The Wankel rotary engine: technique; models; history; future

The motor Wankel it can be considered one of the most original ideas conceived by looking for valid alternatives to the usual internal combustion engine scheme. Its realization is due to the German engineer Felix Wankel, who put the principle into practice in collaboration with some technicians of the NSU brand, including the slightly less famous Walter Froede.

The real evolution and consecration of this technical experiment, however, is to be attributed to the Japanese brand Mazda that in 1961, after having acquired the license and the patent of this new technology, opened the Mazda Rotary Engine Research Division with the aim of making it more reliable and scalable and applying it to its production models, starting from the Cosmo Sport 110S to arrive to the better known RX-7 and RX-8.

A bit of technique

The Wankel is completely different from traditional engines while still remaining endothermic. Its pistons are not cylindrical but have a shape called “Reuleaux’s triangle” (a kind of equilateral triangle with slightly convex sides) and instead of making a linear alternating movement, they rotate eccentrically around the crankshaft inside a chamber stator combustion of a form called epitrochoidal.

Motor Wankel
Motor Wankel

The contact between the stator (combustion chamber) and rotor (piston) occurs through the vertices of the triangle that slide along the stator wall. This, just like in the 2-stroke engines of scooters, is equipped with intake and exhaust lights (openings) while on the opposite wall there are candles that guarantee ignition.

The contact allows the simultaneous formation of 3 distinct chambers from which 3 different Otto cycles are triggered, offset by 120 °, with intake, compression, ignition / expansion and exhaust. From this it can be deduced that at each revolution of the piston (rotor) 3 different cycles are performed which are equivalent to 3 revolutions of the crankshaft. This is one of the reasons why the Wankel engine is capable of developing levels of specific power superior to those of classic engines.

Pros and cons

Another of the main advantages of the rotary engine can be identified in the ease of production favored by its very simple design and by only two moving elements. Furthermore, the absence of the reciprocating motion of the pistons reduces to zero the second order inertia forces which, in addition to being difficult to balance, can create considerable problems of vibrations.

However, this solution also presents problems whose solution has long engaged the manufacturers that have tried their hand at it, ending up making them desist almost all except, precisely, Mazda: among the most difficult to solve, the premature wear of the sealing elements of the rotor, high fuel and lubricant consumption and low torque at low engine speeds.

Motor Wankel

Many sports and a triumph

In addition to the NSU, which introduced it on the ’64 Spider and then on the famous RO80 sedan, the Wankel engine ended up under the hoods of the Citroen GS, in a specific version called the Birotor, and of numerous prototypes including the Citroen M35, the Mercedes C111 and the Chevrolet Aerovette.

Its greatest diffusion, however, as already mentioned, came with Mazda, which proposed it as an alternative or as a single engine on many sports cars including the famous RX-3, RX-7 and finally RX-8, considered the song of the swan.

Motor Wankel
Motor Wankel
Motor Wankel

At the top of its popularity this engine has even equipped a racing car, the Mazda 787B, which in 1991 conquered the 24h of Le Mans setting an unmatched record, that of the first and only car equipped with an engine of this type to win the famous endurance race.

Today, the Wankel engine is preparing to resurrect once again with Mazda planning to integrate it as an on-board generator on an electric range extender model.

Template Production year Power
NSU Spider 1964 50 CV
Mazda Cosmo Sport 110 S 1967-1972 110-128 CV
Mazda R100 1968-1975 100 CV
Mazda Eunos Cosmo 1990-1995 300 CV
Mazda RX-7 1992-2002 280 CV
Mazda RX-8 2003-2012 192-231 CV

Source: Italia – News by

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