Mazda has patented a supercharged two-stroke engine for some reason

Wednesday, 2 March 2022

Mazda is working hard to keep the combustion engine relevant, with tricky spark-controlled compression ignition (SCCI) engines coming from the firm in recent years and biofuels and hydrogen being tested as we speak. Mazda is also thinking about other ways to evolve ICE power, one of which being a new supercharged two-stroke design.

It’s not real just yet, only existing as a patent, but it certainly looks interesting.

Two-stroke engines are different to the conventional four-stroke engine because they produce power twice as often for the same amount of cycles. The intake part of the cycle happens at the same time as the spark, thanks to a vacuum being formed underneath the piston. As the fuel ignites and forces the piston down, the exhaust gas exits the chamber at the same time as the fresh fuel is pulled up into the compression area and mixed with air.

Two-stroke engines are also typically less complex than four-stroke engines, as they don’t necessarily require camshafts, poppet valves, or other moving machinery in the top part of the engine.

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However, because two-strokes are also a total-loss system, meaning they burn oil as well as petrol during operation, they produce more emissions than a comparable four-stroke. For that reason they have been largely dropped, aside from small applications like chainsaws and some motorbikes.

But Mazda seems to think it has cracked it. Going by the patent drawing, it looks like an engine closer to a four-stroke than a traditional two-stroke, and uses Mazda’s SCCI technology. That means it can in a lean-burn, spark-controlled compression ignition mode at low and medium power and as a conventional spark-ignition engine at high power.

And, for good measure, Mazda has bolted a Roots-type supercharger to the engine as well.

The variable valve timing system allows some incoming air to escape, effectively lowering the compression ratio, while also allowing both valves to be opened to pull exhaust gases from the engine. VVT also allows the compression ratio to be adjusted on the fly, for more power or more efficiency, depending on circumstances.

But there’s still the niggle of emissions. In the patent, Mazda says: “In this embodiment, the engine does not include a catalyst for removing NOx but may include a catalyst for removing NOx.' That means, if the engine does get through to production in some shape or form, it might require extra work in the exhaust system to keep emissions down.

And on that, there’s no word if Mazda wants to actually produce the engine. The patent just shows what the company is thinking about, and wants to protect from other manufacturers. If it does arrive, we could see it as a small-capacity single-cylinder range extender (which may not need the extra NOx catalyst), or a multi-cylinder powertrain.

It might even run on hydrogen, considering Mazda and Toyota are working closely on things of such a nature…