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#5 12-12-2010, 08:23 AM

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ROTARY TECHNICAL INFORMATION

In the 1950s the German engineer Felix Wankel developed his concept of an internal-combustion engine of a radically new design, in which the piston and cylinder were replaced by a three-cornered rotor turning in a roughly oval chamber. Rotary engines remain a mechanical oddity in an industry that worships standardisation and volume.

The following appeared recently in New York's New York Times Newspaper:
"In the 1960's and 1970's, the rotary engine was viewed, for a time, as the next step in automotive evolution. It came closer to anything yet in displacing the industry's established technology. At the peak of rotary enthusiasm, companies produced rotary-powered motorcycles, outboard boat motors, airplane engines and even lawn mowers. General Motors and American Motors both had plans to use rotary engines in production models � plans never realised.

The engine's appeal lay in its elegant simplicity. The Wankel rotary, also known as the Wankel � after its German inventor, Felix Wankel � has only a handful of parts, compared with about 40 pieces in a four-cylinder piston engine.

Its central rotor, a triangular piece of metal that revolves in a chamber, does the work of multiple reciprocating pistons. In the four-stroke cycle of a piston engine, valves move up and down to bring air in and extract gases out. But the rotor of a Wankel engine allows the four-stroke process to occur simultaneously. As the rotor turns, it uncovers slots in the housing, admitting air and then letting exhaust out. As a consequence, the rotary engine is lighter and more powerful for its size than even the latest high-compression V-8's.

The rotary's main benefit was to take the same combustion process that works so well in a conventional engine and arrange it in a far more compact design. The rotary produces twice the power of a conventional engine of similar size. The rotary motion and the timing of the power pulses run with uncanny smoothness.

Today, with billions of dollars committed to research on electric cars, fuel cells and other futuristic technologies, the rotary engine offers a cautionary tale of how a can't-miss technology can fail to live up to expectations. Displacing established technology is never easy, but the Wankel came closer than anything else in the auto industry. By the late 1950's, when a German manufacturer, NSU, first took interest in the rotary engine.

The Wankel was introduced at an auspicious time. NSU's introduction in 1961 of the Prinz, the first production car to use the Wankel engine, captured the imagination of auto engineers worldwide, even though the car proved unreliable.
NSU built one more car with rotary power, the Ro80 sedan, before being folded into the fledgling Audi group in the late 1960's. By then, rotary development was under way on three continents under Wankel licenses.

The president of General Motors, Edward N. Cole, saw the Wankel design as delivering some of the benefits of gas turbine engines, which were a continuing research program at the company, in a relatively low-cost design. In Japan, Kenichi Yamamoto, president of Toyo Kogyo, which later became Mazda, also saw the rotary's potential and introduced it into several models, including the Cosmo Sport, 110 S. In 1969, Mercedes began experimenting with a series of C-111 sports car prototypes that could reach 180 m.p.h. with four-rotor engines; those cars were never brought to production.

But the oil crisis of the early 1970's brought rotary-engine development to a near standstill. The rotary had two serious drawbacks: relatively high emissions and poor fuel economy. During this time, G.M. canceled its production plans.

Among automakers, only Mazda persevered. The company's engineers improved the fuel economy, reliability and emission performance, and went on to develop a series of sedans and sports cars with rotary engines, winning races at Le Mans and gaining a loyal following. The new RX-8 rotary produces as much power as its predecessor without the use of turbochargers.

Recent research shows the shape of the combustion chamber in a rotary engine is well suited to using pure hydrogen as a fuel. Hydrogen is particularly clean, ending up mainly as water when burned. Mazda has been working for several years on the potential of a hydrogen-fueled rotary engine."

The fuel-air mixture is drawn in through an intake port and trapped between one face of the turning rotor and the wall of the oval chamber. The turning of the rotor compresses the mixture, which is ignited by a spark plug. The exhaust gases are then expelled through an exhaust port through the action of the turning rotor. The cycle takes place alternately at each face of the rotor, giving three power strokes for each turn of the rotor. The Wankel engine's compact size and consequent lesser weight as compared with the piston engine promised to give it increasing value and importance with the rise in petroleum prices during the 1970s and 1980s. In addition, it offers practically vibration-free operation, and its mechanical simplicity provides low manufacturing costs. Cooling requirements are low, and its low centre of gravity contributes to driving safety.

A rotary engine uses the same four engine cycles, intake, compression, expansion and exhaust, as a piston-engined car. But instead of using pistons which move up and down, a rotary engine features two or three rotors which spin around inside a chamber. There are no camshafts, no lifters, no pushrods, no rockers, no valves and no springs. Below is a picture of the 20B rotary engine.

Here you can clearly see the 3 rotors. Ports are used to allow air and fuel into the engine and let exhaust gases escape. 'Porting' a rotary involves making these ports bigger to therefore produce more power. For a list of the types of portings available for a rotary engine click here.
The rotary engine is known for its smoothness because of the fact that the rotors continually spin around in the same direction, unlike pistons which have a frantic stop/start/stop/start activity. The smoothness allows rotary engines to rev much higher and ported versions can be revved to around 8000rpm. Unfortunately, the early rotary engines were hampered by problems such as excessive fuel consumption and unreliability. But regular servicing and good care of the engine (such as warming up) will help towards achieving good mileage. A lot of people also don't realise that a rotary engine uses oil as part of it's cooling system, therefore increasing the amount of oil consumed by the engine, people's lack of familiarity with this knowledge can lead to the motor's destruction due to overheating and a lack of oil. The Internet is a great place to find out information about how to look after a maintain a rotary engine with a huge number of forums and sites offering tips. A point of interest is that Mazda won the American IMSA GTU Championship from 1980 through to 1987. Eight consecutive championships show that results like this take two things, POWER to be first and RELIABILITY to stay first. The Mazda rotary engines had both of these things.

General Information about the Rotary Engine Types

10A Rotary Engine
The Cosmo 110S Sport, Mazda's second rotary engine car, the R100, and the RX-3 were powered by the 10A engine. It had a capacity of 491cc x 2 and was available in naturally aspirated form only using a carburetor.

12A Rotary Engine
The 12A engine had displacement of 573cc x 2. It was first introduced in May 1970 in the RX-2. The size of the rotors were the same as the 10A, yet their width increased by 10mm as did the rotor housing to increase the engines capacity. It was also available in the RX-3, RX-4 and RX-7 as well as the Japanese model Cosmo. In Australia it was only available in naturally aspirated, carburetor form. There is a fuel injected, turbo charged version available though which was in the Japanese RX-7 and Cosmo.
Pictures: 12A Turbo, 12A Naturally Aspirated

13B Rotary Engine
The original 13B rotary engine was introduced in December 1973, mounted in the RX-4 (or Luce in Japan). The 13B engine displaces 654cc x 2, the width of the rotors and rotor housings are increased by a further 10mm over the 12A. The 13B was available in the RX-4, RX-5, second & third generation RX-7s, the JC Cosmo and the later model Luce (929). The last two models were only available in Japan. Originally only available in naturally aspirated and carburetor form, later versions were fuel injected and featured one turbocharger, twin sequential turbochargers or a six port induction system, similar to Honda's VTEC system. It is the most common and popular rotary engine to modify, with many EFI 13B Turbo's finding new homes inside older model RX's.
Picture: 13B Turbo

20B Rotary Engine
The 20B is currently Mazda's largest production rotary engine. With a displacement of 3 x 654cc, an extra rotor is added to the 13B engine to create the 20B, the rotor width remains the same as the 13B. The 20B is a much torquier unit, due to the extra rotor, and also does not need to be revved as hard to make as much power. This helps to make the 20B a very efficient and powerful engine. Only available in the JC Cosmo, it is a rare engine.

Name	Capacity	Rotor Information	Induction
10A	982cc (1 litre)	2 x 60mm wide rotors	Carbureted
12A	1146cc (1.2 litres)	2 x 70mm wide rotors	Carbureted/EFI
13B	1308cc (1.3 litres)	2 x 80mm wide rotors	Carbureted/EFI
20B	1962cc (2.0 litres)	3 x 80mm wide rotors	EFI