How to use TEGs to create power with your exhaust heat

[California98Civic]

Originally Posted by CapriRacer

This sounds like something that an F1 team could develop into a viable system for street usage. They spend a lot of money and the fruits of this are right where they would benefit.

Apparently, they are developing them and have been for a few years (though not TEG, it seems). Check this out:
2014 Formula One exhaust energy recovery system explained | Electric Vehicle News

[freebeard]

That's relevant to another thread.

Originally Posted by Electric Vehicle News

In terms of sound, the engine note is not as loud as the current V8 because of two factors: the lower engine speed and the fact that the turbocharger sits in the exhaust flow, recovering energy from it that would otherwise be lost as heat and sound.

I remember a picture that Google can't find of a Baja Bug with a 'teepee' header (4-into-1 straight up in the air) with a rusty turbo bolted on top as a muffler.

[serialk11r]

Originally Posted by California98Civic

Apparently, they are developing them and have been for a few years (though not TEG, it seems). Check this out:
2014 Formula One exhaust energy recovery system explained | Electric Vehicle News

No that's different, the current F1 engine are what are called turbocompounding, where the turbo's excess turbine power is used to generate electricity. The turbine power comes from the excess pressure in the cylinders that is otherwise wasted.

TEGs are what would be called combined cycle, where the waste heat is used to generate power. A more efficient way to do this is BMW's Turbosteamer, which uses a heat exchanger and a separate steam turbine loop. The TEG's beauty is that it is solid state and tiny.

It would be neat if F1 cars started tacking those onto the exhaust, although they probably wouldn't be worth their weight/mass. Maybe it would work if they could be somehow set into the heads so the coolant system doesn't need additional components.

[gumby79]

Thermal paste them to the inside of a pice of Al pipe square, hex for 3 searies. then run your hot pipe through the middle. Add some cement for filler .Add a layer of 1/8" foam between the filler and the teg. like the flexable sheet stuff they wrap new dvd player's in . This will vaporize out during the brakein period leaving a small air gap to alow for thermal expansion of the chip sets. Also the cement would act like a capacitor, slowing and evening out the temperature spikes.
Also changing from direct transfer to IR only
---
Side effect that hasn't been bought up yet .
It will keep charging when you turn off the car ,the exhaust is hot for a long time after shut down, this may make up for some of the shprt commings. .Active cooling may be necessary for cool down.
---
Would just after the catalytic converter be the best place as it is a constant temp when active.? With good temperatures at low engine load.?

The average light off temperature at which the catalytic converter begins to function ranges from 400 to 600 degrees F. The normal operating temperature can range up to 1,200 to 1,600 degrees F. But as the amount of pollutants in the exhaust go up, so does the converter's operating temperature.
Sorce
https://www.google.com/url?sa=t&sour...EReJtF7R359yJA

[serialk11r]

Originally Posted by gumby79

Would just after the catalytic converter be the best place as it is a constant temp when active.? With good temperatures at low engine load.?

Hmmm, that's a good point. It's not constant temperature as almost all the fuel is burned by the time it enters the exhaust system, but the catalyst will definitely reheat it a little at lower load when the combustion efficiency is lower.

I think residual engine coolant should be enough to keep the TEGs from overheating once the car is off. A metal pipe has very little thermal capacity.

[RedDevil]

I don't think it is necessary to cool the TEGS after key-off.
Once the engine stops the heat sinks will cool them down quickly even if the power drain is cut off.
The engine generally won't be at full blast shortly before cutoff. I don't park at WOT

[gumby79]

Originally Posted by RedDevil

I don't think it is necessary to cool the TEGS after key-off.
Once the engine stops the heat sinks will cool them down quickly even if the power drain is cut off.
The engine generally won't be at full blast shortly before cutoff. I don't park at WOT

WOT to park no no agreed. The cat starts working minutes after start up and is working for some time after shut down till it gets under 6-800f . Theas have started many fires from people driving at slower than ecomodder speeds , was a major problem when they first came out. Finding the happy spot or controlling the hot side temp is the problem the high temp TEG are too spendy and 12-1600f is way too hot .
If your cooling pump or fan used say 10% of power production then why not let it top up the battery recapturing more of the energy already invested? Cost /w is high at this stage of development, so by the eg in the beginning we are only able to use a fraction of whats needed. By charging 120% of running time the % just got bigger.
---
a way to extend cat heat/power production @900f add 1 drop fule. the cat will catalyze the pure hydrocodone yealding heat allowing (just a guess) 10-15mun extension of charge time per drop.alowing for 2-500% charge timeV drive time.

[IamIan]

Sense the high temperatures are a product of the rate of energy flow being soo tightly confined to that small volume/area (heating and cooling)

How about spreading that same power (energy rate) over a larger area .. it would dilute that same exhaust heat energy over a larger area .. thus if the cooling were the same , it would yielding a lower temperature hot side for harvesting .. of course leaving it small for the cat which needs the higher temps .. but the rest of the plumbing doesn't need the higher temps .. The larger surface area , might also make mounting easier , as well as more of them on a given exhaust line .. and starting with a larger hot side , also means a larger cold side , thus also increasing the cold side energy flow rate in the same outside environmental conditions , and with that increase it would also further reduce the hot side temperatures.

The other side benefit is decreasing ICE back pressure from the larger plumbing.

[RedDevil]

Originally Posted by gumby79

WOT to park no no agreed. The cat starts working minutes after start up and is working for some time after shut down till it gets under 6-800f . Theas have started many fires from people driving at slower than ecomodder speeds , was a major problem when they first came out. Finding the happy spot or controlling the hot side temp is the problem the high temp TEG are too spendy and 12-1600f is way too hot .
If your cooling pump or fan used say 10% of power production then why not let it top up the battery recapturing more of the energy already invested? Cost /w is high at this stage of development, so by the eg in the beginning we are only able to use a fraction of whats needed. By charging 120% of running time the % just got bigger.
---
a way to extend cat heat/power production @900f add 1 drop fule. the cat will catalyze the pure hydrocodone yealding heat allowing (just a guess) 10-15mun extension of charge time per drop.alowing for 2-500% charge timeV drive time.

Once the engine is killed the flow stops and the reaction in the cats stops too. If it didn't the cats would normally do a bad job, as the exhaust gas has to be treated in the fraction of a second it takes to pass through them.
The (relatively heavy and bulky) cats will remain hot for a while; park in high dry grass on a hot day and you'll start a fire.
The pipe behind it will cool rapidly however, especially with a herd of heat sink TEGs scavenging heat.
The residual exhaust gas has hardly any thermal mass, unlike the TEGs. The only remaining heat source it conductive though the exhaust pipe from the cats. I can't see how the temperature could rise after key-off?
If it is safe to run them, nothing can harm them afterwards.

[CFECO]

Back when I was designing a car to compete in the Auto X-Prize Competition, I was working on a exhaust heat recovery generator. I planned to create steam which would drive a small engine, either piston or turbine, which would turn a generator. My first test boiler was a length of stainless brake line coiled inside of a housing, that the exhaust from a small engine emptied into the middle of the boiler at the bottom. It went up the inside of the coil, flowing over the top of the coil and and exited at the bottom outside of the coil. On the few tests I was able to perform, steam was produced in less than a minute, so the ability to remove heat from the exhaust was easily accomplished. Work was halted when I was forced to move, lost my workspace, and most of my computer files including drawings and calculations. Such is life. The "engine" I was going to test first, was a turbine out of a pneumatic wrench, and the second was a multi cylinder 2 stroke engine for RC aircraft. There would have to be other systems constructed, pressure pump, condenser, and the generator head itself. The F-1 guys have simplified this greatly by have a direct drive generator driven from the turbo shaft, Nice! I wonder what kind of generator works at those RPM levels? Oh well, my two cents worth.