Isn't this what turbos do, extract the waste heat from the engine exhaust?

I'm happy to be corrected, but I don't think that the main power source of turbochargers is heat extracted from the exhaust gas - it is the kinetic energy from the exhaust gas. It may also cool the exhaust somewhat, the hot side of a turbocharger does get very hot, but I think that is unintentional.

On the cold side of a turbocharger, which is pushing air into the engine, it is more efficient when the air is cold. Intercoolers are even used to cool the air. So the heat from the exhaust seems to be a problem, rather than a benefit.

Edit: Just adding that the heat in turbos seem to be less of a problem than it used to be. More advanced materials perhaps? Definitely no turbo-timers anymore!

The people on the youtubes doing the high-HP turbo stuff I watch try really, really hard to keep as much heat in the turbos (using thermal blankets, hi-tech coatings and whatnot) in an effort to extract as much usable energy out of the exhaust gasses as possible.

The cold side heats up due to the compressive 'forces' (or whatever it's called) AFAICT. Same reason superchargers need also need aftercoolers to run at peak efficiency.

One of those pesky laws of thermodynamics seems to imply that if a turbo only used the kinetic energy of the exhaust it would not be able to overcome the losses of transferring the energy into the intake and would be a net drain on power.

Of course, I'm no thermodynamic engineer and am more likely to be wrong than not.

--edit--

Though, certainly, a turbo is harnessing some of the lost energy of the combustion process since the piston can't do a 100% energy conversion.

The law of thermodynamics you’re referring to is in a closed system. In this case, energy is being introduced by the burning gasoline pushing the pistons, and as a byproduct of that, exhaust gases are vented at a certain speed and volume. That is wasted energy as it just goes out the tailpipe more forcefully which adds minimal forward momentum to the car.

The reason turbos work is not because they are forcing more air, it’s because they are forcing more air which ALSO raises the compression ratio and the amount of fuel detonating (the MAF will sense the increased air density and add additional fuel to compensate). I.E. a turbo burns more fuel and therefore it produces more power.

Hot air is less dense than cold air (why heat rises). Probably keeping the hot side of the turbo hot helps with gas expansion, perhaps that increases the force on the turbine? I’m not sure about that. But the intercooler is to cool the air on the compression side because cold air is denser. Which means more air into the cylinder, which means more fuel. Probably the colder air helps with auto detonation too which lets you push the compression ratio further if the pistons and cylinders can handle it.

> One of those pesky laws of thermodynamics seems to imply that if a turbo only used the kinetic energy of the exhaust it would not be able to overcome the losses of transferring the energy into the intake and would be a net drain on power.

Turbos aren't really about transferring energy into the intake. It's about getting more air (oxygen) into the intake, so you can burn more fuel per engine stroke. The extra power comes from combusting more inputs.

> The cold side heats up due to the compressive 'forces' (or whatever it's called)

A gas heats up when it is compressed.

As a side note a lot of exhaust/turbo isolation in tuned cars also has to do with melting/overheating other things in the engine bay. Especially on street cars.

Turbo-pumps on rocket engines do an equivalent thing. Exhaust gases can be used to drive a compressor that pumps fuel into the combustion chamber. Other designs have a separate rocket engine whose sole purpose is to drive the turbo pump.

This innovation was key to the success of the V2's rocket engine.

Looks like one can place say a 100 of 2x2in 100wt $10 Peltier coolers from AMZN around the exhaust and get 10kw.

and that doesn't chemically interfer with the catalyzer?

you would place them onto external surface of the exhaust pipes. As the meaningful location would be the upper portion of the exhaust, upstream of the catalyzer, it would decrease the temperature of the exhaust coming to the catalyzer, so it may potentially affect it work when engine is at low-power.

Current F1 cars (until 2026 rules change) use a unit called MGU-H to do something similar in spirit.

The commercial version is the Garrett E-Turbo [1] Effectively it is an electric motor on the shaft that connects the turbine and the compressor, allowing electric spin-up on low RPM (reducing turbo lag) and electricity generation when the exhaust energy exceeds the compressor requirements. By dynamically controlling the boost pressure you can also consistently run at a stoichiometric ratio, reducing emissions and further increasing efficiency. Pretty smart!

[1] https://www.garrettmotion.com/news/newsroom/article/what-is-...

The applications of this technology in this particular space seem limited, given the inevitable demise of the internal combustion engine as a mass market technology. Barring any massive breakthroughs, thermoelectric generators are simply not efficient enough to adequately offset the heat energy losses in ICEs.

It is a 2012 article. ICE cars had no rival, EV were still in its infancy.

Priuses were already popular then; the writing on the wall was already visible.

> The applications of this technology in this particular space seem limited

Thermoelectric generators have applications in basically any space where you're generating excess waste heat (and you're able to maintain a temperature gradient). Off the top of my head, industrial scale distillation, desalination, garbage incineration, high energy lasers and pyro/electrometallurgy. The advancement of the technology for the automotive space would really have served as a springboard to increase efficiency in other areas.

> thermoelectric generators are simply not efficient enough to adequately offset the heat energy losses in ICEs.

Any amount of waste heat that can be converted to electricity and used or stored is good. Why not try to get every last joule out of your fuel?

You're right that the technology has been inefficient. For typical ceramic thermoelectric generators the conversion ratio from heat to electricity is low, it only works if you can maintain a temperature gradient and you have to contend with self-heating, but addressing the inefficiencies is exactly what JPL would have been trying to do. You couldn't ask for a better partner to push the technology further.

Why is NASA working on this?

The "NASA Global Climate Change" group will probably be laid off very soon.

Quite a few space missions (some of which are mentioned in the article) depend on this technology. It's useful in situations where solar isn't effective (eg the outer planets)

The article, while informative, is somewhat outdated as it was published in 2012.

Because the relationship between heat gradients and electricity is an important part of space travel. There are no doubt countless situations where one might make use of this either to heat/cool or generate power via RTGs.

Since everything NASA do can be used to observe global climate change, what does the NASA Global Climate Change group do?

The exhaust manifolds on the Land Rover series 2 2.25 4 pot engine are perfectly spaced to take cans - I always used to jam a can of beans, a can of sausages, and a can of tomatoes between them before driving the crew down to the boat club (20 minutes), and we’d have hot breakfast before our outing.

Take that, waste heat.

You likely won't care but i'll advice against it. The cans are typically lined with plastic.

You might enjoy Manifold Destiny: The One! The Only! Guide to Cooking on Your Car Engine! by Chris Maynard and Bill Scheller.

https://www.eater.com/23749614/manifold-destiny-the-one-the-...

Put (2012) in the title please.

Additionally, there are hybrid vehicles available in the market that utilize exhaust heat for climate control functions. Like Prius and RAV4.

So stirling engines? Peltier and similar solid state device could theoretically work too, but don't really come anywhere near the efficiency of a stirling engine which is basically the most efficient heat engine ever created and there are many companies that produce them.

This would be great if the USs institutions like NASA itself were not being dismantled.

I read an article yesterday about a prototype on this very topic. They were talking about getting 50 watts which sounds totally uneconomic.

That and the fact that the parent article is 13 years old indicates to me that this is not a promising area of research.

https://techxplore.com/news/2025-02-prototype-car-helicopter...

there is a direct, mechanical aproach to exhaust energy recovery, dating to 1950, called turbo compound engines, that were complicated, but very fuel efficient, the practice has been revived for use in highway truck engines now also other schemes to generate electricity from an exhaust turbine if both were be combined, with a high temp heat storage block, then best efficiency and lowest emisions could be possible