Reciprocating engine – also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion.

Piston (animation) – This mechanism is used to convert between rotary motion and reciprocating motion, it works either way. Notice how the speed of the piston changes. The piston starts from one end, and increases its speed. It reaches maximum speed in the middle of its travel then gradually slows down until it reaches the end of its travel.

The main types of piston engines

  • internal combustion engine, used extensively in motor vehicles
  • steam engine, the mainstay of the Industrial Revolution
  • special application Stirling engine
Simplified representation of a double acting cylinder.

Reciprocating engine cylinders are often classified by whether they are single or double acting, depending on how the working fluid acts on the piston.

  • Single acting cylinder
  • Double acting cylinder

That’s engineering

  • compression – raising the pressure and reducing the volume of gases
  • compression ratio of an engine – the ratio of the volume of space in a cylinder when the piston is at the top of the stroke to when it is at the bottom of the stroke. A higher compression ratio generally means higher engine efficiency.

Engineering ideas

  • combustion, internal combustion, reciprocating pistons, pressure, rotating motion, cylinder, compression ratio, volume, stroke, efficiency