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Coupled Heat recovery generator circuit for cars, trucks, etc

Retrofit heat recovery circuit between engine, exhaust and radiator
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DISCLAIMER - Ok I searched and searched, found some similar ideas, but not quite the same as this. Bear with me, then flame away.


The idea consists of a retrofit closed heat recovery loop that uses the normal engine cooling channels on the engine for primary heating of a <non-water> coolant. A modified exhaust manifold or post-turbo heat exchanger would comprise the secondary heater. I'd have to work the numbers more, but perhaps the intercooler could be used as a pre-heater as well. The heated coolant is then run through a turbine to extract energy. The condenser [here's the good bit] in the circuit would be cooled by the coolant from the radiator of the car.

The interesting part is that the existing radiator is already capable of handling the heat loads. All we are doing is closed-loop separating the radiator circuit from the engine-and-exhaust coolant circuit, and using the temperature difference to generate some elecricity. The engine coolant would be a refrigerant with the right phase change characteristics; I'd have to do a bit more research, I'm thinking something like a light alcohol or hydrocarbon that goes supercritical somewhere between 50 and 100 degrees celcius. Yes we'd try to find a non-explosively flammable liquid as opposed to, say pentane or whatever you were thinking. Perhaps a halogenated hydrocarbon (fairly inert).

I've read where one company has installed heat recovery (using thermoelectrics - very low efficeincy and high purchase price) to a prime mover engine that generates 1kW. I really think that given the heat loads involved, a decent 2-stage heating and turbine loop could beat this significantly.

Custardguts, Feb 01 2007


       Hmmmm.... this is actually interesting. I'm holding off on a bun until I have a little more think about it, especially that //good bit// you mention. Something seems fishy about that.
BunsenHoneydew, Feb 02 2007

       I don't see any reason this wouldn't work. With some work, you might even be able to use water as the closed loop: if you lower the pressure below atmospheric, you get a lower boiling point and you can then superheat the steam to avoid water droplets in your turbine.   

gardnertoo, Feb 02 2007

       Cool. Or rather, cooling.   

       The explosion hazard is a little unnerving, but what about using gasoline as the coolant? It's already onboard and compatible with all materials inside the engine. You'd have to keep the flow moving right along to guarantee you don't have something blow up, but with a properly filled coolant system - no oxygen to support combustion - this could work.   

       I don't think gasoline has the same heat capacity as water-based coolant, so the coolant passages may have to be made larger or more numerous.   

       Brilliant concept, tricky to implement. Shunt past the turbine during warm-up.   

       Can you offer a link to the thermoelectric heat recovery article? I've fantasized about an alternatorless car and would like to see their approach.
elhigh, Feb 02 2007

       What would you do with it?
jhomrighaus, Feb 02 2007

       um... [Jhom] was that question aimed at [elhigh]?   

       --I'll go looking for the link tonight.   

       [bunsen] - not too fishy I hope, I just thought one of the better features would be the fact that it could use much of the existing hardware. Given the way radiators work I can't see to many issues.   

       [gardner] - you are right, but running a reduced pressure system gets very complex. The advantage to using a liquid with a lowerboiling point is that you can achieve the high pressures needed for good energy recovery at lower temperatures than with steam.   

       [elhigh] - I think using gasoline as the coolant would be very scary. A hot turbo or any spark at all will easuily ignite heated gasoline. Any system leaks and you'd have a catastrophic engine fire in no time. I'd rather use an effectively inert gas, perhaps one of the non-ozone depleting fluoro/chloro-hydrocarbons, something like that. They're used in fire supression systems, so I think the flammability is pretty low. As to the cooling capacity, that'd be up to experimentation - increased flowrate for increased cooling. Perhaps it would work out that you'd need a specifically designed engine with more coolant channels, and if so I'd need to find a friendly engine manufacturer, wouldn't I?
Custardguts, Feb 04 2007

       The turbine in question isn't the turbocharger. It isn't in the path of hot exhaust gases, only expanding gasoline vapor.   

       Yeah, the explodomobile potential is pretty high. I reckon you'd need some mighty big head bolts on this thing, and maybe wrap the entire engine compartment in ballistic fiberglass armor...   

       Some of those chlorofluorocarbons don't take to heat too well, and decompose into nasty other compounds that will acidize your oil or clog the passages. Choose wisely, young Jedi.   

       Wiser than gasoline, anyway.
elhigh, Feb 08 2007

       Yes, this would work well on a hybrid vehicle where the electricity could be put back into the main storage battery to drive the car/assist the engine.
mecotterill, May 11 2008

       Wow, over a year old and nobody has mentioned using a Stirling engine.
marklar, May 12 2008


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