> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of James Newtons Massmind
> Sent: Tuesday, December 19, 2006 4:37 PM
> To: 'Microcontroller discussion list - Public.'
> Subject: RE: [EE]:: Bimota centre hub steering
> 
> Ok, now we understand the confusion:
> 
> Steve is talking about NOX emissions and Tachi is on about 
> greenhouse gasses.
> 
>  http://www.epa.gov/otaq/crttst.htm NOX data  
> http://www.fueleconomy.gov Greenhouse gas data
> 
> But the NOX issue is due to the sulfur content in the fuel, 
> no? And the newest small diesel cars even filter that out and 
> will have lower NOX as well as lower everything else.

NOx comes from the design of the engine.  High combustion temperatures
combine the N2 and O2 from the air into NO2 and NO3.  This can happen in
gas engines if they run a little bit lean, because lean mixtures burn
hotter.  But gas engines generally don't emit that much NOx.  Diesel is
much higher compression and much hotter combustion temperature, so
generate lots of NOx.  Doesn't have much to do with the fuel, other than
the fuel burning supplies the heat.

I think the low sulphur allows the use of exhaust filtering, including
some way of storing the NOx, and then using a brief rich cycle to reduce
(or oxidize?) the NOx.  Basically some out of cylinder fuel burning to
balance the lean and hot conditions in the cylinder.

> I have a friend who purchased one out of state (which is 
> legal) and is running bio-diesel in it. I wonder what the 
> emissions are from that? And does it matter, since the plant 
> has to have absorbed all that when it was growing? And if we 
> can't have diesel cars, how will we brew bio-gasoline?

I've read in various places that bio diesel has lower emissions, but
given the above I don't see how it can make much difference in NOx.
Maybe, given it's origin, the particulates are more "friendly" than
petro diesel.  The EPA doesn't rate diesel engines on biodiesel.  Other
groups may have tested biodiesel, but how comparable are their results
to EPA testing (and therefore to gas cars)?

> 
> Over all the future of diesel cars looks good to me.

In Europe diesels are apparently just as clean or cleaner than gas
engines.  I don't know any details, just know that this came up about a
month ago on the diy_efi list and that was one of the results.  For 2007
diesels supposedly have to meet the same pollution requirements as gas
engines, but emissions ratings are just as much politics as they are
science.  A diesel engine may have literally the same number as the gas
engine, but will it be tested on the same schedule or a more forgiving
one?

What I don't have much hope for is heavy duty diesels, and that's where
most of the pollution comes from anyway.

--steve


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