This paper on the Corn stover collection project is no longer available on-line. I am making it available as a public service.
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The Ergosphere 
May 2, 2007 at 12:25 am |
EP,
I’d like to get your opinion on something.
What do you think about constructing a hybrid car that consists of a hydraulic accumulator, connected to a pneumatic drive motor, with an energy battery electric motor keeping the accumulator charged?
I was thinking about that because apparently current electrical regenerative braking tech is only 30% efficient, but the pneumatic recapture is about 70% efficient.
The accumulator could act sort of like a cheap ultracapacitor, allowing the batteries to be optimized for energy storage rather than power burst AND storage. And this would not interfere with the eventual electrification of transportation, as other types of pneumatic hybrids might.
May 2, 2007 at 12:46 am |
The hydraulic systems have high efficiency but a relatively low specific energy. This makes them very good for short start-stop cycles (e.g. garbage trucks) but not so good for typical passenger car cycles; you would need a very large and heavy accumulator (relative to the vehicle) to absorb all the braking energy.
I went searching for the 30% figure, because I was wondering about the methodology and the split with the friction brakes. The one hit I found was a pointer to a page which is now 404. Regardless, larger batteries (e.g. PHEV-class) will have a higher regeneration efficiency because they can absorb more power.
May 2, 2007 at 1:29 am |
I wonder how much energy could be stored in a compressed air tank of reasonable size. Those tanks are pretty heavy, though as you point out. Perhaps a carbonfiber tank? Crash protection would also be a worry.
May 2, 2007 at 2:11 am |
There have been several compressed-air cars, including one now being promoted in India. The problem with using air for regenerative braking is that it’s hard to package all the filtration, intercooling, drying and such gear that stationary high-pressure compressors have, and the tanks for low-pressure would be mighty big.
May 21, 2007 at 9:47 pm |
You’ve probably seen this:
http://www.businessweek.com/autos/content/mar2007/bw20070319_949435.htm?campaign_id=rss_topDiscussed
Probably a very small light wt vehicle, but interesting. Doesn’t say if there is any regenerative braking, though. If there is not, then there’s even room for improvement.
January 11, 2008 at 12:30 am |
Are we ever going to get another blog post?
January 12, 2008 at 12:20 am |
There’s plenty in the pipeline but I can’t seem to get anything finished.
This is partly because I’m swamped for time. I won’t bore you with the details, but I don’t have any prospects this weekend or the next.