The Wankel (Rotary) Engine

The workings of a Wankel Engine

The Wankel engine (also known as the Rotary Engine) was invented by Felix Wankel, a German mechanical engineer in the early 1950's and underwent development during the 50's. A complete running prototype was ready in 1957 and it was then sold on to other companies who added their own improvements.
It is an internal combustion engine and does run on Otto cycle, BUT has no pistons.

It is a very compact and lightweight engine compared to its counterparts and as such has been very popular in a variety of vehicles since. Vehicles with wankel engines include automobiles, racing cars, water craft, go karts and have been put into devices such as chainsaws. It has been widely used in car making by Mazda, which fitted the rotary (Wankel) engine to many of its cars, including the Mazda RX8 (below)


The Wankel Powered Mazda RX-8

The wankel engine is generally more poweful than a conventional four stroke because in one revolution of the triangular rotor, there is one ignition (watch point a on the apex of the triangle on the animation above!) this means one power stroke in one turn of the drive, as oposed to one for every two turns of the drive shaft in a conventional engine.

Minimizing the space around the rotor is key to increasing pressure in the engine, making its output more powerful.

Advantages:

• Much smaller than a conventional 4 stroke, meaning it can be used in a wider range of applications.
• A better power output due to the one ignition - one rotation system.
• Very few moving parts compared to an ordinary engine, making it less suseptable to breaking down or suffering from wear.
• Very fast reaction to throttle changes
  
• They do not die, if a wankel engine goes wrong it will maintain and ever lowering power output as opposed to instantly dieing, maybe life-saving in aircraft

Disadvantage:

• More complex engineering involved and lots of seals needed (between rotor tips as well as against the chamber ends)
• The constant moving and heating in the engine can effect the seals and reduce efficiency
• As the stroke duration is half of the standard 4 stroke, the fuel has half the time to enter the chamber in the right place to be ignited, due to the way the three chambers rotate. The fuel-air mixture cannot be pre-stored as there is no intake valve.
• The surface/volume-ratio problem is so complex that you cannot make a direct comparison between a reciprocating piston engine and a Wankel engine in relation to the surface/volume-ratio. The flow velocity and the heat losses behave differently and surface temperatures behave absolutely differently. Engines with higher compression ratio have a worse surface/volume-ratio.