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TDI (Diesel) Emissions This is a discussion about emissions from TDI's. Pro's cons of Diesels (including biodiesel) effects on the environment and how they compare to Gasoline and other fuel sources for Internal combustion engines.

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Old November 21st, 2013, 08:17   #1
TDIMeister
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Default Chemical Reaction Kinetics of EGR in an Internal Combustion Engine-A Layman's Analogy

Consider the combustion in the cylinders of an engine as a dance in a big hall. The oxygen (O2) molecule is a girl. I'll consider myself a fuel molecule and another group of guys as nitrogen (N2) molecules. In a room of, say, about 21% girls, 78% nitrogen and 1% fuel -- which reminds me of my University days, but we didn't even have it this good with 21% girls -- the nitrogen and the fuel are all in competition to pair up with the girls, but each at different rates of success: oxygen and nitrogen don't find each to be other attractive mates at all -- kinda like dating a sibling -- and have rather slow chemical reaction kinetics -- unless it gets REALLY HOT in places, like over 2000C -- so they pair much less easily and frequently than fuel, where there's definitely lots of chemistry . Also, the incestuous offspring of nitrogen and oxygen are quite nasty, called NOx. If you pack the dance hall with more or fewer number of people (increase/decrease the pressure) but keep the percentages of the girls, nitrogen and fuel the same, your chances as a fuel molecule pairing with a girl remains about the same.

On the other hand, suppose now a whole bunch of other people come to the dance - goths, stoners, LGBT, eunuchs, etc., but also a bunch more nitrogen joining them. They have no interest or ability to pair with the girls; we'll call this group of people EGR or "inert species." Nevertheless, they pack the room and now the mix of people is about 10.5% girls, 39% nitrogen and 0.5% fuel from the original group and the rest (50%) are EGR. The party atmosphere in the dance hall has taken a decided turn for the worse with the presence of EGR; the reaction kinetics of the whole dance has been disturbed. Now girls almost don't pair at all with nitrogen, and even I am finding it more difficult to find a girl on the dance floor and when I do, it takes a lot more time and effort to pair with a girl successfully and the result is rather less passionate.

The important part is, the pairing of nitrogen and oxygen are greatly reduced or almost eliminated, so that we get a lot less of their nasty offspring NOx.

This is how EGR works in a dance hall - I mean, internal combustion engine.
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Old November 21st, 2013, 08:34   #2
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LOL. I love this explanation Dave. Now, can you explain how EGR is NOT a big, bad, boogie man to your engine, in layman's terms?
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Old November 21st, 2013, 09:00   #3
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Pretty sure I used the exact same analogy almost 5 years ago somewhere. I need to find that post.
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Old November 21st, 2013, 09:16   #4
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Too bad all those stoners just walked through mud to get to the dance hall and leave a trail of filth wherever they go.

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Old November 21st, 2013, 12:19   #5
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Sad news is, some of the offspring of the complete and successful consummation of fuel and oxygen (CO2 and H2O) become EGR... Soot are fuel/oxygen's quick lustful romps in a dance hall with far too much- or poorly distributed fuel for the available girls. When soot come back as EGR, like the dirty way in which they were created, they don't bother to clean themselves in the corridor to the dance hall and they cake up everything in their path.

Now, if the bouncer outside (EGR valve) locks the door shut to the EGR entry line, none can enter into the dance hall, but a lot more NOx leaves at the end of the night. Newer dance halls have a screening room on the way out where the soot are imprisoned and burned in eternal damnation (coming out as reformed normal offspring of fuel and oxygen (CO2 and H2O), the rest as garbage ash that must be purged from time-to-time lest they fill-up and clog the screening room). When they come back in to the dance floor in the future, the hallways are a lot cleaner since there's a lot less soot in the first place.

Some dance halls also have a type of additional room in the exit where NOx, the incestuous offspring of nitrogen and oxygen, get born again by a baptism of reductant (urea or HC), heat and a special bed of Zeolite or rare-earths - depending on reactant - to yield nitrogen and less-noxious species before going back out to the world.

You don't want to know what are HC and CO in this analogy... .

Anyone want to tackle explaining HCCI in similar terms?
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Old November 22nd, 2013, 21:33   #6
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This is awesome.
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Old November 23rd, 2013, 08:10   #7
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So, I suppose defeating an EGR is the equivalent of raw dogging any girl you can get your hands on, damn the consequences.
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Old November 23rd, 2013, 08:16   #8
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Quote:
Originally Posted by RabbitGTI View Post
So, I suppose defeating an EGR is the equivalent of raw dogging any girl you can get your hands on, damn the consequences.
Damn the torpedoes, full speed ahead!

I'm OK with my engine not eating its own feces in an attempt to recycle it, like some dogs do.
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Old November 23rd, 2013, 08:18   #9
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Quote:
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Damn the torpedoes, full speed ahead!

I'm OK with my engine not eating its own feces in an attempt to recycle it, like some dogs do.
Dogs detect undigested protein and don't want to waste it. They are much like Prius drivers who hypermile.
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Old November 24th, 2013, 04:49   #10
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Default egr

hi can any tell me if a small vacum leak from the brake servo can cause the egr valve not to work properley,the problem im having is lack of power 3rd and 4th auto gear box thanks pete
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Old November 25th, 2013, 05:05   #11
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EGR also allows you to have higher dynamic compression with less parasitic loss.
Example:
You run 1.3 bar absolute boost for IQ of 20 (around what stock does).
Without EGR to get that intake boost of 0.3 bar the turbo needs to do X work to do Y flow at 1.3 PR. Power is work times time. In a turbo, that is basically pressure ratio * flow.


With egr on, stock EGR map says 560 mg/s so it will reduce the flow Y-some value (based on temperature etc). Boost is still 0.3 bar at the intake, but the flow is less... so less work done by the turbo, less loss of energy for the same dynamic compression.

Not sure whether EGR on or off in that condition makes more EMP or not, but that would also increase dynamic compression.
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Old November 25th, 2013, 07:01   #12
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Great explanations. Dances were much less complicated when I went to school.
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Old November 25th, 2013, 07:28   #13
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Nice :thumbup:

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Old November 25th, 2013, 15:18   #14
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I almost snorted coffee all over my keyboard when I read that....



Quote:
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Dogs detect undigested protein and don't want to waste it. They are much like Prius drivers who hypermile.

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Old November 26th, 2013, 08:28   #15
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Quote:
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Dogs detect undigested protein and don't want to waste it. They are much like Prius drivers who hypermile.
Or TDI drivers who try to "hyperrange" on a tank of fuel!
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