Exhaust Heat Recovery - Steam Power

[Frank Lee]

Originally Posted by MARTINSR

The "Mag" does take energy to spin it though.

Brian

Aw nuts. I'll have to stick with the diesel then. No- the diesel pump must take power too. R/C aircraft style glowplug engine? With a "T" style high-mount gas tank for gravity feed so there's no power consuming fuel pump?

[Patrick]

Originally Posted by MARTINSR

I don't think they get anywhere near that when you are driving normal and not "spinning it up" the turbo with the ICE at high RPM for performance.

I am thinking a super low geared reduction box may very well do the trick. A turbo in the exhaust, with a 1000 (?) to one little reduction unit spinning the alternator! (OR A/C?) This seems VERY feasible to me.

Brian

1000:1 is too much. You need something more like 40:1 or 50:1 to reduce the turbo speed to something usable for an automotive alternator.

[Patrick]

Originally Posted by MARTINSR

The "Mag" does take energy to spin it though.

Brian

Very little in comparison to the modern car's electrical system load on an alternator. And you do have to have some kind of ignition system if it's a gas engine.

[Phantom]

Originally Posted by Daox

Where might one get a 1000:1 reduction gearbox inexpensively that will handle the power?

Built one.

If you are turning an alt you are not going to need it to take a lot of power just have the first stage bearings able to hold the RPMs like ones in an engine, turbo, or supercharger.

Starting RPM 200,000
First gear set (pullies) 10" to 1" Ending rpm 20,000
Second gear set (running from the spindle of the 1") 10" to 1 ending RPM 2,000

I think 2,000 RPM would be fine to use to turn an alternator.

Also the turbo will not be turning that fast at idle to 2500RPM and can be controlled with a waste gate (or electric exhaust cut out) that is set to open when the pressure or RPM of the turbo reaches X.

[Dr. Jerryrigger]

I've been laying on the beach for the last week, so it took me a little wile to catch back up on this.
So If we could run at one pressure, ether; with a sensor that controls the water pump, or a blow-off regulator, than we could go with a generator, and run it at a high speed, or lower, or whatever we want (with the right generator). Come to think about it, I have a 120V DC 1hp motor from a tread mill. And it has fly wheel that is about 10lbs on it... I think I need to do some fiddling...

[mpgx2]

Ok Folks,

Sorry if I missed any posts but after more research I've had some
(other peoples) idea's about this.

A friend of mine said he was getting electric power out of some
peltier devices hooked to the exhaust. One or two amps perhaps.

What to do with that electric power ?

rig an electric blower motor or two to provide some forced air
injection.

garden blower supercharger - Google Search

Combine with some water and/or steam injection.

Comments?

[Daox]

Peltiers have been talked about in other threads. The conclusion is they are not efficient and you'd need tons in order to get a usable amount of power.

[ConnClark]

Lets look at what is known

If you ran an engine in a steady state...

A Kalina cycle would be ideal for this but hauling large amounts of ammonia in a car poses safety risks.

A Stirling engine would probably be next best.

A steam cycle would work okay.

Since cars don't operate in a steady state none of the above would be very efficient due to the fact that they operate best with a steady input and power output.

A Nitinol engine will work but has a low power output and is relatively inefficient.

Thermal Electric Generators (Peltiers) will work with consistent efficiency across varying heat input but is inherently inefficient.


Due to their simplistic nature Thermal Electric Generators are about the only system an average Joe could install. Of course the number required to get any significant energy out is large and therefore the cost benefit isn't very good.

These reasons are why exhaust heat recovery isn't very common.

[davidgrey50]

Originally Posted by Daox

So, we have 9hp available for the taking out of the exhaust.

I realize this goes right back to the beginning of this thread, AND that it doesn't illuminate the problem of steam recovery, but...do we? Do we have 9 hp available? I mean, isn't the backward-spewing exhaust equally-and-oppositely propelling the car forward?

[Patrick]

Originally Posted by davidgrey50

I mean, isn't the backward-spewing exhaust equally-and-oppositely propelling the car forward?

No, the energy available to the engine has already been used on the power stroke of each piston. But it is still hot and expanding in the exhaust system and that energy normally goes to waste unless the engine has a turbocharger.