Automotive

Duke Engines' incredibly compact, lightweight valveless axial engine

Duke Engines' incredibly compa...
The Duke Axial Engine is lighter, more compact and already slightly more powerful than a typical equivalent engine, even though this is just a prototype
The Duke Axial Engine is lighter, more compact and already slightly more powerful than a typical equivalent engine, even though this is just a prototype
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The Duke Engine – Version 2
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The Duke Engine – Version 2
The Duke Engine – Version 3
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The Duke Engine – Version 3
The Duke Engine – Version 3
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The Duke Engine – Version 3
The Duke Engine features axially mounted pistons that drive a star-shaped reciprocator
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The Duke Engine features axially mounted pistons that drive a star-shaped reciprocator
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Duke Engine
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Duke Engine
The Duke Engine features cylinders that rotate past spark plugs, intake and exhaust ports at the perfect moment
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The Duke Engine features cylinders that rotate past spark plugs, intake and exhaust ports at the perfect moment
The Duke Engine features cylinders that rotate past spark plugs, intake and exhaust ports at the perfect moment
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The Duke Engine features cylinders that rotate past spark plugs, intake and exhaust ports at the perfect moment
The Duke Engine features a star-shaped reciprocator that spins the drive shaft as it moves around it
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The Duke Engine features a star-shaped reciprocator that spins the drive shaft as it moves around it
Duke Engine dyno testing
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Duke Engine dyno testing
The Duke Engine boasts five cylinders and only three spark plugs
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The Duke Engine boasts five cylinders and only three spark plugs
Axial piston movement pushes a star-shaped reciprocator in the Duke Axial Engine
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Axial piston movement pushes a star-shaped reciprocator in the Duke Axial Engine
The Duke Axial Engine is lighter, more compact and already slightly more powerful than a typical equivalent engine, even though this is just a prototype
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The Duke Axial Engine is lighter, more compact and already slightly more powerful than a typical equivalent engine, even though this is just a prototype
The Duke Engine features axially mounted pistons that drive a star-shaped reciprocator
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The Duke Engine features axially mounted pistons that drive a star-shaped reciprocator

New Zealand's Duke Engines has been busy developing and demonstrating excellent results with a bizarre axial engine prototype that completely does away with valves, while delivering excellent power and torque from an engine much smaller, lighter and simpler than the existing technology. We spoke with Duke co-founder John Garvey to find out how the Duke Axial Engine project is going.

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.

The Duke engine is an axial design, meaning that its five cylinders encircle the drive shaft and run parallel with it. The pistons drive a star-shaped reciprocator, which nutates around the drive shaft, kind of like a spinning coin coming to rest on a table.

The Duke Engine features axially mounted pistons that drive a star-shaped reciprocator
The Duke Engine features axially mounted pistons that drive a star-shaped reciprocator

The reciprocator's center point is used to drive the central drive shaft, which rotates in the opposite direction to the reciprocator. "That counter-rotation keeps it in tidy balance," says Duke co-founder John Garvey. "If you lay your hand on it while it's running, you can barely detect any motion at all, it's quite remarkable."

That's borne out by the video below, where the engine revving doesn't even cause enough vibrations to tip a coin off its side.

Low vibration engine with lighter weight

Instead of cam- or pneumatically-operated intake and outlet valves, the cylinders rotate past intake and outlet ports in a stationary head ring. The spark plugs are also mounted in this stationary ring – the cylinders simply slide past each port or plug at the stage of the cycle it's needed for and move on. In this way, Duke eliminates all the complexity of valve operation and manages to run a five-cylinder engine with just three spark plugs and three fuel injectors.

The Duke engine ends up delivering as many power strokes per revolution as a six cylinder engine, but with huge weight savings and a vast reduction in the number of engine parts.

Duke Engines

The engine has shown excellent resistance to pre-ignition (or detonation) – potentially because its cylinders tend to run cooler than comparable engines. Duke has run compression ratios as high as 14:1 with regular 91-octane gasoline. This suggests that further developments will pull even more power out of a given amount of fuel, increasing the overall efficiency of the unit.

Alternative fuels would appear to be a promising possibility. In a 2012 interview, Garvey said "we just switched it over [to kerosene jet fuel] one day and it just ran straight away, as well if not better than it was running on petrol."

Garvey tells Gizmag "we've developed the engine to the point where we feel it's ready to be commercialized. But we're still without funding, and we're looking for the right application to build toward. The engine seems suitable for a wide range of functions, but we need to find the right funding partner to develop it toward a niche that can maximize its advantages."

That's unlikely to be automotive in the immediate future; car manufacturers have already sunk a lot of money into their own engine technology. But aeronautics, portable generators and marine outboard motors are uniquely placed to take advantages of the Duke engine's high output, compact dimensions and low weight.

The Duke Engine – Version 3
The Duke Engine – Version 3

Another key opportunity might lie in range extender motors for plug-in hybrid vehicles – engines that don't drive the wheels, but run at high efficiency to drive generators and top up the battery of electric drive cars.

Duke has partnered with engine development company Mahle in the US, formerly Cosworth in the UK, and is ready to begin commercializing the technology once the right customer comes along.

"The estimate is that it's probably a process of a couple years to get it to production ready," says Garvey. "This has been a huge undertaking, and sometimes you wonder if you should have started in the first place – but we've built an engine with some impressive advantages over current technology. It's the smallest and lightest engine around for its displacement and power output.

"Even our prototypes are outperforming established engines of the same displacement and there's a lot of development left in there for further weight reduction and performance gains. So we're very optimistic."

Source: Duke Engines

64 comments
citfreak
Hark! another axial piston engine from down under & surroundings (well, that's my mid-european view, hope nobody will be offended), after AGM Mitchell's crankless engine from about 1920. As hydraulic pumps and motors run well using the swash plate principle, why not an IC engine? Fuel efficiency will not be its main merit, as friction losses will be higher, but vibrations should be lower and in a less obtrusive direction, I think.
GeoffG
I wish them every success. The number of alternative I.C. engines that have been invented over the years is incredible, yet where are they all? Australian Ralph Sarich had some great rotary and non-rotary engines and became a millionaire selling rights to many world engine manufacturers back in the 70's - yet where are they? Concentrating on non-automotive applications seems to be the right approach - car manufactures are just too conservative. Only NSU and Mazda had the guts to try alternatives.
Bob809
Duke Engines, please do not disappear. Do not let your company be bought up by a large manufacturer who will then dump all the work you have done, and only resurrect it once the so last century combustion engine in use today is finally deemed not fit for purpose by those in power. The rest of us all know that day passed some time ago, and that Tech like yours is more than overdue. best of luck with your endeavours, but beware.
digi_owl
I dunno. Seems like a overcomplicated Wankel engine to me.
Mel Tisdale
Judging by the illustration, both the big and little ends look vulnerable to wear, so it would be nice to know if there has been any endurance testing of this design. Running continuously at max power (with breaks for necessary servicing) will be essential if there is going to be confidence in using it for aeronautics. I wonder if it will run backwards. Such a facility would be handy for slowing small light aircraft on landing, especially 'tail draggers' and boat planes, not to mention many boat applications. Overall, it looks like a very innovative design.
Dziks
fantastic news! At least for me as I did not hear about DUKE before... I was hoping that Wankel engine will success but it looks like it is too problematic. I would love to see some true revolution in motor business.
MattII
Being a kiwi myself I really hope this comes off.
BigGoofyGuy
I think that is way cool. I hope it does not go by the wayside due to lack of funding. Perhaps a kickstarter type fund raiser might help? I wonder if it would work in a small car like the Fiat 500, Smart Fortwo or other similar sized vehicles? It would be neat to tell someone that ones small car has a 5 cyclinder engine in it.
Mzungu_Mkubwa
I hope they've done their homework on patent searches to be sure they don't violate existing patents. This cylindrical arrangement is the same used by the CEM design from Eddie Paul Industries, except that instead of the "tilted star" idea, EPI used a sine wave shaped plate to act as a cam, with cam rollers mounted on the piston rods and the rods moving linearly. EPI used the exact same valve-less head design, tho, if I recall, and had the advantage of having pistons/cylinders on both ends of the rods, doubling the engine's capacity within not much more space & weight. Link: http://www.epindustries.com/cemco.html I also recall a company developing aircraft engine years ago that used the same layout, except that the cylinders & pistons were stationary while the central drive-shaft and sine-wave-cam rotated. They dropped off the scene almost as quickly as they appeared, tho... don't know what happened to them - seemed like a great idea. The fixed cylinder block design had to utilize traditional valving, tho. Still, it was compact enough for aviation applications, it seemed.
Catweazle
Swashplate type engines in numerous configurations have been about from steam engine days, and despite many potential advantages, have never lasted very long. The aviation industry in particular produced numerous, such as the Almen engine, as the configuration, giving as it does a very low frontal area, appeared suitable for the purpose. Lets hope this one does better, but history is against it. Somewhat off topic, back in the 1970s Honda produced the Juno 175cc scooter using a variable transmission comprising a concentric swashplate hydraulic pump/motor unit with the "swash" of one component (I can't remember which) being controlled by a left hand twistgrip to alter the gear ratio. It was beautifully engineered but sadly failed dismally.