The rotor turns once for every three turns of the eccentric shaft â but it has three faces, so each rotor still fires once per shaft revolution: a two-stroke firing rate with nothing reciprocating.
Each of the rotor’s three faces runs a complete four-phase cycle every rotor revolution, so one chamber’s cycle spans 1080° of shaft rather than a piston engine’s 720°. Three faces sharing a 3:1 reduction cancel exactly, which is why a single-rotor engine fires as often as a two-stroke single. The housing is an epitrochoid because that is precisely the curve the rotor’s apexes trace at that ratio â it is the geometry that lets three chambers stay sealed from one another with no valves anywhere.
The firing RATE matching a two-stroke says nothing about the power: chamber volume, breathing and sealing all differ. And the same geometry that removes the valves gives a long, thin combustion chamber and enormous overlapping ports, which is most of why the design is thirsty and hard to make clean.
Estimate with the rule, then check it against the calculator that models it properly.
Open Engine Cycle Simulator →The rotor turns once for every three turns of the eccentric shaft â but it has three faces, so each rotor still fires once per shaft revolution: a two-stroke firing rate with nothing reciprocating. Each of the rotor’s three faces runs a complete four-phase cycle every rotor revolution, so one chamber’s cycle spans 1080° of shaft rather than a piston engine’s 720°.