IgnitionSubmitted To:

Sir Rizwan Zafar

Submitted By:

Umar Fayyaz

Adnan Imran

Introduction

• An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture.

Energy Required for Ignition System

• The required energy is depends upon to an extent on the rise time and pulse width of arc

• Energy level for a standardized mixture may be low as 0.002mJ.

• In general it may be considered that 1mJ. Is sufficient to produce ignition of fuel-air mixture.

Spark Energy & Time Duration

• Spark energy & duration are to be sufficient to initiate the combustion

• For a homogenous mixture spark energy of 1mJ for duration of few micro seconds suffice to initiate the combustion

• If spark energy exceed to 40mJ & duration is longer than the 0.5 micro second, reliable ignition is obtained.

Ignition System

• The ignition systems are classified depending upon how the primary energy for operating the circuit is made available as:

1. Battery Ignition System

2. Magneto Ignition System

Requirements of Ignition System

• It should provide a good spark b/w the electrodes of the plugs at the correct timing

• It should function efficiently over the entire range of engine speed

• It should be light, effective & reliable in service

• It should be compact and easy to maintain

• It should be continent and easy to handle

Battery Ignition system

Battery Ignition system• It consist of following parts

1. Battery

2. Ignition Switch

3. Ballast Resistor

4. Ignition coil

5. Contact breaker

6. Capacitor

7. Distributor

8. Spark plug

1 2 3 4

5 6 7 8

Ignition Parts

• Battery: Provides power for system

Two types of battery are used for spark ignition engines

I. Lead acid Battery

II. Alkaline Battery

• Ignition Switches: Allows driver to turn ignition on and off.

Battery is connected to primary winding of the ignition coil through an ignition switch & ballast resistor.

Ignition Parts

• Ballast Resistor: Ballast resistor is provided to regulate the primary current

The object of resistor to prevent the injury to spark coil by overheating if engine should operate for a long time.

• Ignition coil: Changes battery voltage to 30,000V during normal operation and

has a potential to produce up to 60,000V.

The ignition coil consist of magnetic core of soft iron wire or sheet & two insulated conducting coils called primary & secondary windings.

Ignition Parts

• Contact Breaker: it is mechanical device use to making & breaking the primary circuit of ignition coil.

It consists of essentially a fixed metal point against which another metal point bears which is being on spring loaded pivoted arm.

• Capacitor: The principle of ignition capacitor is same like the electric capacitor which is very simple: two metal plates are separated by insulated material-are placed face to face.

Ignition Parts

• Distributer: The function of distributer is to distribute the ignition surges to the individual spark plugs in the correct sequence & at the correct instant in time.

• Spark Plug: The spark plug provides the two electrodes with a proper gap across which the light potential discharges to generate a spark and ignite the combustible mixture within the combustion chamber.

Operation Of Battery Ignition System

• Source of ignition energy is ignition coil

• Coil stores the energy in magnetic felid and provide it at the instant ignition in the form of high surge voltage current through the high tension ignition cables to the correct spark plugs

• Storage energy is depend upon the inductive process

Limitations Of Battery Ignition System

I. The primary voltage decrease as the engine speed increase

II. Time available for the build-up of the current in the primary coil & storage energy decrease as the engine speed increase

III. The system is sensitive for side tracking across the spark plug insulator because high source impedance is about to 500kΩ

IV.Increased current cause the rapid reduction in breaker point life and system reliability s

Dwell Angle

• The period, measured in degree of cam rotation, during which the contact point remain closed is called Dwell Angle or Cam Angle.

• The Dwell angle must be large so that the magnetic saturation is more in primary coil

• Too small Dwell Angle will results in lower secondary voltage & hence poor sparks or even misfiring

• The magnitude of Dwell Angle depends upon the b/w the points & also the angle b/w the cam lobes

• Gap b/w the points is 0.35mm to 0.55mm

Dwell Angle Cont.

• As the no. of cylinder increase, the dwell angle is decreased because more opening and closing

• In four cylinder Dwell Angle is about to 50 degree

• In six cylinder it is 38 degree

• In eight cylinder it is about 33 degree

Dwell Period=1000 ×𝐷𝑤𝑒𝑙𝑙 𝐴𝑛𝑔𝑙𝑒 (𝐷𝑒𝑔𝑟𝑒𝑒)

6 ×𝐸𝑛𝑔𝑖𝑛𝑒 𝑆𝑝𝑒𝑒𝑑 (𝑟𝑒𝑣/𝑚𝑖𝑛)

• This formula shows in which way Dwell Period is expressed as a function of Dwell Angle & the engine speed

Advantages of 12V Ignition System

• For transmitting equal power without excessive voltage drop

• Twice the power for ignition coil during the starting surge

• 12V system has adequate electric power to supply the increasing the number of electrical accessories used

Magneto Ignition System

It is special type of ignition system with its own electric generator to provide the necessary energy for the system

• It is mounted over the engine and replace the all parts of coil ignition system except the spark plug

• Magneto when rotated by the engine it is capable to produce the high voltage & dose not need a battery as external source

Schematic Diagram

Comparison b/w Battery Ignition & Magneto Ignition

Modern Ignition System

Modern attempts are given below:

• Transistorized Coil Ignition (TCI) System

• Capacitive Discharge Ignition (CDI) System

Transistorized Coil Ignition (TCI)System

It provide the higher output voltage & use the electronic triggering to maintain therequired timing. These system also called the high energy electronic ignition system

These are the following advantages of TCI System:

• Reduce ignition system maintenance

• Reduce the wear of the components

• Increased reliability

• Extend spark plug life

• Improved Ignition of lean mixture

Schematic Diagram of TCI

Capacitive Discharge Ignition (CDI) System

• A capacitor rather than the induction coil is used to store the ignition energy.

• The capacitance and the charging voltage determine the amount of energy stored.

• Ignition transformer step up the primary voltage generated at the time of spark bythe discharge of capacitor through the thyristor to the high voltage required at thespark plug.

• The CDI trigger box contain the capacitor, thyristor power switch, charging device,pulse shaping unit & control unit

Schematic Diagram of CDI

Fire Order

• Every engine cylinder must fire once in one cycle

• Three factor must be considered before deciding the optimum firing order of an engine

i. Engine vibration

ii. Engine cooling

iii. Development of back pressure

• 4 stroke 4 cylinder ignition system must fire for every 180 degree of crank rotation

• For six cylinder engine only 120 degree of crank rotation

Spark Advance Mechanism

Two Advance Mechanism used are:

1. Centrifugal Advance Mechanism

2. Vacuum Advance Mechanism

Centrifugal Advance Mechanism

• Control the ignition timing for full-loaded operation

• The cam is mounted over the distributor shaft so that the speed increase, the flyweights which move farther & farther outward, shift the cam in direction of shaft rotation

• The cam lobes make contact with the breaker leaver rubbing block, thus shifting the ignition point in early or advance direction

Centrifugal Advance Mechanism Cont.• A typical advance mechanism showed in figure given below:

Vacuum Advance Mechanism

• Mechanism that shift the ignition point under part load operation

• The diaphragm of a vacuum unit is moved by changes in gas pressure

• Position of diaphragm is determined by the differential at any given movement b/w the prevailing vacuum & atmospheric pressure

• Vacuum advance mechanism is operates independent of the centrifugal advance mechanism

• Vacuum advance mechanism operates in conjunction with the centrifugal advance mechanism to provide the total adjustment required when engine is operating under the part load

Vacuum Advance Mechanism Cont.

• A typical advance mechanism showed in figure given below:

Ignition Timing & Exhaust Emission

• Idling, declaration & running richwith closed throttle are someengine operating conditions whichproduce excessive unburnthydrocarbons & carbon monoxidein exhaust.

• The emission quality is greatlyeffected by ignition timing .

Typical distributor advance curve for lower HC & CO exhaust emission

How Ignition System Works

Engine Electronics

(Sensors)

Introduction

• The performance and emissions thattoday's engines deliver would beimpossible without the electronics thatmanage everything from ignition andfuel delivery to every aspect of emissionscontrol. Electronics make possible V8engines that deliver excellentperformance, good fuel economy andproduce almost no pollution. But there'sa price to be paid for today's technology,and that price is complexity.

Inductive Sensors

• Inductive sensors in today’s vehicles, mainlyare used for measuring the rpm anddetermining the position of crankshaft orcamshaft at engine management systems, aswell as measuring the speed (rpm) of thewheels at ABS systems, ESP systems, etc. TheRPM sensors typically can be Hall or inductivetype. The operation of these sensors isfundamentally similar in all instances,although the construction can vary dependingon the type of sensor, its intended use ormanufacturer application.

Components of an Inductive Sensor

1. Sensor housing

2. Output signal wires

3. Coaxial coated protection

4. Permanent magnet

5. Inductive coil

6. Pole pin

7. Trigger wheel

G. Air gap

Hall Effect Sensors

• Unlike inductive sensors, the output signalfrom a Hall effect sensor is not effected by therate of change of the magnetic field. Theproduced output voltage typically is in therange of milli volts (mV) and is additionallyamplified by integrated electronics, fittedinside of the sensor housing. On the figure it isshown typical build of a Hall Effect sensor.

Motor Operated Potentiometer

• The motor operated potentiometer (MOP) isan auxiliary unit for use with electronic speedgovernors or automated parallelingequipment. Some MOPs are built into theunits they control; others are separate andmust be wired into their control circuits. TheMOP is used primarily for adjusting the speedreference potentiometer to the necessaryspeed setting on an electronic governor.

Schematic Diagram of MOP

Linear Variable Differential Transformer (LVDT)

• LVDT is a positive or Magnetic Displacement Transducer, it is commonly used to measure Force, Weight, Pressure and Acceleration which depend upon Force in terms of amount and direction of Displacement.

Schematic Diagram of LVDT

Electro Optical Sensors

Electro-optical sensors are electronic detectors thatconvert light, or a change in light, into an electronicsignal. They are used in many industrial andconsumer applications, for example:

• Lamps that turn on automatically in response to darkness.

• Position sensors that activate when an object interrupts a light beam.

• Flash detection, to synchronize one photographic flash to another.

• Photoelectric sensors that detect the distance, absence, or presence of an object.

Types of an Electro Optical Sensors

There are many different kinds of optical sensors, the most common types are:

• Photoconductive devices convert a change of incident light into a change of

resistance.

• Photovoltaic commonly known as solar cells, convert an amount of incident light

into an output voltage.

• Photodiodes convert an amount of incident light into an output current.

• Phototransistors are a type of bipolar transistor where the base-collector junction

is exposed to light. This results in the same behaviour of a photodiode, but with an

internal gain.

Strain Gauge Sensor

• Generally the strain of any object could be possiblydetermined using strain gauge device. This toolpreviously invented by Edward Simmons andArthur Ruge in 1938 and the most common type ofthis strain gauge is consisted of an insulatingflexible backing which supports a metallic foilpattern. The suitable adhesive is used to attach thegauge to the object of interest.

• Whenever the object is deformed, the foil isdeformed as well, resulting in its electricalresistance to change.

• In order to determine the changes in resistance aWheatstone bridge is applied which is related tothe strain by the quantity known as the gaugefactor (Simmons).

Coolant Sensor

• The coolant sensor is used to monitor thetemperature of the engine coolant. Its resistancechanges in proportion to coolant temperature.Input from the coolant sensor tells the computerwhen the engine is warm so the PCM can go intoclosed loop feedback fuel control and handleother emission functions (EGR, canister purge,etc.) that may be temperature dependent.

• The coolant sensor is a pretty reliable sensor, butif it fails it can prevent the engine control systemfrom going into closed loop. This will result in arich fuel mixture, excessive fuel consumption andelevated carbon monoxide (CO) emissions - whichmay cause the vehicle to fail an emissions test.

Oxygen (O2) Sensor

• Used on both carbureted and fuel injected engines since 1981, the oxygen (O2) sensor is the keysensor in the fuel mixture feedback control loop.

• Mounted in the exhaust manifold, the O2 sensor monitors the amount of unburned oxygen in theexhaust. On many V6 and V8 engines, there are two such sensors (one for each bank of cylinders).

• The O2 sensor's responsiveness and voltage output can diminish with age and exposure to certaincontaminants in the exhaust such as lead, sulphur, silicone (coolant leaks) and phosphorus (oilburning). If the sensor becomes contaminated, it may not respond very quickly to changes in theair/fuel mixture causing a lag in the PCMs ability to control the air/fuel mixture.

Manifold Absolute Pressure (MAP) Sensor

• The MAP Sensor is mounted on or connectedto the intake manifold to monitor intakevacuum. It changes voltage or frequency asmanifold pressure changes. The computer usesthis information to measure engine load soignition timing can be advanced and retardedas needed. It performs essentially the same jobas the vacuum advance diaphragm on an oldfashioned mechanical distributor.

Throttle Position Sensor

• Mounted on the throttle shaft of thecarburetor or throttle body, the ThrottlePosition Sensor (TPS) changes resistance asthe throttle opens and closes. The computeruses this information to monitor engine load,acceleration, deceleration and when theengine is at idle or wide open throttle. Thesensor's signal is used by the PCM to enrich thefuel mixture during acceleration, and to retardand advance ignition timing.

Crankshaft Position Sensor• Used on engines with distributorless ignition

systems, the Crankshaft Position (CKP)Sensor serves essentially the same purpose as theignition pickup and trigger wheel in an electronicdistributor. It generates a signal that the PCM needsto determine the position of the crankshaft and thenumber one cylinder. This information is necessary tocontrol ignition timing and the operation of the fuelinjectors. The signal from the crank sensor also tellsthe PCM how fast the engine is running (engine rpm)so ignition timing can be advanced or retarded asneeded.

• On some engines, a separate camshaft positionsensor is also used to help the PCM determine thecorrect firing order. The engine will not run withoutthis sensor's input.

Knock Sensor

• The knock sensor detects engine vibrations thatindicate detonation is occurring so the computercan momentarily retard timing. Some engines havetwo knock sensors.

• Knock Sensor Strategies: A failure with the knocksensor can cause spark knock and engine damagingdetonation because the PCM will not know toretard ignition timing if knock is occurring.

Barometric Pressure Sensor

• The Barometric Pressure Sensor measuresbarometric pressure so the computer cancompensate for changes in altitude and/orbarometric pressure that would affect the fuelmixture or timing. Some MAP sensors also performthis function.

Vehicle Speed Sensor

• The Vehicle Speed Sensor or VSS, monitorsvehicle speed so the computer can regulate torqueconverter clutch lockup, shifting, etc. The sensormay be located on the transmission, differential,transaxle or speedometer head.

• Vehicle Speed Sensor Strategies: A problem withthe vehicle speed sensor can disable the cruise-control system as well as affect transmissionshifting and converter engagement.