Editing Compression (physics) (section)

== In engines ==

=== Internal combustion engines ===
In [[internal combustion engine]]s the explosive mixture gets compressed before it is ignited; the compression improves the efficiency of the engine. In the [[Otto cycle]], for instance, the second stroke of the piston effects the compression of the charge which has been drawn into the cylinder by the first forward stroke.<ref>{{Cite book |last=Heywood |first=John |url=https://books.google.com/books?id=OmJUDwAAQBAJ |title=Internal Combustion Engine Fundamentals 2E |date=2018-05-01 |publisher=McGraw Hill Professional |isbn=978-1-260-11611-3 |language=en}}</ref>

=== Steam engines ===
The term is applied to the arrangement by which the exhaust valve of a [[steam engine]] is made to close, shutting a portion of the exhaust steam in the [[cylinder (engine)|cylinder]], before the stroke of the piston is quite complete. This steam being compressed as the stroke is completed, a cushion is formed against which the [[piston]] does work while its velocity is being rapidly reduced, and thus the stresses in the mechanism due to the inertia of the reciprocating parts are lessened.<ref name="Wiser">{{cite book|title=Energy resources: occurrence, production, conversion, use|last= Wiser |first= Wendell H.|year= 2000|publisher= Birkhäuser|isbn= 978-0-387-98744-6|page= 190|url= https://books.google.com/books?id=UmMx9ixu90kC&dq=steam&pg=PA190}}</ref> This compression, moreover, obviates the shock which would otherwise be caused by the admission of the fresh steam for the return stroke.