The main advantages of the Wankel-type rotary engines are:
Simple - with only two or three moving parts low part count means less cost few moving parts means less to wear out Powerful for their size efficient packaging Uses the efficient four-stroke combustion process solid fuel economy low emissions Vibration-free engine can be hard mounted smooth operation at high RPM Reliable reduces the cost of maintenance
The main historical disadvantage:
Poor sealing: Mazda did have a sealing problem early in their product lifecycle. This was quickly and easily solved by going to a harder material for the apex seals. Poor emissions performance: The high surface to volume ratio of the combustion chamber can lead to more quenching and higher emissions. The Rotapower's charge cooled configuration increases the rotor face and incoming charge temperature which results in less quenching and better combustion. Poor fuel economy: In oil cooled rotary engines, fuel consumption suffers at low power due to oil sloshing losses. In the Rotapower, charge cooling eliminates this source of lost efficiency.