When it comes to future-proofing the combustion engine, the thinking so far has been quite conventional with ideas such as hybrid powertrains or synthetic fuels. Porsche seems to now be going another, radically different way. The German sports-car maker has just filed a patent for a new type of powerplant that is best described as a six-stroke engine.

Filed under US patent application 18/585,308, it is described as follows:

Method for a combustion engine has a working cycle of three revolutions of the crankshaft. The method includes: feeding a fuel mixture into a combustion chamber of a cylinder while moving a piston from a second top dead center (TDC) to a first bottom dead center (BDC); compressing an air-fuel mixture in the combustion chamber while moving the piston from the first BDC to a first TDC; burning the air-fuel mixture while moving the piston from the first TDC to a second BDC; compressing the gas mixture in the combustion chamber while moving the piston from the second BDC to the first TDC; burning the gas mixture while moving the piston from the first TDC to the first BDC; and expelling the gas mixture from the combustion chamber while moving the piston from the first BDC to the second TDC.

It sounds confusing and is certainly different from anything else on the market right now, although the patent claims priority over a German one from last year. In a nutshell, the engine completes its cycle not with two crankshaft rotations like a four-stroke, but with a full 1,080° crankshaft rotation, effectively running as a six-stroke engine.

Interestingly, it has two sets of three-stroke processes, each with its own power and compression phases. So, you could say that—instead of suck-squeeze-bang-blow as with a four-stroke—this engine goes suck-squeeze-bang-squeeze-bang-blow.

The cylinder setup is key to making this method work. It uses a piston connected to a planet wheel via a connecting rod. The planet wheel, which engages with an annulus, rotates within it and connects to the crankshaft.

This setup shifts the rotation center, subtly reducing the piston’s travel to a lower bottom dead center during the extra strokes. It also changes the compression ratio since the piston doesn’t reach as high a TDC in the cylinder. As a result, this engine actually features two distinct top and bottom dead centers.

Why did engineers go through all this trouble? The idea is to deliver more power and better efficiency. In a standard engine, only one out of four strokes produces power. This setup tweaks that ratio to one power stroke in three, while also achieving more complete combustion of the fuel mixture. It does bring with it a lot of added complexity, so if we will ever see this setup in a production car remains to be seen.