Spark plug

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Several sizes of spark plug (electrodes at the bottom)
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Spark plug operation (the red/yellow star near the end of phase 2) in a four-stroke engine

A spark plug is an electrical device used in an internal combustion engine to produce a spark which ignites the air-fuel mixture in the combustion chamber. As part of the engine's ignition system, the spark plug receives high-voltage electricity (generated by an ignition coil in modern engines and transmitted via a spark plug wire) which it uses to generate a spark in the small gap between the positive and negative electrodes. The timing of the spark is a key factor in the engine's behaviour, and the spark plug usually operates shortly before the combustion stroke commences.

Contents

The spark plug was invented in 1860, however its use only became widespread after the invention of the ignition magneto in 1902. Diesel engines use compression ignition (instead of spark ignition), therefore they do not normally use spark plugs.

Design

The main elements of a spark plug are the shell, insulator, central electrode and side electrode (also known as "ground strap"). The main part of the insulator is typically made from sintered alumina (Al2O3), a hard ceramic material with high dielectric strength. [1] [2] [3] In marine engines, the shell of the spark plug is often a double-dipped, zinc-chromate coated metal. [4]

A spark plug passes through the wall of the combustion chamber, therefore it must also form part of the seal for the high-pressure gases within the combustion chamber.

Electrodes

Sparkplug.jpg
Design with one side electrode
Sparkplug3.jpg
Design with two side electrodes

The central electrode is connected to the terminal through an internal wire. The central electrode setup as the cathode from where the electrons are ejected. [5] This is because the central electrode is usually the hottest part of the plug, and thermionic emission principles mean it is easier to eject electrons from a hotter surface. [6] The sharp tip of the central electrode also increases the electrical field strength, thus increasing the emission of electrons. [6] The side electrode (which is colder and blunter) requires up to 45 percent higher voltage, [6] therefore only wasted spark systems use the side electrode as the cathode. [7]

The side electrode is made from high-nickel steel and is welded or hot forged to the side of the metal shell.[ citation needed ]

Spark plugs can contain up to four side electrodes surrounding the central electrode. Multiple side electrodes generally provide longer life, as when the spark gap widens due to electric discharge wear, the spark moves to another closer ground electrode.[ citation needed ] The disadvantage of multiple side electrodes is that a shielding effect can occur for each electrode, leading to a less efficient burn and increased fuel consumption.[ citation needed ]

Gap size

Spark plug gauge Spark plug gauge.jpg
Spark plug gauge

The distance between the tip of the spark plug and the central electrode is called the "spark plug gap" and is a key factor in the function of a spark plug. Spark plug gaps for car engines are typically 0.6 to 1.8 mm (0.024 to 0.071 in).[ citation needed ] Modern engines (using solid-state ignition systems and electronic fuel injection) typically use larger gaps than older engines that use breaker point distributors and carburetors.

Smaller plug gap sizes usually are more reliable at producing a spark, however the spark may be too weak to ignite the fuel-air mixture. A larger plug gap size will produce a stronger spark, however the spark might not always be produced (such as at high RPM). Gap adjustment is not recommended for iridium and platinum spark plugs, because there is a risk of damaging a metal disk welded to the electrode. [8]

Wasted spark applications

Wasted spark systems place a greater strain upon spark plugs since they alternately fire electrons in both directions (from the ground electrode to the central electrode, not just from the central electrode to the ground electrode). As a result, vehicles with such a system should have precious metals on both electrodes, not just on the central electrode, in order to increase service replacement intervals since they wear down the metal more quickly in both directions, not just one. [9]

Indexing of plugs

"Indexing" of plugs upon installation involves installing the spark plug so that the open area of the gap (i.e. the side not shrouded by the side electrode), faces the center of the combustion chamber. This is claimed to improve ignition by maximising the exposure of the fuel-air mixture to the spark in every cylinder.

Indexing is accomplished by either:

Heat range

Longer insulator tip (in gray) for the "hotter" spark plug Spark plug heat.svg
Longer insulator tip (in gray) for the "hotter" spark plug

An important factor for a spark plug is the temperature that the tip is designed to withstand, called the heat range. Typical heat ranges for passenger car engines are usually between 500 and 850 °C (932 and 1,562 °F). [10] [11] A hotter spark plug has more insulation between itself and the cylinder head, causing less heat to be dissipated from the spark plug and therefore the spark plug remaining hotter. [12] Temperatures higher than 450 °C (842 °F) are needed to prevent carbon build-up on the spark plug, while temperatures over 800 °C (1,470 °F) can cause overheating of the plug. [13]

Switching to a higher heat range is sometimes used to compensate for fuel delivery or oil consumption problems, however this increases the risk of pre-ignition. [14]

History

Belgian-French engineer Étienne Lenoir is generally credited with the invention of the spark plug in 1860, due to its use in the early Lenoir gas engine. [15] [16] [17] [18]

Several patents relating to electrical ignition systems were filed in the late 1890s, including from Serbian engineer Nikola Tesla, [19] British engineer Frederick Richard Simms [20] and German engineer Robert Bosch. [21] The use of high-voltage spark plugs in commercial viable engines was only made possible after 1902 however, due to the invention of magneto-based ignition systems by Bosch engineer Gottlob Honold. Early manufacturers of spark plugs included American company Champion, [22] British company Lodge brothers [23] and London-based KLG (who pioneed the use of mica as an insulator).

During the 1930s, American geologist Helen Blair Bartlett developed an alumina ceramic-based insulator for the spark plug. [24]

Polonium spark plugs were marketed by Firestone from 1940 to 1953. While the amount of radiation from the plugs was minuscule and not a threat to the consumer, the benefits of such plugs quickly diminished after approximately a month because of polonium's short half-life, and because buildup on the conductors would block the radiation that improved engine performance. The premise behind the polonium spark plug, as well as Alfred Matthew Hubbard's prototype radium plug that preceded it, was that the radiation would improve ionization of the fuel in the cylinder and thus allow the plug to fire more quickly and efficiently. [25] [26]

See also

Related Research Articles

A stratified charge engine describes a certain type of internal combustion engine, usually spark ignition (SI) engine that can be used in trucks, automobiles, portable and stationary equipment. The term "stratified charge" refers to the working fluids and fuel vapors entering the cylinder. Usually the fuel is injected into the cylinder or enters as a fuel rich vapor where a spark or other means are used to initiate ignition where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher compression ratios without "knock," and leaner air/fuel ratio than in conventional internal combustion engines.

<span class="mw-page-title-main">Four-stroke engine</span> Internal combustion engine type

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum in the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.

In spark-ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel–air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

<span class="mw-page-title-main">Spark gap</span> Two conducting electrodes separated in order to allow an electric spark to pass between

A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound, light, and heat.

Pre-ignition in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.

<span class="mw-page-title-main">Ignition system</span> Electric spark system to ignite a fuel-air mixture

Ignition systems are used by heat engines to initiate combustion by igniting the fuel-air mixture. In a spark ignition versions of the internal combustion engine, the ignition system creates a spark to ignite the fuel-air mixture just before each combustion stroke. Gas turbine engines and rocket engines normally use an ignition system only during start-up.

<span class="mw-page-title-main">Contact breaker</span>

A contact breaker is a type of electrical switch, found in the ignition systems of spark-ignition internal combustion engines. The switch is automatically operated by a cam driven by the engine. The timing of operation of the switch is set so that a spark is produced at the right time to ignite the compressed air/fuel mixture in the cylinder of the engine. A mechanism may be provided to slightly adjust timing to allow for varying load on the engine. Since these contacts operate frequently, they are subject to wear, causing erratic ignition of the engine. More recent engines use electronic means to trigger the spark, which eliminated contact wear and allows computer control of ignition timing.

<span class="mw-page-title-main">Electrical breakdown</span> Conduction of electricity through an insulator under sufficiently high voltage

In electronics, electrical breakdown or dielectric breakdown is a process that occurs when an electrically insulating material, subjected to a high enough voltage, suddenly becomes a conductor and current flows through it. All insulating materials undergo breakdown when the electric field caused by an applied voltage exceeds the material's dielectric strength. The voltage at which a given insulating object becomes conductive is called its breakdown voltage and, in addition to its dielectric strength, depends on its size and shape, and the location on the object at which the voltage is applied. Under sufficient voltage, electrical breakdown can occur within solids, liquids, or gases. However, the specific breakdown mechanisms are different for each kind of dielectric medium.

Dieseling or engine run-on is a condition that can occur in spark-plug-ignited, gasoline-powered internal combustion engines, whereby the engine keeps running for a short period after being turned off, drawing fuel through the carburetor, into the engine and igniting it without a spark.

<span class="mw-page-title-main">Otto engine</span> Large stationary single-cylinder internal combustion four-stroke engine

The Otto engine was a large stationary single-cylinder internal combustion four-stroke engine designed by the German Nicolaus Otto. It was a low-RPM machine, and only fired every other stroke due to the Otto cycle, also designed by Otto.

<span class="mw-page-title-main">Ignition coil</span> Automobile fuel ignition system component

An ignition coil is used in the ignition system of a spark-ignition engine to transform the battery voltage to the much higher voltages required to operate the spark plug(s). The spark plugs then use this burst of high-voltage electricity to ignite the air-fuel mixture.

Homogeneous Charge Compression Ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction produces heat that can be transformed into work in a heat engine.

<span class="mw-page-title-main">Electric spark</span> Abrupt electrical discharge through an ionised channel

An electric spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures. Michael Faraday described this phenomenon as "the beautiful flash of light attending the discharge of common electricity".

<span class="mw-page-title-main">Oil burner</span>

An oil burner is a heating device which burns #1, #2 and #6 heating oils, diesel fuel or other similar fuels. In the United States, ultra low sulfur #2 diesel is the common fuel used. It is dyed red to show that it is road-tax exempt. In most markets of the United States, heating oil is the same specification of fuel as on-road un-dyed diesel.

<span class="mw-page-title-main">Ignition timing</span> Timing of the release of a spark in a combustion engine

In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.

<span class="mw-page-title-main">Model engine</span>

A model engine is a small internal combustion engine typically used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight, control line aircraft, or ground-running tether car model.

<span class="mw-page-title-main">Glow plug (model engine)</span>

A glow plug engine, or glow engine, is a type of small internal combustion engine typically used in model aircraft, model cars and similar applications. The ignition is accomplished by a combination of heating from compression, heating from a glow plug and the catalytic effect of the platinum within the glow plug on the methanol within the fuel.

Trionic T5.5 is an engine management system in the Saab Trionic range. It controls ignition, fuel injection and turbo boost pressure. The system was introduced in the 1993 Saab 9000 2.3 Turbo with B234L and B234R engine.

The Delco ignition system, also known as the Kettering ignition system, points and condenser ignition or breaker point ignition, is a type of inductive discharge ignition system invented by Charles F. Kettering. It was first sold commercially on the 1912 Cadillac and was manufactured by Delco. Over time, it was used extensively by all automobile and truck manufacturers on spark ignition, i.e., gasoline engines. Today it is still widely used in coil-on-plug, coil-near-plug and in coil packs in distributorless ignitions. An alternative system used in automobiles is capacitor discharge ignition, primarily found now as aftermarket upgrade systems. Electronic ignition was a common term for Kettering inductive ignition with the points replaced with an electronic switch such as a transistor.

<span class="mw-page-title-main">Internal combustion engine</span> Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.

References

  1. ↑ "Denso's "Basic Knowledge" page". Globaldenso.com. Retrieved 2011-09-17.
  2. ↑ The Bosch Automotive Handbook, 8th Edition, Bentley Publishers, copyright May 2011, ISBN   978-0-8376-1686-5, pp 581–585.
  3. ↑ Air Commodore F. R. Banks (1978). I Kept No Diary. Airlife. p. 113. ISBN   0-9504543-9-7.
  4. ↑ "Marine Spark Plug Savvy". MarineEngineDigest.com. 29 April 2012. Retrieved 1 December 2012.
  5. ↑ V.A.W., Hillier (1991). "74: The ignition system". Fundamentals of Motor Vehicle Technology (4th ed.). Stanley Thornes. p. 450. ISBN   0-7487-05317.
  6. 1 2 3 International Harvester, Truck Service Manual TM 5-4210-230-14&P-1 - Electrical - Ignition Coils and Condensers, CTS-2013-E p. 5 (PDF page 545)
  7. ↑ NGK, Wasted Spark Ignition
  8. ↑ "How to Choose Proper Spark Plugs for Your Engine". VIN Sonar | help - Automotive Guides and Online Tools. 2022-01-27. Retrieved 2022-05-12.
  9. ↑ See p. 824 of the 2015 Champion Master Catalog. http://www.fme-cat.com/catalogs.aspx Archived 2018-06-01 at the Wayback Machine
  10. ↑ "Spark Plug Heat Range". www.enginebuildermag.com. 20 May 2011. Retrieved 12 March 2023.
  11. ↑ "Guide to Understanding Spark Plug Heat Ranges". www.carfromjapan.com. 25 June 2020. Retrieved 12 March 2023.
  12. ↑ "10 factors that influence correct spark plug heat range for street and racing". www.motortrend.com. 9 July 2020. Retrieved 12 March 2023.
  13. ↑ "Spark Plug Basics". NGK Spark Plugs. 9 May 2019. Retrieved 12 March 2023.
  14. ↑ "Understanding Spark Plug Heat Range". NGK Spark Plugs. 9 May 2019. Retrieved 12 March 2023.
  15. ↑ "Madehow.com's "How a spark plug is made" page". madehow.com.
  16. ↑ "1886 Gas Engine patent #345,596 for Ettienne Jean Joseph Lenoir". Figure 6.
  17. ↑ Denton, Tom (2013). "Development of the automobile electrical system". Automobile Electrical and Electronic Systems (revised ed.). Routledge. p. 6. ISBN   9781136073823 . Retrieved 2018-08-20. 1860[:] Lenoir produced the first spark-plug.
  18. ↑ Donnelly, Jim (January 2006). "Albert Champion". www.hemmings.com. Retrieved February 6, 2019.
  19. ↑ Tesla, Nikola (16 August 1898). "Electrical Igniter For Gas-Engines" . Retrieved 13 March 2023.
  20. ↑ "Who Invented The Spark Plug?". www.drivespark.com. 8 January 2022. Retrieved 5 April 2023.
  21. ↑ "1886-1905: From first workshop to factory". Bosch Global. Retrieved 5 April 2023.
  22. ↑ "A.S.E.C.C.'s History of Spark Plugs". www.asecc.com. Archived from the original on 4 March 2016. Retrieved 17 September 2011.
  23. ↑ "Lodge Plugs". Gracesguide.co.uk. 2011-08-30. Retrieved 2011-09-17.
  24. ↑ "Women in Transportation - Automobile Inventions". wwwcf.fhwa.dot.gov. Archived from the original on 2016-06-23.
  25. ↑ "Radioactive spark plugs". Oak Ridge Associated Universities. January 20, 1999. Retrieved October 7, 2021.
  26. ↑ Pittman, Cassandra (February 3, 2017). "Polonium". The Instrumentation Center. University of Toledo. Retrieved August 23, 2018.
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