Capturing Waste Heat with Quantum Mechanics

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."

Comments

Adsorption refrigerator to cool intake charge.

[Nick Driver]

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.

[cgleba]

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. . .

Re:Adsorption refrigerator to cool intake charge.

[dfenstrate]

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.

Re:But what do you do with the light?

[Anonymous Coward]

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.

Re:Not quite

[nusuth]

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.