Dr. Felix Wankel was a German tinkerer who started with drawings and prototypes of rotary engines in the 1920s. His first patent for a rotary engine was granted in 1936. But it was not until the 1950s, when motorcycle manufacturer NSU, used his designs.
Early Wankel engines were of a design called “drehkolbenmaschine” (DKM) in which an inner rotating housing and rotor move around a fixed central shaft. The DKM was remarkably smooth in operation, and could run at over 20,000 rpm. The DKM engine design had drawbacks, though, so the “kreiskolbenmotor” (KKM) was developed. In the KKM, the rotor and output shaft rotate with in a fixed housing. All the rotary engines that Mazda made were of the KKM design.
The main advantages of a Mazda Wankel KKM engine were size, simplicity, and smoothness. A double-rotor Wankel has just three moving parts (!) – two rotors and the crankshaft. Because intake and exhaust timing are taken care of by ports in the housing, there are no camshafts or valves. This makes a KKM design a very simple engine to build.
Disadvantages, yes there are some. Because of the long, narrow combustion chamber shape, the Wankel is less efficient than a regular four-stroke piston engine. Fuel consumption was can be high too high, especially in the earlier, less-sophisticated engines. As far as emissions go, nitrogen oxide emissions are lower than in a piston engine but carbon monoxide and unburned hydrocarbons are higher.
So does the rotary have a future? It might. Emissions can be problematic running on gasoline but, guess what, the Wankel seems perfectly happy running on hydrogen and emissions are very low when that is the fuel used. To date, Mazda has built and tested several hydrogen-powered rotary concept vehicles and is working on others. Don’t count the Dr. Wankel’s little powerhouse out just yet.
Earthgarage – Greener Car. Fatter Wallet.