Return of the Rotary?

wankelMazda’s signature three-sided Wankel rotary engine has been used in production since the late 1960’s; however, they discontinued its use in 2012 with the RX-8 due to poor fuel economy and emissions. The downside of the engine are issues with insufficient rotor sealing and slow combustion.

This engine design does have many advantages over a typical internal combustion engine. It is much lighter and more compact, creating a higher power to weight ratio. Torque is also provided over two-thirds of the combustion cycle rather than the one-quarter of a cycle that normal combustion engines make.

wankelFurthermore, it has no reciprocating parts, so there is virtually no vibration and it can reach higher revolutions per minute. Since there are less parts to the engine, it is also less expensive to produce.

Rotaries, though prized for their compact design and smooth operation, typically burn more oil than piston engines do. Mazda has continued to work on the technology, and company officials have previously suggested that if they can get it to perform as well as a reciprocating engine, it will bring the design back to power a conventional sports car. A recent patent application shows that they may have found the answer.

The technical drawings accompanying the application show twin spark plugs positioned at different angles to the combustion chamber, rather than the parallel arrangement used in the last Mazda rotary. Better control of the combustion process was paramount to improving the engine’s efficiency, so this could contribute to that end. But the spark plug may play a smaller role in the new rotary, with a possible use of diesel-style Homogeneous Charge Compression Ignition, or HCCI.

Essentially, Mazda has flipped the engine upside down, moving the intake to the bottom and exhaust up top. This allows for a longer intake passage, which creates a dynamic forced-induction effect, while shortening the exhaust passage to a turbocharger, which reduces back pressure, according to a description in the application. Just as important, this creates more room above the engine to mount a turbocharger, helping meet the desired goal of designing a motor that can be efficiently mounted even in a small engine bay. Perhaps like the one under the incredibly low hood of the RX-Vision Concept.

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Once the engine has proved itself in the automotive market, it may be used as a range extending electricity generator for when the battery runs out of charge on an electric vehicle. The appeal of the rotary in this application is the high power density afforded by its compact design, and its smooth-running nature.

In any case, the answers could be coming soon. 2017 marks the 50th anniversary of Mazda’s first rotary-powered car, so the timing — ignition or otherwise, couldn’t be better for its return.

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