Porsche patents cleaner, more powerful six-stroke engine design

Porsche has patented a revolutionary six-stroke combustion system. Unlike all modern internal combustion engines that operate on the four-stroke Otto cycle, which typically has a compression and ignition phase, Porsche’s system adds another.

The result is that in one cycle the piston compresses the fuel-air mixture in the combustion chamber twice, rather than once, with two combustion events and therefore two power strokes. The second recompresses the waste product of the first. The six-stroke cycle is more like two mini-cycles of three, with intake, compression, power in one, followed by compression, power and exhaust in the next.

This is achieved by a crank that rotates around a planetary gear and simultaneously rotates itself. This means that it does not just rotate around a fixed center. Rather, there are two top dead center and two bottom dead center positions within the rotating ring. This also means that the piston stroke and compression are different in the two top and bottom dead center states. Simply put, there is no fixed compression and stroke like in a four-stroke engine with a fixed crank.

The result is greater efficiency and, more importantly, greater power, albeit with a little more complexity. Since power is now delivered every three strokes instead of every four, it stands to reason that there should be more of it. The combustion process should be cleaner, with the second compression phase effectively “scavenging” gases from the first combustion and burning them again, similar to how an exhaust gas recirculation system works, without actually having to recirculate. The thermal efficiency potential of a six-stroke engine is up to 50 percent, compared to the 30 percent considered average for a four-stroke engine.

What might this mean for the feel of an engine? As mentioned above, power on every third stroke instead of every fourth sounds good, but what does a six-stroke cycle mean for throttle response, engine speed, and also sound? We don’t know yet, but given the added complexity and potential for vibration, one has to wonder if this technology is suitable for high-revving applications like a 992 Porsche 911 GT3.

As is always the case with patent applications, there is no mention of the production intention or any associated problems or drawbacks of the design. What is clear and reassuring, however, is that Porsche is employing some of its brightest minds to think about how the combustion engine could evolve for a new era. In parallel, they are working hard on the development and production of e-fuels and electrification.