How does a Wankel engine work?
In contrast to a reciprocating piston engine, a rotary piston engine turns combustion energy directly into rotary motion without needing to go through the stage of a stroke motion. The interaction between the triangular piston – known as the rotor – and the ovular housing surrounding it is crucial. All three corners of the rotor must always rest against the inner wall of the housing via three sealing strips. This creates three chambers which are closed off from one another. During rotation, these chambers migrate and constantly change their volume, and as they do so this creates the prerequisite for four strokes.
- INTAKE – When the rotor passes the intake slot, the fuel/air mixture is sucked in.
- COMPRESSION – The fuel/air mixture is compressed.
- IGNITION – A spark from the spark plug then ignites the compresseed fuel/air mixture. The explosion drives the eccentric shaft via the rotor.
- EXHAUST – The burned gases are then pushed out of the combustion chamber.
No connecting rods or crank pins are required due to the direct translation of the combustion energy into rotary motion. The triangular rotary piston autonomously sucks the gas mixture through an inlet opening due to its motion and pushes the combustion gases back out through an outlet opening. There is therefore no need for any valves or valve train in the form of a crankshaft, rocker arm and valve springs. In contrast to the reciprocating piston engine, the rotary engine ignites on each revolution of the eccentric shaft.
KKM 250 – The rotary engine in a driving test stand, 1960
On 19th January 1960, the results of existing research into the NSU/Wankel engine were presented to an expert audience from the Association of German Engineers (VDI) at the Deutsches Museum in Munich. A rotary engine with a chamber volume of 250 cc represented the new system on trial runs. This prototype, which was now slightly larger, had previously completed 100-hour full load runs and achieved continuous performance of around 30 hp at 5,000 rpm on the test stands in Neckarsulm. Contrary to general expectations, the KKM 250 demonstrated that the NSU/Wankel engine would also work well in medium speed ranges. In order to adjust the tests to reflect the conditions of the road, some versions of the KKM 250 were installed in an NSU Prinz III as a “driving test rig”. This meant the engines were exposed to the constantly changing loads that automotive drive systems face in both traffic and ever-changing road inclines.
NSU Prinz III
ENGINE: KKM 250
DISPLACEMENT: 250 cc Single Rotor
POWER: 30 hp @ 5,000 rpm