In geometry it is an exact half of a sphere. It also refers to half of the Earth, such as the "Northern Hemisphere" (that part of the Earth north of the equator), or "Western Hemisphere" (the half of the Earth west of a line running from the North Pole through England to the South Pole, includes the Americas) Sphere.
A hemispherical combustion chamber is a type of combustion chamber in a reciprocating internal combustion engine with a domed cylinder head. The hemispherical shape provides a number of advantages over a reverse-flow cylinder head but comes up short in others, particularly in carbureted engines.
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