Recovering heat from exhaust gases for efficiency
 

70-80% of the chemical energy going into a gasoline engine ends up being lost via heat, and a lot of this is lost via the hot exhaust gases. So there's a fair amount of scope to recover some of this lost heat and turn it into useful energy.

But to be honest, given the relatively low delta-T's involved, I really didn't think anyone would be able to crack this problem soon with any kind of practical setup.

Which is why I'm so surprised that BMW appear to have achieved exactly that!

http://www.greencarcongress.com/2005...ing_.html#more

Incredible! :shade:

Didn't Brits put tiny turbine driven generator on display?
 

Clett-didn't I see something here recently about some Brit engineers using a tiny turbine to drive a generator and recharge a hybrids batteries during hy driving?Nothing new about a turbine,of course,but it could make a gasoline hybrid more competitive with TDI diesel hybrids-which will always be heavier-noisier.A gasoline hybrid has no advantage over a regular gasoline vehicle(in fact,it is heavier,so it is at a disadvantage) and is at great disadvantage in hy cruising vs a diesel(well,it should be,but..).Heck,they could even make the mufflers lighter.
The tiny steam engine is pretty clever-wonder what it weighs?

Charlie

Re: Recovering heat from exhaust gases for efficiency
 

Brilliant. So sexy it brings a tear to my eye. And I've learned a thing or two about steam systems.

2 loops- one flashed from exhaust gas, the other from engine coolant AND from condensing the primary loop. Both superheated- extending turbine blade life.

The temps (<450F) and pressures are certainly low enough to be able to use stainless, which lets you get away with mostly ignoring boilerwater chemistry issues. This needs to be a seal-it-and-forget-it system; perhaps its not even water that's used as the working fluid? Refrigerant of some sort, perhaps- the better to flash at lower temps near atmospheric pressure and avoid corrosion issues.

"Elegant" comes to mind as a description. Of course "elegant" is code for 'rather complex and pretty cool when it works, but a bear to keep running reliably.'

Re: Recovering heat from exhaust gases for efficiency
 

I think this kind of technology could have a BIG impact on heavy truck transport because what you need is continuous 'assist', hybrids are great for short-term assist.

Re: Recovering heat from exhaust gases for efficiency
 

I don't think it would be practical in Canada or US because all steam boilers/pressure vessels and associated hardware are highly regulated. I think there would be too much certification/red tape to get through. A good idea none the less..

refer to www.tssa.org

Re: Recovering heat from exhaust gases for efficiency
 

Being that this is purely research on BMWs part for now...

Does this fall under regulatory jurisdiction, for lack of a better term? What are the temps/pressures/power requirements to require regulation? I don't know anything about boiler regs, and where they simply fall off the radar, if ever. Depending on the stats of the system, a case could be made that this is no different or more dangerous than working on an air conditioner- which is regulated, but not overly difficult.

Analagously, low-voltage lighting does not require an electrician's license or permitting to install, but 120v does. Most systems have a cutoff below which regs are trivial, nonexistent, or assumed to be met through ISO-style process management. This is a VERY small steam plant, after all. Something an undergrad would build/operate in thermo lab.

We'll see. All speculation until/unless they make more noise about it.

Re: Recovering heat from exhaust gases for efficiency
 

I hope this hits the streets....even the heat from the catalytic converter can do some good now. :)

Re: Recovering heat from exhaust gases for efficiency
 

Seems like this would be a great idea to bundle with a big pickup truck that needs a large high-torque engine to pull trailers. This little bit of "free" torque would offer a similar benefit to hybrid drivetrain without the limitations (ie battery depletion under constant load). Combined with cylinder shutoff and engine on/off you could dramatically improve the fuel economy of such a vehicle without even using a hybrid system.

I'm surprised something like this hasn't been attempted before, collecting waste heat from the exhaust seems fairly simple from a technological perspective.

Re: Recovering heat from exhaust gases for efficiency
 

It's done all the time, just not in autos. Cogen power plants use steam generated from gas turbine exhaust; ships and remote facilities use diesel jacket cooling water & exhaust gas as the heat source to distill fresh water.

On US Navy CGs and DDs, the waste heat boilers sitting in the exahust from the 2.5MW gas turbine generators (2 normally online) generate 150psi wet steam, used for H20 distillation @ 8,000gpd, hot water heating, cooking, etc for a crew of 400. Also has the nice side effect of reducing IR signature a by a few hundred degrees. FFG7 class uses diesel jacket water- 2 x 1MW generators normally online, distilling & heating 4000gpd.

The problem with a variable heat source (the ICE in a truck) is that you will see a lag between when you call for the extra power with your foot and when you get it, measured in seconds. The engine has to burn the extra fuel, the steam needs to absorb that extra energy, then transfer it to the turbine...each process has its own lag. If you're mostly at a steady load then its not so much of an issue- a truck would indeed benefit more than a car.

Re: Recovering heat from exhaust gases for efficiency
 

While we're on the subject of other waste-heat recovery systems, this one's a cracker, and I just can't understand why it's not been receiving more press:

http://www.wowenergies.com/pages/1/index.htm

They reckon their system can increase the efficiency of a coal power station from 30% to 60%!

Back to BMW's ICE version though, if they manage to add 15% efficiency to a diesel engine, as they appear to have managed for the gasoline variant, that could equate to a 60% efficient combustion process.... which is a good bit better than the 50% efficiency a fuel cell provides! In fact, thinking about it with this advance an H2 fuelled vehicle could actually turn out to be more efficient with an ICE than with a fuel cell!