The rotor is shaped by the space it has to seal
A rotary engine’s “triangle” is a three-sided rotor with gently curved faces, not a sharp-cornered triangle. It moves inside a specially shaped housing, while seals at its three tips keep neighboring working spaces apart. The rotor’s shape lets those spaces change size as it turns: a chamber grows to draw in air and fuel, then shrinks to compress the mixture and later expand the hot gases.
A round rotor would not create this repeating pattern of sealed, changing chambers in the same housing. The three-sided form makes the geometry work: each face helps bound a chamber, and the moving tips trace the housing closely enough for the engine to operate.
One rotor, three overlapping cycles
The chambers are spaced around the rotor, so they are at different points in the process at the same time. While one is taking in a fresh mixture, another is compressing its charge and another is sending expanding gas through the exhaust. Burning fuel pushes on a rotor face; the rotor’s off-center connection turns that push into rotation of the output shaft.
That arrangement avoids the repeated up-and-down motion of pistons and gives the engine a compact, smooth-running layout. But the geometry also makes sealing and combustion difficult: the tip seals must hold pressure as they slide along the housing, and the long, narrow combustion space can leave fuel harder to burn completely. The triangle is therefore not a stylistic choice—it is the moving boundary that makes the engine’s compact cycle possible, along with its distinctive engineering compromises.
