Squish (piston engine)

Squish is an effect in internal combustion engines which creates sudden turbulence of the air-fuel mixture as the piston approaches top dead centre (TDC).

[1][2] In an engine designed to use the squish effect, at top dead centre the piston crown comes very close (typically less than 1 mm[2]) to the cylinder head.

Squish effect may be found in any fuel type internal combustion piston engine.

Turbulence in the combustion chamber due to this squish helps with air-fuel mixing, cylinder wall heat transfer, thermal efficiency, and overall engine performance.

This is the most common way to create a squish piston engine because it is the smallest and easiest part to manufacture.

To promote turbulence and mixing of the air–fuel mixture, the piston crown must have a recess parallel to the angle that the fuel is injected.