Monday, August 11, 2008

That's kinda interesting.

Researchers have apparently been messing around with using thermoelectric generation, a process that converts heat (temperature differentials, actually) to electricity, to generate enough juice to replace a vehicle's alternator. Having been used in the space program, it's not like this is untried technology that's never been exposed to harsh elements either, although you don't get much in the way of slush and road salt in space...

Use a big enough battery to handle the load until the exhaust gas gets up to temp, or put a magnetic clutch in the alternator like the one on the a/c compressor, and you could remove a large source of parasitic drag from the car's engine. Surely you've noticed how your gas mileage improves when you turn off the air conditioning, right? Imagine being able to turn it even off-er.

12 comments:

Dr. StrangeGun said...

You get a little thermodynamic boost too for using waste heat.

Sean_Galt said...

Kick ass. Couple it with regenerative braking and an on-demand hydrogen/oxygen generator & injection system, and get big fuel savings. Sweetness.

staghounds said...

The Atmos clock, from the 1930s, runs solely on changes in air pressure due to ambient temperature changes.

Like tides, it seems as though intelligent people would have figured this out long ago.

SpeakerTweaker said...

I love this blog! Snarky, to be sure, but ever so educational!

I mean, who else can invent words like "off-er"!

;)

That mag-clutch alternator thing would be sweet.

Off-er, indeed.



tweaker

Rabbit said...

They've been using thermocoupled heat exchangers in Finland and Iceland for several years to generate power. Saw it in Home Power mag awhile back. Helps to have thermal springs around to create the differential delta T.

Regards,
Rabbit.

bedlamite said...

The problem with this is that the alternator doesn't require that much power to begin with. A 100A alternator at 14.4v and 67% efficiency only requires about 3hp from the engine. It's only the first few minutes that you use that much power, after the battery is recharged it drops to a few hundred watts, which is about the same time the exhaust heats up. I seriously doubt the added cost and complexity will ever be cost effective.

Tam said...

You logical people and your damned science! You take the fun out of everything! ;)

DJ said...

No, Tam, we make it possible to have LOTS of fun without it being so damned much work, and we take the mystery out of it so it doesn't seem to be magic. The stuff we do for real is much better than the stuff that Hollywood fakes.

Don Meaker said...

Thermo-electrics are really nice. In the old days in Siberia, used copper-iron wires hooked up to a cold plate (outside) and hot pipe (chimney flue) to generate electricity. No moving parts, just you had to be careful not to get too much voltage and fry your radio.

It is like a standard 2 temperature engine, but uses electrons rather than a gas as the working fluid. It also runs backward, generating either refrigeration or heat. Heating or cooling rates are proportional to amperage, not to power, so you can get good performance where high voltage is not a good idea.

We now return you to the regularly scheduled comments.

Neutrino Cannon said...

Now we just need to power the cars using a radioisotope thermoelectric generator!

Imagine, if you will, a car that you can drive for ten years straight! No emissions! No need to refuel!

Don't ever wreck it!!!

Mike Gallo said...

I'm backing up bedlamite here - I drag race, and the difference in engine output on the dynomometer with and without an alternator is basically within the error of the brake, i.e., negligible. Most guys that don't run an alternator when racing do it for the weight/size/simplicity, not for the parasitic drag. I suppose some MIGHT do it to save on power loss because they're uninformed...

Anonymous said...

You really would not need a clutch to disengage the alternator. Except for friction and the cooling fan built into the alternator pulley, the torque required is proportional to the output power. If you disengage the alternator field, it will draw next to no power from the engine.

You can test this with a simple DC motor by turning the shaft with and without the terminals shorted.

One complication in using a thermoelectric generator on the exhaust is that the regulator would have to handle the entire load while in a system using an alternator, the regulator just has to adjust the field current which is significantly easier.