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Date:         Fri, 8 Mar 1996 06:06:08 -0500
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         DHaynes57@aol.com
Subject:      EGR Purpose in Life

--PART.BOUNDARY.0.29559.mail06.mail.aol.com.826283167

========================================================================= Date: Sender: Vanagon Mailing List <vanagon@vanagon.com> From: Subject:

I write variuos articles for Gass and Limbo. The attached is a piece of Emissions Part two that will be published in upcoming issues. It is obvious from the postings on the list that very few people have any understanding of what this system does. I hope that this file helps to clear the "Air" so to speak. What is key here is that EGR system fills some of the cylinder space with an "INERT" gas. In other words, the spent exhaust does not burn,(fuel) or support combustion,(no oxygen). This lowers the "PEAK FLAME TEMPARATURE". This is critical in an air cooled engine running lean mixtures. Raising the peak flame temparature is what helps burn pistons and melt heads in late model air cooled VW's

Hope this helps. Dennis H.

PS. I did not post the complete article because I write these articles to attract VW fanatics to join these clubs. Thanks and Keep on Bussin'

--PART.BOUNDARY.0.29559.mail06.mail.aol.com.826283167

========================================================================= Date: Sender: Vanagon Mailing List <vanagon@vanagon.com> From: Subject:

Although the AIR system and the CAT did an outstanding job of reducing C= arbon Monoxide, the lean mixtures and higher operating temperatures brou= ght us another problem. Oxides of Nitrogen. These are formed when high = "peak flame" temperatures and excess oxygen cause oxygen and nitrogen to = combine. Nitrogen Oxide and Unburned Hydrocarbons are the primary source= of ground level Ozone and Smog. The primary methods used to reduce th= e Nitrogen Oxide was to lower the compression ratio, (reduces performance= , and efficiency), and to recirculate some of the exhaust gases back int= o the combustion process. This is done through the Exhaust Gas Recircula= tion system, (EGR). The EGR system fills some of the cylinder space with= a small amount of exhaust gas while the engine is operated at part throt= tle. As this "spent" gas is inert, it has the same effect as lowering t= he compression ratio, which reduces the "Peak Flame Temperature" of the c= ombustion process. This reduces the formation of Nitrogen Oxides. The a= dvantage of the EGR system over a reduced compression ratio is that it ca= n be set-up to be disabled at idle and full throttle to restore idle effi= ciency and full throttle performance. In the Air Cooled VW engine, the = EGR adds the additional benefit of letting the engine run cooler with the= leaner mixtures required in 70's and 80's cars. It is unfortunate that= most people have removed the EGR system thinking they have increased per= formance. Other cars benefit by the EGR system as it reduces an engines = desire to knock and ping. =

As we entered the 80's, the auto industry found another, more effective= way to handle the Nitrogen Oxide problem. This came in the form of the = Three Way Catalytic Converter. This Cat is of a Monolithic (one piece) d= esign that is very compact, lightweight, efficient, and it does not rest= rict exhaust flow. As long as the fuel mixture is perfect, (14 to 1 or "= Lambda"), this Cat can reduce unburned hydrocarbons, carbon monoxide, a= nd nitrogen oxides. To provide the precise mixture control needed for th= is system, an oxygen sensor was added to provide "Closed Loop" control o= r fine tuning of the fuel system. The heart of this system is the "Oxyge= n Sensor". Some late model cars use multiple sensors to provide even mor= e control. =0D

--PART.BOUNDARY.0.29559.mail06.mail.aol.com.826283167--


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