Dr. Paul Engine? 5

[mcspeed]

What's the concensus on the 'Dr. Paul' Opposed Piston engine talked about in this Youtube video:

part1:

http://il.youtube.com/watch?v=Fz8Z9geyOkk&feature=related

part2:

http://il.youtube.com/watch?v=K6ahbdkJTN8&feature=related

part3:

http://il.youtube.com/watch?v=hTnxsqX9FhE&feature=related

part4:

http://il.youtube.com/watch?v=ihR1fCeEobQ&feature=related

part5:

http://il.youtube.com/watch?v=y6OuUN2LlV8&feature=related

It was briefly referenced in this thread by someone who seemed to have been involved with the DARPA work on it:

http://www.eng-tips.com/viewthread.cfm?qid=237389&page=8

It sounds too good to be true of course, but it also sounds like too much development went into it for it to be worthless.

What's the deal?

 

[MikeHalloran]

What's that? Five videos of a guy talking?
I clicked on some of the other stuff provided by U-Tube; much more interesting.

The deal with opposed piston engines is that some of them can be made to actually run, but that's not enough. Some of them have actually made it into production, because of some particular virtue that made them well adapted for a specific mission, where their faults could be tolerated.

Most of them suffer from one big flaw; mechanical complexity greater than current production engines. In turn, that means additional manufacturing cost and/or higher service cost and/or more difficult packaging constraints.

In today's world, with many operations capable of EOQ of one, and computer aided design and simulation, odd engines stand a better chance than ever before of actually being constructed, and tested. They don't stand a better chance of reaching mass production, because of new constraints and better analysis tools.



Mike Halloran
Pembroke Pines, FL, USA

 

[mcspeed]

Some juicy claims about prototypes of the particular opposed piston engine described in the video:
1. 80% efficiency
2. full fuel burn - no detectible pollution is emitted
3. can output ~900hp/liter due the design's extreme tolerance for boost
4. eliminates the piston scuffing issue
etc.

It does drive four crankshafts, which I'm sure complicates things, but it sounds pretty interesting. What am I missing?

This blog lists a bunch of details from the video:

http://dreamer3000.wordpress.com/80-thermally-efficient-opposed-pistons-engine/

 

[MikeHalloran]

It must be the electric turbocharger that makes the difference.



Mike Halloran
Pembroke Pines, FL, USA

 

[black2003cobra]

"This blog lists a bunch of details from the video:

http://dreamer3000.wordpress.com/80-thermally-efficient-opposed-pistons-engine/

"

Wow! I think that wins the prize for the most poorly written article I have ever read. (Well...OK...just part of it, because I couldn't stomach it any more.)

 

[mcspeed]

Yes, the blog post is egregious, but it has some value as a thumbnail reference for those who want to witness the shocking claims without watching the 35 minute video.

It's all about the electric turbochargers lol:
This design supposedly allows 147psi of boost and 30:1 compression because it eliminates the head and gives the combustion chamber two movable surfaces to absorb the shock.

Even if it were REALLY expensive to make, I think it'd find a green market somewhere since people could brag that it emits no greenhouse gas or pollution and can be up to 80% efficient using normal diesel, blah blah blah.

Assuming that it could be made to work, can anyone guess what it would be like based on previous opposed piston designs?
Would it have a usable rev or boost range or would it just have to hit a sweet spot and sit there?

Can anyone say it's impossible? If so, why?

 

[MikeHalloran]

The claims are suspicious.
{
1. 80% efficiency
2. full fuel burn - no detectible pollution is emitted
3. can output ~900hp/liter due the design's extreme tolerance for boost
4. eliminates the piston scuffing issue
}
1. Maybe you can 'measure' high efficiency with an electric turbo, by not counting the electricity into the motor. That's probably the only way to get 'measured' efficiency this high.
2. If you're detecting no pollution from a combustion process, you have a broken detector.
3. Extreme tolerance for boost? I don't get it. You mean because two cranks support each piston?
4. I don't get this either. Two cranks and two rods per piston might in theory get rid of side loads. Which is a good thing, because there's no place to put a skirt on the piston. You've also got the piston trying to separate the cranks by wedging the rods in there, with everything at a bad angle. I see it as heavy, or fragile, or both.

With 30:1 compression plus 147 psi of boost, is there ROOM for enough fuel to combust all the air?




Mike Halloran
Pembroke Pines, FL, USA

 

[dicer]

So what? More bearing area more losses. Not much new there.
It runs on air real good, lots of talk that is all.

 

[mcspeed]

Thanks Mike.
For the sake of dialogue, I'm going to play devil's advocate with what was said in the video:

1. The whole system was 80% efficient including the electric supercharger (I imagine there was a sweet spot involved).
2. They were equipped with state of the art detectors circa 1988+. The cleanliness was the result of very late fuel injection and the extremely high pressures. To illustrate the pressure: the exhaust would be very cool because of liquid nitrogen that would instantiate in the chamber.
3. The fixed head/headgasket is usually a limiting structural element for boost. Here, the head is gone and the combustion chamber is a cylinder with movable ends which can withstand, and harness, outlandish compression + boost extremes.
4. With one conrod per piston they'd get ovoid issues but with two they balanced it out so the piston stayed centered under stress.

Dicer, again, playing devil's advocate - if it can run 80% efficient and shoot butterflies out the tailpipe then bearing losses and supercharger complexity are less of a big deal.

 

[TDIMeister]

Snake oil.

 

[mcspeed]

TDImeister,
What is it that makes this design foolish and the Hofbauer/Ecomotors OPOC design worthwhile?

In the Ecomotor design I see that the crank situation is taken care of; and balance doesn't seem to be an issue. What else makes the Dr. Paul concept a dead end?

 

[TDIMeister]

Ummm, the 80% efficiency claim doesn't ring any alarm bells???

 

[MikeHalloran]

Nobody _here_ said the OPOC was worth a crap, either.


Mike Halloran
Pembroke Pines, FL, USA

 

[TDIMeister]

Indeed.

 

[mcspeed]

Lots of things about it ring alarm bells so I'm seeking expert insights. I understand that the claims are so absurd as to be dismissed without blinking BUT the presentation seems straightforward, transparent and not at all smooth or salesy. And I've never heard of that kind of compression/boost situation; or liquid-nitrogen-forming chamber pressure; so I'm curious how to determine whether it's pure fancy or uncharted territory.

Extravagant claims aside, what about the 'Dr. Paul' concept it makes it absurd?

 

[black2003cobra]

OK. I endured through some of the video, too, and they are just as bad. Egregious, as was said. That alone should give one reason not to believe.

As one simple example...He says a compression ratio of 20:1 increases pressure from 14.7 psi to 294 psi. That's wrong. The compression ratio is a volume ratio...not a pressure ratio. (Yes, high rc improves therm efficiency, but he got that basic fact wrong. That speaks volumes.) Or another example. He states that the reason engines are so inefficient is because the fuel isn't burned and just goes out the exhaust. At stoich, the combustion efficiency of an SI engine is very high...well in the high 90% range...so not a lot of unburned fuel going out the tailpipe. For DI engines which burn lean, it is nearly 100%. The reason for "low" fuel-conversion efficiency is due to lower thermal-conversion efficiency, which has nothing to do with how much of the fuel is burned. It's more how the energy in the fuel is utilized. Things like heat loss through the chamber walls, or heat loss out the exhaust from limited expansion, etc. Then as someone else mentioned, there will be emissions. At stoich, there is H2O, CO2, and N2 (complete combustion, low temps). With dissociation at high temps, all kinds of stuff. So no...no butterflies coming out of there.

The videos reminded me of that famous statement by Wolfgang Pauli, "This isn't right. This isn't even wrong."

As to the geometry, as Wai Cheng (MIT) summarized it during one class, there are very good reasons why the basic construction of current-day engines is the way it is.

Well...good luck to them.

 

[naturalextraction]

I agree with black2003cobra. I didn't see any video's of an operating engine...are there any? Also still sounds like a bunch of parasitic loss there. How do they get 80% efficiency with rotational and frictional losses, unless I'm just not seeing it.

 

[HRHtex]

Mcspeed continues to ask why the "Dr. Paul" engine is impossible - the answer is that it probably is possible - just highly impractical and the claims are exaggerated.
There is nothing magical about the "Dr. Paul" engine layout that would make it more able to withstand the internal pressures. Tractor pull diesels reportedly operate at 300psi boost (although not with 30:1 CR). A diesel's boost and CR are limited only by the mechanical strength of the engine.
A "Dr. Paul" (or conventional) engine of 30:1 CR and 147psi boost could be built (and in fact probably has been built in conventional form) but would have to be enormously strong and heavy to stay in one piece for more than a few seconds. By my calculation 30:1CR/147psi boost equates to about 17000psi (probably less than this depending on cam timing but maybe still 10000psi or so) after compression and would be several times this after combustion.
The 80% claim probably comes from the fact that a 30:1 expansion ratio would give about this theoretical thermal efficiency - but nowhere near this much in real life.
A more practical engine would be a conventional diesel with a 30:1 CR and Atkinson Cycle to limit the compression pressure - research engines like this have been built and tested.
"Dr. Paul" engine - possible but unlikely.

 

[mcspeed]

Thanks for the feedback guys. I learned a lot.

For clarification, the Part 4 @ 3:50 talks about using some kind of liquid nitrogen setup to cool the exhaust which happened to reduce pollutants - I guess by avoiding the disassociation temps blackcobra2003 mentioned. I'd previously thought he said the liquid nitrogen was forming in the combustion chamber and being somehow utilized from there.

 

[tbuelna]

mcspeed,

I worked with Marius Paul on the TRC opposed piston diesel project almost 20 years ago. I did some redesign on the reciprocator test rig hardware (pistons, liner, rings, etc.). The TRC concept was never run as a complete system, with the opposed piston reciprocator, rotary expander/compressor and turbocharger.

We did some dyno work with just the 2 stroke uniflow reciprocator and fuel system, with the scavenge work done by an electric screw compressor. The engine was run at some very high cycle pressures and BMEP rates. We never got good reliability from the engine, but while it was running it seemed to be getting some excellent SFC/thermal efficiency numbers, even after adjusting for pumping losses. Nowhere near 80% though, it was closer to 52%.

Regards,
Terry