n The Wankel engine appears to be the
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only type of rotary unit of the positive-displacement type that has successfully been developed for automotive and industrial uses. Have other forms of rotary engine been evolved operating on the spark-ignition or compression-ignition principle?
AIt is said that more than 2000 types of
positive-displacement rotary engine — as distinct from gas turbine — had been patented as early as 1910. And it is reported that Felix Wankel assessed the merits of more than 600 designs before deciding to produce a unit with an epitrochoidal bore, various versions of which have been developed by different licensees. Rolls-Royce has evolved a diesel version which is a two-bank twostage engine.
The operating principle of virtually any type of rotary pump could be used in the design of a rotary engine with the exception of the gear pump. Many of the earlier designs were, it is understood, based on the reciprocating-vane principle. It is known that Renault produced an experimental rotary unit some years ago in conjunction with the American Motor Corporation, but no news of the engine has been released for some time. In this case, a four-lobe rotor operates in a five-lobe (five-chamber) housing. A diesel version has poppet valves, while a spark-ignition type is equipped with disc valves.
According to authoritative opinion, a number of promising rotary engines had poor combustion efficiency because of the large surface-to-volume ratio of the combustion chamber. It is claimed that the use of a compressor stage in the Rolls-Royce Wankel diesel enables this ratio to be considerably reduced. The combustion chamber is, therefore, relatively compact.