Duke Engines' compact, lightweight valveless axial engine • Hacker News Board

Re: Duke Engines' compact, lightweight valveless axial engine

#41

Post by aunty_helen » Thu, Nov 06, 2014, 1:38 AM UTC

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 always find it interesting that when hp/l stats are quoted they often neglect to include motorcycle engines... which have been in the 180-210 hp/l realm for about 5 years now.

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.

Re: Duke Engines' compact, lightweight valveless axial engine

#42

Post by IanDrake » Thu, Nov 06, 2014, 2:10 AM UTC

MattBearman wrote: post #20

IanDrake wrote: post #16

Earlier quoted context omitted.

Learned stick on my second gen RX-7... -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

No torque at low RPM is true, but I've not found it to be an issue. I use the engine in the same way as I do on my motorcycle - pretty much always above 4000. 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…

> I've never flooded mine

Neither had I...just never let a valet, mechanic, or relative try to start your old RX-7 ;)

Re: Duke Engines' compact, lightweight valveless axial engine

#43

Post by iaw » Thu, Nov 06, 2014, 2:21 AM UTC

noir_lord wrote: post #32

iaw wrote: post #21

Earlier quoted context omitted.

I do agree with you but a turbo diesel isn't a valid comparison because it is: 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).

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 specific ranges of operation) 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.

Re: Duke Engines' compact, lightweight valveless axial engine

#44

Post by desdiv » Thu, Nov 06, 2014, 3:20 AM UTC

JoeAltmaier wrote: post #37

jdietrich wrote: post #35

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 cat…

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

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.

Re: Duke Engines' compact, lightweight valveless axial engine

#45

Post by JoeAltmaier » Thu, Nov 06, 2014, 12:59 PM UTC

desdiv wrote: post #44

JoeAltmaier wrote: post #37

Earlier quoted context omitted.

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

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.

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.

Re: Duke Engines' compact, lightweight valveless axial engine

#46

Post by JoeAltmaier » Thu, Nov 06, 2014, 1:02 PM UTC

jdietrich wrote: post #35

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 cat…

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!

Re: Duke Engines' compact, lightweight valveless axial engine

#47

Post by JoeAltmaier » Thu, Nov 06, 2014, 1:02 PM UTC

aidenn0 wrote: post #40

JoeAltmaier wrote: post #27

Earlier quoted context omitted.

How about hp per pound? Isn't that the advantage of this thing?

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?

Re: Duke Engines' compact, lightweight valveless axial engine

#48

Post by bradleyland » Thu, Nov 06, 2014, 3:27 PM UTC

JoeAltmaier wrote: post #45

desdiv wrote: post #44

Earlier quoted context omitted.

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.

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.

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.

Re: Duke Engines' compact, lightweight valveless axial engine

#49

Post by bradleyland » Thu, Nov 06, 2014, 3:41 PM UTC

aunty_helen wrote: post #41

mikeytown2 wrote: post #28

Earlier quoted context omitted.

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 always find it interesting that when hp/l stats are quoted they often neglect to include motorcycle engines... which have been in the 180-210 hp/l realm for about 5 years now. 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.

It's difficult to compare the specific output of engines of dramatically different displacement. As a general rule, displacement and specific output are inversely correlated. That's not to say that motorcycle engines aren't an absolute marvel of engineering and technology, but it's not possible to compare them directly to engines with twice the displacement because you can't simply scale up the motorcycle engine and get the same results at the larger displacement.

Re: Duke Engines' compact, lightweight valveless axial engine

#50

Post by JoeAltmaier » Thu, Nov 06, 2014, 3:42 PM UTC

bradleyland wrote: post #48

JoeAltmaier wrote: post #45

Earlier quoted context omitted.

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.

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