Editing Spark plug (section)

{{short description|Device that generates sparks in internal combustion engines}}
{{Other uses}}

[[File:sparkplug.jpg|right|thumb|Spark plug with single side electrode]] [[File:Spark-plug01.jpeg|thumb|right|An [[electric spark]] on the spark plug]] A '''spark plug''' (sometimes, in [[British English]], a '''sparking plug''',<ref>{{cite book|title=The Bosch book of the Motor Car, Its evolution and engineering development|publisher=St. Martin's Press|year=1975|lccn=75-39516|oclc=2175044|pages=206–207}}</ref> and, colloquially, a '''plug''') is a device for delivering [[electric current]] from an [[ignition system]] to the [[combustion chamber]] of a [[spark-ignition engine]] to ignite the compressed fuel/air mixture by an [[electric spark]], while containing combustion pressure within the engine. A spark plug has a metal [[Screw thread|threaded]] shell, electrically isolated from a central [[electrode]] by a [[ceramic]] insulator. The central electrode, which may contain a [[resistor]], is connected by a heavily [[Insulator (electricity)|insulated]] wire to the output terminal of an [[ignition coil]] or [[ignition magneto|magneto]]. The spark plug's metal shell is screwed into the engine's [[cylinder head]] and thus electrically [[Ground (electricity)|grounded]]. The central electrode protrudes through the porcelain insulator into the [[combustion chamber]], forming one or more [[spark gap]]s between the inner end of the central electrode and usually one or more protuberances or structures attached to the inner end of the threaded shell and designated the ''side'', ''earth'', or ''ground'' electrode(s).

Spark plugs may also be used for other purposes; in [[Saab Direct Ignition]] when they are not firing, spark plugs are used to measure ionization in the cylinders – this ionic current measurement is used to replace the ordinary cam phase sensor, knock sensor and misfire measurement function.<ref>{{cite journal |last1=Lagana |first1=A. A. M. |last2=Lima |first2=L. L. |last3=Justo |first3=J. F. |last4=Arruda |first4=B. A. |last5=Santos |first5=M. M. D. |title=Identification of combustion and detonation in spark ignition engines using ion current signal |journal=Fuel |date=2018 |volume=227 |page=469-477 |doi=10.1016/j.fuel.2018.04.080|bibcode=2018Fuel..227..469L |s2cid=104060623 }}</ref> Spark plugs may also be used in other applications such as furnaces wherein a combustible fuel/air mixture must be ignited. In this case, they are sometimes referred to as '''flame igniters'''.{{Citation needed|date=December 2011}}