[jdietrich]

This isn't a new engine, it isn't a new idea, and it isn't a particularly good idea.

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.

[1]http://www.dukeengines.com/technology/overview/

[aunty_helen]

Ah! Good point about the reciprocating mass. I did wonder why they suggested them for marine and aviation (semi-static rpm) applications but not cars etc.

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.

[JoeAltmaier]

Maybe useful for a stationary generator? Currently my options for a natural-gas generater are one: Honeywell makes a line of 5-12KW device. But they are god-awful noisy; its all any of the reviewers talk about.

But this gadget would shine there! Quiet, no vibration, run it at a single optimum speed all the time. Where can I get one!

[JoeAltmaier]

Do the pistons rotate, or does the disk? The disk would have less mass I suppose.

[desdiv]

The pistons rotate. Not just the pistons, but the cylinders and the connecting rods as well. It's basically the entire engine block rotating against a stationary cylinder head.

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.

[JoeAltmaier]

So why not connect the disk to the shaft, and have it rotate instead? Not a mechanical engineer, but that would have way less mass, way less clever mechanical linkages for valving, spark.

[bradleyland]

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.

[JoeAltmaier]

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 magnetic memory stationary. Didn't take but 2 years to turn that around and invent disk drives.

[bradleyland]

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.