Enthusiasts shed many a tear over the demise of the rotary Wankel engine. Last sold in the Mazda RX-8, these complex engines never took off in mainstream vehicles – as despite being smooth, free-revving and brilliant fun, they also drank fuel, burned oil and tended to blow up at a moment's notice.
But Mazda thinks a new application would be ideal for the rotary engine. Rather than fitting one to a performance car, the technology is set to be revived in battery-powered, self-driving Toyotas.
Rather than powering the wheels directly, the rotary engines will be used to run generators to recharge the vehicle's batteries. They'll power Toyota's upcoming driverless delivery fleet, which will carry everything from cargo to passengers.
"This is a very suitable engine to run a generator because it's compact and lightweight, with no noise or vibration, and it has very good fuel economy," said Masahiro Moro, president of Mazda in North America.
Rotary engines don't use traditional pistons to compress and combust fuel. Instead, a rotating triangular element creates all four stages of combustion.
The idea of rotary engines as range extenders isn't a new one, and it's one that has significantly higher chances of success than allowing a rotary to take the place of a normal engine. When acting as a generator, a rotary engine can run at a constant speed - reducing wear on the components and ensuring greater fuel and oil economy.
Mazda ditched the rotary engine from its range in 2012, following the demise of the RX-8. The company cited the difficulty of bringing the rotary in line with contemporary emissions regulations as a key reason for dropping it – a move that saddened enthusiasts, as the brand had offered a rotary engined option in its range since 1965.