Mazda's rotary engine makes a 180-degree turn

Mazda’s efforts to revive the rotary engine have taken a twist.

The automaker discontinued the use of rotaries in 2012, due largely to their relatively poor fuel economy and emissions, but a patent application uncovered by AutoEvolution suggests that its engineers are leaving no stone unturned they work to redesign the company’s signature engine.

Rotaries, though prized for their compact design and smooth operation, typically burn more oil than piston engines do. They also produce less torque. Mazda never stopped working on them, however, and several of its executives recently confirmed their intention to bring the design back.

But they’ll only do it only if they can get it to perform on par with conventional motors, which Mazda R&D chief Kyoshi Fujiwara claims has been achieved. While the details of how his team achieved that goal have yet to be officially revealed, the patent filing offers a possible partial explanation.

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 backpressure, according to the 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 room.” (Perhaps like the one under the incredibly low hood of the RX-Vision Concept.)

The technical drawings accompanying the application also show twin spark plugs positioned at different angles to the figure-8-shaped combustion chamber, rather than the parallel arrangement used the in the last Mazda rotary. Fujiwara has said that better control of the combustion process was paramount to improving the engine’s efficiency, so this could contribute to that end. However, he also said that the spark plug may play a smaller role in the new rotary, a possible nod to its use of diesel-style Homogeneous Charge Compression Ignition, or HCCI, at some engine speeds.

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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