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.
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.
But this gadget would shine there! Quiet, no vibration, run it at a single optimum speed all the time. Where can I get one!
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.
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.
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.
- 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.
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.
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.
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.
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.
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
Seems convenient to use a pretty lame reference engine to make yourself look good. 3 liter engines have made near 1000HP for years now.
[1] http://en.wikipedia.org/wiki/List_of_automotive_superlatives...
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.
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.
"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."
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.
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).
What about other applications? Would this work well for marine, aviation, factory, or other purposes?
I can't find enough information on their "reciprocator" to see how it differs from other swash/wobble-plate based axial engine designs.
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.
I think the more interesting interaction is between the number of pistons and the size of the pistons.
