Date: Fri, 25 Sep 2015 22:24:42 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Fryeday - Bio-Diesel Exhaust/Emissions
In-Reply-To: <20150925153218.FCQAO.8740.imail@eastrmwml206>
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Diesels have a lot of excess oxygen since they don’t have throttles. Excess air combined with the high compression and high peak flame temperatures make for a lot of NOx. The soot is due to the poor vaporization and not getting all the fuel to react with oxygen even though there is an excess of it. Sulfur is from the fuel. Modern diesel is <15ppm beginning from 2007. This was to support the use of exhaust after treatment such as selective catalyst reduction and other means to reduce particulates and NOx.
As bio-diesel often has a lower BTU content it may produce lower temperatures while burning which would help to lower NOx emissions. I think in most areas now all diesel at the pump has up to 20% bio diesel content. My motorhome has lost a good mpg from when I bought it in 2004 to the fuel available now. From 8.5 to 7.5. Yes about 12%. Really sucked when fuel was $5/gallon. Just think of the added operating cost if this was a 2007 or newer and needed the diesel exhaust fluid.
Being a 2004 Caterpillars attempt to control emissions was their ACERT technology. Basically injector delivery magic and variable intake valve lift to reduce the excess air. Also low compression. The high tech fuel injection also makes for some very expensive repairs when it fails. Caterpillar avoided egr and other stuff as long as they could. They completely left the on-road business after the 2009 model year.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Dave Mcneely
Sent: Friday, September 25, 2015 3:32 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Fryeday - Bio-Diesel Exhaust/Emissions
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
