A four-chamber Otto cycle rotary engine, the Szorenyi Rotary Engine, has been invented and developed by the Rotary Engine Development Agency (REDA) in Melbourne, Australia. The engine concept has been awarded a U.S. Patent (Number 6,718,938 B2).A prototype engine has been constructed and a successful proof-of-concept engine test was achieved in 2008.The stator of the Szorenyi engine is a similar shape to a Wankel engine. However, the geometric shape of the engine rotor is a rhombus, which deforms as it rotates inside the contour of the mathematically defined stator. This geometry translates to a rotary engine with four combustion chambers. Each revolution of the crankshaft produces one revolution of the rotor; a complete engine cycle in each of the four chambers; and therefore four power strokes. In contrast, the Wankel engine produces one power stroke per crankshaft revolution. Additionally, the Wankel engine is rev limited due to the excessive crankshaft bending resulting from the centrifugal forces of the eccentric rotor. The Szorenyi engine has a balanced rotor and so is not rev limited in this regard. However, testing will be required to establish the rev limit.So the Szorenyi engine is a rotary engine with potentially better power density than a Wankel due to the Szorenyi’s higher revving rotor. Other advantages of the Szorenyi engine over the Wankel are a larger space inside the rotor for internal cooling of the rotor; four power strokes per rotor revolution; no need for a balancing flywheel in a single rotor engine; and twice the torque moment arm of the Wankel engine. The Szorenyi engine could be used in any application where the reciprocating and Wankel engines are used.RMIT University has conducted ideal mathematical modelling of the engine geometry and fuel burn. The model analysed the Szorenyi engine, the Wankel, and a reciprocating engine of the same displacement. This modelling has shown that the Szorenyi engine thermal efficiency is 0.46% greater than the reciprocating engine and 0.38% greater than the Wankel engine.The prototype engine used in the proof-of-concept test experienced an internal failure, but now has redesigned rotor hinges. That engine is awaiting a program of further testing to assess engine performance. Also, the RMIT University mathematical modelling of the Szorenyi engine, while providing good results, is ideal and so more complex modelling is required to more accurately predict performance.