Wankel engine: what it is and how it works

Most modern cars now use a piston-type internal combustion engine. But, there are internal combustion engines that have a completely different design. We will talk about one of these engines in this article.

What is a Wankel engine?

What does a Wankel engine look like in section.

From the high school physics course, everyone remembers perfectly well that the operation of a four-stroke internal combustion engine consists of:

  • fuel / air intake;
  • compression, where their mixture becomes one, and then ignited by the spark of the spark plug;
  • working stroke: the piston moves in the opposite direction, doing useful work;
  • exhaust: the remains of the spent mixture are thrown out of the engine.

And everyone remembers the visual teaching aid: a sectional view of a gasoline engine cylinder, which clearly shows all the stages when the handle is rotated. But, not all existing / currently used engines have the same design. In addition to the well-known classic internal combustion engine, there are other design options.

A striking example is the Wankel rotary piston engine. This ICE design was developed in 1957 by NSU employee Walter Freude in collaboration with Felix Wankel.

A distinctive feature of this engine is the use of a triangular rotor in the shape of a Reuleaux triangle, rotating inside a cylinder of a special profile, the surface of which is made along the epitrochoid.

The principle of operation of the Wankel engine

In a Wankel engine, the operating cycle is exactly the same as in a classic four-stroke combustion unit: intake, compression, power stroke and exhaust. But for it, it is not the piston that makes two strokes up and down (forward and backward), but the shaft makes only one revolution of the triangular rotor inside the epitrochoidal chamber of the cylinder, which is the heart of the engine.

The principle of operation of the Wankel engine: 1 - intake of the fuel-air mixture; 2 - compression of the mixture; 3 - ignition and working stroke; 4 - exhaust gases release;

Despite the apparent complexity, the principle of operation of the Wankel engine is quite simple.

  • At the first stage of the cycle, a mixture of gasoline and air enters the engine chamber.
  • Then the rotor turns 45 degrees, compressing it: in this form, the mixture is ignited by the spark from the spark plug.
  • This is followed by the working phase: the burnt fuel-air mixture presses on the rotor, thereby ensuring its rotation.
  • Finally, at the final stage, the rotor turns and the exhaust gases through the exhaust system enter the exhaust system.

And so over and over again. But unlike the classic internal combustion engine, where 2-3 thousand revolutions per minute is an operating mode, for a Wankel engine even 10 thousand revolutions is not the limit.

The eccentric rotation of the shaft is ensured by its shape - with an internal hole and teeth, the rotor rotates around a stationary shaft with mating teeth. It is they who prevent it from slipping and jamming even with particularly intense rotation.

See also : What is a boxer engine and how does it work.

Advantages and disadvantages of the Wankel engine

You may have a simple and predictable question, why under the hood of most cars is not a Wankel engine, but a classic four-stroke ICE... To answer this question, consider the advantages and disadvantages of the Wankel engine. So, the Wankel engine:

  • weighs less and takes up less space in comparison with units of similar characteristics;
  • ​​
  • runs noticeably quieter, the engine is almost inaudible at idle;
  • better balanced, single rotating shaft design, devoid of reciprocating cranks, gives excellent results;
  • provides better dynamics and high top speed;
  • can operate at high speeds for a long time;
  • can operate on low octane fuel;

But, the Wankel engine also has a lot of drawbacks, for example:

  • high, often even excessive (up to 20 liters per 100 km), appetite;
  • increased oil consumption compared to conventional four-stroke engines;
  • operation at low rpm: fuel consumption increases, while the engine resource, on the contrary, decreases;
  • impossible to move in tightness, low level of inertia, it is not possible to brake with the motor;
  • low unit resource;
  • difficulties in repair;

As you can see, the shortcomings are very serious and there are many of them. As a result, now there are no models equipped with a Wankel engine in the production range of mass-produced passenger cars. The last production car under the hood of which this unit was installed, the Mazda RX-8, stopped rolling off the assembly line back in 2012.

At the same time, conventional internal combustion engines are increasingly being installed on already produced cars with a Wankel engine. The unit is considered non-repairable, the minders who are able to make its high-quality restoration can be counted on one hand, most consider them simply "disposable". Therefore, under the hoods of the RX-8, as well as the equally popular predecessor, the RX-7, turbocharged or naturally aspirated inline-fours appear.

See also : What is CRDI engine and how it works.

Video on the topic