Automotive Systems course (Module 09) - Ignition Systems for Internal Combustion Engines

4 de novembro de 2016 | 1
SistemasAutomóveis
Ignition Systems
Mário Alves (mjf@isep.ipp.pt)

SistemasAutomóveis
Outline
• Ignition system: definition, functionality, requirements
• Ignition timing
• Spark generation
• Ignition systems evolution
• Electromechanical ignition systems
• distributor, circuit breaker, condenser, resistor,
vacuum/centrifugal advance, primary/secondary voltage,
dwell, distributor cap, cabling, coils
• ECU-based and distributorless ignition systems
• Capacitive and inductive discharge igniters
• Glossary
• Recommended references

SistemasAutomóveis
Ignition System: definition
• Definition of ignition system
• system that enables to ignite the air-fuel mixture in spark-ignition
(SI) internal combustion engines (e.g. gasoline, LPG, alcohol)
http://www.engihub.com/ignition-systems-of-i-c-engine/

SistemasAutomóveis
Ignition system: functionality
• Functionalities of an ignition system
• detection of crankshaft position/speed
• mechanical switch (circuit breaker)  electronic sensor
• determination of ignition timing/duration
• mechanical  computer-controlled
• creation of high-voltage
• electric transformer (known as ignition coil)
• timely distribution of high-voltage to each cylinder
• mechanical distributor  power electronics
• creation of an electric arc (triggering air-fuel ignition)
• spark plug(s)
…

SistemasAutomóveis
Ignition system: requirements
• Main requirements of an ignition system
• spark must be vigorous (so that all air/fuel mixture is burned)
• requires high-voltage peak (> 15 kV)
• spark/ignition timing must be optimized for all engine conditions
• e.g. RPM, engine load, air/fuel ratio, water temperature,…
• energy-efficient, lightweight, compact, low-cost
• low electrical energy consumption, low heat losses, high-tech
materials and design; these properties may be conflicting
• durable and reliable
• user expectations: the lifetime of the vehicle; these properties
and the former may be conflicting
• minimized generation of electromagnetic interference (EMI)
• EMI impacts electronic/computerized and wired/wireless
communication systems
…

SistemasAutomóveis
Ignition timing: the need for firing the spark before TDC
• Ignition must be triggered before the piston reaches TDC
• air-fuel mixture takes a few miliseconds to ignite – ignition delay
• spark must be fired a few ms before piston reaches TDC
http://suprasport.com/E3-Spark-Plugs_p_1520.html

SistemasAutomóveis
Ignition timing: the need to adapt to engine speed
• Ignition must be triggered in advance to TDC
• this advance timing (t) is reflected in an advance angle ()
• Considering the valve timing diagram in the figure:
• intake valve opens
@ 10° BTDC
• air-fuel mixture is sucked
till intake valve closes
• air-fuel mix is compressed
till spark occurs
@ 12º BTDC
http://4mechtech.blogspot.pt/2014/12/port-timing-diagram-for-two-stroke-petrol-engine.html

SistemasAutomóveis
Ignition timing: the need to adapt to engine speed
• For higher RPM (), same t corresponds to > angle
( = .t)
• thus, the advance angle must be increased with the RPM
http://mechsapiens.com/valve-timing-diagram-mechanical-factor-dynamic-factor-intake-exhaust/
http://www.c5ignitions.com/c5-technology.html

SistemasAutomóveis
Ignition timing: the need to adapt to engine load
• Engine load
• “is the power that the outside world takes away from the engine”
• an engine connected to nothing can have essentially no load,
regardless of throttle opening or RPM
• an engine produces more power and can therefore accommodate
more load when its throttle is open wider, and less power/load
when its throttle is less open
• the amount of power available from the engine at 100% throttle
varies over its operating RPM range; at any given speed, the
maximum power that the engine can output is "full load."
• if the output power of the engine is less than the external
load, the engine will decelerate.
• if the output power of the engine is greater than the external
load, the engine will accelerate.
http://mechsapiens.com/valve-timing-diagram-mechanical-factor-dynamic-factor-intake-exhaust/
http://www.c5ignitions.com/c5-technology.html

SistemasAutomóveis
• The leaner the air/fuel mixture, the longer it takes to burn
• < engine loads  > advance angle
• richer mixtures (higher loads)  < advance angle
http://www.stealth316.com/2-ignitionsystem.htm

SistemasAutomóveis
• Another example with a 3D map representation
http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm

SistemasAutomóveis
Ignition timing: influence of other parameters
• Ignition timing may be optimized according to other engine
operating parameters, e.g.
• engine coolant temperature
• intake air density, temperature, pressure, mass flow rate
• throttle position
• exhaust gas oxygen
• transmission gear
• vehicle speed
• system voltage
• engine knocking
• Nowadays, this is possible due to ECU-controlled ignition
• but it was not quite like that at the beginning 
http://www.stealth316.com/2-ignitionsystem.htm

SistemasAutomóveis
Basic principle of spark generation
https://www.thinglink.com/scene/616979999844466690
• A spark is an electric arc generated by a spark plug
• when a high-voltage (tens of kV) is applied to its terminals
• This is achieved by an electric transformer
(know as ignition coil)
• primary winding  few turns
• secondary winding  many turns
• Operation
1. an electric current circulates in the primary winding
2. this current is switched off (mechanical or electronic switch)
3. there is a sudden drop in the magnetic field generated by the
primary winding (a high counter-EMF appears in the primary)
4. this abrupt drop in the magnetic field induces a very high EMF in
the secondary winding

SistemasAutomóveis
https://www.picoauto.com/library/automotive-guided-tests/secondary-vs-primary-voltage-and-current1
• Example primary current and voltage waveforms
Primary
ON
Primary
OFF

SistemasAutomóveis
https://www.picoauto.com/library/automotive-guided-tests/primary-vs-secondary
• Example primary and secondary voltage waveforms
• …

SistemasAutomóveis
https://www.thinglink.com/scene/616979999844466690
• The spark generation is still the basic principle has been
applied over the years
• sparks are still used
• ignition coils are still used
• But ignition-related technology has evolved tremendously
• spark plugs
• ignition coils
• primary circuit breaker/switching
• engine parameters determination
• ignition timing optimization
• high-voltage distribution

SistemasAutomóveis
Ignition System: evolution over time
https://www.eeweb.com/blog/fairchild_semiconductor/introduction-to-automotive-ignition-systems
Igniter

SistemasAutomóveis
Ignition System: evolution over time
https://www.eeweb.com/blog/fairchild_semiconductor/introduction-to-automotive-ignition-systems
• From a power electronics-oriented perspective
• IGBT’s control IC with diagnosis/protection functions into igniter

SistemasAutomóveis
Ignition coil types
http://www.ngkntk.co.uk/index.php/technical-centre/ignition-coils-tec/ignition-coils-types/
• Different types/generations of ignition coils

SistemasAutomóveis
Distributor types
http://www.auto-repair-help.com/automotive_maintenance/distributor_overview.php
• Different types/generations of distributors
http://www.silvesterv8.co.nz/pages.php?pageid=13 http://www.vintagemodelairplane.com/pages/Downloads/Rover_Tasters/Ignition04.html
http://www.aliexpress.com/w/wholesale-ignition-distributor.html
Coil on cap Igniter No advance1st generation

SistemasAutomóveis
Electromechanical ignition
• Distributor does timing advance and high-voltage distribution
• Mechanical switch
(circuit breaker)
• Centrifugal advance
• Vacuum advance
• Mechanical distributor
(distributor cap)
• High-voltage
wiring
• cylindrical coil
• Voltage divider
(primary resistor)
• Protecting condenser
…http://www.carparts.com/classroom/ignition.htm

SistemasAutomóveis
http://www.motorera.com/dictionary/di.htm
http://www.howacarworks.com/illustrations/inside-a-bosch-distributor
Electromechanical ignition: distributor

SistemasAutomóveis
Electromechanical ignition: circuit breaker
• Circuit breaker (AKA breaker points)
• electrical switch, actuated by distributor cam lobes
• platinum contacts, resilient to electric arc created by CEMF
…http://modelabasics.com/Ignition.htm

SistemasAutomóveis
Electromechanical ignition: primary current/voltage
• When primary current (few A) is cut off, a peak of counter
EMF (hundreds of V) shows up at the breaker terminals
• this creates an electric arc between the breaker points, accelerating
their deterioration
http://www.pikit.co.uk/peugeotmt/scope%20primary%20wave.html
Primary current & voltage waveforms

SistemasAutomóveis
Electromechanical ignition: dwell
• Dwell (angle) is the number of degrees the distributor cam
rotates from the time the points close until they open again
• it affects the magnetic buildup of the primary windings: the longer
the points are closed, the greater the magnetic buildup
• too much dwell can result in point arcing and burning
• too small, the points will open and collapse the field before it has
built up enough voltage to produce a satisfactory spark
• it can be mechanically adjusted
• this concept also applies to
electronic ignitions
http://autonewpro.blogspot.pt/p/all-about-ignition-system.html

SistemasAutomóveis
Electromechanical ignition: dwell
• Spark burn and dwell periods (secondary voltage waveform)
http://www.crypton.co.za/Tto%20know/Ignition/burn%20time.html

SistemasAutomóveis
Electromechanical ignition: condenser
• Electric arc between the circuit breaker terminals causes slower
current drop
• so the magnetic field drop will not be as sharp as it should
• leading to
• smaller voltage spike
• weaker spark 
• A condenser is connected in parallel with the circuit breaker
• avoids electric arc between breaker points
• enables abrupt drop of current/magnetic field drop
• higher secondary voltage spike
• stronger spark 
• condenser charges during the dwell period
• when the breaker opens, the condenser discharges
itself through the primary coil in the opposite
direction to the flow of induced current, reversing
the polarity of the coil and increasing the rate at
which the magnetic field collapses
http://www.uq.edu.au/_School_Science_Lessons/UNPh32.5.html#32.5.5.2
http://www.pikit.co.uk/peugeotmt/scope%20primary%20wave.html

SistemasAutomóveis
Electromechanical ignition: condenser
• The condenser can be mounted inside or outside the
distributor
• typical capacity ≈ 0,2 F
http://www.howacarworks.com/ignition-system/fitting-a-condenser

SistemasAutomóveis
Electromechanical ignition: primary/ballast resistor
• There is a system voltage drop during cranking
• due starter motor peak load (hundreds of A)
• typically around 3-4 V (12  8-9 V)
• This would mean either
• dimensioning the ignition coil for cranking (9 V)
 overvoltage at runtime 
• dimensioning the ignition coil for runtime (14 V)
 undervoltage at engine cranking 
• Thus
• the ignition coil is dimensioned for 9 V
• after cranking, a voltage divider
(ballast resistor) is used (1-2 Ω)
http://cny.mgcarclub.com/electrical_systems.htm

SistemasAutomóveis
Electromechanical ignition: centrifugal advance
• As RPM increases, upper part of the distributor shaft twists in
relation to the lower part of the distributor shaft
• centrifugal force of the inertial masses vs springs force
• (it usually works together with the vacuum advance mechanism)
Low RPM High RPM

SistemasAutomóveis
• Example advance angle versus RPM curve
• note that the distributor speed is half the crankshaft speed
…http://www.sparkingplugs.com/8.html

SistemasAutomóveis
Electromechanical ignition: vacuum advance
• A diaphragm reacts to engine load (intake air pressure)
• < load  leaner mix  > vacuum  > advance (> time to burn)
• > load  richer mix  < vacuum  < advance (< time to burn)

SistemasAutomóveis
Electromechanical ignition: vacuum advance
• Example advance angle vs. intake vacuum curve
• advance angle grows with vacuum
• adjustable mechanism
…http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor

SistemasAutomóveis
• Combination of centrifugal and vacuum advance
• these mechanisms work together for controlling the timing advance

SistemasAutomóveis
Electromechanical ignition: mechanical distributor (cap)
• High-voltage is transmitted from center terminal, to rotor
head, to side terminals (head rotates with distributor shaft)
• precise synchronization between high-voltage peak and rotor position
http://www.counterpersontraining.com/index.cfm?go=lms.module&moduleid=71&mode=train&contentIndex=12&topicId=269
http://newautoaa.blogspot.pt/p/secondary-circuit-of-ignition-system.html

SistemasAutomóveis
Electromechanical ignition: high-voltage cabling
• Requirements
• high dielectric insulation
• high EMI suppression
• high temperature resistance (> 200ºC)
• high mechanical robustness
• robustness to salt water, oil, petrol and acids
• High electrical resistance feature
• ignition cables feature high electrical resistance (several kΩ)
• this minimizes EMI radiation; since electrical current is
minimized, the radiated electromagnetic field is also minimized
• this does not affect the spark plug voltage peak
• ignition cables conduct a high-voltage low-energy signal
https://www.ngk.de/en/technology-in-detail/ignition-cables/principles/
http://www.my-cardictionary.com/zuendung/zuendleitungen-zuendkabel.html

SistemasAutomóveis
• There are three different types of ignition cables
• copper cables (EMI suppression resistor in the connectors/plug)
• carbon cables (carbon resistance in the cable)
• ignition cables with inductive resistor
• They mainly differ based on
• the material used for the conductor
• the type of resistor used for interference suppression
http://www.my-cardictionary.com/zuendung/zuendleitungen-zuendkabel.html

SistemasAutomóveis
• Copper ignition cables
• copper core surrounded by a silicone casing (electrical insulator)
• the interference suppression resistor is integrated in the spark plug
connector, in the coil connector or in the spark plug (1-6 kΩ)
http://www.ngk-sparkplugs.jp/english/techinfo/qa/q08/index.html

SistemasAutomóveis
• Carbon ignition cables
• comprised of a fiberglass core with a silicone interior insulation
• interference suppression resistance results from the carbon cable
resistivity:
• 1 m cable ≈ 10 - 20 kΩ
https://www.ngk.de/en/products-technologies/ignition-cables/

SistemasAutomóveis
• Ignition cables with inductive resistance
• like carbon resistor ignition cables, these ignition cables have a
fiberglass core
• over the fiberglass there is a conductive and magnetic silicone layer,
around which a stainless steel wire is wound
• the cable resistance (reactive inductance)
grows with ignition frequency
(thus, with RPM)
• 1 m cable ≈ 2 - 8 kΩ
https://www.ngk.de/en/products-technologies/ignition-cables/

SistemasAutomóveis
Electromechanical ignition: cylindrical coil
https://www.ngk.de/en/technology-in-detail/ignition-coils/design-of-an-ignition-coil/design-of-a-cylinder-ignition-coil/
• Filled with oil
• …

SistemasAutomóveis
Electromechanical ignition, transistor-assisted
• An igniter alleviates the circuit breaker job
• primary current is several A and inductive!
• switching it off is a hard job (counter EMF peak between
breaker contacts)
• igniter drives the primary winding, reducing the control current (at
the circuit breaker) to tens of mA, non-inductive
• longer circuit breaker lifetime 
• no need for condenser in parallel 
• accumulation of dirt in the breaker contacts 
…http://what-when-how.com/automobile/electronic-ignition-automobile/
Basic
circuit

SistemasAutomóveis
Electromechanical ignition, with igniter and position sensor
• A position sensor substitutes the circuit breaker
• inductive (magnet + pickup coil)
• hall-effect (magnet + hall-effect sensor)
• optical (LED + photodiode or phototransistor)
• Ignition advance is still based on centrifugal and vacuum
mechanisms
• no ECU
…http://www.jetav8r.com/Vision/Ignition/CDI.html

SistemasAutomóveis
ECU + distributor with sensing and high-voltage distribution
• Distributor functionalities are restricted to
• sensing crankshaft position/speed
• distributing high-voltage to sparks
• (no mechanical advance)
• ECU functionalities
• receiving position
& speed
sensor data
• computing ignition
timing/duration
• sending ignition timing
signal to ignition coil
…http://www.teglerizer.com/fi/bem/Basics%20of%20engine%20management.htm

SistemasAutomóveis
ECU + distributor restricted to high-voltage distribution
• Distributor functionality is restricted to
• distributing high-voltage to sparks
• (just the distributor cap)
• Crankshaft position/speed sensor is located in the flywheel

SistemasAutomóveis
Distributorless, 1 coil per 2 cylinders (wasted spark)
• Distributorless = no distributor
• no mechanical parts, no friction, no electric arcs
• Each coil generates two simultaneous sparks
• one is wasted spark at the cylinder ending the exhaust stroke
http://pantera.infopop.cc/eve/forums/a/tpc/f/5650045562/m/1021035995

SistemasAutomóveis
• Wasted spark, dual tower ignition coil
http://www.tdotperformance.ca/mallory-140052-firestorm-ignition-coil-dual-tower-waste-spark.html

SistemasAutomóveis
• Wasted spark, but with integrated igniter & coil
• in previous example, igniter is in the ECU
http://www.maxxtuning.eu/products/engine-control-and-electronics/ignition/ignition_coils/ignition-coil-4-cyl-ws-with-integrated-amplifier

SistemasAutomóveis
Distributorless, 1 coil per cylinder
• Each cylinder/spark has a dedicated coil
• High-voltage wires (from coils to plugs) outside the engine
block

SistemasAutomóveis
Distributorless, coil-on-plug
• One coil per cylinder
• no high-voltage wiring
• but primary coil currents travel
outside engine block
https://www.ngk.de/en/technology-in-detail/ignition-coils/design-of-an-ignition-coil/design-of-a-pencil-coil-single-spark-coil-coil-on-plug/

SistemasAutomóveis
Distributorless, coil-on-plug (with integrated igniter)
A – igniter
B – ignition coil
IGt – ignition timing
IGf – ignition fail
1. primary coil
2. secondary coil
3. voltage protection circuit
4. current protection circuit
5. pulse generator
6. locking circuit
7. amplifier
8. control circuit
http://toyota-club.net/files/faq/04-11-20_faq_az_eng.htm
http://dbnst.nii.ac.jp/english/detail/1784

SistemasAutomóveis
Transistorized (inductive discharge) ignition
• TAC – Transistor-Assisted Contacts
• circuit breaker controls T1
• T1 controls T2 (power transistor)
• T2 drives primary current
http://what-when-how.com/automobile/electronic-ignition-automobile/

SistemasAutomóveis
Transistorized (inductive discharge) ignition
• Breakerless ignition
• Inductive pickup replaces circuit breaker

SistemasAutomóveis
Capacitive discharge electronic ignition
• A capacitor charges with a high voltage (300-500 V)
• Switching device (mechanical breaker or thyristor) triggers
the capacitor discharge over the primary winding
http://www.daytona-twintec.com/tech_ignition.html

SistemasAutomóveis
• Capacitor (C) (dis)charge is controlled by a Thyristor (Th)
• Thyristor (Th) ON  C discharges on primary winding

SistemasAutomóveis
• Charging voltage is achieved through unstable transistor pair
+ full-wave rectifier

SistemasAutomóveis
Capacitive vs. Transistorized ignition systems
• CDI  very short & very high V spike, constant with RPM
http://www.rotaryeng.net/Why-CDI.html

SistemasAutomóveis
• CDI  consumed energy grows linearly with RPM
• XL grows with frequency/RPM
• primary winding XL 
• XC decreases with frequency/RPM
• primary winding XL 
• charge capacitor XC 

SistemasAutomóveis
• Bottomline, CDI is preferred
• Higher voltage spike
• W proportional to RPM
• But, due to the very short voltage spike
• it requires extremely precise synchronization
• For distributor-based ignition systems, this was problematic
• it required constant tuning
• it was only used in high-performance/race vehicles
• This problem has been overcome with distributorless ignition
systems
• distribution timing is controlled by ECU
• no mechanical tuning is required

SistemasAutomóveis
Technology trends
• …
• …
https://www.newswire.com/press-release/car-alternator-market-global-technical-data-and-growth-2020

SistemasAutomóveis
Glossary (English/Portuguese)
• …

SistemasAutomóveis
Recommended references
• http://www.superchevy.com/how-to/additional-tech/1601-everything-you-wanted-to-
know-about-vacuum-advance-and-ignition-timing/
• http://www.worldphaco.net/uploads/CAPACITIVE_DISCHARGE_IGNITION_vs_MA
GNETIC_DISCHARGE_IGNITION..pdf/

Automotive Systems course (Module 09) - Ignition Systems for Internal Combustion Engines

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