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Old 03-27-2015, 04:59 PM   #11 (permalink)
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World’s most efficient thermoelectric material developed
"The new material, which is based on the common semiconductor telluride, is environmentally stable and is expected to convert from 15 to 20 percent of waste heat to electricity."

And for those ready to try this now:
http://thermonamic.en.alibaba.com/pr..._Recovery.html
Type: Thermoelectric Generator
Hot Gas: Temperature > 673 K
Output Power: 350 W
Open circuit voltage: 48 VDC
Matched Load Output Voltage: 24 VDC
Matched Load Output Current: 15 A
Internal Resistance: 1.6 Ohm
Dimension Size: 595 mm * 140 mm * 265 mm
Weight: 17.8 Kg

For those wanting to start out smaller:
http://www.ebay.com/itm/Thermoelectr...-/251817363025
Dimensions: hot side - 62 x 62 mm; cold side - 62x62 mm
Produces 13 W matched load.
Temperature differential: Tc = 50 Celsius; Th = 280 Celsius.
U-oc - 3.4 V
R-in - 2 Ohm
R-load - 2 Ohm
U-load - 1.33 V

Pretty expensive technology though, considering you'd need about 10 of the smaller units above to produce vehicle voltage. So you're looking at an initial investment of about $800 to produce a measly 13 watts maximum.


Last edited by Cycle; 03-27-2015 at 05:17 PM..
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Old 03-27-2015, 05:39 PM   #12 (permalink)
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My plan is to use the exhaust heat to preheat water to just below its latent heat of vaporization. I'll then use a new ECU that'll control all the normal engine components (fuel injector, spark timing, etc.) but also control a water injector in the intake manifold.

That injection water, being at such a temperature from the exhaust that it's just about ready to flash to steam, will absorb heat in-cylinder and flash to steam.

That has a couple advantages... it'll act as an octane boost, it'll slow down the lean burn so it's less explosive, it'll act as internal cooling and it'll contribute to cylinder pressure (and thus engine output). The trick is to get the water hot enough that it's just about ready to flash to steam before it's injected, so it flashes quickly once in the cylinder, to inject it in a fine enough mist that it can absorb heat quickly, and to inject enough to contribute to cylinder pressure while not so much that we're washing the oil off the cylinder walls.

The new ECU will have a fuel map and a water map, so it'll be easy to tweak things just right.

I'd use direct injection of the water, but my cylinder is so tiny that there's not a lot of room in there. Direct injection would let me time the water injection to just after combustion initiation, so the water follows along behind the flame front, absorbing the heat and flashing to steam. But unless I can find an exceptionally tiny injector, there's no way I can fit it in.

Last edited by Cycle; 03-27-2015 at 05:48 PM..
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Old 03-27-2015, 06:39 PM   #13 (permalink)
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That underlines my doubts.
350 Watt and 17.8 kilogram means less than 20 Watt per kilogram, and the cooling side has not even been constructed then.

I have a Seebeck element like the one in that link but the power output is disappointing.
You can use a Peltier element as an efficient heater or semi efficient cooler, but it is quite inefficient at producing power from a temperature difference. To my regrets, but nonetheless.
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It always takes longer than you expect, even when you take into account Hofstadter's Law.
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Old 03-27-2015, 10:47 PM   #14 (permalink)
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0.268 = 200W/746W ...or... about 1/4-1/3 Hp.

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