precombustion chamber
noun
: an auxiliary space in which combustible gases are ignited and combustion started ahead of the main combustion chamber of a jet or gas engine
The glow plug is an electrically operated device that protrudes into the precombustion chamber. When energized the glow plug tip heats to a dull red. The swirling, highly compressed air-fuel mixture is heated by the glow plug tip. 
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Word History
First Known Use
1914, in the meaning defined above