Wankel engine

The Wankel rotary engine is a type of internal combustion engine, invented by German engineer Felix Wankel, which uses a rotor instead of reciprocating pistons. This design promises smooth high-rpm power from a compact, lightweight engine; however Wankel engines are criticized for poor fuel efficiency and exhaust emissions.

Disadvantages

The design of the Wankel engine requires numerous sliding seals and a housing that is typically built as a sandwich of cast iron and aluminum pieces that expand and contract by different degrees when exposed to heating and cooling cycles in use. These elements led to a very high incidence of loss of sealing, both between the rotor and the housing and also between the various pieces making up the housing. Further engineering work by Mazda brought these problems under control, but the company was then confronted with a sudden global concern over both hydrocarbon emission and a rise in the cost of gasoline, the two most serious drawbacks of the Wankel engine.

Related Topics:
Cast iron - Aluminum - Mazda - Hydrocarbon - Emission - Gasoline

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Just as the shape of the Wankel combustion chamber prevents preignition, it also leads to incomplete combustion of the air-fuel charge, with the remaining unburned hydrocarbons released into the exhaust. At first, while manufacturers of piston-engine cars were turning to expensive catalytic converters to completely oxidize the unburned hydrocarbons, Mazda was able to avoid this cost by paradoxically enriching the air/fuel mixture enough to produce an exhaust stream which was rich enough in hydrocarbons to actually support complete combustion in a 'thermal reactor' (just an enlarged open chamber in the exhaust manifold) without the need for a catalytic converter, thereby producing a clean exhaust at the cost of some extra fuel consumption.

Related Topics:
Catalytic converter - Exhaust manifold

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Unfortunately for Mazda, their switch to this solution was immediately followed by a sharp rise in the cost of gasoline worldwide, so that not only the added fuel cost of their 'thermal reactor' design, but even the basically lower fuel economy of the Wankel engine caused sales to drop alarmingly.

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Another disadvantage of the Wankel engine is the difficulty of expanding the engine to more than two rotors. The complex shapes of the rotor, housing, and output shaft and the way they fit together requires that engines with more than two rotors use an output shaft made of several sections assembled during the assembly of the rest of the engine. While this technique has been used successfully in Wankel powered racing cars, it negates a great deal of the relative simplicity and lower cost of the Wankel engine construction.

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The main problems with the engine, however, have been fixed in the engine of the RX-8. The ports, formerly on the sides, are now placed to the rear of the engine. Fuel consumption is within normal limits while passing California State emissions requirements.

Related Topics:
RX-8 - California

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