Rotary engines based on the Wankel principle were developed with two fundamentally different approaches to cooling the rotor. Mazda, Audi, Suzuki, Ingersoll-Rand and others used the oil-cooled rotor. It is an expensive, heavier and more complicated design, which achieved specific fuel consumption in the range of .55 to .6 lbs/hp hr. This is about 15% to 20% poorer than a typical four-stroke piston engine. The other approach taken by Outboard Marine Corporation (OMC), Fichtel Sachs and Norton was to use the incoming air-fuel mixture (“charge”) to cool the rotor. This design was much lighter, less expensive and through the use of roller bearings and very low rotor cooling losses achieved a specific fuel consumption between .45 and .5 lb/hp hr, which was close to the 4-stroke piston engine.
Historically all of the charge-cooled rotary engines that were developed used an arrangement where the fuel-air mixture passed through the rotor from one side to the other. This design cooled the rotor unevenly, which lowered engine rotor bearing life and increased friction between the rotor and the end housing.
In 1985 Moller International acquired the major rotary engine assets of OMC. OMC’s main product was the Johnson and Evinrude outboard engine and they were the world leader noted for their product’s reliability. OMC reportedly spent over $200 million between 1970 and 1985 developing a number of different rotary engine models including a 530cc displacement model that went into volume production and used in a snowmobile as a test product. Emissions requirements were one of the key motivators for this program. OMC believed that they would not be able to meet the proposed emissions standards proposed for the late 1980’s with their two-stroke engines and therefore chose to develop a lightweight low emission 4-stroke rotary engine. Fortunately for our Company the proposed emission standards were not enacted as originally planned and OMC stayed with their two-strokes, allowing Moller International to purchase their rotary engine technology.
Since acquiring the OMC charge-cooled rotary design, Moller International has spent ~$35 million on further development, testing and product integration efforts related to its rotary engine, preparing it for use in its aeronautical products as well as for use in a wide range of other suitable applications.