The Nitrogen Oxides that end up in diesel exhaust have nothing to do with anything present in the fuel itself.  They are produced because the diesel engines operate at temperatures high enough to burn atmospheric nitrogen.  They are removed from exhaust flow by catalytic reactions in the converter.  The most effective way to do that is by injecting urea, which contributes to a reaction that turns the oxides back into atmospheric nitrogen.

So far as sulfur compounds in diesel exhaust, they do come from the fuel.  Modern diesel is much cleaner in this regard than the stuff we used to have, but not completely without sulfur.  Again, catalysis is supposed to remove that, whether a diesel or a gasoline engine.  Vegetable oil properly refined may or may not have lower sulfur concentration, depending on the source.  Most sulfur in vegetable material is in proteins, which good processing should remove from the oils.

Soot is a product of burning diesel fuel at too low a temperature or with too rich a mixture, so that the conversion from hydrocarbon to carbon dioxide is incomplete.  Proper tuning and fuel mixture are supposed to eliminate that pollution.  Whether vegetable or petroleum is the source of the fuel, this problem can occur.

Hope this helps, and I am sure that others will point up any errors I have made.  mcneely

---- Anthony Egeln <regnsuzanne@YAHOO.COM> wrote: 
> OK....with al the press about the VW diesel scandal out there, and since it is Fryeday, I thought I'd ask the list a question, or perhaps a confirmation.  Someone here must know this stuff.
> Is it true that bio-diesel doesn't emit the same noxious emissions as does the petro-diesel?
> When I say bio-diesel, I am just referring to diesel created from "fresh" veggie oil, not the retreaded cooking oil variety.  Let's say it is fuel created from algae, canola, peanut, sunflower, soybean etc., sometimes referred to as SVO, or straight vegetable oil.
> Cheers!  Ant

--
David McNeely