Ignition systems are used byheat engines to initiate combustion by igniting the fuel-air mixture. In aspark ignition versions of theinternal combustion engine (such as petrol engines), the ignition system creates a spark to ignite the fuel-air mixture just before eachcombustion stroke.Gas turbine engines androcket engines normally use an ignition system only during start-up.

Coil-on-plug ignition device

Distributor cap

Diesel engines usecompression ignition to ignite the fuel-air mixture using the heat of compression and therefore do not use an ignition system. They usually haveglowplugs that preheat thecombustion chamber to aid starting in cold weather.

Early cars usedignition magneto andtrembler coil systems, which were superseded byDistributor-based systems (first used in 1912). Electronic ignition systems (first used in 1968) became common towards the end of the 20th century, withcoil-on-plug versions of these systems becoming widespread since the 1990s.

Anignition magneto (also called ahigh-tension magneto) is an older type of ignition system used inspark-ignition engines (such as petrol engines). It uses amagneto and atransformer to make pulses of high voltage for the spark plugs. The older term "high-tension" means "high-voltage".

Used on many cars in the early 20th century, ignition magnetos were largely replaced by induction coil ignition systems. The use of ignition magnetos is now confined mainly to engines without a battery, for example in lawnmowers and chainsaws. It is also used in modern piston-engined aircraft^{[citation needed]} (even though a battery is present), to avoid the engine relying on an electrical system.

Asbatteries became more common in cars (due to the increased usage of electric starter motors), magneto systems were replaced by systems using aninduction coil. The 1886Benz Patent-Motorwagen and the 1908Ford Model T used atrembler coil ignition system, whereby the trembler interrupted the current through the coil and caused a rapid series of sparks during each firing. The trembler coil would be energized at an appropriate point in the engine cycle. In the Model T, the four-cylinder engine had a trembler coil for each cylinder.^[1]

An improved ignition system was invented byCharles Kettering at Delco in the United States and introduced in Cadillac's 1912 cars.^[2] The Kettering ignition system consisted of a single ignition coil, breaker points, acapacitor (to prevent the points from arcing at break) and adistributor (to direct the electricity from the ignition coil to the correct cylinder).^[3][4][5] The Kettering system became the primary ignition system for many years in the automotive industry^[6] due to its lower cost and relative simplicity.^{[citation needed]}

The first electronic ignition (acold cathode type) was tested in 1948 byDelco-Remy,^[7] whileLucas introduced atransistorized ignition in 1955, which was used onBRM andCoventry ClimaxFormula One engines in 1962.^[7] Theaftermarket began offering EI that year, with both the AutoLite Electric Transistor 201 andTung-Sol EI-4 (thyratron capacitive discharge) being available.^[8]Pontiac became the first automaker to offer an optional EI, the breakerless magnetic pulse-triggered Delcotronic, on some 1963 models; it was also available on someCorvettes.^[8] The first commercially available all solid-state (SCR) capacitive discharge ignition was manufactured by Hyland Electronics in Canada also in 1963.Ford fitted a FORD designed breakerless system on theLotus 25s entered atIndianapolis the next year, ran a fleet test in 1964, and began offering optional EI on some models in 1965. This electronic system was utilized on the GT40s campaigned by Shelby American and Holman and Moody. Robert C. Hogle, Ford Motor Company, presented the, "Mark II-GT Ignition and Electrical System", Publication #670068, at the SAE Congress, Detroit, Michigan, January 9–13, 1967. Beginning in 1958, Earl W. Meyer at Chrysler worked on EI, continuing until 1961 and resulting in use of EI on the company'sNASCARhemis in 1963 and 1964.^[8]

Prest-O-Lite's CD-65, which relied on capacitance discharge (CD), appeared in 1965, and had "an unprecedented 50,000 mile warranty."^[8] (This differs from the non-CD Prest-O-Lite system introduced onAMC products in 1972, and made standard equipment for the 1975 model year.)^[8] A similar CD unit was available from Delco in 1966,^[7] which was optional onOldsmobile, Pontiac, andGMC vehicles in the 1967 model year.^[8] Also in 1967,Motorola debuted their breakerless CD system.^[8] The most famous aftermarket electronic ignition which debuted in 1965, was the Delta Mark 10 capacitive discharge ignition, which was sold assembled or as a kit.

TheFiat Dino was the first production car to come standard with EI in 1968, followed by theJaguar XJ Series 1^[9] in 1971, Chrysler (after a 1971 trial) in 1973 and by Ford and GM in 1975.^[8]

In 1967, Prest-O-Lite made a "Black Box" ignition amplifier, intended to take the load off the distributor's breaker points during high rpm runs, which was used byDodge andPlymouth on their factory Super StockCoronet andBelvederedrag racers.^[8] This amplifier was installed on the interior side of the cars' firewall, and had a duct which provided outside air to cool the unit.^{[citation needed]} The rest of the system (distributor and spark plugs) remains as for the mechanical system. The lack of moving parts compared with the mechanical system leads to greater reliability and longer service intervals.

A variation coil-on-plug ignition has each coil handle two plugs, on cylinders which are 360 degrees out of phase (and therefore reachtop dead center (TDC) at the same time); in the four-cycle engine this means that one plug will be sparking during the end of the exhaust stroke while the other fires at the usual time, a so-called "wasted spark" arrangement which has no drawbacks apart from faster spark plug erosion; the paired cylinders are 1/4 and 2/3 on four cylinder arrangements, 1/4, 6/3, 2/5 on six cylinder engines and 6/7, 4/1, 8/3 and 2/5 on V8 engines.^[10] Other systems do away with the distributor as a timing apparatus and use a magneticcrank angle sensor mounted on the crankshaft to trigger the ignition at the proper time.

Modern automotive engines use anengine control unit (ECU), which is a single device that controls various engine functions including the ignition system and thefuel injection.^[11][12] This contrasts earlier engines, where the fuel injection and ignition were operated as separate systems.

Gas turbine engines (including jet engines) usecapacitor discharge ignition,^{[citation needed]} however the ignition system is only used at startup or when thecombustor(s) flame goes out.

Theignition system in a rocket engine is critical to avoiding ahard start orexplosion. Rockets often employpyrotechnic devices that place flames across the face of theinjector plate, or, alternatively,hypergolic propellants that ignite spontaneously on contact with each other.^{[citation needed]}

• Electromagnetism
• Faraday's law of induction
• History of the internal combustion engine