Exhaust Heat Recovery: Simulation of a Rankine Cycle System

[Daox]

Here we have a very interesting paper where they analyse using exhaust heat to power a rankine cycle system to recover power. I've long wondered how much power you can really harness from the exhaust.

http://www.evs24.org/wevajournal/php...J3-3260191.pdf

I did not read the whole paper, but I've cut up a bunch of the info to share here.

Here we have the general premise. Capture heat from the exhaust to vaporize a fluid, use the resulting pressure to spin a pump/turbine, condense the gas back to a liquid, and pump it back into the high pressure side to turn back into a gas again.






Basically, they used a 2nd gen Prius as an example vehicle under two operating points. Point #1 is about 5kW engine output, point #2 is 20 kW.





And, here we have the power recovery they calculated. Php is the high pressure side pressure, Plp is low side pressure.

[darcane]

The Rankine cycle is commonly used in power plants since it's a very efficient power cycle but it wouldn't work well for the primary power source for a car due to the constant changing power needs. Using it to capture waste heat and charge a battery is a solid plan though.

I think you're going to start seeing these on production vehicles shortly. First will likely be on heavy duty trucks.

This study is a little late though. BMW has had functional prototypes (search for Turbosteamer) for over a decade, and many other manufacturers have already been studying these systems.

[sqidd]

I heard that Formula 1 engines use 1/3 of the fuel energy for power, 1/3 goes out the exhaust as heat and 1/3 is radiated through the coolers.

That 2/3's is a lot of wasted energy.

[maxc]

Build the boiler around the converter. Better yet converter around the cylinder head then the boiler.

[Cobb]

This type of thing is neat, but on the flip side you got vehicles with electric and fuel assisted heaters that heat the coolant to maintain operating temperature cause the vehicle cant maintain it. I see this a lot with diesels including the big trucks.

[maxc]

Originally Posted by Cobb

This type of thing is neat, but on the flip side you got vehicles with electric and fuel assisted heaters that heat the coolant to maintain operating temperature cause the vehicle cant maintain it. I see this a lot with diesels including the big trucks.

Put coolant/heater system on the outlet of exhaust. Still enough heat there. Put preburner(with limited air injection) in converter to get heat up fast(some already have that)just enough too vaporize fuel send that(exhaust from preburner) back too engine.

[markweatherill]

Originally Posted by sqidd

I heard that Formula 1 engines use 1/3 of the fuel energy for power, 1/3 goes out the exhaust as heat and 1/3 is radiated through the coolers.

That 2/3's is a lot of wasted energy.

But if they didn't 'waste' that energy making the engine run, the engine would not be able to get that 1/3 energy out of the fuel.

A turbocharger sounds like the obvious way to recover exhaust energy and I wonder why this system is better?

[sqidd]

Originally Posted by markweatherill

But if they didn't 'waste' that energy making the engine run, the engine would not be able to get that 1/3 energy out of the fuel.

Absolutely.^^^

But if the F1 guys were allowed under the rules to recover some of the spent exhaust gas heat (they recover the exhaust energy with turbos this year) and the spent radiant heat they would have even more power.

A turbocharger sounds like the obvious way to recover exhaust energy and I wonder why this system is better?

Turbo's really don't do much for economy. They allow you to retain economy (out of boost) and still have the option of having power (on boost). My F-150 gets fantastic mileage if I mostly stay out of the boost. But when I spool them up look out! Fuel gets used. It's fast though.

[oil pan 4]

Do you know how big the boiler heater is going to be?

[oil pan 4]

Originally Posted by sqidd

Turbo's really don't do much for economy. They allow you to retain economy (out of boost) and still have the option of having power (on boost). My F-150 gets fantastic mileage if I mostly stay out of the boost. But when I spool them up look out! Fuel gets used. It's fast though.

I put the turbo on my diesel I instantly got 2 to 2.5 MPG increase. Then adding the second turbo and intercooler got me maybe another 0.5mpg.

Turbos just don't really increase the fuel economy of gas engines. On a gas engine the turbo and throttle fight each other constantly, any gains are lost there.