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Science Technology

Capturing Waste Heat with Quantum Mechanics 235

Posted by michael from the grease-monkeys-replaced-with-electron-monkeys dept.
TheMatt writes: "There is a summary of a Phys.Rev.Lett. article up at Nature Science Update that describes a design for a 'quantum afterburner' that would improve the efficiency of an Otto engine. It improves the efficiency by using a laser and maser to extract energy from the hot exhaust of the engine. In fact, the process could enhance performance beyond that of the "ideal" Otto engine."
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Capturing Waste Heat with Quantum Mechanics More

Capturing Waste Heat with Quantum Mechanics

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  • Big deal... (Score:5, Funny)

    by nurightshu ( 517038 ) <rightshu@cox.net> on Wednesday January 30, 2002 @10:42PM (#2929026) Homepage Journal

    I used a laser and a maser to extract energy from the waste heat generated by my Athlon. I've been running everything in my house but my computer off that exhaust tap!

  • But what do you do with the light? (Score:2, Insightful)

    by Anonymous Coward

    So I get that you convert waste heat into light, first with the maser to get microwaves, and then with the laser to get some other wavelength. What then?

    • Re:But what do you do with the light? (Score:4, Funny)

      by mrpotato ( 97715 ) on Wednesday January 30, 2002 @10:53PM (#2929077)
      You put them on the head of those friggin sharks.

    • Re:But what do you do with the light? (Score:2, Interesting)

      by Anonymous Coward
      Diffuse the laser beam and point it at a small, high-efficiency solar cell (around 23-25% efficiency for a cell used on satellites - not cheap though). Send power to an electric motor.
      • This is an extremely inefficient method, and solar cells are extremely expensive for what you get out of them. Which is exactly why this whole crazy idea will never happen until the economics work out....and until there is a good use for a laser in a car. It's a waste to convert the energy to another form, every time you do that, you lose tremendous amounts of energy. The heat in the exhaust should be used directly (for heating) or the laser sould be used directly if possible, and economical. Somehow I don't think any useful laser can be powered from exhaust, and a battery would surely be needed anyways.

        I think that the laser should be used in some way for a laser guidance system. Although this is more suited to rockets, and projectiles, but who knows. Based on what happened in 20th century, the future is almost impossible to predict.

    • Its simple!

      Step 1 : Convert heat into light
      Step 2 : ???
      Step 3 : Profits!!!

      Gotta love those slips-stealer gnomes ;)
      I just hope they'll not figure step 2 as : convert light into heat by aiming said laser on something to burn ;)

    • Re:But what do you do with the light? (Score:4, Insightful)

      by Anonymous Coward on Wednesday January 30, 2002 @11:14PM (#2929163)
      The author doesn't mention anything about this. I reread the article several times and still don't understand what is going to be done with the extracted energy. Do you use it to increase the density of the air entering the engine, much like a turbocharger does now? I suspect it would be better to turn the extracted energy into something that could drive another engine, like an electric assist motor. As for increasing the thermo efficiency higher than the ideal otto cycle, I believe this is impossible based on the second law of thermodynamics. They might be able to approach the ideal efficiency, but noone has ever built anything better.
      • The second law of thermodynamics really only says that spontaneous processes increase the entropy in the universe. Extremely loosely speaking, this means that whenever you do something, the net entropy of the universe goes up. I don't think you were right when you said that it is impossible to raise the efficiency higher than the ideal Otto cycle. However, it is more or less impossible to be more than perfectly efficient (you get more energy out then you put in). This would just push the line a little closer to perfect.

        Slightly off topic, but interesting, many physicists believe that entropy (disorder, related to temperature) is only statistical, that it is possible for a closed system to have a decrease in entropy. For example, all of the air in the room could condense to a solid and run laps around the room at the exact speed and direction, thus having almost no entropy. That probably won't happen though, so for almost all real purposes, entropy always increases.
        • Slightly off topic, but interesting...
          Yes, very interesting - I keep trying to get this point of view across to people. Entropy is a statistical model of a multitude of microscopic interactions. The reason people refer to entropy is that it is too difficult to accurately model the actual processes, and entropy does an excellent job of modelling the process on a macroscopic scale.

          The problem comes when people start to forget it's only a model. Ask a biologist (with little other chemistry knowlege) why converting ATP to ADP releases energy, and they will happily tell you it's because a bond has been broken. And believe it!

          Also, as we all know, radioactive materials never fully decay, the amount of radioactive material simply halves every n years. Doesn't hold up to scrutiny when you talk about single atoms....

          Sorry for the rant, but you've managed to remind me of a pet hate of mine.
      • I reread the article several times and still don't understand what is going to be done with the extracted energy.

        The extracted energy is a laser beam. The obvious use for it is to blast the idiot that just cut you off without signalling.

        -
    • Use the laser beam to destory your opponents in Ultimate Machine Combat [slashdot.org]

      See, the debate over which weapon system to use in that competition is finally over. :)
    • How many times have you been driving along and said to yourself, "I sure wish I had a laser right now, because I'd blast the guy in front of me." Finally, a solution!

  • Adsorption refrigerator to cool intake charge. (Score:3, Insightful)

    by Nick Driver ( 238034 ) on Wednesday January 30, 2002 @10:46PM (#2929039)
    Why not simply use an adsorption type "refrigeration" (ammonium hydroxide & water) system to cool the air/fuel intake charge to make it more dense and get some more efficiency out of the internal combustion engine? The waste heat going out the exhaust and radiator could run the adsorption-cycle cooling system.

    • Re:Adsorption refrigerator to cool intake charge. (Score:4, Insightful)

      by cgleba ( 521624 ) on Wednesday January 30, 2002 @10:59PM (#2929103)
      I've been thinking about that for years. There are a few papers on that, too. . .I can't find them off-hand.

      Two useful things that I thought of for that are:

      1) Free air-conditioning
      2) Use as an intercooler for turbocharged engines.

      The problem with ammonia, however (and the reason why they stopped making propane-run absorption refrigerators a long time ago) is that under certain conditions I guess ammonia is explosive and not to mention not too good for you :).

      But I don't know much for IANAC (I am not a chemist). If anyone knows anything about this (even though it is edging on off-topic) I would love to hear a discussion as I have pondered this a LOT. . .
      • The amount of ammonium hydroxide needed would be pretyt small. Heck, it's still used in propane powered refrigerators for camping trailers and RV's. I had a 35' camping trailer just a few years ago that had one, so not *all* adsorption refrigerators are out of production... just ones for standard in-home use. The amount of gasoline you carry onboard in the fuel tank poses a vastly greater safety hazard.
      • I've been thinking about this for years also. The concept of the adsorption heat pump is very sound and has been around for decades. One reason you don't see them nowadays is because compressor-driven heat pumps are more efficient overall. Of course, if you are utilizing waste heat, the driving force for the process is free. The ammonia-water system is the most prevalant, and I've even seen a patent on connecting one to a vehicle's internal combustion engine (look it up). Another widely used system is the lithium bromide-water system. This are found in nuclear submarines, solar-powered ice plants (3rd world), industrial plant water chillers, and other places where you don't want ammonia floating around. I plan to experiment on integrating one of these with the coolant system of a vehicle some day to supply cooling for air conditioning or refrigerated trucks.
      • I'm a ChE, but i've been out of practice for some time....

        My guess would be that the compressor needed to cause a drop in temperature from the NH4OH would cause enough power loss from the engine to make it undesireable. Remember, the power for everything onboard has to come from somewhere. That's why small cars get such bad acceleration when the AC is on. Plus, the engine runs hotter than the outside air, so you would have more heat to pump. The only other option would be to increase the size of the heat dissapation area so the compressor has to do less work... but the raidator in most cars is as big as it's going to get without being mounted outside the body (and thus exposed to solar heating).

        If anyone has another idea, i'd love to hear it
      • Pure ammonia (as in these refrigerators) is extremely poisonous, when it's used as a household cleaner it's pretty dilute. It's more poisonous than the chlorine used as a war gas in WWI, except that ammonia (NH3) is lighter than air so it would rise away from the target, while Cl2 is heavy and went down into the trenches where the troops were.

        But compared to lots of other things in our lives (automobiles for instance), ammonia isn't very dangerous. You get the plumbing joints tight, test them before filling the system, and run away fast if you smell it leaking -- and you _will_ run away if dangerous amounts leak, because it's one of the most godawful smells ever. If the smell is merely annoying, the dosage is not harmful, but you won't need to know it's poisonous to want to do something about the source. Since ammonia is a common naturally occurring poison, mammals (and possibly everything with a nervous system) avoid it by instinct.
    • Apparently some aircraft engines do that. I don't have a reference, but I remember a professor talking about failures of certain engines because of the failure of that part. The waste heat doesn't run it though, as the extra machinery would reduce efficiency more than it would help it for that.
    • Want to give us a first and second law analysis? Wanna show that to us on a T-s diagram? I might bring this up in my thermo II class tomrrow.
      • As mentioned in one of the other replies the efficiency of the gas that is used is not increased, thus no more work per unit gasoline is done.

        The thing it does do is increase the efficiency of the whole automobile much like a turbocharger does by harnessing the exhaust pulses into a charge which increses the engine's power-to-weight ratio -- which does nothing for situations where the engine does not propel itself (like in cars, airplanes, etc).

        This may not apply to your thermo-II class.
    • Because for Otto combustion engines, the efficiency is primarily a factor of compression ratios, not temperature or density. You could get a very efficient engine if you could compress the fuel infinetly (of course, gasoline won't stand for much compression) before igniting it.

      If you increased the density, then you could compress it less, probably resulting in less efficiency. Increasing air flow is usually a good thing though.
    • actually, this is kinda what is going on here and it is why the article is misleading.

      an ideal heat engine extracts work by operating between two heat baths of different temperature.

      the ideal efficiency of the engines is given in terms of the two temperatures of these heat baths.

      if the temperature difference is large, then the engine can extract more work. so one way of "improving" the "ideal efficiency" is to add a second heat bath of either very low temerature (a fridge) or very high temperature.

      to claim that this improves the amount of work that can be extracted is true, but to claim that this improves the efficiency above that of an ideal engine is crap because you are cheating by adding a third temperature bath.

      in the case of the quantum afterburner described in the article, the maser/laser acts as a zero temperature heat bath (sometimes called negentropy) which allows one to extract work from the exhaust. of course, in doing so, you use up the negentropy so it is acting more like a type of fuel.

      the article (both the nature one, and the original in Phys. Rev. Lett.) are interesting, but I wish physicists wouldn't try to sensationalize things just to make their results appear more interesting than they really are.

  • I sure hope this doesn't alter global warming (Score:3, Funny)

    by nizo ( 81281 ) on Wednesday January 30, 2002 @10:50PM (#2929060) Homepage Journal
    Thus spake the article:


    The hot gases belching out of your car's exhaust are not just useless waste. They are a laser waiting to happen, says physicist Marlan Scully


    I sure hope this doesn't change the global warming going on or all that beachfront-after-the polar-icecaps-melt property I bought will remain high and dry (scuba diving in downtown LA whoohooooo)

  • Not quite (Score:1, Insightful)

    by Anonymous Coward
    First off, so-called gas-dynamic lasers have been known for years if not decades, so this is old news. Secondly, the energy efficiency is not increased beyond the theoretical limit of an Otto engine.
    • That's what I thought. An ideal machine has no waste energy whatsoever; the useful work you get out of it is equal to the energy you put into it in the first place. "Better than ideal" would violate the 1st Law of Thermodynamics. This just brings it a bit closer to the ideal.

      • Re:Not quite (Score:3, Insightful)

        by nusuth ( 520833 )
        Ideal otto engine efficiency!=ideal heat engine efficiency. No heat engine can beat Carnot cycle in terms of thermal enegry->work conversion, but an "enhanced" otto cycle engine can beat usual otto cycle, without violating any thermodynamic laws provided that it doesn't beat carnot cycle's efficiency.


        On a related note, heat engines are much less efficient that 100% you seem to imply with "it should give same amount blah blah." The reason is second law of thermodynamics. You can convert all heat energy you put in the engine to work, since doing so would require heat transfer with no temperature gradient.

    • Ack! The story summary is misleaded. An ideal Otto engine DOES NOT ACHIEVE the maximum efficiency possible for a heat engine (so improving it doesn't violate anything). A Carnot engine is the engine with max efficiency which you are thinking of. Exceeding the efficiency of a Carnot engine (which is still less than one) is equivalent to breaking the Second Law of Thermodynamics.
  • I think this idea is genial, but the cost/effeciency on a car would be "hard" to achieve. What I find interesting, is that this duo laser/maser only require heat from an exaust : nearly the same thing as evaporated water from nuclear reactor. This could lead to a better efficiency of nuclear reactor, and the cost of such laser/maser would be minimal compared to electricity generated by that system.
    • "cost/effeciency on a car would be "hard" to achieve"

      The biggest problem in harnessing heat from exhaust on automobiles is that it tends to take heat away from the catalytic converter which in turn causes the car to produce more pollutants.

      "cost/effeciency" probably could be accounted for with innovation and economies of scale, but the catalytic problem is a biggie. It has killed the adoption of so many innovations that use the exhaust in some way.
  • The hot gases belching out of your car's exhaust are not just useless waste. They are a laser waiting to happen...
    If only this could be applied to the hot gases belching out my laptop's rear vent. Could they be a DVD player's laser waiting to happen? Better yet, could they be used to shore up the battery's charge?

    Ideally, if the excess heat was converted back into electricity, I wouldn't need to waste electricity on the fan, and I could substantially extend my battery life. Oh well, I can still dream.

  • In this house you will obey the laws of thermodynamics! -Homer

    But really are they saying they can improve the efficiency of a Carnot engine, or just the Otto cycle?
    • just otto. Infact in "Science" it is reported that the device is coupled with a carnot engine to check for an experimental fluke. The device, as expected/hoped, did not work at all.
  • My first thought when reading this title (nothing to do with the article:

    "Producing Hot Air with Quantum Mechanics."

    -Paul Komarek
    • That might not merit any kind of identification as a "new thing" as I think that goes back a year or two.

      On another note: It's just a pity the massive trolling going on tonight (not by the parent of this, I'm just too lazy to submit the complaint separately) is a sign of some people's vast need to get a life.

  • Cars with frickin' laser beams on their heads .. And for once I might actually get them :-)

  • Original Paper (Score:5, Informative)

    by Asparfame ( 96993 ) on Wednesday January 30, 2002 @11:06PM (#2929135)
    Can be found here [aip.org] (in PDF form), for all those who like reading physicists physics.
  • Hmmm... could be modified to improve my car's performance...?

  • Efficiency (Score:2, Insightful)

    by AntipodesTroll ( 552543 )
    After reading the article, its not as far fetched as it sounds, atleast at a low efficiency.

    The problem as I see it though is this, what is the engine going to do with the laser light anyway? Laser light isnt that usefull in a car as an energy source. And I cant see the intensity of light being enough to do something cool, like dissasociate water to H2 and O. This is probably in the "neat-things" file for quite some time. Though maybe they can use this technology for fixed poer generation (coal, nuclear) where the gasses temperatures are higher and there is more volume.

    • Laser light isnt that usefull in a car as an energy source

      On the other hand, it's one more annoying way to mod your car - goes well with neon underbody lights

  • Question (Score:3, Funny)

    by sconeu ( 64226 ) on Wednesday January 30, 2002 @11:11PM (#2929150) Homepage Journal
    Do Quantum Mechanics work for Maxtor now?
    • Yes, we do, actually.
    • Totally off topic, but I have karma to burn...

      Every time I see that Ben Franklin quote, I'm reminded that while many Americans risked (and lost) their lives to throw off British rule, Franklin "suffered" by staying in France during the revolution. I guess he didn't mind his own safety being secure while other people fought. Hypocrite.

      -jon

  • Wow. This is a neat idea. But not really a new one. Not new that is in terms of trying to find some way to use all the wasted energy. Right now we are still using technologies that are terribly inefficient. All this heat going out the exhaust pipe of our vehicles. What about the heat exhaust from your furnace? Your gas water heater? It seems that if we can generate X amount of energy, we should be able to use every last scrap of it in some way, rather than just simply releasing it into the environment. Does anyone know of any other projects out there to reclaim and use some of this lost energy?

    I wonder if I could then direct that laser at the moron who's tailgating me while yacking on his cell phone. b-)

    • Re:So much waste and inefficiency (Score:4, Interesting)

      by Waffle Iron ( 339739 ) on Wednesday January 30, 2002 @11:22PM (#2929194)
      Does anyone know of any other projects out there to reclaim and use some of this lost energy?

      Well, the university I went to had its own electrical power station. They used the waste heat to generate steam that was sent all over campus for heating. Even the dorms' clothes dryers used steam heat exchangers.

      They seemed to have so much heat capacity available that they didn't think that proper thermostats were a priority. A lot of people had to regulate the heat on subzero days by opening the windows.

      • That university woulddn't happen to have been Purdue, would it? I remember the dorm radiators with 2 settings: "off" and "surface of the Sun". We used the windows as ad-hoc thermostats, too. Plus, the steam tunnels fueled many legends of secret paths from the dorms to the classrooms that didn't involve braving Midwestern winters.
        • That university woulddn't happen to have been Purdue, would it? I remember the dorm radiators with 2 settings: "off" and "surface of the Sun".


          You had off??? Consider yourself lucky! Over at Carnegie Mellon, in some dorms that was impossible -- and opening the windows only brought the room temperature down to about 85!

    • Are _ external _ combustion engines that can be run (with appropriate mods) from ANY heat difference.

      Although displaced by the internal combustion engine, the stirling engine has still continued to advance. Modern Stirling engines can be smaller than a coin & used in satellites, or larger than a house.

      They are ideal for the recovery of energy from waste heat, exhaust's, furnace flues, domestic heat, etc.
  • ...The Fast and the Furious? I mean they had everything else: NOS stickers, neon lights on the undercarriage, ad naseum. Why not a laser in the engine?
  • Not only can this improve your efficiency, you can shoot frickin laserbeams out of your headlights!!

    It'll make me feel like James Bond, without being British, or having so many STD's...

  • Could the exhaust gas heat be used to make a car heater that doesn't take so long to fire up?

    • Re:A better heater (Score:2, Informative)

      by adamjone ( 412980 )
      I interned at Delco Electronics (now Delphi Automotive [delphiauto.com]) who develop HVAC and electronic systems for automobiles, and I asked a similar question. Why not pipe the exhaust through the seats and use it to quickly heat the interior? It turns out that the risk of leaking exhaust fumes into the cabin is too great to allow such a design. The exhaust could quickly overcome the driver, and lead to an accident or death, even if parked.
      • "It turns out that the risk of leaking exhaust fumes into the cabin is too great to allow such a design."

        Not to mention the noise, too.

        A better solution that I thought of a long time ago would be rather then bringing the exhaust into the cabin, bring the antifreeze to the exhaust. That way the exhaust heat would heat the antifreeze faster then the engine and produce heat in the cabin before the engine could. I would also warm up the engine faster. All you need is a thermostat to cut it off after the engine is hot.

        Only draw-back is that a new exhaust system would be that much more expensive but if they made it out of stainless steel in the first place that would not be too much of a concern. . .
  • This sounds a lot like some of the rocket-powered gas lasers proposed for Reagan's "Star Wars" project. The MIRACL laser [fas.org] first worked in 1985, produces megawatt-power continuous beams, and is still used now and then. MIRACL burns ethylene in nitrogen trifluoride, which generates free, excited fluorine atoms. The exhaust from combustion is mixed with deuterium and helium, and the resulting gas mixture is then lased in a mirrored cavity. So it's really lasing rocket exhaust.

    But MIRACL is using a far more reactive fuel at far higher temperatures than anything you find in auto exhaust.

  • If you can get enough energy out of the exhaust laser, you can use the radiation pressure of the light to get the car to go faster!

    (I know the pressure produced would be minimal - the sun's light generates a force of what? 80 tonnes?)

    This would sure give a new meaning to 'back-firing'.
  • Er, I otto nae break them, anyway.

  • Whole new meaning to " back off a$$ hole" (Score:1, Funny)

    by Anonymous Coward
    Just think, no more tailgaters once they get these lasers mounted!

    Thinking of jacking my car? Think again! I'll shoot you with my..uh...mini me...stop humping the...

  • Quantum Mechanics (Score:5, Funny)

    by Jarvo ( 70205 ) on Thursday January 31, 2002 @12:02AM (#2929286)
    If this makes it into your average car, would you have to take it to a normal mechanic AND a quantum mechanic? The price of the devices used in research had better come down before it happens.

    I can see it now...

    QM: (Wipes hands on oily rag) Well, if you lookee here, yer muffler wall is causing the maser beam to create destructive interference.

    Car owner: uhuh.

    QM: That, combined with the alignment of the quantum magnetic dipole is causing yer car to stall.

    Car owner: But how much will it cost?

    QM: Yer salary fer the next two years.
    • If this makes it into your average car, would you have to take it to a normal mechanic AND a quantum mechanic?
      "Yeah, Mr. Schrodinger, we've got your car hooked up to some diagnostic equipment in the other garage, but we haven't opened the garage since we hooked it all up, so..."

      "Ya see, we're kinda afraid that if we observe the problem it might alter the system and give you a totally different problem..."

      "Well, we're not quite sure where your car is, but we do know exactly how fast it's moving... Would you prefer the other way around? 'Cause I can do that instead if you want..."

      --
      Damn the Emperor!
  • I can see a possible application for this: speed detector jamming. Lots of people buy radar/laser/microwave detectors for their cars to try to beat the cops. There are even some [yahoo.net] on the market which claim to scramble the speed detector in such a way to disable the readout. With the quantum laser/maser setup, the faster you drive, the hotter your exhaust, and the hotter your exhaust, the more ferociously you jam anyone attempting to gauge your speed. Great!

  • The importance of the paper is more than just $$$ (Score:5, Interesting)

    by efuseekay ( 138418 ) on Thursday January 31, 2002 @12:16AM (#2929313)
    Quantum Mechanics has been known to be a time-trasnlation invariant theory. In layman's term, it means that you can run the clock backwards and everything is fine. There is no "irreversible" process. (For the jargon-empowered, QM does not have a natural "arrow of time").

    However, we know the Thermodynamics 2nd law tells us that even *ideal* processes are essentially irreversible if we do work, i.e. waste heat is inevitable.

    So the idea to use QM to improve this "ideal"-ness (classically speaking) is an intersting step towards understanding the *other* big issue in science : which is how the 2nd Law fits into the grand scheme of things. (Grand Unified Theories do not incorporate 2nd law since microscopically are processes are essentially reversible. The 2nd law drove many people nuts, including Roger Penrose.)

    So the point of the paper is not "get more $$$" for you engine. It's an interesting gedenken-experiment (sp?) that proves a point.
    • Nit to pick: you mean time-reversal invariance, not time-translation. Symmetry under time-translation is related to conservation of energy, not reversibility.
    • Quantum Mechanics has been known to be a time-trasnlation invariant theory. In layman's term, it means that you can run the clock backwards and everything is fine.

      Same with classical mechanics, and more so, as QM has the "destructive measurement" hypothesis, that by merely measuring that an object is in a given state, you collapse any state superposition in which it might have been. Besides, Statistical Physics and Thermodynamics have borrowed quite a lot from QM (particles being in given states among a number of possible ones, etc.)

      However, we know the Thermodynamics 2nd law tells us that even *ideal* processes are essentially irreversible if we do work, i.e. waste heat is inevitable.

      Yes, this comes from the fact that there exists a great many more possibilities that waste heat will be irrecoverably produced. It might stay in a usable form, just as you might open a bottle of ink under water, and the ink might flow out and then all crawl back into said bottle. It is just highly unlikely.

      There is no need for an arrow of time at the microscopic level for that.

      As for the paper itself, if I understand the summary correctly, it is ingenious but I'd look for a catch, such as the maser requiring at least as much power to function as that you can extract from the waste heat... Wouldn't that be annoying?

    • I have recently read an article on violating the 2nd law by a quantum heat engine so yes, it is an interesting topic and it is really science.

      Alas *this* paper has nothing to do with violating 2nd law. It is not a gedanken experiment either, its a real device. I guess you should read the article from time to time.

    • There are actually several papers in Physics Today (if you have access to old issues and want to do some reading) discussing interpretations of the Second Law, some of which note that the Second "Law" isn't a deterministic law. It simply notes that a system is most likely to evolve from a state of lower entropy to a state of higher entropy. When you have a lot of particles (like 6.02 * 10^23, let's say), this "most likely" becomes so close to "certain" that we just round it off in our speech. (Even Boltzmann noted this.)

      The Second Law is really a statement about probabilities and how you count macrostates and microstates, and so doesn't have to be present in microscopic physical laws because it doesn't mean much there anyway.

  • So, um, how do you use this combo maser/laser beam to do soemthing usefull?

  • Just A Thought (Score:2, Interesting)

    by spudwiser ( 124577 )
    if you could route the laser back to the combustion chamber, you could use it in turn to burn extra fuel (similar to the way nos affects combustion). the increased fuel being burned would create more exhaust. wash, rinse, repeat until nearly 100% of the fuel in the chamber is being burned and the car reaches maximum feasible efficiency. probably not all that feasible though, since routing lasers is expensive at best.
  • If I understood this article correctly, the laser transforms heat (disorganized energy) into laser light (more organized?). Wouldn't this cause a net decrease on entropy in the system?
    • "Young lady in this household we obey the second law of thermodynamics!" - Homer Simpson

      But seriously... you shave a little here, you get a little back... $$$ is the issue, and this sounds expensive. Plus its probably better for large scale applications, like collecting waste heat that is done in power plants... I asked a prof if it would make sense to do so on a smaller engine... and the benefits are tiny when you've really just got another link to fail and throw your whole idea of power production off on the smaller engine.
    • Read some of the posts higher up for an explanation of why this is okay. Or do this simple experiment: Clean your house. Or room. Or sock drawer. Hey presto! Less entropy.
  • Something similar to this was posted a bit ago on Slashdot, but what the hell.

    With a turbine engine, kinetic energy is extracted by hot-air through turbines, which in turn suck in air, compress it, combust it, etc. Cyclic compression and expulsion creates thrust, or rotational energy on the turbine shaft (which is what turbo-prop airplanes, APU's, helicopters and generators use).

    This technology might have applicability for turbines which use rotational energy from the shaft. For instance, the APU on a 777 is a fairly large turbine engine. Would it be possible to lower its running RPM by using converted heat from the exaust stream as a secondary source of power? This would of course lower fuel consumption while the APU is running, as well as extend the time between overhaul for it.

    Anyhow, essentially: this technology, if viable, could have serious use within turbine engines, since they waste a significant amount of heat in operation.
  • Stirling engines are really cool carnot cycle engines that run on temperature gradients. This company [stirlingcycle.com] makes various stirling engines including large industrial installations to recover waste heat. They can be made pretty simply and (within the tuned operating range) have darned good efficiency. Almost definitely better than a heat->laser->photoelctric-cell.

    The whole idea seems like a good way to write a paper, get published and generate hot air, but not a good way to increase energy efficiency. Kinda like our current projects to build a fusion reactor ("We've already got one, fer Christ's sake! It's called the sun.").

  • And all these years I thought quantum mechanics just meant when you get one part on your car fixed, another part breaks.

  • I've read the paper ... (Score:5, Interesting)

    by Doctor K ( 79640 ) on Thursday January 31, 2002 @02:43AM (#2929656) Homepage
    and it is a pretty interesting idea. I'm not sure about the practical feasibility of the concept for reasons I'll get into below. But, it shows that quantum effects might be usefully exploited to make better engines and will probably prompt a fair amount of thought and experiment into the matter.

    Warning: Ph.D. punditry follows.

    Suppose a molecule has three possible states ("a", "b" and "c") with energies E_c, E_b, E_a respectively (E_c is the ground state and E_b is the between E_a and E_c ... thanks lameness filter ... less than signs could never be useful).

    Suppose further, microwave (maser) energy transitions are possible from state "b" to "c". Optical (laser) transitions are possible from "a" to "b".

    For lasing to occur, you must have a population inversion ... more molecules must be in one of the upper states than in the lower states. However, in a gas at thermal equilibrium, this is usually not the case ... the probabiliy of finding a given quantum state in state with energy E is proportional to exp(-E / kT ). Here, k is Boltmann's constant and T is the ambient temperature. At low temperatures, the ground state will be where most of the molecules are.

    If the hot exhaust gas is first passed through a maser cavity tuned to the "b"-"c" transition containing a radiation field at the temperature of the cold reservior, the "b" and "c" populations will quickly come to thermal equilibrium with the low temperature radiation field ... "b" molecules to preferentially transistion into the ground state (state "c"). However, the "a" population won't be able to come to equilbrium that fast (provided the spontaneous emission rate is sufficiently low and the maser cavity isn't tuned to enhance the transition rate out of "a" state). This net impact of the maser is to create a population inversion between the "a" and "b" states. By passing the non-thermal maser cooled gas into a laser cavity tuned to the "a"-"b" transition, this inversion can be extracted as laser energy. This is the quantum afterburner part.

    From a quantum standpoint, nothing is particularly new here. Using rapid cooling of a selective population to create inversion is pretty unique but nothing that can't be explained with the standard laser rate equations.

    From a purely statistical mechanics standpoint, the net effect is to extract extra useful work from internal degrees of freedom of the working fluid. Statistical mechanics is not my forte so I can't really say if this is particularly out there.

    From a practical standpoint, it might be hard to find gases at engine temperatures and gas pressures where the low spontaneous emission lifetimes necessary to sustain the inversion is possible. My intuition says that collisional de-excitation (high temp and pressures) would wipe out the inversion. Also, the exact scheme discussed in the paper is more complicated ... involving passing the gas back and forth through two pistons. I'm pretty sure that materials and a simplified engine design could be made to validate the claims though.

    As a thought experiment, though, this shows that it may be possible to improve the efficiency of an Otto engine. (By the way, the paper notes that a Carnot cycle efficiency doesn't get a boost from the technique.)

    Kevin
    • I'm still not quite sure I understand how this works given that description, but in the exhaust flow from a well-tuned engine, much engineering goes into the exhaust system, the timing of exhaust pulses as they leave the valves, travel through the manifold to the point where the separate cylinder's exhaust pipes merge. Where the exhaust pulses overlap, more backpressure is created, causing the engine to (generally) work harder to expel exhaust gasses, whereas, if the lengths and diameters of these pipes are precisely arranged, the pulses can be spaced in-between eachother, and even to the point where the departure of one pulse from the joining point, actually helps to "pull" the next pulse through (as is the case in "tuned exhaust headers"). Many different factors can affect the total outcome, and drastically increase or decrease the efficiency and power of the engine. (In Aircooled VWs, I've heard of cases where engine output can vary as much as 80% based on the geometry of the exhaust system - between optimal systems, and systems that have been designed by people who don't have any idea what they're doing, and even systems by people who think they know what they're doing).

      That said, if this process works via changing "the net efect . . . of extracting extra useful work from internal degrees of freedom of the working fluid" - we're talking about what here, the cooling of the exhaust gas - thereby reducing the pressure of the individual pulse? I can say this, if there's any mechanical intervention involved (valves or pistons were mentioned in the article) then that's going to have it's own negative impact on efficiency, and may even destroy the delicate timing balance that some exhaust systems are engineered to. This is definately not something you can just bolt onto an existing engine - I suspect it's something that's going to have to be built into the design of a new engine from the ground up, with this in mind. The end result may bear little resemblence to what we currently see sitting under the hood of most cars.

      On the other hand, I wonder if this could be applied to a gas-turbine?
      • Two things should be noted about the proposal.

        (1) His paper is more a thought experiment. Assuming the author does not have an auto-mechanic background, I doubt he is even aware of the intricate details of exhaust design (I know I'm pretty oblivious to it). However, the standard thermodynamic treatments of such matters don't consider these details either. Nevertheless, the thermodynamic treatment of an idealized engine cycle allows you to put limits on the performance of any engine (regardless how nifty you make the exhaust design).

        (2) The extra work is in the form of laser energy. It is not obvious what to do with it in a practical sense. It is "useful" in the theromodynamic sense that the laser energy has a higher equivalent temperature that the engine's cold temperature reservior. Thus, you could theoretical use the laser to perform additional work. How best to do it is difficult to say (a reheat cycle maybe?)

        So, I agree, the proposal is not something you can just bolt onto an existing engine design. However, the proposal is interesting as it does give a way to beat the standard Otto cycle (apparently without violating any cherished laws ... like Carnot). And Otto cycles are pretty important.

        As far a gas turbine is concerned, your guess is a good as mine. If I recall correctly, turbines run a Brayton cycle, not an Otto cycle. I'm sure in theory you could apply the technique to get laser extraction off the exhaust (assuming a suitable working fluid / pressues / cavities) but it is not obvious that it results in an overall improvement to the theoretical Brayton cycle efficiency.

        Kevin
  • Not to start whining again about the second law of theromodynamics, but the laser and the maser also have to be powered. Since one uses the laser to depopulate the second excited level, the laser emission has to come from the 1-> 0 transistion. The emitted laser emission is probably of less energy than the first one.

    Also laser and maser have to be powered and somehow I think this takes a whole lot of energy more than a normal car enigine can supply.

    Then also the fact remains as already noticed by other replies what does one want to do with the laser-light obtained? (this also follows the 2nd Law)

  • kinda funny... (Score:3, Informative)

    by bpowell423 ( 208542 ) on Thursday January 31, 2002 @07:25AM (#2930100)
    Doesn't anybody else find it at least slightly funny that someone is proposing putting a Quantum Afterburner (TM) on a piston engine, the essential design of which is 125 years old? After all, there are other ways to recover waste heat in the exhaust that we could be using now, but aren't. Peltier junctions could be used to generate electricity to supplement or replace the function of the alternator once the engine was hot. Someone else here mentioned stirling engines. Maybe that'd be another way to increase the efficiency. Again, maybe you could drive the alternator with it. Of course, the alternator only uses maybe 1 or 2 horsepower anyway, so even eliminating that drag on the engine is only going to be a small improvement.

    Than again... how many horsepower does a car use when cruising? Maybe eliminating 1 or 2 horsepower would make a difference. I would assume that this Quantum Afterburner (TM) would be able to recover a much greater amount of the waste heat, too, so maybe it would make quite a difference.

    P.S. -- before anybody starts to rant on me for using horsepower, remember, there are metric horsepower too! According to my unit converter, one horsepower equals 1.01387 metric horsepower. Guess the French have different sized horses than the English! Cheers!
  • I'm no engine expert, but doesn't anything that impedes the flow of exhaust gasses interfere with the internal combustion process, making the engine less efficient? The two-poston contraption these guys are using would certainly seem to fall into that category, if they tacked it into the car's tailpipe.
  • Sort of on topic, considering the number of comments being posted about heatsink fans (even though the article has little to do with it): why noone ever figured out a way to use the hot air being expelled by the system fan to turn something that would generate electricity. Can't some of it be recycled back to power the system?

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