highest brake thermal efficiency heat engine recorded?

[HydroScope]

Hi guys

I remeber a thread that discussed the difference between 2 stoke engines and 4 storke engines, one member pointed out that the highest acheived thermal efficiency was acheived by a 2 stoke engine in a large cargo ship, diesel cycle. I searched through the 40+ pages of threads title's here and couldn't find it!!!

I am interested in the highest break thermal efficiency of ANY heat engine recorded. operating on any cycle, otto, diesel etc.

thanks

 

[GraviMan]

At the risk of threadjacking...

"Reputed mechanical efficiency of hard working human: 40%"

Hmm, for man powered flight the estimate is 1kW heat dissapation for 200Watts mechanical output. This makes cooling, without introducing drag, an interesting problem. I make that 20%, which probably falls into line with Gregs comments. For more relaxed cycle touring, that output is nearer 100Watts (still at 20% I assume).

Kindof makes you wonder why we don't all commute in light aerodynamically shelled recumbent bicycles...

Mart

 

[ivymike]

Kindof makes you wonder why we don't all commute in light aerodynamically shelled recumbent bicycles...
because it'd be too darn hot inside, and most people would just fall over.

 

[crysta1c1ear]

The CSIRO Energy Centre (researching use of hydrogen) in newcastle has over 1 million dollars worth of solar cells on the roof of their building, not one follows the sun! why? It would require more enrgy to follow the sun then they get back from each cell, interesting!!

I can't believe that's true. Though I can believe they might think it. My son bought a couple of crêpes about a month back and the guys cooking the crepes were using reflectors to shine sunlight onto the bottom of the metal plate that the pancake mix cooked on - a solar powered crêpe cooker. To make the reflector follow the sun they had a crude mechanism with a chain driven by an electric motor and probably some gearing - I didn't study it in detail, I was just buying a crêpe for a 6 year old.

The electric motor was connected to two small solar cells, say about 6 square inches each (ie 6" by 1"), and I had the impression it was just used to determine a voltage difference. Whichever cell generated the bigger voltage or current or whatever would determine which way the motor turned, if at all.

They had a couple of strange old glass bottles (filled with water) where the diameter seemed to have been chosen to focus a large width of sunlight onto the narrow solar cell strip.

So if the reflector was a bit off track, one cell would produce more than the other, feed the motor, motor would run a touch, and gearing would move the reflector.

==

In the Science and Industry Museum at Manchester they have a toy for kids to play with. Its a marble sphere weighing just under 100 kilograms, over 200 pounds say if you want to think imperial units. My 6 year old used to have fun spinning it round as fast as he could.

The point is it takes very little force to spin it, since it revolves around its own centre of gravity. So while you cannot stop it or start it moving quickly in a short time, it is surprisingly easy to manipulate given that the thing is near impossible to lift up. It is litterally child's play.

Moving something around its center of gravity once in a day takes very little work.

==

So the problem might be that you have a load of experts in hydrogen power where solar power experts are required. Or they might be over engineering things.

If you stir a scotch on the rocks, the drink doesn't warm up until the ice cubes have melted. If you over-engineer that problem you could have teams of scientists studying deflections in the gulf stream and trying to calculate net global changes in ocean temperatures due to global warming, instead of just saying nothing much happens until Greenland is green again. Trying to calculate the temperature at any point in your scotch on the rocks is a pointless exercise for the people that haven't grasped the basic principle that the drink only really starts to warm up after the ice has melted.

 

[Warpspeed]

Yes I agree with you up to a point, but it is not that simple. Concentrating radiant solar heat with a tracking and focusing system to generate high temperatures is fairly simple.

But with solar panels you will have a vast exposed area that needs to be kept perpendicular to the incident solar radiation without concentrating or focusing it.

Suppose you have five hundred square meters of panels, a tracking mechanism will be a fairly impressive piece of hardware no matter how you go about it. And then there is also the problem of wind loading, especially gusts and turbulence on the structure.

All things considered it is usually more economical to just increase the area of panels rather than attempt to build a tracking system.

 

[HydroScope]

crysta1c1ear,

most of your points have been talking about using solar thermal energy and not using solar light energy (solar cells)

As you pointed out you can use two solar cells when one has more light the cells can be rotated until both are equal. this in fact would ensure a large percentage of solar cells are never exactly facing the sun at any point in time (same as if they are fixed), and then some of the energy from the cells receiving low level light goes towards turning the motor. thus you are back to square one you may as well have them fixed in one position. the idea is too investigiate this before putting them in place Im sure the csiro has done this and they know what they are doing.

The point I was trying to make is that if the tracking of the sun require an amount of energy that comprimises the overall energy obtained from the cells then you obviously are not talking about much energy obtained from the cells in the first place.

 

[j2bprometheus]

Hi-
The highest reported brake thermal efficiency that I have seen was 57 % for an opposed piston diesel operating at very high cylinder pressures. The place where I think that I saw this reported was in WARD's Automotive Weekly. This was a research project probably done for the US army and/or the EPA.
The peak temperatures were quite high, which is part of how they achieved such high brake thermal efficiencies.
The designers of this engine did NOT try to recover any of the exhaust waste heat, so the potential brake thermal efficiency was even higher.
Recovery of some of the exhaust energy is possible for IC engines but generally the added cost / complexity make it not worth the effort.

 

[GraviMan]

"The highest reported brake thermal efficiency that I have seen was 57 % for an opposed piston diesel operating at very high cylinder pressures."

Now that is interesting! Any further info?

Mart

 

[ivymike]

The designers of this engine did NOT try to recover any of the exhaust waste heat

It was a diesel w/o turbochargers?

 

[j2bprometheus]

Hi-
This was a diesel with turbochargers. The exhaust temperatures out of the turbocharger were still pretty hot. By "recover the exhaust heat", I meant use a Rankine cycle (steam cycle) or other bottoming cycle to recover more work from the exhaust heat.
I believe that this project was sponsored by the US government so there must be more info out there somewhere. I don't know where the info is.
If I remember correctly, the engine had two connecting rods per piston to deal with the large forces generated. Cylinder pressures were very high and emissions were probably very high as well.

 

[patprimmer]

The only opposed piston diesel I ever saw was the Commer Knocker.

It had 2 con rods per piston, because it only had one crank and used piston, con rod, rocker arm, con rod, crank layout.

Maybe I don't have a clear picture of the layout you refer to, but I can't imagine how two smaller rods would be stronger than one large one.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GraviMan]

"I believe that this project was sponsored by the US government so there must be more info out there somewhere. I don't know where the info is."

Thanks J2prometheus, I'll do some googling...

Mart

 

[harrisj]

Pat:

There are lots more opposed piston diesel engines, just in the UK.

The English Electric 'Deltic' was famously successful in rail locomitives from 1950s to 1980s - developed 3300 hp.

Chieftain tanks used a multi-fuel 2-stroke 6-cylinder (12 piston) blower-scavenged engine developing about 750 hp. Designed by Leyland and called the L60. A smaller brother (K60) powers the ubiquitous FV 430 vehicle.

Don't know about efficiencies of these, though.

Cheers - John

 

[HomoFaber]

scania`s DTC1101 turbocompund diesel in mid-90`s has the brake effinciency 46%, todays scania`s turbocompound engines might be also somewhere there if not higher.
However, the highest brake efficiency is (was) reached by large low-speed Sulzer 2-stroke engine, uniflow scavenging, turbocharged, and it is (was) 56%.

 

[crysta1c1ear]

Don't shoot the messenger if you disagree. I was just checking the CO2 figure for the car (CO2 figure of 81 g/km) and noted that they gave a figure relevent to this thread.

http://motoring.excite.co.uk/display/visualizzanews.php3?id=9162

These Volkswagen diesels are capable of converting up to 43 per cent of the thermal energy in the fuel into mechanical energy for powering the car, better than for any other liquid-fuelled production car.

 

[harrisj]

NickE says "I'm not sure what your asking for, but AFAIK the ultimate limit for specific HP is 2.0, thats 2.0 HP/Lb fuel/hr."

Converting that number to figures I'm familiar with gives a specific fuel consumption of 303.6 g/kWh - which is not very good. Diesels should get around 220 g/kWh and I've heard of 200 as an achievable figure. Possibly large marine low-rpm diesels can get substantially better than this.

Perhaps NickE was talking about petrol engines, which I'm not so familiar with.

In either case, there must be a limiting theoretical system efficiency assuming a 'perfect' cycle and frictionless bearings etc. I'll dig around in my old thermodynamics text books and see if I can come up with a number.

John

 

[crysta1c1ear]

Perhaps NickE was talking about petrol engines, which I'm not so familiar with.

Maybe more important than knowing what engine he was talking about is what fuel is he talking about.

Based on fundamentals.
I calculate the energy density of Octane to be 44,877,982 Joules/kg, not shown here.
Dividing by 3600 that's 12.466 kilowatt hours/kg
And taking reciprocals, that's 80 grams per kilowatt hour.

Based on NickE, harrisj
A pound is 0.453515 kg.
An hour is 3600 seconds.
So dividing these, a pound per hour is 0.0001259763 kg/s.
2 HP is 1491 Joules per second.

Dividing one by the other gives
11,840,748 Joules per kg or
0.000000084454 kg per Joule,
take your pick which unit you like on the top.
A Joule is a Watt for a second. Multiply the later number by 3600 seconds per hour ...
0.000304034834 kg per Watthour and move the word kilo to get
304 grams per kiloWatt hour, as harrisj said.

=================

So when NickE says "... the ultimate limit for specific HP is 2.0, thats 2.0 HP/Lb fuel/hr." we can interpret that for a particular fuel.

We can compare the 80 grams per kilowatt hour of Octane with 304 grams per kiloWatt hour embedded in NickE's statement determine that his ultimate limit would be 80/304 efficiency, or 26%.

His limit may be different. I depends on the fuel he is referring to.

 

[NickE]

harrisj & crysta1c1ear - I was referring to petrol engines. wich I believe is supported from Hydroscope's post following mine. However the number I gave is from a story about the Bourke Engine in this thread:

javascriptpenindex(450,350,'

http://www.tipmaster.com/includes/refinfo.cfm?w=450&h=350')

(I hope that worked) if not here is the link to the story.

http://www.niquette.com/books/sophmag/bourke.htm

and If you follow the hyperlink at the bottom of the explanation of 2.0 you get:

"Hypernote: The expression "specific horspower" (hp/lb/hr) has been adopted for the general audience in place of "specific fuel consumption" (lb/hp-hr), which is the more common technical phraseology, inasmuch as "specific fuel consumption" has been appropriated in recent times to characterize fuel economy of motor vehicles (variously gm/mi, gal/ton-mile, kg/tonne-kilometre). Typical specific fuel consumptions run about 0.5 lb/hp-hr for gasoline engines and 0.4 lb/hp-hr for Diesels." -by Paul Niquette

Nick
I love materials science!

 

[GregLocock]

The Prius mk I uses a petrol, spark ignition, engine. Its maximum efficiency is 36%. The new model may be more efficient.

26% isn't even in the ballpark of an ultimate limit.



Cheers

Greg Locock