Mazda patents emissions technology for rotary engines

Mazda has a soft spot for rotary engines, with a new patent hinting some in the company are keen on a rotary-powered sports car.

In a patent lodged with US Patent and Trademark office at the beginning of the year, and just discovered by CarBuzz, Mazda proposes an exhaust gas recirculation (EGR) system for Wankel rotary engines.

The patent describes how exhaust from the engine is primarily pushed out from its side port, with a much smaller amount coming out of the peripheral port.

In Mazda's new system, the hot exhaust gas from the side port will be channelled into a turbocharger to improve power and torque.

The cooler gas from the peripheral port would be cooled further by engine coolant before being fed back into the engine to help reduce its operating temperature and lower the production of harmful oxides of nitrogen (NOx) gases.

In a more traditional setup, the cooling system for the EGR system needs to be quite large and bulky as the amount of cooling required is rather larger. In this proposed system, only cooler exhaust from the peripheral port is fed through the EGR setup, the cooling system is much more compact and can be located within the area immediately adjacent to the engine.

When the car doesn't need EGR, exhaust gases are dumped straight into the drivetrain's second catalytic converter. 

Naturally, we have to caution that a patent doesn't equal production intent, or even that the technology can ever be put into production. It merely signals that there's work going on somewhere and that ideas are being tested out. Indeed, it could be just another dead end on the Wankel's long and tortured path through time and space.

Given the presence of a turbo in the patent design, it's likely this setup would be for a vehicle where the rotary engine drives the wheels. The last model to feature a rotary engine driving the wheels was the RX-8, which went out of production in 2012.

The RX-8 featured a naturally-aspirated 1.3-litre twin-rotor Wankel rotary, dubbed Renesis II, that made between 143kW/198Nm and 173kW/216Nm depending on the spec.

It wasn't the last production car to feature a rotary engine, though, with that honour belonging to the short-lived MX-30 R-EV, which had a 55kW/116Nm 830cc rotary engine. Its sole purpose was to recharge the SUV's 17.8kWh whenever it was low on charge. 

Sold mostly in Europe and Japan, the R-EV never made it to Australia. The MX-30's unusual freestyle door layout, compromised interior, and limited EV range resulted in slow sales. The MX-30 was discontinued in Australia in 2023, although it soldiered in Europe until this year.

Ever since the RX-8's demise, there has been a steady drip of rumours pointing to new rotary models on the horizon, whether they be sports cars or range-extended electric vehicles. 

Mazda has fanned the flames by releasing rotary-powered concepts every few years. The latest was the Vision X-Coupe at the 2025 Tokyo motor show. Under its slinky four-door body, the X-Coupe featured a turbocharged twin-rotor engine as part of a 375kW plug-in hybrid drivetrain.

This was preceded by the Iconic SP concept at the 2023 Tokyo show, which sported an even sexier two-door body. That concept was said to be powered by a 275kW range-extender drivetrain with a  twin-rotor engine at its heart.

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