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.
I know, that's not a Duke engine. Just wondering who got it wrong the first day and went down this path. Like the old 'drum memory' systems that rotated the heads and left the magnetic memory stationary. Didn't take but 2 years to turn that around and invent disk drives.
-Almost no torque at low rpm - worse
-Easy to flood, then once flooded major work - worse
-Feed it a quart of oil every 1,000 miles - worse
The flooding issue I mentioned. It may have been different with the RX7, but the RX8 has a de-flood procedure that works 9 times out of 10. And failing that a bump start usually does it. Although I've never flooded mine, I'm always careful not to shut her down cold.
Oil usage in the real world is not much worse than many other performance cars, in fact it's better than most Honda S2000s. But for people who are not used to having to regularly top up oil I could see it being a ball ache.
Neither had I...just never let a valet, mechanic, or relative try to start your old RX-7 ;)
wank-wank-wank-wank-BANG!-wank-wank-wank-wank
The turbo is irrelevant though, the IC has a turbo, they work and are reliable the rotating engine doesn't but that doesn't rule out a basis for comparison.
It comes down to fuel efficiency, emissions, maintenance and cost and I can't see this engine winning (for cars).
I don't have time to do more thorough research right now, but the Ford Duratec 30 series of engines [1] is roughly comparable in both displacement and cylinder count and produces between 200 and 240 HP depending on configuration which puts this engine slightly ahead of normal engines from a performance perspective (smaller form factor and lighter).
Is there any apples to apples comparison that you can find that actually makes this development look substantially inferior? I get that you used a diesel because historically that gave the ICE an advantage but with modern diesel technology and forced induction they aren't the same animal.
[1] http://en.wikipedia.org/wiki/Ford_Duratec_V6_engine#3.0_L
Edit: changed 'pre-combustion' to 'pre-compression' for clarity on volumetric efficiency definition.
The Turbo allows a given displacement to output more power for a given displacement, indeed volvo have 2 litre putting out 450hp (uses staged turbo's one of which is electrically driven), I wasnt comparing the nearest ICE equivalent to the rotary.
Yes, ported intake/exhaust solves the problem of rotating the disk instead of the cylinders, but porting comes with its own set of drawbacks. Ask any engineer who has worked on Wankel Rotary engine design and they'll tell you all about it. Ported engine designs include the Wankel Rotary design, as well as 2-stroke, reciprocating, piston-in-sleve (traditional 2-stroke ICE) engine designs. Both have issues meeting emissions requirements because of inherent limitations of ported engine designs.
Cam operated valves have some very specific advantages that play a large role in the ICE's ability to reach current specific output levels. With a ported engine, you cannot vary the intake/exhaust profiles; with a cam, you can. Variable overlap in intake/exhaust, as well as variable intake/exhaust opening area are key aspects of state-of-the-art ICE design. You give up both of these with ported engine designs.
Wondering about these kinds of things is great, but be conservative with your assumptions, and generous in your interpretation. It's condescending and narcissistic to assume that you can take a cursory look at the Duke engine, wave your hand, and solve a massive design flaw.
Its great to hear from an expert, though one that's clearly invested in the current popular technology to the exclusion of admitting any benefit to this one. I thought you'd be right on board with speculating about where this went wrong. Sorry to have misjudged.
> I thought you'd be right on board with speculating about where this went wrong. Sorry to have misjudged.
You've misread me. There's no thing wrong with asking questions. For example, take the question:
"Why can't we rotate the disc instead of the cylinders?"
Versus your statement
"The idea of valve-less cylinders via rotating ports can be done either way - rotating cylinders or rotating shaft - so reverse them."
You state this as if it's obvious, and it is obvious. It's also obvious (to someone with domain knowledge) that it's not a simple matter. I took us part way down the rabbit hole, and I'm always happy to do that, but it really gets under my skin when questions are states as presumptuous declarations such as, "so reverse them." Not to mention this one:
"Just wondering who got it wrong the first day and went down this path."
This presumes that the Duke solution is the wrong one, and your solution is the right one, but you aren't even familiar enough with ported engine designs to know the basic drawbacks. Again, I'm not an expert, but I know enough to know that I can't make these kinds of presumptions. You don't, and my suggestion is that you should recognize and start with questions rather than insulting someone else's work.
I know this comes across as a scolding, but I genuinely don't mean to be harsh. I just felt like I should say something because of the way your writing came across.
And also including turning the problem on its head. If shaft momentum is such a well-known and pernicious problem, then its not out of line to question why somebody went down that road at all. Obvious really. Its called returning to fundamentals, and anybody can do it.
So, what's the problem with using rotation to port air and exhaust, if the disk is turning instead of the now-stationary cylinder block? A mechanical linkage between the disk and a ported sleeve should do the trick. If its still desirable at all - a stationary cylinder block lets you do it the valve way too if desired.
Anyway, I'm actually astonished that anybody ever thought it was a good idea to rotate essentially the entire engine. Centripetal forces, heavier bearings, linkage issues - it invents all sorts of problems. Whereas the idea of pushing against a tilted disk doesn't require that at all. I can't get over that fundamental notion, and I'm sure its fair to ask "where did they go wrong" without being accused of backseat driving. If there's some obvious need to NOT rotate the disk, I'm all ears. But I didn't read that anywhere.
