How harnessing exhaust gases can up performance

I've been thinking of something similar for a couple years now. Instead of using a turbocharger to increase the intake pressure of the ICE, how abour runing a turbine which adds electric power either directly to the electric motors or recharges the battery instead? It seem quite viable, and I'm a bit shocked that neither Honda, Toyota or Ford has come up with this yet. Theoretically, the Miller cycle is the most efficient 4 stroke cycle. Bleed energy off the turbocharger and dump power right back into the batteries.

I'm not an automotive expert, so if this is just fanciful, someone please knock me down a peg or two. :lol:

Peace,
Cosmo

 

Oops,

I guess I should have read the article first. It mentioned the same point I did. Duh.

Peace,
Cosmo

 

Sounds like another free energy scam to me.
If this device "harnesses" energy from the exhaust gas, it will necessarily increase the exhaust gas pressure.
This would result in a decreased engine efficiency even if the alternator efficiency were improved.

 

Sounds interesting. Turbochargers use exhaust gas to power them while superchargers are belt driven, and generally turbochargers are more popular, suggesting there might be some merit to using exhaust gas to perform useful work. It does seem like increasing exhaust pressure will reduce the power density of the engine, which might limit how far you can push this technique. Of course you can add on electric powered supercharging to balance that out, but only turn on the supercharger when extra power is needed, and normally keep it off, since a supercharged engine generally has lower effieciency. Lots of interesting things to play with.

You could also adjust the loading of exhaust powered generator to reduce the need to throttle the engine during light load conditions, and that seems like it would be an efficiency winner. Throttling(restricting the air intake) to control engine speed wastes lots of energy. Part of the reason diesels are so effiecient is because they don't require (air) throttles. I'll stop rambling now.

 

A different version of this article came across Green Car Congress in late SEP. As I recall there were quite a few posts from engineer types who seemed to think it was a good idea. I'm not an engineer so I kinda just got an overview. Kiloran, there were some auxilliary links on the GCC site that gave pretty "gory" details on the switched reluctance generator described by the article.

http://www.greencarcongress.com/2005/09/tigers_exhaust_.html

In particular note the post by Engineer-Poet. He speaks to the pressure problem that you mention.

 

Thanks for the posts.
I am have a mechanical engineering degree although I've worked in software since graduation (so my eng. skills are dated).
If you apply the Okkam's Razor test to this, you may find yourself asking, "If harnessing the pressure (potential energy) and/or kinetic energy of exhaust gasses produced more energy than the amount the increased backpressure reduced the engine efficiency by, wouldn't engineers have figured out how to make these devices long ago?"
I seem to recall a professor brining this proposition up as a class topic and then subsequently debunking it. (It's possible I could be misremembering.)

 

yeah. That's certainly possible. On the otherhand perhaps it was one of those things that nobody cared about. I could certainly see that in the 60s and 70s when gas cost less than water that nobody cared about trying this sort of thing. It's not like it is a huge boost in efficiency and does require a battery (I assuming something more than the 12V starter battery) because at idle the system supposedly shuts off. I suppose that if it's feasible it'll happen sooner or later. It just seems that with the vast majority of the energy being wasted in an ICE that there's gotta be some way to harness some of that waste.

 

Maybe, ....but once the ICE is on, seems it doesn't take much to make a little more power than it normally does to fullfill it job at hand.
Similiar action takes place when the engine revs up to charge the batteries as well as do the job at hand.
If it took "more" energy from the ICE to make that energy to charge the batteries than the batteries would in turn deliver later, you would lose overall efficiency rather than increase it?.. Seems toyota thinks this works or they wouldn't be doing it.
Once the engine is up to its specified rpms etc, seems it is "very" efficient for a little extra work load.

It would mainly help offset the highway driving whereas you would have a steady flow of air from the exhaust while at highway speeds.
The city driving would only gain minimal benefit since the ICE is off much of that time?

It would be a nice way to balance efficiency.. right now, city driving mpg is typically higher than highway... but with this addition, they may balance out as highway mileage increases, or maybe even superceeds city driving?

All that being said.. the city driving should go up also.... since the turbine would make energy while the ICE was engaged too!

It would be very interesting to see the improvement that modification would make with a prius.. I"m sure it will never hit the market if it doesn't work well.

 

The thing is, ICEs actually perform pretty close to their theoritical maximum efficiency, mess with it and the ICE efficiency will probably take a significant hit.

 

No, I didn't mean that just that perhaps no one was motivated to find a way to do anything useful with it.

Yes. That's true but it's theoretical max efficiency sucks!

 

So does entropy. Can't be helped.