Avoiding the problems of the Wankel engine
The most obvious comparison is with the Wankel engine. The Libralato engine is a very different design which avoids the problems of the Wankel engine:
The Wankel engine has a high surface to volume ratio at top-dead-centre (TDC) and a shallow and elongated combustion chamber - This 'long flame path' is principally responsible for the Wankel engine's high fuel consumption and high level of unburned fuel (HC) emissions.
The Libralato engine's second stage compression forces the intake air into a tightly contained combustion chamber. The force of combustion acts against an acute angle working surface area during the expansion phase. The surface area of the rotor face expands as it rotates, due to the sliding action of the rotors. This helps maximize the work extracted as the combustion pressure starts to drop and is particularly well suited to lean burn combustion.
The Wankel engine suffered from unstable geometry of the rotor housing due to localized high temperature. It is known for having a 'hot side'. This tends to deform the rotor housing and to reduce the effectiveness of the engine sealing.
The Libralato engine scavenges the residual exhaust gases with fresh air from the first stage compression. This cools the expansion chamber and reduces the temperature gradient across the engine. The design facilitates a small amount of internal exhaust gas recirculation, reducing NOx emissions.
The Wankel engine seals at the three apexes of the triangular rotor present a very small surface area and therefore tend to allow 'blow by' gas escaping.
The Libralato rotors have much larger sealing surfaces, with no narrow apexes, therefore chamber sealing is much more effective.