Spark plug
A spark plug (also, very rarely nowadays, in
British English: a sparking plug) is an elec-
trical device that fits into the cylinder head of
some internal combustion engines and ig-
nites compressed fuels such as, aerosol gas-
oline, Ethanol, and Liquefied petroleum gas
by means of an electric spark. Spark plugs
have an insulated center electrode which is
connected by a heavily insulated wire to an
ignition coil or magneto circuit on the out-
side, forming, with a grounded terminal on
the base of the plug, a spark gap inside the
cylinder.
Early patents for spark plugs included
those by Nikola Tesla (in U.S. Patent 609,250
for an ignition timing system, 1898), Richard
Simms (GB 24859/1898, 1898) and Robert
Bosch (GB 26907/1898). Some historians
have reported that Edmond Berger invented
an early spark plug on February 2, 1839[1].
Karl Benz is also credited with the invention.
But only the invention of the first commer-
cially viable high-voltage spark plug as part
of a magneto-based ignition system by Robert
Bosch’s engineer Gottlob Honold in 1902
made possible the development of the intern-
al combustion engine.
Reciprocating
internal combustion en-
gines can be divided into spark-ignition en-
gines, which require spark plugs to begin
combustion, and compression-ignition en-
gines (diesel engines), which compress the
air and then inject diesel fuel into the heated
compressed air mixture where it autoignites.
Compression-ignition engines may use glow
plugs to improve cold start characteristics.
Spark plugs may also be used in other ap-
plications such as furnaces where a combust-
ible mixture should be ignited. In this case,
they are sometimes referred to as flame
igniters.
Operation
The plug is connected to the high voltage
generated by an ignition coil or magneto. As
the electrons flow from the coil, a voltage dif-
ference develops between the center elec-
trode and side electrode. No current can flow
because the fuel and air in the gap is an
insulator, but as the voltage rises further, it
begins to ch