page_title: Wankel engine
section_title: Other uses
hierarchical_section_title: Wankel engine / Applications / Other uses
caption_attribution_description: UEL UAV-741 Drohnen Wankelmotor
context_page_description: The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into rotating motion.
  Compared to the reciprocating piston engine, the Wankel engine has more uniform torque and less vibration and, for a given power, is more compact and weighs less.
  The rotor, which creates the turning motion, is similar in shape to a Reuleaux triangle, except the sides have less curvature. Wankel engines deliver three power pulses per revolution of the rotor using the Otto cycle. However, the output shaft uses toothed gearing to turn three times faster giving one power pulse per revolution. This can be seen in the animation below. In one revolution, the rotor experiences power pulses and exhausts gas simultaneously, while the four stages of the Otto cycle occur at separate times. For comparison, in a two-stroke piston engine there is one power pulse for each crankshaft revolution and, in a four-stroke piston engine, one power pulse for every two revolutions.
context_section_description: Small Wankel engines are being found increasingly in other applications, such as go-karts, personal water craft, and auxiliary power units for aircraft. Kawasaki patented mixture-cooled rotary engine (US patent 3991722). Japanese diesel engine manufacturer Yanmar and Dolmar-Sachs of Germany had a rotary-engined chain saw (SAE paper 760642) and outboard boat engines, and the French Outils Wolf, made lawnmower (Rotondor) powered by a Wankel rotary engine. To save on production costs, the rotor was in a horizontal position and there were no seals in the down side. The Graupner/O.S. 49-PI is a 1.27 hp (950 W) 5-cc Wankel engine for model airplane use, which has been in production essentially unchanged since 1970. Even with a large muffler, the entire package weighs only 380 grams (13 oz).
  The simplicity of the Wankel engine makes it well-suited for mini, micro, and micro-mini engine designs. The Microelectromechanical systems (MEMS) Rotary Engine Lab at the University of California, Berkeley, has previously undertaken research towards the development of Wankel engines of down to 1 mm in diameter, with displacements less than 0.1 cc. Materials include silicon and motive power includes compressed air. The goal of such research was to eventually develop an internal combustion engine with the ability to deliver 100 milliwatts of electrical power; with the engine itself serving as the rotor of the generator, with magnets built into the engine rotor itself. Development of the miniature Wankel engine stopped at UC Berkeley at the end of the DARPA contract. Miniature Wankel engines struggled to maintain compression due to sealing problems, similar to problems observed in the large scale versions. In addition, miniature engines suffer from an adverse surface to volume ratio causing excess heat losses; the relatively large surface area of the combustion chamber walls transfers away what little heat is generated in the small combustion volume resulting in quenching and low efficiency.
  Ingersoll-Rand built the largest-ever Wankel engine, with two rotors, which was available between 1975 and 1985, producing 1,100 hp (820 kW). A one rotor version was available producing 550 hp (410 kW). The displacement per rotor was 41 liters, with each rotor being approximately one meter in diameter. The engine was derived from a previous, unsuccessful Curtiss-Wright design, which failed because of a well-known problem with all internal combustion engines: the fixed speed at which the flame front travels limits the distance combustion can travel from the point of ignition in a given time, thereby limiting the maximum size of the cylinder or rotor chamber which can be used. This problem was solved by limiting the engine speed to only 1200 rpm and the use of natural gas as fuel. That was particularly well chosen, since one of the major uses of the engine was to drive compressors on natural gas pipelines.
  Yanmar of Japan produced some small, charge-cooled rotory engines for chainsaws and outboard engines. One of its products is the LDR (rotor recess in the leading edge of combustion chamber) engine, which has better exhaust emissions profiles, and reed-valve controlled intake ports, which improve part-load and low rpm performance.
  In 1971 and 1972, Arctic Cat produced snowmobiles powered by Sachs KM 914 303-cc and KC-24 294-cc Wankel engines made in Germany.
  In the early 1970s, Outboard Marine Corporation sold snowmobiles under the Johnson and other brands, which were powered by 35 or 45 hp (26 or 34 kW) OMC engines.
  Aixro of Germany produces and sells a go-kart engine, with a 294-cc-chamber charge-cooled rotor and liquid-cooled housings. Other makers are: Wankel AG, Cubewano, Rotron and Precision Technology USA.
  The American M1A3 Abrams tank will use an auxiliary rotary-engined power unit, developed by the TARDEC US Army lab. It has a high-power-density 330-cc rotary engine, modified to operate with various fuels such as high octane military grade jet fuel.
caption: UEL UAV-741 Wankel engine for a UAV
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