View Full Version : Exhaust Heat -> Electricity
08-11-2008, 04:13 AM
I want one:
Now only if I could get a good electric vehicular AC unit?
08-11-2008, 02:55 PM
Funny how for years it's been said that only one third of the energy in a gallon of gasoline is used for propulsion. One third is lost as waste heat and the final third goes out the tailpipe. But now it's suddenly only 1/4 is used for propulsion.
I thought all of these modern gee-wizmo's were increasing the internal combustion engine's efficiency?
That being said, the concept looks good to me. I wonder what their conversion efficiency is.
08-11-2008, 04:24 PM
Funny how for years it's been said that only one third of the energy in a gallon of gasoline is used for propulsion...now it's suddenly only 1/4 is used for propulsion
If I remember correctly in Uni physics courses, we calculated it was on the region of ~4-5% and the prof didn't dispute our numbers. I've never understood where the 20%+ came from...
I wonder what their conversion efficiency is.
I'm not sure and if this increases backpressure or simply is a heat exhanger I'm unaware.
08-11-2008, 11:47 PM
Sign me up! I'll take two if I can apply one to the neighborhood cats in heat.
08-12-2008, 01:40 PM
Here's an article that says the cost per watt generated by thermoelectrics is similar to, maybe less than, the cost per watt when generating electricity using solar power.
And the technology works with a relatively small difference between the source of warmth and the ambient temperature. The article mentions a demonstration where a small TV was powered by thermoelectric unit exposed to warm water left over in a bathtub. They're even talking about using human body warmth to power electronics built into clothing.
This makes me think that thermoelectrics could work with a passive solar hot water system. The sun heats the water stored in large bottles, tubes, tanks or bladders during the day, and the thermoelectric system extracts energy from the water in the form of electricity to power lights and other low voltage systems in the evening. Hmmmm....
08-14-2008, 11:26 PM
The efficiency of internal combustion engines has improved over the last 110 years.
In most readers' adult lifetimes, carbureted gasoline engines were 20-25%. With electronic fuel injection they've improved to ~32%.
Currently, vehicular diesels are as high as 46% (my 906 = 0.32 lb/hp-hr = 0.43 lb/kw-hr. Doing the math yields this number. I can go through the calculation if someone doesn't believe me.
Some marine diesels are as high as 55%. Detroit Diesel/Daimler has come out with the DD15 truck engine which has turbocompounding: the turbo is mechanically linked to the flywheel, lower fuel consumption 10% at a given power output; I'd guess the DD15 is ~0.29 lb/hp-hr, or ~50%.
The rule of thumb with IC engines has been that about half the waste energy is exhaust heat and half water jacket heat (if water cooled).
The theoretical maximum efficiency of a diesel is ~75%; that would require ceramic pistons and block liners to prevent heat loss into the engine, among other things.
In the first decade of the 20th century efficiencies were less than 10%.
I suppose thermoelectric plus turbocompounding could get up to 55% but lowering exhaust temp too much increases backpressure and therefore limits efficiency increases.
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