Single Cylinder.

Twin Cylinder.

In-Line.

V Pattern (eg V-8).

Delta (Δ).

W Pattern.

X Pattern.

Y Pattern.

+ Pattern.

Outward Facing Opposed Piston (Boxer).

Inward Facing Opposed Piston (O-P).

Radial (Single,Double,Triple,Quad Banks).

Radial Rotary. (Found almost exclusively in WWI vintage aircraft such as the Fokker TriPlane flown by the Red Baron plus some motorcycles)

Rotary.
^ Jet Engine.

Wankel.