Electrics & Electronics: Ignition Systems

Ignition systems	Basic ignition	The ignition system is the means by which the fuel is ignited in the gasoline/petrol engines and allows the engine to run.
	Ignition principles	When the air/fuel mixture in the cylinders is richer or leaner than the ideal ratio of 14.7 to 1, a higher level of electrical energy is required to ignite it.
	Ignition components	The primary components of the automotive ignition system are: Battery; Spark plug; Engine timing; Distributor; Spark intensifiers; High tension (HT) leads.
	Vacuum & centrifugal units	The timing of the spark is critical to the operation of the engine. For any given engine speed the correct spark timing varies according to a number of factors.
	Plug firing voltage	The plug firing voltage needed to establish the spark is higher than the spark voltage needed to sustain the spark.
	Faraday's law	A practical automotive example of Faradays law is contained in automotive ignition systems which use an induction coil, to step up the nominal battery voltage of 12 volts to the voltage needed to bridge the gap across the spark plug electrodes.

Contact breaker ignition	Contact breaker system	Contact breaker ignition systems provide a simple means of establishing and interrupting the current flowing in the primary ignition circuit.
	Primary & secondary windings	The secondary winding, with about 100 times as many turns as the primary winding, can have an induced voltage about 100 times greater than the primary induced voltage. However, the actual firing voltage depends on many factors, including whether the engine is idling, or operating under load.
	The ballast resistor coil	A ballast resistor coil is designed to operate at approximately 7.5 volts and still provide the step-up transformer action needed, for secondary circuit operation.
	Dwell angle	The dwell angle in contact breaker systems is designed to allow sufficient time for current to flow through the primary winding and establish the necessary magnetic field.
	Spark timing	The ignition timing point can be advanced by a centrifugal type mechanism according to engine speed and by a vacuum operated mechanism, according to load.

Contact breaker components	Battery power source	The battery is used to supply a voltage to the system components.
	Ballast resistor	A ballast resistor is used to reduce the voltage to the ignition coil during normal running conditions.
	Ignition coil	A standard ignition coil has a secondary winding with 15000 to 30000 turns of very thin enamelled copper wire, wound around a laminated iron core. The primary winding with a few hundred turns of heavier copper wire is wound on the outside of the secondary.
	Ignition switches	The ignition switch has more functions than simply starting the vehicle. The common points on an ignition switch include: Lock; Off (not on all vehicles); Accessories; On; Start.
	Contact breaker	The contact breaker is a mechanically operated electrical switch in the primary ignition circuit. The contacts open and close automatically with engine rotation.
	Capacitor/condenser	A capacitor is used to assist in the rapid collapse of the magnetic field in the ignition coil.
	Distributors	The distributor in a contact breaker system distributes the high tension voltage surges to the spark plugs in the correct sequence and at the correct instant in time in the engine cycle.
	Distributor types	The distributor uses one of several different systems to create the timing of the ignition spark.
	High-tension leads	High-tension leads are used to transmit the high voltage required by the spark plugs to ignite the fuel air/mixture in the cylinders.
	Spark plugs	Spark plugs are identified by thread size or diameter the reach or length of the thread and by the heat range.
	Spark plug components	Most passenger car spark plug wires snap onto the terminal of the plug, but some wires have spade connectors which are fastened onto the plug under a nut.
	Advance & retard mechanisms	Ignition timing can be varied by a centrifugal advance mechanism, according to engine speed and by a vacuum advance unit according to engine load.

Electronic systems & components	Induction	In electronic ignition systems the contact breaker is eliminated and the switching or triggering of the primary circuit is carried out electronically.
	Inductive system operation	Low inductive ignition coils have a low number of primary turns and a low primary resistance. The ignition module limits maximum primary current to a safe value.
	Induction wiring	Inductive type pulse generators use the principles of electro-magnetic induction to produce an AC voltage. This can be used to signal an ignition module to turn the primary circuit ‘on’ and ‘off’.
	Hall effect sensors	A Hall effect sensor provides voltage pulses that are generated by alternately shielding the sensor from a magnetic field, then exposing it.
	Hall effect operation	Voltage pulses from a Hall generator can be used by an ignition module to control the operation of the primary circuit.
	Optical type sensors	Optical type sensors inside the distributor can be used to sense crank angle position. This information can be used by an engine management electronic control unit, to control ignition system operation.

Distributorless systems	Distributorless ignition systems	In a waste spark system, each spark plug is fired by a high voltage impulse from an ignition coil shared with a companion cylinder.
	Insulated coils	In systems which employ an individual coil for each cylinder, the coils can be placed in an insulated cassette with each coil connected directly to its spark plug.
	Distributorless ignition system timing	The lack of moving parts compared with the mechanical system leads to greater reliability and longer service intervals. For older cars, it is usually possible to retrofit an EI system in place of the mechanical one.

Ignition procedures	Checking ignition timing	It is not necessary for the technician to alter the timing from the manufacturer's specifications. In some cases, serious damage could result.
	Checking & changing a spark plug	The leads which come from the distributor must be removed from the spark plug in such a way that you can identify which cylinder they belong to.
	Removing & replacing contact points	The contact breaker points are normally found in the base of the distributor below the distributor cap and the rotor.