Published March 12, 2012
By Huw Evans
Current-spec Mazda Renesis rotary.
You have to give Mazda credit. When NSU gave up on Felix Wankel’s smooth but thirsty and problematic rotary engine in the mid-1970s, Toyo Kogyo, having launched it in the futuristic 1967 Mazda Cosmo Sport 110, continued development, leading to the hallowed line of RX-7 sports cars and more recently the four-door RX-8.
However, despite considerable advancements, including notable increases in power, along with lower emissions and better reliability, the engine’s apex seals, as well as fuel economy have remained an Achilles’ heel. Even today’s RX-8 struggles to achieve more than 23 mpg on a good run.
As a result, with tougher fuel economy and emissions standards on the horizon, once RX-8 production ends in June, it won’t have a replacement, at least in the short term.
We say short term, because according to Mazda’s general manager, powertrain development, Mitsuo Hitomi, the Hiroshima-based automaker has been working on a next-generation rotary that will be capable of meeting future government fuel mileage and smog output regulations.
“We think we’ve found a way to improve the rotary’s fuel economy to be truly equal to that of conventional piston engines and if so, we believe we can reintroduce the rotary to market,” he said speaking to Ward’s Auto.
As to how this can be achieved, Hitomi so far hasn’t revealed much, but did say that by altering the shape of the engine’s troichoid housing, the apex seals can remain flush with it, essentially eliminating one of the biggest issues, namely that gas pressure in the combustion chamber causes the seals to lift at low rpm, causing blow-by and thus potentially engine failure.
By aligning the seals flush with the chamber and replacing the spark plugs with a laser injection system (the traditional recessed location of the plugs on a rotary tends to cause spark issues, requiring more fuel for ignition), the result is noticeably better fuel economy.
Combined with the rotary’s traditional attributes of smoothness, compact dimensions and high specific power output for displacement, this technology could make it suitable as a range extending generator for future electric vehicles, something that Hitomi hinted during his interview with Ward’s.
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