Just when you thought Porsche was phasing out internal combustion the Stuttgart sports car maker has decided to re-invent the whole process.
Porsche has now developed a six-stroke combustion system which adds an additional compression and power stroke to increase efficiency and horsepower. If the tried and tested four-stroke Otto cycle can be best remembered by the order ‘suck, squeeze, bang, blow’ then Porsche’s method is ‘suck, squeeze, bang, squeeze, bang, blow’.
A patent application described as a “method for combustion machine with two times three strokes” reveals a crankshaft that spins inside a ring on planetary gears. 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. Adding the extra strokes should deliver a more complete fuel burn for better power, efficiency and reduced emissions.
The idea of a six-stroke engine has been around since Samuel Griffin devised a system in 1883, while more recently Bruce Crower came up with a six-stroke diesel which 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.
