Not long ago, there was a lot of talk from carmakers about switching to all EV fleets, and finally letting go of the jumping, oily pistons that got them where they are today. But now a lot of carmakers are walking that pledge back, and realizing that they may be dealing with combustion engines for a bit longer after all. Gasoline is so energy-dense, it’s hard to quit it, after all. In light of this, it’s interesting to see how combustion engine development is being pushed forward, especially when it comes to really strange stuff like what’s seen in this Porsche patent application for a six-stroke engine.
Yes, six-strokes! Or, as the patent application confusingly titles it, “METHOD FOR A COMBUSTION MACHINE WITH TWO TIMES THREE STROKES.” Why the hell did they call it that way instead of saying “six strokes?” Is there some technical reason I’m missing?
I suppose a four-stroke engine takes two rotations of the crankshaft, and a two-stroke takes one, so this six-stroke one takes three rotations. Maybe it’s because of that? I’m really not sure.
The engine described in the patent application is pretty interesting. Here’s how the patent abstract describes what’s going on:
A 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 to a first bottom dead- center; compressing an air-fuel mixture ni the combustion chamber while moving the piston from the first bottom dead-center to a first top dead-center; burning the air-fuel mixture while moving the piston from the first top dead-center to a second bottom dead- center; compressing a gas mixture ni the combustion chamber while moving the piston from the second bottom dead-center to the first top dead-center; burning the gas mixture while moving the piston from the first top dead-center to the first bottom dead-center; and expelling the gas mixture from the combustion chamber while moving the piston from the first bottom dead-center to the second top dead-center.
That’s uh, kinda tricky to follow, so let’s just simplify what they’re talking about into a description of strokes, because that’s at the root of all of this. First, let’s refresh what a four-cycle engine does:
Okay, now what this patent application proposes is this:
So, what they’re doing is adding on an extra compression stroke after the power/combustion stroke, and then another power/combustion stroke, then exhaust to clear everything out.
Essentially, it seems like it’s compressing and combusting the same charge of fuel and air twice. Is there that much unburnt fuel after combustion in a modern engine, enough to get some usable benefit from burning everything twice? Maybe?
The extra compression and power stroke have a different top- and bottom-dead-center than the first compression and power strokes because the piston is on a crankshaft that rotates within a planetary gearset, so it’s also a variable-compression engine.
You can see the crankshaft and piston planetary gear design in the patent drawings:
That’s a lot of manufacturing complexity to get that extra power stroke.
There have been six-stroke engines before, starting with Samuel Griffin’s 1883 design, which you likely know as the Kilmarnock engine you use to run your private power plant:
There were also some six-cycle engines that included a water-injection cycle, but this Porsche concept feels very different from all of those. Frankly, I’m not at all sure how much benefit an engine like this could have over a conventional four-cycle; it must get some more power and efficiency, sure, but enough to justify all the extra complexity and potential points of failure?
But I’m not an engineer! And who knows why Porsche patented this, it could just be to prevent anyone else from getting any fancy six-stroke ideas. You know how patents work.
I guess we’ll just have to see what happens, like we always do, eventually.
I don’t know who needs to read this, but I attempted to watch the embedded video for Torch Drives in this article and before I was two minutes into the video I had to sit through no less than 8 30-second ads….needless to say I pulled the plug on trying to watch…
Interesting… not sure if it’ll be worth anything, but at least it might sound cool.
I recall reading a report about 10-15 years ago about Honda working on a 6 stroke engine as an alternative to the Atkinson cycle engine.
And as far as I can tell, nothing ever came of it.
I’m not fully getting it either but I’m guessing it’s mostly about reducing emissions.
The engine that makes YOU go Hmmm.
“…it seems like it’s compressing and combusting the same charge of fuel and air twice. Is there that much unburnt fuel after combustion in a modern engine, enough to get some usable benefit from burning everything twice? Maybe?”
No, there is not enough unburnt fuel(or oxygen) to ignite again in a modern engine’s exhaust gas(or a really old engine for that matter). And that’s not what Porsche is doing here. The graph with a helpfully labeled “scavenging” section describes it quite nicely; it is literally just alternating between being a four stroke and a two stroke, for a total of six strokes. After the power stroke, it is doing some two stroke-style scavenging through the ports, then back to four stroke operation. So the second compression and power stroke is happening with some fresh air/fuel, not the old burnt stuff.
Why they decided that idea was even worth writing down, I do not know. What I do know is that each cylinder effectively has its own uneven firing order, so this thing would sound really weird and the “inertial supercharging” effect of a tuned intake and exhaust would not work very well. I see literally zero advantages of alternating between two stroke and four stroke: it seems like it just neuters all of the advantages of a two stroke engine.
Yeah I think you’ve got it.
It’s hard work wading through intentionally-vague patent wording, but I think the key thing is hiding in the indefinite/definite articles (emphasis mine):
The mixture you feed in might not be the exact same as what is compressed in the first compression (?)
However the result of that compression IS then ignited.
The mixture that is compressed in the second compression is not the same either. Probably due being mixed with some scavenged gases.
The wording makes me think that some of the initial intake is “set aside” in order to be used for the second squeeze-bang cycle, knowing that it will be mixed with some scavenged gas that will give it different characteristics.
It’s a lot of work though
If this works can we ditch catalytic converters?
Could probably ditch EGR valve, as this seems to take care of the unburnt exhaust
Suck-Squeeze-Bang-Squeeze-BangAgain-Blow?
I think I saw that in a porno flick.
I’m thinking Suck-Squeeze-Chitty-Chitty-Bang-Blow… LOL
Works for me.
I was trying to explain this to a friend the other day and the best I could come up with is it functions like a 4 stroke engine until the end of the expansion stroke, then it behaves like a 2 stroke for an intake/exhaust compression stroke , then after the expansion stroke it completes the exhaust stroke like a 4 stroke engine (though I can’t tell if they’re bringing in fresh charge via the ports exposed at UT’’ and opening the exhaust valve or if that’s an exhaust port and they pop the intake valve, but former seems to be the case). Anyway definitely seems like there are thermal efficiency benefits and the longer relative expansion strokes should help, and the scavenging of the cycle will I’m sure benefit from a healthy amount of boost (electric turbo maybe?).
But will the thermal efficiency benefit significantly outweigh the added friction from that whole ring gear contraption? I’m sure the specific output or efficiency will have to have a big benefit to justify production, but if anyone has the margins to add this much cost to an engine, it’s Porsche!
I’m not sure how the scavenging part works, does it behave like a two-stroke diesel for part of the cycle? Those ports at the second bottom-dead center make me think that fresh air is being introduced after the first power stroke, which implies that the exhaust valve would be open briefly. So unless you’re adding fuel too, the second combustion stroke would be lean and hot, with most of the burned and unburned gasses from the first combustion stroke, like an extreme version of EGR.
I think you’d also get some of the advantages of a true Atkinson cycle engine, since the power stroke is effectively longer than the intake stroke. So you’re expanding the gasses to a bigger volume than they were going in.
It’s an interesting design. I’m not sure how oiling the piston and rings would work. Either you’d have too much oil and it would go out through the transfer ports, or not enough oil to prevent piston wear. It could also be killed by carbon buildup causing a ring to snag on the ports.
Same way every other ported engine cylinder works. When the piston travels up and the ports no longer communicate with the combustion chamber, the piston skirts cover the ports so they don’t communicate with the crankcase either, and oil is prevented from majorly splashing out of the ports. Yes, some amount of oil will go out of the ports, but not that much.
Some engines, like a Detroit, have an extra piston ring or two at the bottom of the skirt to help keep the oil down in the crankcase. Like you said, though, that definitely reduces the amount of oil accessible to the top rings. That is somewhat less of a concern on a diesel since diesel fuels have much better lubricity.
I immediately thought of the Miller cycle used in the Mazda Millenia but that only uses 5 “strokes”
I only recently (as in this week) learned that the Volkswagen EA211 engine (the current 1.5 gas turbo used in multiple vehicles) runs a modified Miller cycle. Makes me wonder whether the 2.0T from the GTI is the same.
Regarding the Kilmarnock: I love that the “Smellie & Co.” organization is touting their engines’ “absence of noxious vapors”.
Going to be that guy, but since it’s in my line of work:
This is not a patent just yet. It’s a publication of the application Porsche filed. That said, it has been allowed and the issue fee paid so it’s just a matter of the actual patent issuing.
Sometimes, large companies will file patent applications on things their teams have worked on that may be of marginal value because there are rewards for the engineers for getting a patent, and/or because the engineers like having their names on a patent. Maybe that’s the case here?
Thank you. As a fellow patent practitioner, it bugs me to no end all the articles in media talking about some company “patenting” something when really it’s just still an application. At least here, despite the headline, it is made clear in the first paragraph that it is an application. As for why bother filing if they aren’t going to implement, corporate patent strategies can be complex and are very much specific to each company. Rewarding the engineers with this recognition, while not overlooked, is seldom the sole reason for filing just due to the expense involved. I see in the ADS there is a university listed as the second applicant, so my bet is this is the result of some sort of joint-development or research project that the inventors were engaged in. Who knows what the contractual relationship there requires for patent application obligations among the parties.
This is just the number-of-blades-on-a-razor all over again.
Porsche have only gone to six because Gillette went to five.
Ferrari will now go up to seven, forcing Lamborghini up to eight.
I imagine Honda are either working on fractions of a stroke or will blindly insist that four is best.
The blades in razor analogy reminds me of bicycles where there has been a steady escalation in cogs in a cassette with groups going from 10 or 11 around 2010 to 13 speed groups coming out.
Generally, those large more modern cassettes allowed dispensing with the front derailleur and extra rings, so it was ultimately a reduction in overall gear ratios (ignoring the near duplicates that reside within traditional 2x or 3x setups, of course).
Yeah I understand the value of 1x drivetrains but I’m cheap/retro and my MTB is still 2×9 and 26″ wheels and my “road” bike is 2×10. I see the value of no front derailleur and shifter, but a 13 speed cassette pushes the limits because cog spacing is so tight
I’m not into the newest stuff, either. My bikes range from 1912 to 2000 and I ride the former far more than the latter. I don’t like those thin chains of those modern cassettes and I prefer friction shifting to indexing most of the time, especially with my odd customs as they don’t require readjustment as often and trimming is just part of shifting. For me, one of the greatest things about the bicycle is that it should last indefinitely with minimal maintenance and waste and (usually) great flexibility, which the newest plastic junk with short-lived standards will not. The inch-pitch chain on the 1912 is likely not original, but is certainly old and is still good. It also takes a 1″ stem, 700c (originally wood 28″ American tubulars, but I didn’t want to risk riding those and couldn’t find appropriate tires, so I built some modern wood clinchers for riding), and 1/2 pedals if I needed to change that stuff (though that’s a kid bike size today). Front hub is 90 OLD, but they’re out there. The 2-piece BB is very much its own thing. Thankfully, it’s robust design, well made, and easy to maintain once I figured out how to take it apart (and made a tool).
Roller width difference is .2mm between 7/8 speed and 9/10/11/12 speed. The narrower 9-12 speed chains are usually stronger with the shorter pins.
I get being a curmudgeon, and even I haven’t bought into the electronic shifting (yet), but modern mechanical drivetrains are pretty great.
1x makes more sense than 2x and 3x and is a cleaner design, for sure, with no ratio redundancies, easier for the average person to manage, and arguably less maintenance with a single derailleur for what’s likely a largely incidental difference in parts lifespans. It’s not strength I care about (I haven’t broken a chain since my BMX bike as a kid), it’s resiliency. These wide range cassettes require greater angularity on a narrower chain and the narrow sprockets are built light to save less weight than I sweat out over a mile wear faster so they wear faster. Yeah, they’re relatively cheap, but not as cheap as they could be when they have to produce and stock more product that costs more to produce per unit (and it’s not so much the cost, it’s the waste). In isolation, though, it’s not the drivetrains that bother me, it’s pretty much everything (dammit, I do like disc brakes) from short lived standards that offer little to no meaningful improvement—or are even inferior, like some recent BB designs—but require specialized frame design and possibly tools to the proliferation of plastic frames and, most definitely, electronic shifting, which is like the touchscreen replacing switches. It would also make the kind of customs I’ve made more difficult, but that’s a very specialized problem (pun intended). If all that crap stays at the high end, great, but these things tend not to and that’s my problem both as someone who abhors waste and who wants more people on bicycles, even if they only ride a few times a year. I fully recognize that this is yelling at phantom clouds as the whole argument is based on pedal bikes when it’s E-bikes that are really taking over.
Thing that bothers me about those, other than the increased chain angle and inability to downshift under load, is that the rear cassette is so damn big. It bothers me and seems like it would get damaged somehow, even though I’m sure that’s not the main concern.
The dinner plate sized cassette seems to work OK based on a demo and a rental, but the small chainring still looks weird
Reminds me of one of my favorite articles from a sister of the German Lighting Site:
https://theonion.com/fuck-everything-were-doing-five-blades-1819584036/
Former sister.
Ah, yes… Sad times. It’s disheartening to see what’s happened to them all. Thankfully we have the Autopian though 🙂
The Onion may be in good hands, though. Long may she wave.
That was the most sexy poetry I’ve ever read. Thank you.
Yeah, but who will go to 11?
“These go to 11”
It wasn’t hard for me to find another article explaining why they call it 2×3 stroke, which also expanded on the possible benefits of such a design
https://interestingengineering.com/innovation/porsche-6-stroke-engine-innovation
https://www.roadandtrack.com/news/a62258759/porsche-six-stroke-combustion-engine-patent-documents/
Do they really expand on it though? Nvm that the first article has a super clickbaity headline, I don’t see much explanation of the benefits beyond “every third stroke is a power stroke instead of every fourth” which in and of itself doesn’t mean much unless we know how much power can actually be extracted from the spent fuel mixture. Adding 2 extra strokes to the cycle for like a 5% power benefit for example doesn’t sound like much of an innovation, considering the added complexity and lubrication issues. Especially not an innovation that “could rewrite automotive engineering”
I think this is just one of those corporate patent applications that have little to no intention of being utilized in an actual product. Seems like a much better idea for VC than Nissan’s Mickey Mouse implementation and more fully utilized with maybe some thinking about Atkinson or even a multi-expansion steam engine thrown in as inspiration. Potential advantages in economy and emissions are great, but what about noise from those spur gears, friction, rpm capability, torque, balance, and anticipated long term durability? Obvious questions aside, I love this kind of stuff and I hope they build a test model and release a video of the running.
So, a hit-and-miss engine?
Not if they’re firing the plug and igniting combustible residue.
I had six strokes trying to figure this out.
Comment #2:
The ultimate EGR System?
Pro: maybe it would be very fuel-efficient and wouldn’t require a catalytic converter.
Con: holy adding many parts and 1000 gear teeth to the engine, batman!
Yeah but it’s German, so it will be a simple & inexpensive fix!
Better this than catalyzing unburnt fuel. Even a few percent of thermal efficiency gained would be huge!
I drove my three-cylinder, two-stroke SAAB 96 to work today and 3×2=6, so there we have it: prior art. It’s right there in the math.
HalfLife 3 Confirmed?
I think how it goes is: Intake Upcharge Compression Upcharge Ignition Exhaust
Jason, you need to remember; to a German engineer, extra complexity and points of failure are a defining feature, not a problem to be overcome!
And a way to charge 50% more!