si engine and basic ignition system

7/30/2019 SI ENGINE and BASIC IGNITION SYSTEM

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Guided By

Presented By

SHRVAN .S. HIRDE B-62

B.E. VI Semester

Department of Mechanical EngineeringG. H. Raisoni College of Engineering, Nagpur

2012-13

Date: 20/12/2012

APower Point Presentation

on

Under TAE parameter-ECII( ENERGY CONVERSION II)


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Classification of I.C. Engines

. According to the used.

. According to the the fuel

.. According to the per cycle

.. According to the


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Classification of I.C. Engines (contd..)

According to the

.

According to the.

According to the

According to the


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Basic Idea of I.C. Engines

The basic idea of internal combustion engine is shownin Fig. (Basic idea of I.C. engine). The cylinder which isclosed at one end is filled with a mixture of fuel andair. As the crankshaft turns it pushes cylinder. Thepiston is forced up and compresses the mixture in the

top of the cylinder. The mixture is set alight and, as itburns, it creates a gas pressure on the piston, forcing itdown the cylinder.

This motion is shown by arrow . The piston pushes

on the rod which pushes on the crank. The crank isgiven rotary (turning) motion as shown by the arrow . The flywheel fitted on the end of the crankshaftstores energy and keeps the crank turning steadily.


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Constructional details of I.C. Engines

A cross-section of an air-cooled I.C. engine with principalparts is shown in Fig. (Air-cooled I.C. engine).


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Constructional details of I.C. Engines(contd..)

The details of the I.C. Engine parts are:

It is one of the most important part of the engine, in which thepiston moves to and fro in order to develop power. Theengine cylinder has to withstand a high pressure

. Thus thematerial for the engine cylinder should be such that it canretain sufficient strength at such a high pressure andtemperature. For ordinary engines, the cylinder is made ofordinary . But for , it is made of

.

Sometimes, a liner or sleeve is inserted into the cylinder,which can be replaced when worn out. As the materialrequired for liner is comparatively small, it can be made ofalloy cast iron having long life and sufficient

to the fast moving reciprocating parts.


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Constructional details of I.C. Engines (contd..)

It is fitted on one end of the cylinder, and act as a cover toclose the cylinder bore. Generally, the cylinder headcontains inlet and exit valves for admitting fresh chargeand exhausting the burnt gases. In petrol engines, thecylinder head for igniting thefuel-air mixture, towards the end of compression stroke.

The cylinder head is cast as one piece and bolted to oneend of the cylinder. The cylinder block and cylinder

head are made from the same material.is provided between the engine cylinderand cylinder head to make an air-tight joint.


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3. Piston It is considered as the heart of an I.C. engine,whose main function is to transmit the force exerted by theburning of charge to the connecting rod. The piston are generallymade of aluminum alloys which are light in weight. They have

good heat conducting property and also greater strength athigher temperature.4. Piston rings These are circular rings and made of

special steel alloys which retain elastic properties even at hightemperatures. The piston rings are housed in the circumferential

grooves provided on the outer surface of the piston. Generally,

there are two sets of rings mounted for the piston. The function ofthe upper rings is to provide air tight seal to prevent leakage ofthe burnt gases into the lower portion. Similarly, the function ofthe lower rings is to provide effective seal to prevent leakage ofthe oil into the engine cylinder.


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It is a link between the piston and crankshaft, whose mainfunction is to transmit force from the piston to thecrankshaft. Moreover, it converts reciprocating motion of the

piston into circular motion of the crankshaft, in the workingstroke. The upper (i.e. smaller) end of the connecting rod isfitted to the piston and the lower (i.e. bigger) end of thecrank.

The special steel alloys or aluminum alloys are used for themanufacture of connecting rods. A special care is requiredfor the design and manufacture of connecting rod, as it issubjected to alternatively compressive and tensile stresses aswell as bending stresses.


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It is considered as the backbone of an I.C.engine whose function is to covert the reciprocating motion ofthe piston into the rotary motion with the help of connecting rod.This shaft contains one or more eccentric portions called cranks.This part of the crank, to which bigger end of the connecting rod

is fitted, is called crank pin. Special steel alloys are used for themanufacture of crankshaft. A special care is required for thedesign and manufacture of crankshaft

It is a cast iron case, which holds the cylinderand crankshaft of an I.C. engine. It also serves as a sump for thelubricating oil. The lower portion of the crank case is known asbed plate, which is fixed with the help of bolts.

It is a big wheel, mounted on the crankshaft,whose function is to maintain its speed constant. It is done bystoring excess energy during power stroke, which, is returnedduring other stroke.


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Terms relating to I.C. Engines

The various terms relating to I.C. engines are elaborated in Fig.The inside diameter of the cylinder is called bore.

As the piston reciprocates inside the engine cylinder,it has got limiting upper and lower positions beyond which itcannot move and reversal of motion takes place at these limiting

positions. The linear distance along the cylinder axis between twolimiting positions, is called stroke.

The top most position towardscover end side of the cylinder is called topdeadcentre. In case ofhorizontal engines, this is known as inner dead centre.

The lowest position of the pistontowards the crank end side of the cylinder is called bottom dead

centre. In case of horizontal engines it is called outer dead centre.


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Terms relating to I.C. Engines (contd..)

The volume contained in the cylinder above the top of the

piston, when the piston is at top dead centre, is calledthe clearance volume.

The volume swept through by the piston in moving

between top dead centre and bottom dead centre, iscalled or . Thus,

when piston is at bottom dead centre,


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Two-stroke and Four-stroke Cycle

In a , the working cycle iscompleted in two strokes of the piston or onerevolution of the crankshaft. This is achievedby carrying out the suction and compressionprocesses in one stroke (or in inward stroke),

expansion and exhaust process in the secondstroke (or in outward stroke).

In a , the working cycle iscompleted in four strokes of the piston or two

revolutions of the crankshaft. This is achievedby carrying out suction, compression,expansion and exhaust processes in eachstroke.


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Two-stroke Cycle Petrol Engine

In this cycle, the andtakes place during two strokes of the piston. There is

one working stroke after every revolution of the crankshaft.A two stroke engine has ports instead of valves. All the fourstages of a two stroke petrol engine are described below:

In this stage, the piston, whilegoing down towards bottom dead centre uncovers

both the transfer port and the exhaust port. The fresh fuel-air mixture flows into the engine cylinder from the crankcase, as shown in Fig.

In this stage, the piston,while moving up, first covers the transfer port and thenexhaust port. After that the fuel is compressed as the pistonmoves upwards as shown in Fig. In this stage, the inlet portopens and fresh fuel-air mixture enters into the crank case.


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Two-stroke Cycle Petrol Engine (contd..)

Shortly before this piston reachesthe top dead centre ( during compression stroke, the chargeis ignited with the help of a spark plug. It suddenly increases thepressure and temperature of the products of combustion but thevolume remains constant. Due to rise in the pressure, the piston ispushed downwards with a great force as shown in Fig. The hotburnt gases expand due to high speed of the piston. During thisexpansion, some of the heat energy produced is transformed intomechanical work.

- In this stage, the exhaust port is

opened as the piston moves downwards. The products ofcombustion, from the engine cylinder are exhausted through theexhaust port into the atmosphere, as shown in Fig. This completesthe cycle and the engine cylinder is ready to suck the chargeagain.


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Four-stroke Cycle Petrol Engine

It requires four strokes of the piston to complete one cycle ofoperation in the engine cylinder. The four strokes of a petrol enginesucking fuel-air mixture (petrol mixed with proportionate quantity ofair in the carburetor known as charge) are described below:

In this stroke, the inlet valve opens and charge is sucked into thecylinder as the piston moves downward from TDC. It continues tillthe piston reaches its BDCas shown in Fig.

In this stroke, both the inlet and exhaust valves are closed and thecharge is compressed as the piston moves upwards from BDC toTDC. As a result of compression, the pressure and temperature ofthe charge increases considerably. This completes one revolution ofthe crank shaft. The compression stroke is shown in Fig.


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Four-stroke Cycle Petrol Engine (contd..)

Shortly before the piston reaches TDC, the charge is ignited with thehelp of a spark plug. It suddenly increases the pressure andtemperature of the products of combustion but the volume,practically remains constant. Due to the rise in pressure, the

piston is pushed down with a great force. The hot burnt gasesexpand due to high speed of the piston. During this expansion,some of the heat energy produced is transformed into mechanicalwork. During this working stroke, as shown in Fig., both thevalves are closed and piston moves from TDCto BDC.

In this stroke, the exhaust valve is open as piston moves from BDCtoTDC. This movement of the piston pushes out the product ofcombustion, from the engine cylinder and exhausted through theexhaust valve into the atmosphere, as shown in Fig. Thiscompletes the cycle, and the engine cylinder is ready to suck thecharge again.


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Comparison of Petrol and Diesel Engines

Petrol Engines1. A petrol engine draws a

mixture of petrol and airduring suction stroke.

2. The carburettor is employedto mix air and petrol in therequired proportion and tosupply it to the engine duringsuction stroke.

3. Pressure at the end ofcompression is about 10 bar.

4. The charge (i.e. petrol and airmixture) is ignited with thehelp of spark plug.

Diesel EnginesA diesel engine draws only airduring suction stroke.

The injector or atomiser is

employed to inject the fuel atthe end of combustion stroke.

Pressure at the end ofcompression is about 35 bar.

The fuel is injected in the form

of fine spray. The temperatureof the compressed air issufficiently high to ignite thefuel.


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Ignition System

Provides a method of turning a spark ignition engine

on & off.Operates on various supply voltages (Battery & Alternator)

Produces high voltage arcs at the spark plug electrode.

Distributes spark to each plug in correct sequence.

Times the spark so that it occurs as the piston nears the TDC on thecompression stroke.

Varies the ignition timing as engine speed, load and other conditions change.


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Parts of Ignition System

provides power for system.

allows driver to turn ignition on and off.

changes battery voltage to 30,000V during

normal operation and has a potential to produce up to 60,000V.

mechanical or electronic switchthat operates Ignition coil

uses high voltage from ignition coil to produce an arcin the combustion chamber.

connect components.
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IGNITION COILS

The heart of any ignition

system is theThe coil creates a high-voltage spark by

electromagneticinduction.

Many ignition coilscontain two separate but

electrically connectedwindings of copper wire.

FIGURE 1 Internal construction of an oil-cooled ignition coil. Notice that

the primary winding is electrically connected to the secondary winding.

The polarity (positive or negative) of a coil is determined by the direction

in which the coil is wound.


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Distributor

A mechanical timingdevice.Drives off engine camshaft.Can controls both primaryand secondary circuits.May contain advance units.


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SPARK PLUGS

Spark plugs are

manufactured from ceramicinsulators inside a steel shell.

The threads of the shell arerolled and a seat is formed to

create a gastight seal with thecylinder head.

FIGURE 2Parts of a typical spark plug.


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BASIC IGNITION SYSTEM


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Magneto ignition system

Magneto is a special type of ignition systemwith its own electric generator to provide thenecessary energy for the system.

Magneto can be either typeor type.


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Magneto ignition system


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Battery ignition system v/s Magneto ignition system

Battery ignition system Magneto ignition system

Battery is necessary.

Current for primary circuit is

obtained from the battery.

A good spark is available at thespark plug even at low speed.

Efficiency of the systemdecreases with the reduction inspark intensity as engine speedrises.

No battery is needed.

Required electric current is

generated by the magneto. During starting, quality of

spark is poor due to lowspeed.

Efficiency of the systemimproves as the enginespeed rises due to highintensity spark.


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ELECTRONIC IGNITION SYSTEM


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IGNITION MODULE

THE IGNITION MODULE USES TRANSISTORS TOTURN THE CURRENT FLOW FOR THE COILPRIMARY WINDINGS ON AND OFF

IT GETS IT SIGNAL TO DO THIS FROM THEIGNITION PICK UP COIL

MOST LATE MODEL CARS HAVE A ENGINECONTROL MODULE (ECM) WHICH COMUNICATES

WITH THE IGNITION MODULE THEREFORECONTROLLING IGN. COIL.


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Hall-Effect Sensors

Most popular electronic ignition triggering device Hall Effect Sensors are used in many ignition system

distributors to trigger the primary circuit (fire the coil) and tomonitor engine rpm.

Produce a constant voltage signal that can change abruptlyfrom maximum voltage to nearly zero and back againregardless of engine speed.

Produces a square wave output signal that can be easily used

by the onboard computer for timing purposes.


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MODERN IGNITION SYSTEMS

In modern automobiles the following two types ofelectronic ignition systems are being used. They are-


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Advantages of TCI

The timing of TCI is moreprecise with the use of theTransistors.

Quicker current build up,

high ignition voltages, longduration of spark.

Increased reliability,reduced wear of contact

points. Extended spark plug life.

Improved ignition of leanmixtures.

Advantages of CDI

Condenser of CDI system can store

much larger energy than TCI system.This allows high output voltages evenat high spark rates.Faster voltage rise as internalresistance is less.Current drawn from battery is smallart lower speeds and increases withincreases with engine speed which isreverse of conventional ignition

system which draws high current atlow speeds.Easier cold starting.Output voltage is independent ofengine speed. This reduces the

chances of misfiring.


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si engine and basic ignition system

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