Talk-Polywell.org

Tom Ligon wrote:You need a steady gradient across these things to achieve long life.

A constant-RPM Stirling driving a generator, steadily charging a powerpack, would have gentler waste heat transients than an IC engine driving the unpredictable primary load. Buffered by being one step further removed from the accelerator pedal. Figure one cycle per driving session.

Both of those look like some PD pumps I have seen.

Lots of wear surface, seems to indicate a high need for lubrication, which is a bad thing from an engine design standpoint regarding efficiency and pollutants.

DeltaV wrote:A constant-RPM Stirling driving a generator, steadily charging a powerpack, would have gentler waste heat transients than an IC engine driving the unpredictable primary load. Buffered by being one step further removed from the accelerator pedal. Figure one cycle per driving session.

Do notice that the linked article says that even rapidly pulsed heat flow, unless above 1 kHz, causes thermal fatigue in Peltier devices. I suspect, though, that a little modification of the materials and configuration might get around that.

The question for me is, would current TEGs be worth using to scavenge heat from a Stirling-generator device? Efficiencies of Bi-Te chips commonly available are in the 4-7% range. Pb-Te are getting up to 12% and may push to 18% per an earlier thread. But if a Stirling is run at optimal conditions, its converting far better than that, and generators can be extremely efficient. Maybe we're talking 40% or a little better overall. Adding a TEG to the heat flow path would reduce thermal conductivity, and I'd expect it to reduce the overall efficiency of the Stirling engine.

And then there's the prospect of graphene TEGs, in the lab but apparently not yet practical. Theory says 65% or higher may be possible. In which case you pitch the mechanical marvel in the recycle bin.

Meanwhile I'm messing around with an old Peltier cooler I've had since the last millennium, a MPJA surplus unit pulled from a picnic cooler. I stacked a similar chip, calibrated as a heat flow sensor, on it yesterday, in order to try to make some sense of the heat flow curves available for the device. In principle, the ability of a Peltier device to move heat should be symmetrical. Reverse polarity and it should work about as well in one direction as the other. This one is not doing it. It has developed different resistance in the two directions, and the heat flow changes by about a factor of 2. It is producing higher heat flow in the direction with lower current. I'm baffled. I suspect a malfunction. But this particular unit has a history in the Polywell effort, as it kept my lunch cold on the drive to San Diego.

Nothing to add here, just...

I like your stories, Tom

Depending on temperature differences, would the TEGs work on the 'cold' side of a Stirling without reducing the Stirling's efficiency? If I'm understanding function properly, I would think it should work to further reduce the cold side temp while adding to overall efficiency.

Thinking about adding a sterling to an ICE led me in another direction. Has there been any work on compounding a typical piston engine? Would it increase efficiency beyond supercharging?

Now this is an advance in vehicle design that's different.

http://www.msn.com/en-ca/autos/news/con ... li=AAggFp0

I remember reading about someone converting a V-8(?) to Stirling several years ago, but don't have a link.

The key to Stirling engine performance is the regenerator.

Regenerator material (stainless steel wool is good) and amount of "dead" space are critical:
http://www.j-mst.org/On_line/admin/file ... -1255_.pdf

See also
https://www.ohio.edu/mechanical/stirling/

My thoughts on the TEG placement were that it would intercept "waste" heat flux from the heated section that would otherwise escape to the environment. Very long cycle time compared to what the regenerator would experience, since Stirling heaters are typically quasi-steady state. Basically one ramp-up and ramp-down per session, not kHz.

Now that I've looked at the liquidpiston link, I like what I see. 18:1 compression ratio, 3 hp from a 4 lb. motor, they think they can push to 5 hp from 3 lb. If it can hold up to wear, tear and up scaling, would make automobile design interesting.

No way to combine a common air compressor with this modification and make a new HVAC system? Phase change refrigeration is so wasteful.

Would be interesting to see if they could build one of these little motors using Aluminum and Titanium parts. Already a fraction of conventional engine weight, might be worth it.

DeltaV wrote:

Tom Ligon wrote:You need a steady gradient across these things to achieve long life.

A constant-RPM Stirling driving a generator, steadily charging a powerpack, would have gentler waste heat transients than an IC engine driving the unpredictable primary load. Buffered by being one step further removed from the accelerator pedal. Figure one cycle per driving session.

One of the aspects of this that I haven't seen mentioned is conversion efficiencies, especially if you are using a battery storage system.


It's been awhile since I looked at battery storage efficiency, but I think it's something like 50-80% depending on specifics. In other words, a *LOT* of energy is wasted in the process of charging batteries. You only get back a percentage of what you put in.


Electric motors have efficiencies that range around 85% to 95% depending on particulars, and the conversion process for your motor control is also lossy.



I don't know the man's numbers, but I would be surprised if all the losses didn't add up to more than the gains.

It's already been done. The thing is that the oil magnates would rather keep technology in the dark ages.
https://youtu.be/H_Vnxapd5fs