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Duke Engines' compact, lightweight valveless axial engine

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Re: Duke Engines' compact, lightweight valveless axial engine

#51

Post by bradleyland »

mikeytown2 wrote: post #28
erik_landerholm wrote: post #25

"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." Seems convenient to use a pretty lame reference engine to make yourself look good. 3 liter engines have made near 1000HP for years no…

The best naturally aspirated piston engine is 166 hp per liter. The best naturally aspirated Pistonless rotary engine is 188 hp per liter [1]. The Duke is at 71 hp per liter; it has a long ways to go but it's already better than a naturally aspirated Diesel engine (44 hp per liter). [1] http://en.wikipedia.org/wiki/List_of_automotive_superlatives...

I agree that Duke has done relatively well, considering their limited resources. That is to say, Comparing superlatives isn't entirely fair to Duke.

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.

1: http://en.wikipedia.org/wiki/BMW_N52#N52B30

Re: Duke Engines' compact, lightweight valveless axial engine

#52

Post by bradleyland »

JoeAltmaier wrote: post #50
bradleyland wrote: post #48

Earlier quoted context omitted.

The disc contains systems that are not easily reciprocated: the intake and exhaust ports, as well as the ignition system. You can be sure that if it were possible to simply swap the rotation, Duke would have done it. The issue of reciprocating mass is well known by engineers who work with axial engines.

I guess I still don't understand. Lots of engines don't put the valves and ignition on a disk - so don't. The idea of valve-less cylinders via rotating ports can be done either way - rotating cylinders or rotating shaft - so reverse them. 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 magne…

So, you believe that sitting in your armchair, you've identified some fundamental flaw in the Duke engine design that they overlooked from day 1?

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.

Re: Duke Engines' compact, lightweight valveless axial engine

#53

Post by JoeAltmaier »

bradleyland wrote: post #52
JoeAltmaier wrote: post #50

Earlier quoted context omitted.

I guess I still don't understand. Lots of engines don't put the valves and ignition on a disk - so don't. The idea of valve-less cylinders via rotating ports can be done either way - rotating cylinders or rotating shaft - so reverse them. 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 magne…

So, you believe that sitting in your armchair, you've identified some fundamental flaw in the Duke engine design that they overlooked from day 1? 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…

Oh get off your high horse! I'm speculating. You condemned the design in an earlier post, right? There are all sorts of possible geometries, and many have been tried; some are found wanting. Elsewhere I speculated about using such an engine for constant-speed operation e.g. a generator. It might be a win there, where the ICE responsiveness is not a priority.

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.

Re: Duke Engines' compact, lightweight valveless axial engine

#54

Post by aidenn0 »

JoeAltmaier wrote: post #47
aidenn0 wrote: post #40

Earlier quoted context omitted.

Like other engines where the pistons rotate (e.g. Gnome) it does have the weight advantage of not needing a flywheel (since the engine is its own flywheel). Other than that, probably not much.

But its supposed to be 1/3 the weight of an equivalent engine. Sounds like a lot?

Without seeing what engines they are comparing it to, I can't say for sure. My guess would they are comparing at similar RPMs, or have some other restriction. I'm sure it weighs a lot less than a traditional 3L engine, but I would guess it generates a lot less power at redline.

Re: Duke Engines' compact, lightweight valveless axial engine

#55

Post by noir_lord »

iaw wrote: post #43
noir_lord wrote: post #32

Earlier quoted context omitted.

I used diesel as historically cc for cc they have lagged behind petrol engines (though that has largely ended). 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).

The turbo is not irrelevant because it has a direct impact on the ratio of power delivery / fuel consumption due to the recaptured energy from exhaust gasses. The volumetric efficiency (ratio of cylinder pressure pre-compression to atmospheric pressure) of engines with turbo-chargers is almost always >1 while the volumetric efficiency of naturally aspirated engines is always (excluding rare high-performance vehicles…

In this context it is irrelevant since my comparison was purely one of power output against displacement.

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.

Re: Duke Engines' compact, lightweight valveless axial engine

#56

Post by bradleyland »

JoeAltmaier wrote: post #53
bradleyland wrote: post #52

Earlier quoted context omitted.

So, you believe that sitting in your armchair, you've identified some fundamental flaw in the Duke engine design that they overlooked from day 1? 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…

Oh get off your high horse! I'm speculating. You condemned the design in an earlier post, right? There are all sorts of possible geometries, and many have been tried; some are found wanting. Elsewhere I speculated about using such an engine for constant-speed operation e.g. a generator. It might be a win there, where the ICE responsiveness is not a priority. Its great to hear from an expert, though one that's clearly…

I'm a novice, not an expert. I have a great interest in cars and engines in general, and I've pursued them to some degree, but I'm not an engineer. I have no where close to the level of expertise that the Duke engineers do.

> 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.

Re: Duke Engines' compact, lightweight valveless axial engine

#57

Post by JoeAltmaier »

aidenn0 wrote: post #54
JoeAltmaier wrote: post #47

Earlier quoted context omitted.

But its supposed to be 1/3 the weight of an equivalent engine. Sounds like a lot?

Without seeing what engines they are comparing it to, I can't say for sure. My guess would they are comparing at similar RPMs, or have some other restriction. I'm sure it weighs a lot less than a traditional 3L engine, but I would guess it generates a lot less power at redline.

Sure its different, and comparing it via the normal means (litres or rpms) won't work because its so different - those means assume a substantially identical engine or they don't work at all.

Re: Duke Engines' compact, lightweight valveless axial engine

#58

Post by JoeAltmaier »

bradleyland wrote: post #56
JoeAltmaier wrote: post #53

Earlier quoted context omitted.

Oh get off your high horse! I'm speculating. You condemned the design in an earlier post, right? There are all sorts of possible geometries, and many have been tried; some are found wanting. Elsewhere I speculated about using such an engine for constant-speed operation e.g. a generator. It might be a win there, where the ICE responsiveness is not a priority. Its great to hear from an expert, though one that's clearly…

I'm a novice, not an expert. I have a great interest in cars and engines in general, and I've pursued them to some degree, but I'm not an engineer. I have no where close to the level of expertise that the Duke engineers do. > 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 qu…

Cool, I apologize if I offended. But if we're talking radical engine design, then nothing is off the table. Including solving the existing problems with the Duke design. They haven't had 2 centuries of tweaking, so criticisms about where soot collects are getting ahead of things.

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.

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