5 ms·
Duke Engines' compact, lightweight valveless axial engine
- Roboprog 12y agoLooks interesting, but I'm guessing there is a lot of stress on the recipricator mechanism that the pushrods connect to, pushing against an incline to cause the output shaft to rotate.
- bri3d 12y agoI agree, but in a typical combustion engine there is also a comparable amount of stress on connecting rod bearings and the typical design of a crankshaft also puts a lot of side-force on the entire piston and rod assembly. I can't find enough information on their "reciprocator" to see how it differs from other swash/wobble-plate based axial engine designs.
- MadManE 12y agoYeah, I'd be interested in seeing a life expectancy for these. If they're really all that's being said, I'm hopeful for the future.
- ew6082 12y agoIt can be as beefy as it needs to be. There is no constraint there to limit the design. It is actually an extremely flexible concept from what I can tell. Need a longer stroke? Add more angle to wobbler. Need more Torque? Expand the wobbler diameter.
- MadManE 12y agoThere is a limit on the available angle that can be "wobbled". Once you exceed ~20 degrees IIRC, the displacements perpendicular to the stroke start causing problems. I think the more interesting interaction is between the number of pistons and the size of the pistons.
- chiph 12y agoNo mention of meeting fuel economy and emissions requirements. Both of those are big topics that engine builders have to consider, with the 35mpg fleet-wide average that cars sold in the US must meet in about a decade. Having grown up in an age filled with car exhaust from carburated engines, I don't miss it a bit -- I like having clean air. One of the comments to the article mentioned the difficulty in keeping high-pressure seals working. It was in conjunction with Wankel rotary engines, which have always had problems with the rotor tip seals leaking (ask any Mazda RX owner...) This engine has the same problem on the intake/exhaust end, as the piston carrier rotates past the openings.
- BrandonMarc 12y agoThank you. I'd wondered how this would compare to a rotary engine. It's interesting how enthusiastic the rotary-engine crowd is, since my takeaway was always "well if it's so much better why isn't it more common".
- grecy 12y ago> "well if (rotaries are) so much better why isn't it more common". That's a complicated question with a complicated answer, but it basically boils down to there having been hundreds of billions of dollars (trillions?) spent on R&D for traditional (pison, conrod, crank, block) engines, while only a tiny amount has been spent on R&D for rotaries and other "different" designs.
- MattBearman 12y agoAs an RX8 owner (and enthusiast), I can tell you Wankel Rotaries aren't categorically better, or worse. They have strengths and weaknesses: - The vast majority of rotaries will need a full rebuild before 100k - worse - They rev to 10,000 RPM with an unbelievably smooth power delivery - better - I'm lucky to see 22 mpg - worse - The engine is so small and light that the RX8 has perfect 50/50 weight distribution - better - If you turn the engine off before it's warm it can flood - worse - 231 bhp from a 1.3 litre engine? - better Oh, and the noise - BETTER! I do believe with more time and money invested the Wankel Rotary could be better than a standard Otto Cycle IC engine in every way. But electric is the future now, so that won't realistically happen.
- vlucas 12y agoThe money quote, for the TL;DR crowd: "Duke Engines' 3-liter, five cylinder test mule is already making a healthy 215 horsepower and 250 lb-ft of torque at 4,500rpm – slightly outperforming two conventional 3 liter reference engines that weigh nearly 20 percent more and are nearly three times as big for shipping purposes. With an innovative valveless ported design, the Duke engine appears to be on track to deliver superior performance, higher compression and increased efficiency in an extremely compact and lightweight package with far fewer moving parts than conventional engines."
- noir_lord 12y ago215hp out of a 3 litre is shockingly low except for a naturally aspirated carburator engine from the 80's. For example the 2 litre 2015 Mondeo Turbodiesel gets 210bhp. The article is interesting but reads like a marketing release, the weight saving is the interesting take away I think if reliability matches a modern diesel.
- iaw 12y agoI do agree with you but a turbo diesel isn't a valid comparison because it is: 1) turbo charged 2) diesel fueled An inter-cooled turbocharger setup on this engine would likely net an additional 100 HP without much issue (presuming the sealing issues aren't horrific). Generally 100 HP per litre of displacement is the gold standard for naturally aspirated engines (see Ferrari).
- BrandonMarc 12y agoCurious: what's the alternative to naturally aspirated engines? Space-bound rockets?
- Gracana 12y agoThe other side of the coin is forced induction, using a turbocharger or a supercharger or even both. "Natural aspiration" just refers to engine with intake air at atmospheric pressure.
- jff 12y agoIt seems to share some things in common with the rotary, like moving the ignition chamber past the fuel/exhaust ports, rather than opening/closing valves. So it will need some way to seal the cylinder during compression/ignition... will those seals tend to break up at 100,000 miles like a rotary's apex seals?
- gills 12y agoWow. That looks inspired by a helicoptor's swashplate driven from the rotor side. Always fun to see an alternative engine design.
- IanDrake 12y agoThe only ICE advancement that really seems interesting to me is adding an extra cycle to inject distilled water into the cylinder for an extra power stroke. The idea being that the heat from the prior explosive power stroke is used to turn the water into steam. Now you're using wasted heat energy and removing the need for cooling components.
- phkahler 12y agoOne downside to that is that cooling everything will add to NOx in the emissions. A nice hot exhaust is needed for the catalyst to complete clean combustion. Not that it's a bad idea, just that it has an emissions tradeoff.
- ams6110 12y agoDistilled water is corrosive to an engine. Otherwise an interesting idea.
- mikepurvis 12y agoI saw an article about that idea a few years ago, and wondered if it might be possible to combine it with a rotary engine. I ended up creating this rather odd-looking model: http://sandbox.mikepurvis.com/design/engine.svg http://sandbox.mikepurvis.com/design/engine.svg Completely impractical, but an interesting experiment. There's some more general info on Wikipedia: http://en.wikipedia.org/wiki/Six-stroke_engine http://en.wikipedia.org/wiki/Six-stroke_engine
- Animats 12y agoAxial engines go back a long way, to at least 1917. https://en.wikipedia.org/wiki/Axial_engine https://en.wikipedia.org/wiki/Axial_engine That format is widely used in hydraulic systems, and is the basis of continuously-variable hydraulic transmissions. Classically, it has problems at high RPMs, but is well behaved at low ones. It's an idea that might be worth looking at again. With better materials and controls, it might work. The geometry is more flexible than with Wankel engines. The elegant Wankel geometry means there aren't many parameters that can be adjusted to improve combustion. In a piston engine, you can design piston face geometry, cylinder head geometry and fuel and air injection points for better combustion. With a Wankel, you're kind of stuck with the geometry. We'll have to see how this new approach works on pollution control.
- BrandonMarc 12y agoI assume the application most people have in mind is cars. As others have said, electric seems to be the future there, so while this may be a revolutionary engine, it's possible the timing won't help it. What about other applications? Would this work well for marine, aviation, factory, or other purposes?
- erik_landerholm 12y ago"Duke Engines' 3-liter, five cylinder test mule is already making a healthy 215 horsepower and 250 lb-ft of torque at 4,500rpm – slightly outperforming two conventional 3 liter reference engines that weigh nearly 20 percent more and are nearly three times as big for shipping purposes." Seems convenient to use a pretty lame reference engine to make yourself look good. 3 liter engines have made near 1000HP for years now.
- JoeAltmaier 12y agoHow about hp per pound? Isn't that the advantage of this thing?
- aidenn0 12y agoLike other engines where the pistons rotate (e.g. Gnome) it does have the weight advantage of not needing a flywheel (since the engine is its own flywheel). Other than that, probably not much.
- JoeAltmaier 12y agoBut its supposed to be 1/3 the weight of an equivalent engine. Sounds like a lot?
- aidenn0 12y agoWithout seeing what engines they are comparing it to, I can't say for sure. My guess would they are comparing at similar RPMs, or have some other restriction. I'm sure it weighs a lot less than a traditional 3L engine, but I would guess it generates a lot less power at redline.
- JoeAltmaier 12y agoSure its different, and comparing it via the normal means (litres or rpms) won't work because its so different - those means assume a substantially identical engine or they don't work at all.
- jdietrich 12y agoThis isn't a new engine, it isn't a new idea, and it isn't a particularly good idea. Duke Engines have been around since 1993, and built their first prototype in 1996[1]. Axial engines themselves date back to 1911; Their practical use is limited to torpedoes, where the cylindrical form-factor is an advantage. Axial engines have inherently high reciprocating mass compared to conventional piston engines, which is a catastrophic flaw in a performance engine design. Higher reciprocating mass increases inertia (reducing throttle response) and increases the forces at the end of the stroke (reducing maximum RPM). They offer no meaningful advantages in terms of fuel efficiency, and are likely to be less efficient in many applications due to the difficulty of implementing existing efficiency technologies (VVT&L, valve deactivation etc) Both the current Duke engine and their hypothesised next-generation engine offers poorer specific power than current naturally-aspirated designs. The cylindrical form-factor is more difficult to package than a traditional piston engine; Camshafts offer enormous flexibility in terms of layout, allowing the engine to be squeezed into a multitude of shapes and sizes. Axial engines are inherently balanced, but balance is practically a non-issue in modern engines, even for layouts with very poor inherent balance. [1]http://www.dukeengines.com/technology/overview/ http://www.dukeengines.com/technology/overview/
- JoeAltmaier 12y agoDo the pistons rotate, or does the disk? The disk would have less mass I suppose.
- desdiv 12y agoThe pistons rotate. Not just the pistons, but the cylinders and the connecting rods as well. It's basically the entire engine block rotating against a stationary cylinder head. The large rotating mass problem is basically what killed off the pre-WWII-style rotary engines, and the Duke engine suffer from the exact same problem.
- JoeAltmaier 12y agoSo why not connect the disk to the shaft, and have it rotate instead? Not a mechanical engineer, but that would have way less mass, way less clever mechanical linkages for valving, spark.