About Wankel Rotary Engines
A rotary engine (also known as the Wankel engine or Wankel rotary engine) is an internal combustion engine invented in 1954 by the German mechanical engineer Felix Heinrich Wankel as an alternative to the classic reciprocating engine.
After some technical improvements made by engineer Hanns Dieter Paschke, the rotary Wankel engine was for the first time presented to specialists and the press in a meeting of the German Engineers' Union in Munich in 1960.
Due to their simplicity, excellent power-to-weight ratio as well as smooth and quite running, Wankel motors were on everyone's lips in the auto and motorcycle industries in the 1960s. Great attention was received by the NSU Motorenwerke AG in August 1967 for the very modern NSU Ro 80, which had a 115-horsepower Wankel engine with two rotors. It was the first German car selected as "Car of the Year" in 1968.
During the next decades, a number of large car manufacturers signed license agreements for development of Wankel rotary engines, including Ford, Toyota, Mercedes-Benz, Porsche, Rolls-Royce, and Mazda.
After further improvements of the engine, including the solution of the apex seal problem, Mazda successfully used Wankel motors in its sport cars RX series until 2012. The technological edge of the rotary engines in the automotive industry was highlighted in the 1991 24 Hours of Le Mans race, as a car powered by the 4-rotor Mazda 26B engine won the prestigious competition.
These days, Wankel rotary engines, being continuously improved by the likes of Wankel Supertec GmbH, can be found in motorcycles, race cars, airplanes, small vessels and power generators. The next stage of development refers to a use of rotary combustion engines in the coming era of low carbon, environmentally sound, reliable, and affordable energy supply. Therefore, the successful test of the on September 20, 2019 allows Wankel Supertec to look ahead with confidence.
A rotary engine is an internal combustion engine that uses one or more triangular rotors to convert pressure created when the air-fuel mixture is burned into kinetic energy. Gas volumes transported in the spaces between the rotor flanks and the housing alternately do four different jobs: a) Intake; b) Compression; c) Combustion and d) Exhaust. These stages are known as strokes, making the Wankel engine a 4-stroke engine, similar to the reciprocating Otto engine.
During this phase, a drop in pressure caused by the rotor’s motion draws in an air-fuel mixture. This mixture is drawn around the rotor and forced into the second stroke of the cycle.
As the rotor continues to turn, the captured (crosshatched) volume contained between the rotor and housing decreases, compressing the air-fuel mixture.
When the active mixture volume is a minimum, one or more spark plugs initiate combustion, causing rapid rises in pressure and temperature. The sudden expansion of the now gaseous fuel mixture transmits a force to the eccentric through the rotor.
As the rotation proceeds, the expanding gases drive the rotor until the exhaust port is exposed, releasing them. The exhaust process continues as the intake port opens to begin a new cycle.
Thanks to its design, the Wankel engine is far lighter, compacter and simpler than a classical piston engine. There are neither reciprocating mass, nor cranks, valves, rods or other failure prone, complex parts. Wankel engines contain only three moving parts, which makes them more reliable, durable and maintenance-friendly than their reciprocating contenders. Besides, these moving parts are in continuous unidirectional rotation ensuring higher operating speeds, ease of balancing and low level of vibration. With unprecedented power-to-size and power-to-weight ratios, Wankel engines are indispensable in a various applications ranging from the light aircraft sector through combined heat-power-units to the marine industry.
One of the major disadvantages of the Wankel engine refers to its low thermal efficiency. The long, thin and moving combustion chamber results in slow and incomplete burning of the fuel mixture. This leads to higher carbon emissions and lower fuel efficiency, compared to the piston engines. However, this drawback turns into advantage by switching to Hydrogen fuel.
Another weakness of Wankel engines comes from the rotor and apex sealing. Imperfect sealing between the edges of the rotor and the housing – for example due to wear or insufficient centrifugal force on the lower RPM ranges – can result in combustion gas leaking into the next chamber.
Since the combustion only occurs in one section of the rotary engine, there is a high temperature difference in two separate chambers. As a consequence, the different expansion coefficients of the materials lead to suboptimal rotor sealing. Oil consumption is also a problem, as oil needs to be injected into the chambers to add lubrication and help keep the rotor sealed.