Automobile module i

AUTOMOBILE ENGINEERING

Anoop P

Asst. Professor

Dept. of Mechanical Engg:

MITS, Puthencruz

1

DEPARTMENT OF MECHANICAL ENGINEERING - MITS PUTHENCRUZ

OBJECTIVES

impart the basic concepts of Automobile parts

and its working

develop the fundamental ideas used in modern

vehicle technologies.

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AUTOMOBILE

The term automobile stands for a vehicle which can move by itself.

An automobile is made up of a frame, supported by body on it.

It has a power producing unit, a power transmitting unit.

These units are in turn connected to wheels and tire's through transmission system.

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SYLLABUS

Module 1

Engines- Types of engines in automobiles-classifications-

engine components working of various systems-present and

future vehicles, engine construction- intake and exhaust

systems. Different combustion chambers, carburettors, diesel

fuel pumps, injectors, single point and multi point fuel

injection-MPFI and CRDI systems -lubricating and cooling

systems.

Vehicle performance-resistance to the motion of vehicle-air,

rolling, and radiant resistance-power requirement-

acceleration and gradeability-selection of gear ratios.

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Module 2

Transmission prime movers- clutch-principle of friction and

cone clutches –centrifugal clutches, diaphragm clutches and

fluid couplings-Gearbox-necessity and principle. Constant

mesh, sliding mesh, synchromesh gear boxes and epicyclic

gearbox –overdrives. Hydraulic torque converters-semi and

automatic transmission systems - constant velocity and

universal joints. Final drive-front wheel, rear wheel and four

wheel drives-transfer case-Hotchkiss and torque tube drives-

differential-nonslip differential-rear axles-types of rear axles.

Module 3

Steering and Suspension Different steering mechanisms-

Ackermann Steering mechanism. Steering gear boxes -power

steering –types. Suspension systems-front axle, rigid axle and

independent suspensions-anti-roll bar-coil spring and leaf

spring - torsion bar -Macpherson strut- sliding pillar- wish

bone- trailing arm suspensions-Shock absorbers -hydraulic

and gas charged shock absorbers-air suspensions Front axle

types-front wheel geometry-castor, camber, king pin inclination,

toe-in toe out, wheel balancing- wheel alignment.

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Module 4

Chassis, Brakes and Tyres: Types of chassis and body

constructions-crumble zones, air bags and impact beams.

Braking mechanism and convectional brakes- Drum brakes

and Disc brakes. Vacuum booster, hydraulic and power

brakes, components and attachments of mechanical, hydraulic

and pneumatic brakes-Master cylinder-Tandem cylinder-

working. Anti-lock braking systems-Wheels and Tyres-

tubeless tyres-ply ratings- radial tyres. Different tyre wears-

causes

Module 5

Electrical systems - Battery ignition system circuit-

electronic ignition system alternators - voltage regulators

starting system- bendix and follow through drives –

automotive lighting, accessories and dashboard instruments-

head light and horn with relays-circuit diagrams. Automotive

air conditioning Preventive and breakdown

maintenance- engine testing, servicing-engine overhaul-

engine tuning. 6


REFERENCES/TEXT BOOKS

Automobile Engineering (Vol. 1 & 2) - K.M.Guptha

Automotive Mechanics- William H. Course

Advanced Vehicle Technology-Heinz Hesler

Automobile Engineering (Vol. 1 & 2)- Kirpal Singh

Automobile Engineering – R.K.Rajput

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ENGINES

Engine is the power plant of the vehicle.

In general, internal combustion engine with petrol or diesel fuel is used to run a vehicle.

An engine may be either a two-stroke engine or a four-stroke engine.

An engine consists of a cylinder, piston, valves, valve operating mechanism, carburetor (or MPFI in modern cars), fan, fuel feed pump and oil pump, etc.

Besides this, an engine requires ignition system for burning fuel in the engine cylinder.

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ENGINE NOMENCLATURE

9

Cylinder bore

Top dead centre

Bottom dead centre

Stroke

Swept volume

Clearance volume

Compression ratio


ENGINE CLASSIFICATION

Type of fuel used

Petrol engine

Diesel engine

Gas engine

Type of Ignition

Spark Ignition engine

Compression Ignition engine

Cycle of Operation

Otto cycle

Diesel cycle

No. of strokes/cycle

2 stroke

4 stroke 10


Valve location

Overhead valve engine

Side valve engine

Basic Design

Reciprocating

Rotary

Arrangement of cylinders

Inline/Straight engine

V engine

Opposed Cylinder engine

Opposed piston engine

Radial Engine

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Air intake process

Naturally aspirated

Turbocharged

Crankcase compressed

Type of cooling

Air cooling

Water cooling

Application

Stationary Engine

Mobile Engines

Locomotives

Marine Engines

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COMPONENTS OF AN IC ENGINE

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COMPONENTS/PARTS

Cylinder

Cylinder head

Piston

Inlet and exhaust valves

Inlet manifold

Exhaust manifold

Connecting rod

Crank

Flywheel

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Cylinder: It is one of the most important parts of the engine, in which

piston moves to and fro.

Engine Cylinder has to withstand a high temperature and pressure.

Thus the materials for the engine cylinder should be such that it can retain high pressure and temperature. (usually alloys of Iron or Aluminium)

The top of the cylinder is covered by cylinder head.

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Engine Block

The engine cylinders are enclosed with in the engine block.

Usually made of cast iron because of its wear resistance

and low cost.

Passages for the cooling water are cast into the block.

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Inlet and Exhaust Valves

Inlet valves admit the entrance of fuel and air and

outlet valves allow the exhaust gases to escape.

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20


Cam

Is used for opening and closing of Inlet and Exit Valve in

time.

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Piston

Function of Piston is to transmit the force exerted by the

burning of charge to Connecting Rod.

The pistons are usually made of Aluminium Alloy, chrome

nickel alloy, nickel iron alloy, cast steel etc. which are light

in weight.

They have good heat conducting property and also greater

strength at higher temperatures.

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Piston Rings

Circular Rings made of special cast iron housed in the circumferential grooves provided on the outer surface of the piston.

Generally there are two sets of rings.

The function of the upper rings is to provide air tight seal to prevent leakage of the burnt gases into the lower portion named as compression rings.

The function of lower rings is to provide effective seal to prevent leakage of oil into the Engine Cylinder and is termed as oil rings.

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Connecting Rod

Is a tapered link of ‘I’ section connected between the piston

and crank shaft whose main function is to transmit force

from the piston to the crank shaft.

The upper end, called the small end is fitted to the piston

using a gudgeon pin and lower end called the big end is

connected to the crank using crank pin.

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Crank

Is a lever connected between the connecting rod and the

crank shaft.

As the piston reciprocates, it rotates about the axis of the

crank shaft.

Crank Shaft

Function of Crank Shaft is to convert the

Reciprocating Motion of Piston into rotary motion with the

help of Connecting Rod.

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Flywheel

Is a big wheel mounted on the crankshaft whose function is

to reduce fluctuation of speed of the engine within a cycle

and there by maintain speed of the engine constant.

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Crank Case

A cast iron or aluminium case which holds the Crank

Shaft.

crankcase is the housing for the crankshaft. The enclosure

forms the largest cavity in the engine and is located below

the cylinders.

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4 STROKE PETROL ENGINE(SI ENGINE)

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4 STROKE DIESEL ENGINE(CI ENGINE)

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COMPARISON

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36

Compression ratio 6 – 10 16 – 20

Weight Less More

Initial cost Less More

Maintenance cost Less More

Control of Power Quantity governing Quality Governing


2 STROKE ENGINE

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2 STROKE PETROL ENGINE

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2 STROKE DIESEL ENGINE

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COMPARISON

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Aspects

Four Stroke Engines Two Stroke Engines

Completion of cycle

4strokes of the piston or in

two revolutions of the

crankshaft.

2 strokes of the piston or in

one revolution of the

crankshaft.

Flywheel Heavier flywheel is needed. Lighter flywheel is needed.

Power produced Power produced for same

size of engine is small

Power produced for same

size of engine is more

Cooling and lubrication

requirements

Lesser cooling and lubri-

cation requirements.

Lesser rate of wear and

tear.

Greater cooling and lubri-

cation requirement.

Great rate of wear and

tear.


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Valve and valve

mechanism

Contains valve and

valve mechanism.

No valves but only

ports

Initial cost Higher is the initial

cost. Cheaper in initial cost.

Volumetric efficiency


more due to more time

of induction.


less due to lesser time

for induction.

Thermal efficiencies Higher Lower

Applications Used where efficiency is

important.

Used where (1) low cost,

(2) compactness, and (3)

light weight is

important


PETROL ENGINE – AIR SYSTEM

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Air filter Carburetor Engine

Cylinder Silencer


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FUEL SYSTEM

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Fuel Storage

Tank Fuel Pump Fuel Filter Carburetor

Engine Cylinder


INDUCTION OF FUEL IN SI ENGINES

The fuel Induction systems for SI engine are

classified as:

Carburetors

Throttle body Fuel Injection Systems

Port Fuel Injection System

Multi Point Fuel Injection Systems.

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CARBURETOR

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PORT FUEL INJECTION SYSTEM

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THROTTLE BODY FUEL INJECTION SYSTEMS

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MPFI

D MPFI

L MPFI

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D MPFI

Fuel metering is regulated by engine speed and manifold

vacuum

Mixing of fuel takes place inside the manifold pipe

ECU supplies the information for metering and mixing by

means of sensors

D MPFI (D Jetronic)

D- Druck(pressure)

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L MPFI

L MPFI (L Jetronic)

L- Luft(Air)

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MERITS OF FUEL INJECTION IN THE SI ENGINE

Absence of Venturi – No Restriction in Air Flow/Higher Vol. Eff./Torque/Power

Manifold Branch Pipes Not concerned with Mixture Preparation

Better Acceleration Response

Fuel Atomization Generally Improved.

Use of Greater Valve Overlap

Use of Sensors to Monitor Operating Parameters/Gives Accurate Matching of Air/fuel Requirements: Improves Power, Reduces fuel consumption and Emissions

Precise in Metering Fuel in Ports

Precise Fuel Distribution Between Cylinders

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DIESEL ENGINE - FUEL SYSTEM

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Fuel Storage

Tank Fuel filter

Fuel pump (Low

Pressure)

Fuel Injection

Pump (High

Pressure)

Fuel injector

Engine cylinder


DIAPHRAGM PUMP

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l. Cam

2. Rocker arm

3. Link

4. Diaphragm

5. Diaphragm spring

6. Pump chamber

7. Inlet valve

8. Outlet valve

9. Outlet pipe

10. Spring


FUEL INJECTION PUMP

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FUEL INJECTOR

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ELECTRONIC FUEL INJECTION

CRDI (Common Rail Direct Injection)

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`

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Low pressure pump draws fuel from fuel tank to the high

pressure pump through a filter.

High pressure pump supplies fuel to a common rail

High pressure diesel oil is then fed to the individual

injectors.

Injection occurs at equal intervals.

The control rack controls the timing and quantity of fuel to

the cylinders

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MERITS

More power is developed

Increased fuel efficiency

More stability

Pollutants are reduced

Particulates of exhaust are reduced

Exhaust gas recirculation is enhanced

Precise injection timing is obtained

Pilot and post injection increase the combustion quality

The powerful microcomputer makes the whole system more perfect

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NECESSITY OF COOLING

Engine valves warp due to over heating

Lubricating oil decomposes and forms gummy and carbon particles

Thermal stresses are set up in the engine parts and causes distortion

Reduces the strength of materials used for piston and piston rings

Pre- ignition occurs due to over heating of spark plug

Over heating reduces the efficiency of engine

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COOLING SYSTEM

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Air Cooling or Direct Cooling


Advantages

Engine design is simpler

Light in weight

Less space

Disadvantages

Not effective when compared to water cooling

Efficiency of engine is less

Engine parts are not uniformly cooled

Not suitable for multi cylinder engines

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WATER COOLING OR INDIRECT COOLING

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Advantages

Cooling is more efficient

Efficiency of engine is more

Uniform cooling is obtained

Disadvantages

More weight, since it uses radiator, pump, fan etc.

Requires more maintenance

Water circulating pump consumes more power

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LUBRICATION SYSTEM

Functions

Lubricant reduces friction between the moving parts

Reduces wear and tear

Minimizes power loss due to friction

Provides cooling effect

Reduces the noise created by moving parts

Acts as a sealing between the cylinder and piston

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Desirable properties

Should maintain sufficient viscosity under all ranges of

temperature

Oil must not vaporize

Should have high specific heat

Must be free from corrosive acids, moisture etc.

Good adhesive quality

Good cohesive quality

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MIST LUBRICATION SYSTEM

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WET SUMP LUBRICATION SYSTEM

Splash system

Pressure feed system

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EXHAUST SYSTEM

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PERFORMANCE OF IC ENGINES


NOMENCLATURE

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Indicated power(IP) – power produced inside the

cylinder

Brake power(BP) – Power obtained from the shaft of

the engine

IP-FP=BP, FP- frictional power


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Indicated thermal efficiency ήth = Indicated power

Fuel Power

Fuel Power = mass of fuel used / sec (kg/s) x calorific value of fuel (J/kg)

Indicated Power = PxLxAxNxK

P – N/m2 Indicated mean effective pressure

A- m2 Area

N – N/2 for 4S, N for 2S where N= rpm of the engine

K- number of cylinders


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Brake thermal efficiency ήbth = Brake Power

Fuel Power

Mechanical efficiency ήm = Brake power

Indicated power

Volumetric efficiency ήv = Actual volume of air intake

Stroke/ Swept Volume


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ABSORPTION DYNAMOMETER POWER, P= TXW T = FXR F=M X G P= 2∏NT/60


COMBUSTION CHAMBERS IN SI ENGINES

Design of combustion chamber has an important influence

upon the engine performance and its knock properties.

The design of combustion chamber involves the

shape of the combustion chamber,

the location of the sparking plug and

the positioning of inlet and exhaust valves.

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The basic requirements of a good combustion

chamber are to provide:

High power output

High thermal efficiency and low specific fuel consumption

Smooth engine operation

Reduced exhaust pollutants.

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DIFFERENT TYPES OF COMBUSTION

CHAMBERS

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T-HEAD COMBUSTION CHAMBER

Introduced by Ford Motor Corporation in 1908.

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Both inlet and exhaust valves are located in engine block

on opposite sides

Requires two cam shafts for actuating the in-let valve and

exhaust valve separately

High surface- volume ratio, long flame travel

Very prone to detonation.

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L HEAD COMBUSTION CHAMBERS

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This was first introduced by Ford motor in 1910-30 .

It is a modification of the T-head type of combustion chamber.

Both intake and exhaust valves are kept side by side with spark plug located above the valves

Advantages

Valve mechanism is simple and easy to lubricate.

Detachable head easy to remove for cleaning and decarburizing without

Valves of larger sizes can be provided.

Disadvantages

Poor turbulence

Extremely prone to detonation due to large flame length and slow combustion

More surface-to-volume ratio and therefore more heat loss.

Extremely sensitive to ignition timing due to slow combustion process

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RICARDO’S TURBULENT COMBUSTION

CHAMBER

Ricardo developed this head in 1919. His main objective was

to obtain fast flame speed and reduce knock in L head design.

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Advantages

Minimum surface to volume ratio due to hemispherical shape of the

chamber.

This design ensures a more homogeneous mixture of air and fuel

Higher engine speed is possible due to increased turbulence

Ricardo’s design reduced the tendency to knock by shortening

length of effective flame travel.

This design reduces length of flame travel by placing the spark plug

in the center of effective combustion space.

Disadvantages

With compression ratio of 6, normal speed of burning increases and

turbulent head tends to become over turbulent and rate of pressure

rise becomes too rapid leads to rough running and high heat losses.

To overcome the above problem, Ricardo decreased the areas of

passage at the expense of reducing the clearance volume and

restricting the size of valves. This reduced breathing capacity of

engine, therefore these types of chambers are not suitable for

engine with high compression ratio.

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OVER HEAD VALVE OR I HEAD COMBUSTION

CHAMBER

The disappearance of the side valve or L-head design was

inevitable at high compression ratio of 8 : 1 because of the

lack of space in the combustion chamber to accommodate the

valves.

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An overhead engine is superior to side valve at high

compression ratios and is due to following reasons:

Lower pumping losses and higher volumetric efficiency from better

breathing of the engine from larger valves or valve lifts and more

direct passageways.

Less distance for the flame to travel.

Less force on the head bolts and therefore less possibility of

leakage (of compression gases or jacket water).

Removal of the hot exhaust valve from the block to the head, thus

confining heat failures to the head.

Absence of exhaust valve from block also results in more uniform

cooling of cylinder and piston.

Lower surface-volume ratio and, therefore, less heat loss and less

air pollution.

Easier to cast and hence lower casting cost.

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Two important designs of overhead valve combustion

chambers are used .

Bath Tub Combustion Chamber

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This is simple and mechanically convenient form.

This consists of an oval shaped chamber with both valves

mounted vertically overhead and with the spark plug at the

side.

The main draw back of this design are:

both valves are placed in a single row along the cylinder

block. This limits the breathing capacity of engine, unless

the overall length is increased.

However, modern engine manufactures overcome this

problem by using unity ratio for stroke and bore size.

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Wedge Type Combustion Chamber

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In this design slightly inclined valves are

used.

This design has given very satisfactory

Performance.

A modern wedge type design can be seen in

for Plymouth V-8 engine.


F- HEAD COMBUSTION CHAMBER

F- head used by Rover Company

90

F – head used in Willeys jeep.

In such a combustion chamber one

valve is in head and other in the block.

This design is a compromise between

L-head and I-head combustion

chambers.


Advantages

High volumetric efficiency

Maximum compression ratio for fuel of given octane rating

High thermal efficiency

It can operate on leaner air-fuel ratios without misfiring.

Disadvantages

This design is the complex mechanism for operation of

valves and expensive

special shaped piston. 91


COMBUSTION CHAMBERS IN CI ENGINES

The most important function of CI engine combustion

chamber is to provide proper mixing of fuel and air in short

time.

In order to achieve this, an organized air movement called

swirl is provided to produce high relative velocity between

the fuel droplets and the air.

92


C I engine combustion chambers are classified into two

categories:

OPEN INJECTION (DI) TYPE :

This type of combustion chamber is also called an Open combustion

chamber. In this type the entire volume of combustion chamber is

located in the main cylinder and the fuel is injected into this volume.

INDIRECT INJECTION (IDI) TYPE:

In this type of combustion chambers, the combustion space is

divided into two parts, one part in the main cylinder and the other

part in the cylinder head. The fuel –injection is effected usually into

the part of chamber located in the cylinder head.

These chambers are classified further into :

Swirl chamber in which compression swirl is generated

Pre combustion chamber in which combustion swirl is induced

Air cell in which both compression and combustion swirl are induced. 93


DIRECT INJECTION CHAMBERS – OPEN

COMBUSTION CHAMBERS

An open combustion chamber is defined as one in which the

combustion space is essentially a single cavity with little

restriction from one part of the chamber to the other and

hence with no large difference in pressure between parts of

the chamber during the combustion process.

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95

Advantages

Minimum heat loss during compression because of lower surface

area to volume ratio and hence, better efficiency.

No cold starting problems.

Fine atomization because of multi hole nozzle.

Drawbacks

High fuel-injection pressure required and hence complex design of

fuel injection pump.

Necessity of accurate metering of fuel by the injection system,

particularly for small engines.


Shallow Depth Chamber

In shallow depth chamber the depth of the cavity provided in

the piston is quite small.

This chamber is usually adopted for large engines running at

low speeds. Since the cavity diameter is very large, the squish

is negligible.

Hemispherical Chamber:

This chamber also gives small squish. However, the depth to

diameter ratio for a cylindrical chamber can be varied to give

any desired squish to give better performance. 96


Cylindrical Chamber

This design was attempted in recent diesel engines.

This is a modification of the cylindrical chamber in the form of a truncated cone with base angle of 30°. The swirl was produced by masking the valve for nearly 1800 of circumference.

Squish can also be varied by varying the depth.

Toroidal Chamber

The idea behind this shape is to provide a powerful squish along with the air movement, similar to that of the familiar smoke ring, within the toroidal chamber.

Due to powerful squish the mask needed on inlet valve is small and there is better utilization of oxygen. The cone angle of spray for this type of chamber is 150° to160°.

97


IN DIRECT INJECTION CHAMBERS

A divided combustion chamber is defined as one in which the

combustion space is divided into two or more distinct

compartments connected by restricted passages.

This creates considerable pressure differences between them

during the combustion process.

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RICARDO’S SWIRL CHAMBER

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PRE COMBUSTION CHAMBER

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101

Advantages

(i) Due to short or practically no delay period for the fuel entering the main

combustion space, tendency to knock is minimum, and as such running is

smooth.

(ii) The combustion in the third stage is rapid.

(iii) The fuel injection system design need not be critical. Because the

mixing of fuel and air takes place in pre-chamber,

Disadvantages

(i) The velocity of burning mixture is too high during the passage from pre-

chambers, so the heat loss is very high. This causes reduction in the

thermal efficiency, which can be offset by increasing the compression ratio.

(ii) Cold starting will be difficult as the air loses heat to chamber walls

during compression.


ENERGY CELL

102


M COMBUSTION CHAMBER

103


Advantages

Low rates of pressure rise, low peak pressure.

Low smoke level.

Ability to operate on a wide range of liquid fuels

Disadvantages

Since fuel vaporization depends upon the surface

temperature of the combustion chamber, cold starting

requires certain aids.

Some white smoke, diesel odour, and high hydrocarbon

emission may occur at starting and idling conditions.

Volumetric efficiency is low. 104


RESISTANCE TO A MOVING VEHICLE

When a body moves through a fluid, it is encountered by

resistance (drag)

In order to maintain motion a force needs to be exerted

along the direction of motion of vehicle

When vehicle moves the propulsion unit has to exert a

tractive effort sufficient enough to balance the resistance

offered

105


Wind or Air Resistance

It depends upon:

Shape and size of vehicle body

Air velocity and its direction

Speed of the vehicle

Ra = KAV2

106


Rolling Resistance

Caused due to friction between the wheel tyre and road

surface.

It depends upon the following factors:

Quality of road surface

Road surface material

Wheel inflation pressure

Type of tyre tread

Load on the road wheels

Rr= KW

W- weight of vehicle in N

K- constant of rolling resistance 107


Gradient Resistance

It refers to the steepness of the road

Depends upon:

Weight of the vehicle

Inclination/gradient of the road

Rg=Wsinθ

Total Resistance R = Ra+Rr+Rg

108


109

P = R*V

ήt

P- Power

R- Total Resistance in N

V- Speed in m/s

ήt – transmission efficiency


THANK YOU !!!!!

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