Mazda now has a patent for a two-stroke supercharged engine design in the United States. This is intriguing because two-stroke combustion powerplants are not something you find in any modern automobile. These days, you're more likely to find this type of mill in a leafblower or chainsaw.
As if the engine's two-stroke combustion cycle isn't fascinating enough, there are more features that make this thing fascinating. At low loads, the powerplant runs using compression self-ignition like a diesel and then can transition to spark ignition combustion when under higher loads.
Gallery: Mazda Two-Stroke Supercharged Engine Patent
Mazda's patent also mentions using variable valve timing to maintain a high compression ratio while operating under the diesel-like self-ignition. The timing would change when using spark ignition to reduce the compression ratio to prevent knocking.
If all of this sounds familiar that's because Mazda's Skyactiv-X engine is also capable of transitioning from compression self-ignition to using a spark plug depending on the conditions. In some markets, the automaker sells the Mazda3 with this powerplant.
The patent says this two-stroke supercharged engine has improved fuel economy but doesn't mention to what layout it is comparing that increase. Higher exhaust emissions are generally the major weakness for two-stroke mills, and the documentation doesn't indicate whether this design offers any advantages for that issue.
The filing offers no hints about Mazda's intentions for this engine. It's hard to imagine an automotive application unless this design has emissions and fuel economy significantly better than a traditional two-stroke.
Dirt bikes are one place where two-stroke engines are still fairly common. One possibility is that Mazda could license this design to a motorcycle maker.
With any patent, it's always possible for the engineers to come up with something new and decide to patent the idea. There's no intention for production. Instead, the company just wants to protect the intellectual property.