Duke Engines' incredibly compact, lightweight valveless axial engine
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