Home SCIENCE The Differences Between Piston and Rotary Engines

The Differences Between Piston and Rotary Engines


Rotary engines have featured in some of the world’s coolest cars, but how do they compare to their piston-engined counterparts?A piston engine operates by forcing a tight fitting piston to move inside a cylinder with a high-pressure gas.

source/image: Car Throttle

Since this motion can only be along one axis, it must be converted to rotary motion to drive shafts, wheels, and the like, which is done with a piston rod connected to off-center portions of what we call a crankshaft.

You can see this demonstrated somewhat more simply by looking at the driver wheels on a steam locomotive, whose cylinder is usually driven by high pressure gas from both sides alternately, and whose “piston rod” extends all the way to a driven wheel’s perimeter.


A rotary engine uses a multiple lobed piston inside a chamber, with a high pressure gas exerting force tangential to its radius, eliminating the piston rod and crankshaft.