Basic Working Of A Piston Engine

Piston - Aviatorsbuzz

An aircraft’s piston engine, also commonly referred to as a reciprocating engine, is an internal combustion engine that uses one or more reciprocating pistons to convert pressure into a rotational motion. The aircraft piston engine operates on the same principles as the engines found in most automobiles. Turbochargers and, less commonly, superchargers can be added to piston engines to improve performance.

On what principle does the Piston Engine work?

The piston engine works on the principle of Otto cycle. An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine.

Various properties of a Piston Engine

  • It is a constant volume engine
  • Piston engine converts reciprocating motion into rotatory motion
  • It follows an intermittent cycle
  • It uses high octane fuel

Before learning the operation of a Piston Engine, let us understand the basic terminology of a Piston Engine.

Piston - Aviatorsbuzz
Piston - Aviatorsbuzz
Source: Encyclopedia Britannica
  1. Stroke: It is defined as the linear distance that the piston moves in a cylinder ( from TDC to BDC)
  2. TDC (Top Dead Centre) – when the piston is at the top of the stroke
  3. BDC( Bottom Dead Centre) – when the piston is at the bottom of the stroke

The piston is connected to a crankshaft, when the piston moves from TDC to BDC – the crankshaft rotates 180 degrees.

There are total 4 strokes in the Otto cycle – which makes the crankshaft rotate (180 × 4) = 720 degrees.

Operation of the Otto Cycle:
Piston - Aviatorsbuzz
Source: Encyclopedia Britannica
There are 4 strokes in the Otto cycle:
  • Induction Stroke – The inlet valve opens, permitting flow of gas from atmosphere through the carburettor into the cylinder. The exhaust valve is closed during this process.
  • Compression Stroke – The piston moves upwards, inlet valve closes and the gas is compressed. By squeezing the gas into a smaller space the pressure exerted will proportionally be increased.
  • Power Stroke – Before the piston reaches TDC on the compression stroke the gas is ignited by a spark. Piston is pushed down by the momentum.
  • Exhaust Stroke – Finally the piston moves upwards forcing the remaining gases out of the cylinder. The exhaust valve is left open after TDC to permit the gases to scavenge the cylinder as completely as possible.

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