcase continues till the piston reaches the TDC.

Second Stroke (Downward Stroke of the Piston) of 2-Stroke Diesel(C.I) engine

(c) Expansion and Crankcase Compression: The burnt gases expand and forces the piston to move down, thus useful work is obtained. When the piston moves down, the air is partially compressed in the crankcase. This compression is known as crankcase compression.

(d) Exhaust and Transfer:

Nearly at the end of expansion, the exhaust port is uncovered and the combustion products escape to the

atmosphere. Immediately the transfer port is also uncovered and the partially compressed air from the

crankcase enters the cylinder through the transfer port.

The cycle of the operations are then repeated.

12

13

Four Stroke Petrol engine

Petrol engine is also known as Spark Ignition (SI) engine.

Invented by Nicolaus A. Otto in 1876 that is why petrol engine is also known as Otto engine.

Since ignition occurs due to a spark petrol engines are called spark ignition (SI) engines.

A four stroke engine gives a power stroke in every set of four strokes of the piston or two revolution of the crankshaft.

The petrol engine operates on theoretical Otto cycle.

It is also called as constant volume combustion cycle as the combustion takes place at constant volume with increase of pressure.

The cycle of operation of a four stroke petrol engine consists of the following strokes:

i. Suction or intake stroke,

ii. Compression stroke,

iii. Expansion or power stroke, and

iv. Exhaust stroke.

i. Suction Stroke of 4-Stroke Petrol engine: During this stroke, the piston moves from Top Dead Centre (TDC) to Bottom Dead Centre (BDC) creating a vaccum inside the cylinder. During this stroke, the inlet valve is kept opened and the exhaust valve is kept closed The vacuum created inside the cylinder draws the air petrol mixture (which is also known as charge) into the cylinder through the inlet valve. It is performed till the piston reaches BDC. The above process is known as suction and this stroke is called the suction stroke.

ii. Compression Stroke of 4-Stroke Petrol engine :

During this stroke, both the inlet and exhaust valves are closed. The air petrol mixture is compressed as the

piston moves upwards from BDC to TDC.As a result of this compression, pressure and temperature of the air

fuel mixture or charge is increased. Just before the piston reaches the TDC, the air petrol mixture (charge) is

ignited by a spark plug; suddenly burning of the air fuel mixture takes place almost instantaneously. It increases

the pressure and temperature inside the cylinder. Volume remains constant during combustion. These two strokes

(i.e., suction and compression stroke) complete one revolution of the crankshaft. 14

iii. Expansion or Power Stroke or Working Stroke:

During this stroke, both the inlet and exhaust valves remain closed. The high pressure of the products of

combustion (due to expansion of charge) pushes tile piston from TDC to BDC. It is also called as working

stroke as work is done by the expansion of hot gases. The force above the piston is transmitted to the

crankshaft through the connecting rod and crank mechanism. Excess energy due to the combustion is stored

in the flywheel which helps for the operation of three idle strokes.

iv. Exhaust Stroke: At the end of the expansion stroke, the exhaust valve opens and the pressure inside falls suddenly. Thus during this stroke, the inlet valve is closed and the exhaust valve is kept opened. The upward movement of the piston from BDC to TDC, pushes out the products of combustion from the engine cylinder through the exhaust valve into the atmosphere. The cycle of operation is then repeated. These two strokes (i.e., expansion and exhaust strokes) complete one revolution of the crankshaft.

15

16

Four Stroke Diesel engine

Diesel engine is also known as compression ignition (CI) Engine.

It is invented by Rudolf Diesel (1892)

The four stroke diesel engine is similar to four stroke petrol engine except that it operates at a higher compression ratio (14 to 22).

In a diesel engine, only air is sucked from the atmosphere instead of air fuel mixture during the suction stroke.

In diesel engines, spark plug is not required for igniting the air fuel mixture. Because the fuel is injected and forms an explosive mixture, which ignites spontaneously under pressure.

Diesel engine works on the principle of diesel cycle.

It is also called as constant pressure combustion cycle as the combustion of fuel takes place at constant pressure with increase of temperature.

Since ignition results due to high temperature of compressed air, these are called compression ignition (CI) engines.

The cycle of operation of a four stroke diesel engine consists

of the following strokes:

i. Suction or intake stroke,

ii. Compression stroke,

iii. Expansion or power stroke, and

iv. Exhaust stroke.

i. Suction Stroke:

During suction stroke, the inlet valve opens and the exhaust valve closes. The piston moves from TDC

to BDC. This piston movement reduces the pressure inside the cylinder below the atmospheric

pressure. Due to the pressure difference, the fresh air is sucked into the cylinder through the inlet

valve. 17

2. Compression Stroke:

During this stroke, both the inlet and exhaust valves are closed. The air in the cylinder is compressed as the

piston moves upwards from BDC to TDC.As a result of this compression, pressure and temperature of the

air is increased. Just before the piston reaches the TDC, the diesel is injected into the cylinder in the form

of a fine spray. The fuel gets vaporized and self ignited due to the heat of compressed air. The fuel burns

instantaneously at constant pressure.

3. Expansion or Power Stroke:

During this stroke, both inlet and exhaust valves are closed. The combustion of fresh fuel injected into the

cylinder is due to the high pressure and temperature developed during compression stroke. The fuel is

continuously injected for 20% of the expansion stroke. The high pressure of the combustion products due

to expansion of charge pushes piston from TDC to BDC. It is also called as working stroke as work is done

by the expansion of hot gases.

4. Exhaust Stroke: During this stroke, inlet valve is closed and the exhaust valve is opened The piston

moves from BDC to TDC. The burnt waste gases are sent out through exhaust valve and the cycle is

repeated.

18

19

Working principle of SI engines and CI engines

20

30 21

Otto Cycle / Constant Volume Cycle

Applications of Otto-Cycle

Petrol engine or Spark ignition engine.

Working of Otto-Cycle

The ideal otto-cycle consists of two reversible adiabatic processes and

two reversible constant volume Process as shown in figure.

Process (0-1) Process 0-1 shows the suction stroke during which

piston moves from T.D.C to B.D.C and a proportionate mixture of

fuel and air from carburettor enters the cylinder through inlet valves.

Process (1-2) Process 1-2 shows compression of mixture takes place

isentropically. In this process entropy remains constant. P1V1ᵞ = P2V2ᵞ {PV = mRT} 1Kg of air

( 𝑹𝑻𝑽 ) V1ᵞ = ( 𝑹𝑻𝑽 ) V2ᵞ {P =

𝑹𝑻𝑽 }

T1 V1ᵞ-1 = T2 V2ᵞ-1

𝑻𝑻 = 𝑽𝑽 ᵞ-1 22

Process (2-3) Process 2-3 shows the heat addition constant

volume in which combustion of fuel takes place inside the

cylinder.

Amount of heat added Q2-3 = CV (T3- T2)

Process (4-1) Process 4-1 shows heat rejection at constant

Volume through exhaust valve.

Amount of heat rejected Q4-1 = CV (T4- T1)

Amount of work done W = Amount of heat added Q2-3 – amount of heat rejected Q4-1

= CV (T3- T2) - CV (T4- T1)

Air Standerd efficiency / Thermal efficiency η = Amount of work done W

Amount of heat added Q2−3 =

CV (T3− T2) − CV (T4− T1) CV (T3− T2)

= 1 - (T4− T1) (T3− T2)

we know that

Compression Ratio ‘r’ = V1 V = Expansion Ratio ‘r’ = V4

V

Air Standerd efficiency / Thermal efficiency η = 1 - (T4− T1)

(T4 rᵞ−1 − T1

rᵞ−1) { 𝑻𝑻 = 𝑽𝑽 ᵞ-1 ; T2=T1

rᵞ−1 }

= 1 - (T4− T1)

(T4 −T1 )rᵞ−1 { 𝑻𝑻 = 𝑽𝑽 ᵞ-1 ; T3=T4

rᵞ−1 }

Air Standerd efficiency / Thermal efficiency η = 1 - 1

rᵞ−1

From the above relation we concluded that efficiency of the Otto Cycle is independent of heat supplied, but depends

only on the compression ratio. At higher compression ratio problem of knocking occurs in engines. So in engine based

on Otto cycle compression ratio varies upto 8.

Process (3-4) Process 3-4 shows Expansion of mixture

takes place isentropically. In this process entropy

remains constant. P3V3ᵞ = P4V4ᵞ {PV = MRT} 1Kg of air

( 𝑹𝑻𝑽 ) V3ᵞ = ( 𝑹𝑻𝑽 ) V4ᵞ {P =

𝑹𝑻𝑽 }

T3 V3ᵞ-1 = T4 V4ᵞ-1

𝑻𝑻 = 𝑽𝑽 ᵞ-1

23

Diesel Cycle / Constant Pressure Cycle

Applications of Diesel-Cycle

Diesel engine or Compression

ignition engine.

Working of Diesel-Cycle

The ideal Diesel-cycle consists

of two reversible adiabatic

processes and one constant

Pressure Process, one constant

Volume Process as shown in

figure.

Process (1-2) Process 1-2 shows compression of air

takes place isentropically. In this process entropy

remains constant. P1V1ᵞ = P2V2ᵞ {PV = MRT} 1Kg of air

( 𝑹𝑻𝑽 ) V1ᵞ = ( 𝑹𝑻𝑽 ) V2ᵞ {P =

𝑹𝑻𝑽 }

T1 V1ᵞ-1 = T2 V2ᵞ-1

𝑻𝑻 = 𝑽𝑽 ᵞ-1

Compression Ratio ‘r’ = V1 V

𝑻𝑻 = 𝑽𝑽 ᵞ-1 = rᵞ−1

T2=T1 rᵞ−1

24

Process (2-3) Process 2-3 shows the heat addition constant

Pressure in which combustion of fuel takes place inside the

cylinder due to high temperature of compressed air.

Amount of heat added Q2-3 = CP (T3- T2)

We know that

P2V2𝐓 =

P3V3T3

V2𝐓 =

V3T3

{ P2 = P3 }

T2 = T3

V3 V2 =

T3𝛒 { cutoff ratio 𝛒=V3V2

}

T2 = T3𝛒

Process (3-4) Process 3-4 shows Expansion of mixture takes

place isentropically. In this process entropy remains constant. P3V3ᵞ = P4V4ᵞ {PV = MRT} 1Kg of air

( 𝑹𝑻𝑽 ) V3ᵞ = ( 𝑹𝑻𝑽 ) V4ᵞ {P =

𝑹𝑻𝑽 }

T3 V3ᵞ-1 = T4 V4ᵞ-1

𝐓𝐓 = 𝑽𝑽 ᵞ-1

Process (4-1) Process 4-1 shows heat rejection at constant

Volume through exhaust valve.

Amount of heat rejected Q4-1 = CV (T4- T1)

Amount of work done W = amount of heat added Q2-3 –

amount of heat rejected Q4-1

= CP (T3- T2) - CV (T4- T1)

Air Standerd efficiency / Thermal efficiency

η = Amount of work done W

Amount of heat added Q2−3

= CP (T3− T2) − CV (T4− T1)

CP (T3− T2)

= 1 - CV

(T4− T1) CP

(T3− T2)

= 1 - (T4− T1) CP CV (T3− T2)

From Process (1-2) & Process (2-3)

T2=T1 rᵞ−1 & T2 =

T3𝛒

We get

T1 = T3𝛒 rᵞ−1

We know that

Compression Ratio ‘r’ = V1 V = Expansion Ratio ‘re’ = V4

V

V1 V = r

V1 V x

V3 V = r

V4 V3

x V3 V2

= r { V1 = V4 } 25

V4 V3

x V3 V2

= r { V1 = V4 }

re x 𝛒 = r

re = r𝛒

Air Standerd efficiency / Thermal efficiency η = 1 - (T4− T1) CP CV (T3− T2)

{ 𝐓𝐓 = 𝑽𝑽 ᵞ-1 }

= 1 - (T4− T1) γ (T3− T2) {

𝐓𝐓 = re ᵞ-1 }

= 1 - T3 ( ρ ᵞ−1 r ᵞ−1 ) − (T3 𝛒 r ᵞ−1 )γT3 − γT3 𝛒 {

𝐓rᵞ−1 x 𝛒ᵞ−1 = T4}

= 1 - ( 1 r ᵞ−1 ) ([{ ρ ᵞ−1+1}−1] ρ )γ ρ−1 ρ

Air Standerd efficiency / Thermal efficiency η = 1 - (𝝆𝜸− )𝜸 rᵞ−1 𝝆−

For the same compression ratio, diesel cycle has a lower efficiency than the Otto Cycle. The actual efficiency of

diesel engine is higher than that of Petrol engine.

26

Dual Cycle / Limited Pressure Cycle / Mixed Cycle

Applications of Dual-Cycle

The engines based on Dual-Cycle are used

for mobile Propulsion in vehicles and

Portable machineries.

Advantages

It can provide high power to weight-ratio.

27

Fuel Supply in Petrol Engine

Concept of carburetion

Carburetion is “The process of breaking up the fuel(Petrol, Gasoline etc) into minute particles and mixing it with air” in atomized form.

The device in which atomized form of Fuel+Air is maintained

is known as Carburetor.

Factors on which Carburetion depends

1) Engine Speed

2) Volatility of the fuel

3) Temperature of incoming air

4) Design of the carburettor 28

Air fuel ratio

Air fuel ratio Internal combustion engines use

fuel and oxygen (air) to produce energy through

combustion. A complete combustion takes place

when all the fuel is burned, in the exhaust gas

there will be no quantities of unburned fuel.

Air-fuel ratio(AF or AFR) is the ratio between

the mass of air ma and mass fuel mf, used by the

engine when running.

AFR = 𝑚𝑎𝑚𝑓

stoichiometric air-fuel ratio The ideal

(theoretical) or Correct air-fuel ratio, for a

complete combustion in a gasoline (petrol)

engine is around 14.7:1 approximately equal to

15:1. it means in order to burn completely 1 kg of

fuel (Octane), we need 14.7 kg of air(O2). The

combustion is possible even if the AFR is

different than stoichiometric. For the combustion

process to take place in a gasoline engine, the

minimum AFR is around 6:1 and the maximum

can go up to 20:1. air fuel ratio is of two types

below.

Lean Mixture When the air-fuel ratio is higher

than the stoichiometric ratio. E.g. 16.5:1

Rich Mixture When the air-fuel ratio is lower

than the stoichiometric ratio. E.g. 13.7:1

Spark ignition (SI) engines usually run on gasoline (petrol)

fuel. The AFR of the SI engines varies within the range 12:1

(rich) to 20:1 (lean), depending on the operating condition of

the engine (temperature, speed, load, etc.). Modern internal

combustion engines operate as much as possible around the

stoichiometric AFR (mainly for gas after-treatment reasons).

Compression ignition (CI) engines usually run on diesel

fuel. Due to the nature of the combustion process, CI engines

always run on lean mixtures, with AFR between 18:1 and

70:1.

Note: The main difference, compared with SI engines, is that

CI engines run on stratified (non homogeneous) air-fuel

mixtures, while SI run on homogeneous mixtures (in case of

port-injection engines). 29

Requirements of A/F ratio 1) Air fuel ratio during Starting or Cold engine condition(10:1)

2) Air fuel ratio for Idling (10:1 to 11:1)

3) Air fuel ratio for Cruising range-part loading running (15:1 to 17:1)

4) Air fuel ratio for maximum Power range (12.5:1 to 13.5:1)

5) Air fuel ratio for Acceleration (Rich mixture is required as per Load & Speed)

6) Air fuel ratio for maximum Economy of fuel (16.5:1 to 17.5:1)

30

Simple Carburetor

Function of Simple Carburettor

1) It maintain Fuel/Air mixture in atomized form.

2) It make F/A mixture into the mist.

3) As per required engine speed and load it Increases or decreases

the amount of F/A mixture.

Construction of Simple Carburettor The main parts of a simple

carburetor discussed below

Float chamber: The level of fuel in the float chamber is maintained

slightly below the tip of the nozzle. If the level of petrol is above

then the petrol will run from the nozzle and drip from the carburetor.

If the petrol level is kept low than the tip of the nozzle then part of

pressure head is lost in lifting the petrol up to the tip of nozzle.

Generally it is kept at 5mm from the level of petrol in the float

chamber. The level of the fuel is kept constant with the help of float

and needle valve. The needle valve closes the inlet supply from main

tank if the level rises above the required level. If the level of fuel

decreases then the needle valve opens the supply. Generally the fuel

level is kept 5mm below the nozzle tip.

Venturi: When the mixture passes through the narrowest section its

velocity increases and pressure falls below the atmospheric. As it

passes through the divergent section, pressure increases again.

Throttle valve: It controls the quantity of air and fuel mixture

supplied to the engine through intake manifold and also the head

under which the fuel flows.

Choke: It provides an extra rich mixture during to the engine

starting and in cold weather to warm up the engine. The choke valve

is nearly closed during clod starting and warming. It creates a high

vacuum near the fuel jet which causes flow of more fuel from the jet. 31

Working of Simple Carburettor:

The carburetor works on Bernoulli's principle. A carburetor is to vaporize the Fuel (Petrol, Gasoline etc) by means

of engine suction and to supply the required air and fuel (Petrol, Gasoline etc) mixture to the engine cylinder.

During the suction stroke, air flows from atmosphere into the cylinder. As the air passes through the venturi,

velocity of air increases(Maximum) at throat and its pressure falls below the atmospheric pressure. The pressure at

the nozzle tip is also below the atmospheric pressure. The pressure on the fuel surface of the fuel tank is

atmospheric. Due to which a pressure difference is created, it creates negative pressure. which causes the flow of

fuel through the fuel jet into the air stream. As the fuel and air passes ahead of the venturi, the fuel gets vaporized

and required uniform mixture is supplied to the engine. The quantity of fuel supplied to the engine depends upon

the opening of throttle valve which is governed by the governor or It is further controlled by the driver of the

vehicle or rider of the motorcycle.

Limitations of Simple Carburettor:

1) At a very low speed, the mixture supplied by this Carburetor is so weak that it will not ignite engine properly.

To make remove this problem, some arrangements in the carburettor is required to be made.

2) At high altitudes in case of aircraft, as the rich mixture is unnecessarily available, due to less density of air. So

the working of a simple carburetor is affected by changes in atmospheric pressure (at high altitudes).

3) In the winter season, it will be found to give the too rich mixture. In the summer season, it will be found to

give the too Lean mixture. This is happened due to less density of air with the rise of temperature to a greater

extent than the density of the fuel.

4) It gives the proper mixture at only one engine speed (at constant speed) and load. Fuel/Air ratio may not be

proper at variable engine speeds.

5) In a simple carburetor, the mixture is weakened when the throttle is suddenly opened. Because of Inertia

effect of the fuel which prevents the proper quantity of fuel from flowing immediately.

6) More fuels are consumed.

7) More air emissions.

8) Maintenance costs of Simple carburetor is higher.

Applications of Simple Carburettor: Buses, Trucks, Motorcycles, Scooters, Generators, Vibrators, Cutters etc.

32

MPFI

M.P.F.I. means Multi Point Fuel Injection system. In this system each cylinder has number of injectors to

supply/spray fuel in the cylinders as compared to one injector located centrally to supply/spray fuel in case of

single point injection system.

The term MPFI is used to specify a technology used in Gasoline/petrol Engines. For Diesel Engines, there is a

similar technology called CRDI.

Classification of MPFI System:

1) On the basis of Position of Injection Point

i. Port Injection System (multi point)

ii. Throttle Body Injection System (single point)

2) On the basis of Injection Action

i. Timed or Pulsed

ii. Continuous Injection

3) On the basis of Position of Components in the Control Circuit

i. D-MPFI

ii. L-MPFI 33

Port Injection System in this system the injector is placed on

the side of the intake manifold near the intake port. The injector

sprays gasoline into the air, inside the intake manifold. The

gasoline mixes with the air in a uniform manner. This mixture

of gasoline and air then passes through the intake valve and

enters into the cylinder. Every cylinder is provided with an

injector in its intake manifold i.e. if there are six cylinders,

there will be six injectors.

Throttle body injection system(Single Point injection) in this

system this throttle body is similar to the carburetor throttle

body, with the throttle valve controlling the amount of air

entering the intake manifold. An Injector is placed slightly

above the throat of the throttle body. The injector sprays

gasoline into the air is the intake manifold where the gasoline

mixes with air. This mixture then passes through the throttle

valve and enters into the intake manifold.

The fuel injection system may be either timed or continuous. In Timed injection system; Petrol is sprayed from the injector in

Pulses, while in continuous injection system; Petrol is sprayed continuously from the injector.

The amount of petrol injected depends fully on the load on engine will be used in both injection systems may be Port & Throttle

injection system. D-MPFI electronic system is referred to as D-

Jetronic(German word “D” referred “Druck” means “pressure” and “Jetronic” a word coined by Bosch means “injection”). It works as “Manifold pressure control type”. The main input signal are the intake manifold pressure, engine speed and flow volume of air

which are sent to ECU to control A/F ratio.

L-MPFI electronic system is referred to as L-

Jetronic (“L” comes from the German word “Luft” means “air” ). It works as “air flow-controlled type”. The main input signal are the Air flow rate and engine

speed to regulate fuel quantity injected. 34

Advantage of M. P. F. I.

More uniform A/F mixture will be supplied to each cylinder, hence the difference in power developed in each

cylinder is minimum.

Vibration from the engine equipped with this system is less, due to this the life, functionality and durability of

engine components is improved.

No need to crank the engine twice or thrice in case of cold starting as happens in the carburetor system.

Immediate response, in case of sudden acceleration / deceleration.

Since the engine is controlled by ECM* (Engine Control Module), more accurate amount of A/F mixture will be

supplied and as a result complete combustion will take place. This leads to effective utilization of fuel supplied and

hence low emission level.

The mileage of the vehicle will be improved.

The MPFI system encourages effective fuel utilization and distribution.

The vehicles with MPFI automobile technology have lower carbon emissions than a few decades old vehicles. It

reduces the emission of the hazardous chemicals or smoke, released when fuel is burned. The more precise fuel

delivery cleans the exhaust and produces less toxic byproducts. Therefore, the engine and the air remain cleaner.

The multi-point fuel injection technology improves fuel efficiency of the vehicles. MPFI uses individual fuel

injector for each cylinder, thus there is no gas wastage over time. It reduces the fuel consumption and makes the

vehicle more efficient and economical.

ECM ( Engine Control Module) and its function

The function of ECM is to receive signal from various sensors, manipulate the signals and send control signals to

the actuators.

Note: 1) If ECM fails to send control signal to all actuators then the engine won't get started.

2) If ECM fails to service from all sensors then also the engine won't get started.

3) ECM is a micro-chip based small computer without keyboard or mouse.

Sensors; Sensing different parameters (Temperature, Pressure, Engine Speed etc.) of the engine and send signal to

ECM.

Actuators(solenoid based); Receives control signal from ECM and does function accordingly (ISCA, PCSV,

Injectors, Power Transistor etc.) 35

Common Rail System/Air Less Mechanical Injection

Common rail system is a solid type

fuel injection system in which fuel

is injected directly into the

combustion chamber without

primary atomization. In this System

main units are 1) A Pressurising unit (Pump)

2) An atomizing unit (Injector)

The term Common rail refers to the

fact that all of fuel injectors are

supplied by a common fual rail

which is nothing more than a

pressure accumulator where the

fuel is stored at high pressure. This

accumulator supplies multiple fuel

injectors with high-pressure fuel.

Modern common rail systems are governed an engine control unit (ECU) which opens each injector electronically

rather than mechanically solenoid or piezoelectric valves make possible fine electronic control over the fuel

injection time and quantity and the higher pressure that’s provide better fuel atomization. common rail engines require a very short (10 seconds) to no heating-up time, depending on ambient temperature and produce lower

engine noise and emissions than older systems.

Disadvantage of common rail system is that in case of injection needle sticking in an open position an excess

amount of the fuel may be injected into cylinders. 36

Super-charging and Turbo-charger

Supercharging is the process of increasing the density

of inlet air (mixture) which increases power output of

engine. Supercharging is done by supplying air at a

pressure higher than the pressure at which the engine

naturally aspirates air from the atmosphere by using a

pressure boosting device called a supercharger. In an

unsupercharged engine, the cylinder draws the air

maximum to its displacement volume. But in a

supercharged engine the air is forced into the cylinder at

a higher pressure. The increase in amount of air inducted

per unit time by supercharging is obtained mainly to

burn a greater amount of fuel in a given engine and thus

increase its power output.

Objectives of supercharging

1) To reduce weight per horse power of the engine as required in aero engine

2) To reduce the space occupied by the engine as in marine engines.

3) To compensate for the loss of power due to altitude as in aircraft engines.

4) To obtained more power from an existing engine.

Supercharging of Spark ignition engines in S.I. engines supercharging increases the volumetric efficiency

of the engine. Increased intake pressure and temperature reduces ignition delay and increases flame speed.

Both these effects results in a greater tendency to detonate or pre-ignition. For this reason, the supercharged

petrol engines employs lower compression ratios. This results in lower thermal efficiencies and greater fuel

consumption. Because of its poor fuel economy, supercharging of petrol engines is not very popular and is

used when a large amount of power is needed or when more power is needed to compensate altitude loss.

Super charging is employed only for air craft and racing car engines. 37

Supercharging of C.I. engines Supercharging in case of diesel engines improves the combustion. Due to the

increase in pressure and temperature of the intake air ignition delay reduces. This results in better and smooth

combustion. The increase in intake air temperature reduces volumetric efficiency and thermal efficiency but the

increase in the density due to pressure compensation for this. If an unsupercharged engine is supercharged it will

increase the reliability and durability of the engine due to smoother combustion and lower exhaust temperature.

Superchargers

1) Centrifugal compressor

2) Root blower

3) Vane blower

4) Reciprocating compressor

Turbocharger Turbocharger are the centrifugal compressor which are driven by the exhaust gas turbine approximately 30% of the

total heat input to an engine goes into the Exhaust. A part of the exhaust energy can be used to Run a gas turbine and

hence a compressor to supply more to engine. Such utilization of the exhaust energy boosts engine power and results

in better thermal Efficiency and fuel consumption. By utilizing the exhaust energy of the engine recovers a

substantial part of energy which would otherwise go waste. Thus the turbocharger will not drow upon the engine

power. In order to supply sufficient amount of energy to the turbocharger the exhaust valve is opened much before

The bottom dead centre as compare to a naturally aspirated Engine. This allow the exhaust gases to escape at a

higher Pressure and temperature giving the turbocharger enough Energy to drive the compressor.

Turbocharging Methods

1) Constant Pressure method

2) Pulse Operation Method

3) Pulse Converter Method

38

Limitations of Turbocharging

1) Turbocharging requires special exhaust manifolds.

2) Fuel injection has to be modified to inlet more fuel per unit time. This requires either large pumping elements or

large pumping elements or large nozzles with the same basic fuel injection equipment.

3) A naturally aspirated engine can handle solid particles in the inlet air without undue stress but turbocharged engine

pass only the most minute material particles without damage.

4) The efficiency of the turbine is very sensitive to gas velocity so that it is very difficult to obtain good efficiency

over a wide range of operations.

39

Difference between Supercharger and Turbocharger

Characteristics Supercharger Turbocharger

Power Supply There is a belt that connects directly to the

engine. It gets its power the same way that the

water pump or alternator does.

On the other hand, gets its power from the

exhaust stream. The exhaust runs through a

turbine, which in turn spins the compressor

Trade-off Yes Yes

Efficient It does not use wasted energy in the exhaust

stream for its power source.

A turbocharger is more efficient because it is

using the "wasted" energy in the exhaust stream

for its power source.

Boost up Capacity More A turbocharger causes some amount of back

pressure in the exhaust system and tends to

provide less boost until the engine is running at

higher engine speeds.

Installation Easy Not Easy as Supercharger

Expensive More expensive Less expansive

Physical Space

Requirement

More Less; therefore multiple turbocharger may be

fitted to a single engine

40

Testing of IC Engines

Engine power - indicated and brake power

Indicated Power The total power developed by combustion

of fuel in the combustion chamber is called indicated power.

I.P = P N 60 watt

n = number of cylinders Pim = indicated mean effective pressure in 𝑁 m2 or Pascal

L = length of Stroke, m

A = Area of Piston, m2

K = ½ for 4-Stroke engine 1 for 2-Stroke engine

Brake Power The Power developed by an engine at

the output shaft is called the Brake Power.

I.P = 2 π N T60 watt

N = Speed in rpm

A = Torque in Nm

Efficiency - mechanical, thermal. relative and volumetric

Mechanical efficiency The ratio of Brake Power to

Indicated Power is called mechanical efficiency.

Mechanical efficiency, ηmech = .PI.P

Thermal efficiency The ratio of amount of work done to energy supplied by the fuel. It is of two types.

1) Indicated Thermal efficiency 2) Brake Thermal efficiency

It is the ratio of Indicated Work done to energy It is the ratio of Brake Work done to energy

Supplied by the fuel. Supplied by the fuel.

Indicated Thermal efficiency, ηI.Th = 𝐈.𝐏mf 𝐱 . Indicated Thermal efficiency, ηB.Th =

.𝐏mf 𝐱 .

mf = mass of fuel used in Kg/sec

C = Lower Calorific value of fuel 41

Relative efficiency The ratio of Thermal efficiency of actual Cycle to that of air Standard efficiency of ideal cycle.

Relative efficiency, ηrelative = c a T r a c cyAir Standard efficiency

Volumetric efficiency The ratio of mass of charge actually induced into the engine cylinder during suction stroke to

the mass of the charge corresponding to the Swept Volume of the engine at atmospheric pressure and temperature.

Volumetric efficiency, ηvol = mass of charge actually induced

mass of the charge corresponding to the Swept Volume of the engine at atmospheric pressure and temperature

The average value of volumetric efficiency is varies from 70% to 80% but in case of Supercharged engine it may be

equal to 100%.

Methods of finding indicated and brake power

Method of finding Indicated Power

1) Graphical Method -By Indicator Diagram

2) Analytical Method -By measuring B.P and F.P separately and adding them ( I.P = B.P + F.P)

42