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Duke Engines' incredibly compact, lightweight valveless axial engine


September 3, 2014

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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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 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.

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.

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.

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

About the Author
Loz Blain Loz has been one of Gizmag's most versatile contributors since 2007. Joining the team as a motorcycle specialist, he has since covered everything from medical and military technology to aeronautics, music gear and historical artefacts. Since 2010 he's branched out into photography, video and audio production, and he remains the only Gizmag contributor willing to put his name to a sex toy review. A singer by night, he's often on the road with his a cappella band Suade. All articles by Loz Blain

Seals! They are the bane of the Wankel. How does this thing seal at the power end at the tops of the cylinders? And, how long will they last?


room for them at kickstarter


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.


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.


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.


I dunno. Seems like a overcomplicated Wankel engine to me.


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.

Mel Tisdale

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.


Being a kiwi myself I really hope this comes off.


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.


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.


Does anyone remember the wobble engine of about 20 years back variable capacity

Gavin Roe

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.


Firms that played seriously and produced cars with Wankel were NSU, Mazda but don't forget Citroen with its Birotor GS. Although something shy of only 900 produced, it was a good effort but came out at the wrong time: the fuel crisis hit and the engine put into a lesser model to the DS selling for more money. Citroen pulled the plug. Firms that experimented seriously with Wankel were Mercedes Benz and GM, with Mercedes putting out first a 3 and then a 4 bank unit in an exotic car called the C111. Years later , the DeLorean sure looked like a C111. The AMC Pacer was designed around an intended GM produced Wankel which was still born. AMC's engineers had to rush out a fix to fit an inline 6 which threw off the Pacer's performance. Back in the 30's an free floating piston engine was developed and apparently used for military applications. The piston simply went back and forth in a cylinder with spark plugs at each end. Wonder what happened to it.

Mike Dubois

Many new designs that met resistance from the big automotive companies have come and gone over the years. Resolve and tenacity hopefully will get this innovation past the experimental stages. As Mel T says, real world endurance testing will help make the Duke Axial Engine a proven concept, and I wouldn't be surprised if it's already had considerable bench testing.

But the ultimate test of its mettle may be in Formula 1.


seems the cylinders rotate, that's crazy, as a air conditioning repair guy, i always thought of using a a6 or a sanden 505 as a motor, it uses a swash plate and could be a 10 cylinder direct inject 2 stroke motor with valves (they work and are reliable ) that could produce staggering amounts of power for the size, I could conceive a motor no bigger than a car battery producing 200 hp . that would be impressive !

Jay Finke

Ideal engine for aviation, marine alone & aux power. Mass produce.

Stephen Russell

Another combustion engine, really? The directional conversion in this design will net at least a 10% loss. More fossil fuel nonsense that we have been plagued with for decades, all in the name of big oil...

Fretless Bass

i also remember Smokey Yunik had a similar design back in the sixties that was touted as the best yet...but it never made it past the one prototype.

hummer boy

From what I recollect from some 50 years ago was the fact that MAHLE is a German company. At the time it was manufacturing pistons and sold well along with Goetze brand piston rings. I think they were OEM suppliers to Mercedes in Germany. No way was it a US company !


I've seen this engine pop up for a while now. I like the barrel engine concept in general, but I am extremely skeptical of what is essentially a head gasket surviving many of hours as a plain bearing operating under extreme pressure-velocity and with wild thermal fluctuations. Also, the amount of power stripped away by sliding friction would destroy relative fuel economy.


Does anyone know how well this compares to the Opposed Piston Opposed cylinder engine? I do know that one of the intractable weak areas of the Wankel is the large area swept by seals. Also, how well does this design compare to the German spherical engine/pump design? One of the inherent limits of the Gizmag format is that short little articles do not permit a good comparison of similar ideas in any depth at all, I wish them well in any event. Fewer parts and smaller size with hopefully better performance is still a great trend. Some of today's best common automotive tools started with companies that were far outside the major players. Radial tires and disc brakes were both opposed by major auto companies for a very long time.


there was an engine like this for aviation back in the 80s, was pretty much same principle, but was set up as two of these hooked up end to end, and shared the same 'crank'. was VERY powerful but was too early for its time.


Technology... Always a thrill... the upside. But must ask, what is the downside?

Financing... Unfortunately, I suffer from the same malady: Lack of funding.

I would love to see and hear more.


As the former CEO of a Wankel engine manufacturer, I can see the the article does not address the issue of economic build quantity. We also had "revolutionary" engines on the Wankel patent, but it was impossible to raise enough funding to as volume build on the floor. A one-off engine costs us a good fraction of a $million. Produced in the thousands that price dropped to $thousands.

On the technical side, this engine design has high-pressure sliding seals, that were also a big issue on the Wankels. Seal life and seal materials must be addressed. More than half of our development cycle went into this issue alone. Then we have thermal issues, swash plate life cycle and tooling.

Why are we stuck with the reciprocating engines? Because a plant like the one Ford's 4-cylinder engine costs a few $billion to build, and even a modest rearrangement of the plant floor means a shut down and a major capital expense.

Ken Brody

This mechanism is exactly the same as the Whispergen electrical generator, also from New Zealand. It uses heat to create motion by means of a Stirling cycle. Interesting.


So, as far as I can tell, instead of just piston rings, this engine also needs some kind of large circular seal to isolate the piston chambers as the whole intake/exhaust port housing rotates overhead. They may have done away with complicated valves, but they introduced a complicated seal/bearing assembly very similar to a Wankel. Looks cool tho.


Novel engine configurations are fascinating but they have never sold well. Even Mazda's massive investment in wankel and it's notable racing successes has brought only moderate success and not exactly a stampede for the showroom floor.

They usually attract a small band of devoted enthusiasts who like to be different.


In 1970 I found an engine built and designed on Ontario Canada by a German engineer called George Striegle. After time with the patent agents and a thorough analysis of the design I contacted Mr Blooomingdale (owner of Bloomingdale's in NYC) at his offices in Century City LA. Then with his engineers in Santa Maria we went over the technical designs and specs. The final deal was closed in Ottawa with the past Chairman of American Motors flying here with his two lawyers ion a private jet, George et al was taking to California but the company that the engine was put with went bankrupt, I never found what then happened. The engine was opposing cylinders (4 sets of 2) with a 12" diameter body 2 feet long (max) that developed over 400 HP. The central shaft could be held while the body rotated or the other way around. It was possible to use it as an internal or external combustion engine.

Peter Lawrence

Looks like a vacuum cleaner. (ISTR a line like that about an engine in "Twins".)

Gregg Eshelman

If all you want to do is drive a generator to recharge a battery, you're not going to do much better than a turbine engine - which is what I thought this was! If somebody manufactured a little electric car with an onboard jet-powered generator, that would be practically the coolest car ever! In my opinion anyway :)


Compression much higher than 14.1 would be getting into diesel territory. Looks interesting but I wonder how long the ports will last before eroding from the hot exhaust gases. But there are some pretty amazing materials out there that may make it viable. What would a turbocharger do???


Putting money into new tech for combustion engines is idiotic on many levels.


love to see "Tesla" work with these guys and use this engine to run generators in their cars to recharge batteries for a seemingly unlimited range....(when I can afford a tesla I want one)....but this engine inside a Tesla running on renewable fuels would be fantastic!

Rock Rider

This has actually been around for quite a while. I wrote about it about six months ago and I think it had been around for a good while then. Still pretty interesting. There is some concern with rotary engines and their seal and friction issues though.


Matthew Kaufman

Well, IMHO, they've got a HUGE face seal problem, with all sorts of erosion problems as ports and plug pockets are exposed and closed. How do you keep enough over-pressure on it to hold against that 14:1 ratio and ignition shocks yet still slide freely after 30,000 miles ??

Despite Mazda patiently engineering Wankel 'rotor' seals into 'fair' reliability and, IIRC, RR devising a 'double decker' rotor motor for a super-charged, tank-grade diesel engine, the classic application for an odd piston layout was the swash-plate torpedo...

Nik Kelly

Doesn't Nissan already have them beat?

They have an 88 pound, 1.5 liter engine that produces 400 Bhp. Half the displacement, twice the horsepower...

From a Gizmag caption: "The DIG-T-R weighs 40 kg (88 lb), yet puts out 400 bhp"

Ivan Sudofsky

So it safe to assume this is a gasoline (petrol) engine, because diesel engines don't use spark-plugs!!!

The 1 TaiN

A crankshaft is more efficient and cost effective than this system and many others designed to get around the use of crankshafts over the years. Better off spending your R&D funding on reducing the noise and creating fast power-up systems so small turbines can be used to charge batteries for hybrid vehicles.


It is a shame that the Internal combustion engine will be banned because of nano-particle emmission


if a piston has to go down and then stop and then go back up and then stop and then go back down, the engine will be inefficient. apply a force to an already spinning shaft, rather. the calorific content of a battery, via an electric motor, gets about 80% of that power to drive a wheel. the calorific content of fossil fuel gets about 20%. but with this engine it will be much better ! do you think my lack of a university degree is showing, here ? just stop burning stuff, people. that is so 1900's.


It looks interesting, I'll grant them that, but I see some severe longevity issues with it and would like to see the numbers on how long it can run under full load and what its wear points are. Nothing is said about its lubrication system, surely it's not friction free, is it? Or did I somehow miss that part in the videos? The Massive Yet Tiny toroidal engine puts out some impressive power numbers too, and maybe even have a better power to fuel consumption rate.


Expanded Viewpoint

The key to the ultimate success of this engine will be production costs. If it's too high it will fail. I remember when Mazda produced a wankel engine for use in the RX-7 that was tough, light and reliable. Unfortunately they designed it for performance and the energy crisis of 1974 and onward killed it.

Johnny Bramton

I remember the big advantages the Wankel said to have in the 60's. Then rotor tip seal wear was the thing that was/is? a major problem. I see the the outside piston/cylinder as a major potential wear area due to large centrifugal forces developed as speed increases.


Five will get you ten, that the DUKE engines goes into production. Some Multi-Billion Dollar company will buy the patent rights for the ENGINE. And then bury it in the deepest whole they can find and/or dig. And leave it there! "GREED Triumphs Over, the Needs of the Masses."

Michael Flower
Motorcycles might be a good spot for such an engine. There are numerous motorcycle companies always looking for a selling point to gain market share. Also many motorcycle companies have in depth experience with ported engines from their two stroke models. My personal belief is that either car engines or motorcycle engines that are super easy to swap out and repair for next to nothing in cost would be a huge hit. There is no excuse for the nightmare that exists in auto and motorcycle repair. We seem to have advanced backwards over the decades. Jim Sadler

Nice effort,hope this engine sees the light of the day.

Nand Kumar

Kinda have to agree with Jim-but lets face the future is hybrids


Very nice to see continuing work on new IC engine configurations. I seem to recall that one of the biggest issues of Wankels - beyond the various mechanical issues mentioned by other readers - is the inherently high surface-to-volume ratio which makes it very hard to have complete combustion. This reduce efficiency and increases CO in the exhaust. I believe that then requires a more aggressive aftertreatment with larger catalysts and more air pumped into the exhaust stream(?)

Fast Eddie

I would assume the smaller size and many fewer parts than traditional IC engines would lead to great savings in the manufacturing process. I hope Honda looks into this as a possible investment as it seems to be in their wheelhouse.

EJacob Cornelius

Whether it's too little remains to be seen, but it's certainly too late. In 10 years or sooner, petrol-based cars will likely be the minority of cars sold. Why do you think Apple is getting into cars? They would never be interested in getting into the fossil-fuel business, but now that Tesla and others have done the hard R&D for viable, mass-produced electric cars? No brainer.

Nice engine, but it's 30 years too late.


So similar things have been tried before and were not successful?

Hopefully Duke Engines doesn't employ such slugs in its engineering group. Yes, the use of electric engines are on the rise, but there is a huge amount of fossil fuel being discovered, and battery powered airplanes and generators will likely not succeed.

Keep up the good work, you Kiwis? "You will succeed, yes you will indeed...."

I love that place. I'd love to take my mechanical engineering student son fishing on lake Rotorua. What great fun. Are all the black swans still there?

Tommy Earbob

Time...ta'.....saddle...up with the ...Duke!

Mike Giles
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