Translation guide
A reciprocating engine is a type of heat engine that uses one or more reciprocating pistons to convert pressure into rotating motion. In Japanese, the most common and natural term is レシプロエンジン, a direct loanword from English. The more technical term 往復動機関 is also used, especially in engineering contexts.
The learner wants to refer to a reciprocating engine in everyday or general technical conversation.
This is the most common and widely understood term. It is a loanword from English 'reciprocating engine' and is used in automotive, aviation, and general engineering contexts.
この飛行機はレシプロエンジンを搭載しています。
This aircraft is equipped with a reciprocating engine.
レシプロエンジンの仕組みを教えてください。
Please explain how a reciprocating engine works.
This is the native Japanese technical term. It is more formal and often used in engineering textbooks, patents, or academic papers. It literally means 'reciprocating motion engine'.
往復動機関は内燃機関の一種です。
A reciprocating engine is a type of internal combustion engine.
While 'piston engine' is technically a broader category, it is often used interchangeably with 'reciprocating engine' in casual contexts. However, note that not all piston engines are reciprocating (e.g., rotary engines have pistons but are not reciprocating). Use with caution.
Strictly speaking, a rotary engine is also a piston engine, so this term may cause confusion in precise technical discussions.
古い車にはピストンエンジンが使われています。
Old cars use piston engines.
The learner wants to emphasize the reciprocating mechanism as opposed to other engine types like jet or rotary.
In contexts where the distinction is important, you can use the loanword with the technical term in parentheses, or vice versa, to ensure clarity.
ジェットエンジンではなく、レシプロエンジン（往復動機関）を搭載した機体です。
It's an aircraft equipped with a reciprocating engine, not a jet engine.
In everyday conversation or popular science, レシプロエンジン is perfectly fine. In formal writing, patents, or academic papers, 往復動機関 is preferred. If you are unsure, レシプロエンジン is safer and more widely understood.
Do not attempt to translate 'reciprocating engine' word-for-word as 往復運動エンジン or similar. While understandable, it sounds unnatural. Stick to the established terms.