Duke Engines' compact, lightweight valveless axial engine

http://www.gizmag.com/duke-engines-axial/33631/

by anovio • 12 years ago

82 56 12 years ago

Roboprog• 12 years ago

Looks 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• 12 years ago

I 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.

MadManE2• 12 years ago

Yeah, 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.

ew60822• 12 years ago

It 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.

MadManE2• 12 years ago

There 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• 12 years ago

No 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.

BrandonMarc3• 12 years ago

Thank 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• 12 years 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.

MattBearman2• 12 years ago

As 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.

frankus• 12 years ago

The short answer is that they're difficult to seal and the combustion chamber shape is awful (it looks like a flattened figure eight in cross section).

It's super tempting as an engine designer to take something that works well as a fluid pump and try and turn it into an internal combustion engine. But sealing and lubricating a combustion engine is a much more difficult problem than sealing and lubricating, say, an oil pump. Plus, in order to meet emissions standards, you need to worry about things like flame propagation and avoid little nooks and crannies where unburnt fuel mixture is likely to hide.

Usually the limited success of these sorts of engine designs isn't a case of a mad genius being too far ahead of his/her time, but rather that the advantages, however compelling, don't make up for one or more fatal flaws.

ew60822• 12 years ago

In this case the sealing issue is probably in better shape than the Wankel, since the seal is located outside of the combustion chamber. I could see something similar to a piston ring in a groove with a wave spring behind it being used no problem.

jccooper• 12 years ago

There is a brief mention of efficiency, but that doesn't seem to be a big point. The port structure does make me think it might be a bit dirty--kinda two-stroke-y.

But not all engines go in cars. Might be a nice one for aviation--though aviation engines are maybe even more handicapped against change than those in automobiles. The experimental aircraft market ain't that big. Other markets where Rotax lives might like it; pumps and such.

Anyway, that's probably another one of the reasons they're not expecting automotive applications in the first generation.

vlucas• 12 years ago

The 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_lord3• 12 years ago

215hp 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.

iaw2• 12 years ago

I 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).

jff• 12 years ago

It 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• 12 years ago

Wow. That looks inspired by a helicoptor's swashplate driven from the rotor side. Always fun to see an alternative engine design.

IanDrake3• 12 years ago

The 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.

phkahler2• 12 years ago

One 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• 12 years ago

Distilled water is corrosive to an engine. Otherwise an interesting idea.

mikepurvis• 12 years ago

I 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

Completely impractical, but an interesting experiment. There's some more general info on Wikipedia: http://en.wikipedia.org/wiki/Six-stroke_engine

Animats• 12 years ago

Axial engines go back a long way, to at least 1917.

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.

BrandonMarc3• 12 years ago

I 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• 12 years ago

Seems convenient to use a pretty lame reference engine to make yourself look good. 3 liter engines have made near 1000HP for years now.

JoeAltmaier9• 12 years ago

How about hp per pound? Isn't that the advantage of this thing?

aidenn02• 12 years ago

Like 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.

mikeytown2• 12 years ago

The best naturally aspirated piston engine is 166 hp per liter. The best naturally aspirated Pistonless rotary engine is 188 hp per liter [1]. The Duke is at 71 hp per liter; it has a long ways to go but it's already better than a naturally aspirated Diesel engine (44 hp per liter).

[1] http://en.wikipedia.org/wiki/List_of_automotive_superlatives...

aunty_helen2• 12 years ago

I always find it interesting that when hp/l stats are quoted they often neglect to include motorcycle engines... which have been in the 180-210 hp/l realm for about 5 years now.

And a high hp/l isn't necessarily the best piston engine as it's often at the cost of massive valve train losses resulting in poor fuel efficiency.

bradleyland5• 12 years ago

I agree that Duke has done relatively well, considering their limited resources. That is to say, Comparing superlatives isn't entirely fair to Duke.

BMW makes for good comparison here because they make a lot of 3.0L inline-6 engines. Their N52B30 engine [1] was (mass) produced in a variety of specific outputs, the nadir of which was the 200kW (272 HP) version used in two of their sporty SUVs. This engine makes/made 90 HP/L. The most common variant (used in the mid-tier 3-series) was the 190 kW version, making 86 HP/L. Both of these engines have a better specific output than the Duke engine, but BMW has considerably greater engineering resources, as well as the benefit of nearly 100 years of development.

1: http://en.wikipedia.org/wiki/BMW_N52#N52B30

jdietrich• 12 years ago

This 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/

JoeAltmaier9• 12 years ago

Do the pistons rotate, or does the disk? The disk would have less mass I suppose.

desdiv• 12 years ago

The 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.

aunty_helen2• 12 years ago

Ah! Good point about the reciprocating mass. I did wonder why they suggested them for marine and aviation (semi-static rpm) applications but not cars etc.

Coupled to a automatic or CVT gearbox it may get around this problem.

I do think that your point about it lacking VVTL is somewhat amusing though.

JoeAltmaier9• 12 years ago

Maybe useful for a stationary generator? Currently my options for a natural-gas generater are one: Honeywell makes a line of 5-12KW device. But they are god-awful noisy; its all any of the reviewers talk about.

But this gadget would shine there! Quiet, no vibration, run it at a single optimum speed all the time. Where can I get one!

Duke Engines' compact, lightweight valveless axial engine

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