Porsche patents six-stroke engine

DESPITE espousing the virtues of, and imminent transition to battery electric power, Porsche has revealed a six-stroke combustion engine rekindling technology devised more than a century ago.

The performance car specialist and its parent, Volkswagen Group, appear to be covering all options after sales of BEVs in general have failed to achieve expectations particularly in Europe.

The engine will likely burn e-fuels Porsche has been developing for use in high performance Porsche combustion engine models of the near future and would be a hedge against potential resistance from rusted-on ICE-powered Porsche customers who won’t entertain driving an EV.

As revealed in publication Hagerty, the six-stroke is basically an Otto-cycle four-stroke with a second compression and ignition cycle thrown in.

In rudimentary form, what you are looking at is: suck, squeeze, bang, squeeze, bang, blow or put another way: induction, compression, ignition, compression, ignition, exhaust.

The second compression and ignition cycle of the crankshaft is facilitated by its rotation within a planetary gear giving elliptical rotation and a longer stroke on the second compression/ignition cycle that exposes ports low in the cylinders much like a two-stroke.

According to publication Motor Trend, the first three strokes are very like those in a four-stroke but after that, bottom-dead-centre drops deeper than after stroke one, exposing scavenging ports.

Fresh air is forced in, driving much of the spent exhaust out the overhead exhaust valve.

On the next up stroke, the mixed fresh air and exhaust charge is compressed, and fuel is directly injected, evaporating, cooling, mixing and compressing this charge. At the top of the stroke, it is ignited for the second power stroke.

Conventional exhaust and intake strokes follow.

The six-stroke’s appearance means Porsche is not imminently phasing out internal combustion but merely re-inventing it, making ICE more efficient, smoother and more powerful into the bargain.

It is going through a patent application at the moment where the German car-maker describes the six-stroke as a “method for combustion machine with two times three strokes” and reveals the crankshaft spinning inside a ring on planetary gears.

Patent application details show as the shaft rotates the pistons have two different top-dead-centre and bottom-dead-centre positions. Variable compression is also created as a result.

Porsche would be expecting the technology deliver a more complete fuel burn for better power, efficiency and reduced emissions.

Hagerty’s report says, “the idea of a six-stroke engine has been around since Samuel Griffin devised a system in 1883, while more recently Bruce Crower (of racing camshaft fame) came up with a six-stroke diesel that added water injection as a fifth stroke and a steam flash as the sixth”.

“So far it would appear that the benefits of six-stroke combustion have been outweighed by the complexity and cost of the designs, but perhaps Porsche could use it to cling onto combustion a while longer in conjunction with ramping up production of carbon neutral e-fuels,” the report concluded.