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Author Topic: Should limits on vehicle pollutants be averaged thru driving cycle, not max PPM?  (Read 20135 times)

SteveFish

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Clifford:

I am not responsible for my response to you because, apparently, my head was out to lunch yesterday and I don't have any idea what it was doing. I am concerned about any credit card bills that might unexpectedly show up.

Steve
 

Offline CliffordK

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As far as Pre-CAT engine performance.

Here is an interesting article about retrofitting a Catalytic Converter into an older car that wasn't ever designed for it.

https://webshop.fiat500126.com/index.php/sites/view/57-1-exklusiv_g-kat.html

Quote
As this regulating process is so important, uncontrolled catalytic converters can only clean about 45% of the exhaust fumes, whereas computer controlled catalytic converter systems can clean 90-95%.

Anyway, so one can't just slap a Cat onto an older engine without more work.  And, the engine tuning (and a dynamic oxygen/fuel mix) are vital.

My first car with a Catalytic Converter, an '84 Renault Encore, was probably running a little rich near the end of its days.  I failed a smog test..  yanked the Catalytic Converter...  There was absolutely nothing inside...  Just a bare pipe.  & no, it wasn't reamed.  Either it was a faulty component from manufacture (unlikely).  My interpretation is that I was burning oil or something... and it caused the CAT to run very very hot...  which caused it to destroy itself.
 

Offline Bored chemist

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Odd!
The catalyst is supported on a substrate that is basically a rock. It would cheerfully sit there glowing red hot.
 

Offline Geezer

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Maybe it had a cataclysmic episode?

Or maybe somebody requisitioned it
http://www.edmunds.com/auto-insurance/in-under-two-minutes-catalytic-converter-theft.html?articleid=132109&
although I have to admit it was pretty clever of them to substitute a dummy so you wouldn't notice, so that seems a bit unlikely.

Are you sure it even had a cat? The thing you were looking at might have been some sort of fiendish French pre-muffler tuning thingy to smooth the gas flow after the manifold.

EDIT: It looks like an 84 Encore should have a cat, so it is strange. Perhaps the ceramic substrate shattered (I think they are fairly fragile) and the pieces ended up in the muffler.
« Last Edit: 11/12/2010 07:35:50 by Geezer »
 

Offline CliffordK

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As far as the Renault...
That was a few years ago.

It was an 1984.
Should have had a CAT.  They would have been required from about 1976 or shortly thereafter.

My parents bought the car new.
I got it with a bit over 100K miles.

I did the first SMOG test ever after moving to Portland around 1998, with close to 200K miles.  The old CAT may still be sitting in Scrap metal somewhere...  if so, I'll try to get some photos, but there was nothing inside (not even a hole blown through).

In the first 200K miles, it blew the original muffler, and had 3 replacements.  2 done by a "shop", and one by myself.  Neither myself or my father would have intentionally had the CAT disabled. 

The theory of "cat guts" in the muffler might explain the burnt mufflers.

I haven't seen any other worn out CATS, so I don't know what I should have expected.

The actual repair, in the late 90's was a pain to do, but less than $100 for the replacement CAT.  With the replacement CAT, it barely passed SMOG testing, but that was all I needed.
 

Offline CliffordK

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Nitrogen and NOx.

I left it out of the earlier equations (Page 2) because it is not really from fuel.

Air is about:
78% Nitrogen (N2)
21% Oxygen (O2)
0.93% Argon (Ar)
0.04% Carbon Dioxide (CO2)

So, in the engine, you have a mix of Gasoline or Diesel (hydrocarbons), Nitrogen, and Oxygen.

Your Gasoline does not contain significant amounts of Nitrogen, that comes from the air.

The reason it is called NOx is that it is a mixture of various Nitrogen Oxides (NO, N2O, NO2, N2O3, N2O4, N2O5, (HNO3 & NO3-)).

So...

N2 + O2 --> NOx  (unbalanced)

It is supposed to be a slightly endothermic reaction (requiring energy), which is why there are only small amounts of it in the atmosphere.  And it will break down to N2 & O2.

I believe that it is related to high combustion temperatures, advanced timing, and excess Oxygen.

There are notes that N2O will catalyze the formation of Ozone in the stratosphere.  And, unlike low level O3 that apparently does not get up to the stratosphere, low level N2O may actually get up to the stratosphere to produce more Ozone.

Unfortunately, while NOx may be a benefit in the Stratosphere, it does cause respiratory problems down here on earth.

Notes also indicate that it may be related to the formation of the NO3- radical and HNO3 Nitric Acid.  And thus Acid Rain.  Actually, I see notes that Aqueous Nitric Acid (HNO3) will decompose into Nitrogen Dioxide (NO2) and Oxygen (O2). 

Anyway, it might not be bad to minimize the environment that makes the Nitrogen Oxides.

Note, you have a fine balance on tuning, especially with the NOx.

Hotter Temps, More Oxygen, Advanced Timing --> better combustion, less hydrocarbons, less Carbon Monoxide.
Hotter Temps, More Oxygen, Advanced Timing --> Increased NOx.

So, what gives a "clean running car" for other pollutants, can be problematic with NOx, and visa-versa.

-------------

Diesel vs Gasoline.

Diesel engines are the primary producers of Particulate Matter (PM).  Black smoke from a gasoline engine indicates problems.
Diesel engines also produce higher NOx because of increased cylinder pressures, and leaner fuel/air mixtures. 
Diesel engines consume less fuel, even when taking into account energy density, and thus also produce less CO2.

 

Offline peppercorn

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Note, you have a fine balance on tuning, especially with the NOx.

Hotter Temps, More Oxygen, Advanced Timing --> better combustion, less hydrocarbons, less Carbon Monoxide.
Hotter Temps, More Oxygen, Advanced Timing --> Increased NOx.

So, what gives a "clean running car" for other pollutants, can be problematic with NOx, and visa-versa.

So, is more mechanical work made available from N2's reacting with O2's (absorbing some of the heat - endothermic) to make NOx's ?  Through the resultant Oxides of Nitrogen taking up more room than in elemental form.

Hence:
I mean if we ignore NOx as a pollutant, doesn't it in some instances actually represent an increase in mechanical efficiency when it reacts with air (at post 1200degC I believe) - ie. more expansion via a endothermic reaction.

Also I was under the impression that having ignition timing set too advanced would be fighting the engines momentum, so to state this is more efficient is ambiguous.

As a counter-example:
An ideally set up genset engine (One with a very flat low torque curve - ie. All HP) would have an ignition leading to just the start of positive cylinder pressure at TDC.  That is, as much of the expansion work is available to push the piston down.  Of course, a compromise is made so that ideally all the expansion has occurred by the time the piston reaches the bottom of the stroke (this is where a true Atkinson cycle has an advantage).

Lean-burn is the situation where most concern has been focused about NOx formation - Here NOx is mainly brought about by the greatly reduced effect of charge cooling from fuel evaporation (less fuel to air mass).  The slower flame speed in lean-burn mode can also cause burnt valves and valve-seats and this also feeds-back to create a peak temperature region in the cylinder head near the valve, which can cause additional NOx formation.


I have rambled a bit, but what I really want answered (slightly off-topic though it is, Tut-tut!):  I still don't know for sure whether an engine producing high NOx counts has a better mechanical efficiency than one with next to none - ?
 

Offline Geezer

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I still don't know for sure whether an engine producing high NOx counts has a better mechanical efficiency than one with next to none - ?

As an Anecdotal Physicist, I would have to say yes on the grounds that cats were pushed heavily by California to reduce smog. As soon as they were introduced, everbody started complaining that their cars had no guts at all.

Further anecdotal evidence: The 1.6L Fiat 126 I had in the UK in 1982 would blow the doors off just about any smog equipped vehicle of similar vintage I ever drove in the US, some of which had far larger engines.
« Last Edit: 11/12/2010 20:54:41 by Geezer »
 

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Offline Geezer

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Clifford,

I bet your Encore was a real "babe magnet"  :D

A friend of mine bought a Chevrolet Chevette when he came to the US. The guys at work used to harass him with comments like -

"Oooo please Alistair. Can we go to lunch in your 'vette?"


(In case anyone doesn't know, in the US, 'vette is a common abbreviation for a Corvette, which has slightly better performance than a Chevette.)
 

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Offline CliffordK

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Clifford,

I bet your Encore was a real "babe magnet"  :D
It was better than the "Pumpkinmobile" which it replaced...  otherwise known as a 76 AMC Hornet "Sportabout"...  nothing sporty about it though!!!  Oxidized Pumpkin Orange!!!  Why a stationwagon was called a "Sportabout" is beyond me.

As a real "rebel"...  I tried the pedal to the medal on the Utah freeway with the AMC...  I think I got up to about 75 MPH after a few minutes.

I believe the 76 AMC was the last non-catalytic model.  It was supposed to take unleaded gasoline, but no CAT.  The dealer told Dad how to cut out the little ring in the filler spout to allow any fuel nozzle (during a time before all stations carried Unleaded, and there was a significant price differential).  It had other things like the air pump in the exhaust manifold...  that either oxidized some Carbon Monoxide, or diluted it, nobody was quite sure.

Which is a good point with the "PPM" measurement.....  how does the early air pump affect it?
 

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Offline peppercorn

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A friend of mine bought a Chevrolet Chevette when he came to the US.

D'ya mind! I learnt to drive in a 'vette! To be fair this was a Vauxhall Chevette and I was 16, so not that official!
On the other hand my brother was 13 and had to sit on an old chair cushion to see over the steering wheel :D

Luckily there was a handy bit of waste ground the other side of the railway where we lived to, erm, practice on :P

'Toto, I've a feeling we're not in Kansas any more' - That's how off topic it's becoming :D
 

Offline CliffordK

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Note, you have a fine balance on tuning, especially with the NOx. ...

So, is more mechanical work made available from N2's reacting with O2's to make NOx's ? .... blah blah blah
I don't think making the NOx actually improves the performance. 

For Nitric oxide (NO), you start with dimers and end with a dimer, so you end up with no net change in moles.

N2 + O2 --> 2NO

But, if instead you are making Nitrogen Dioxide (NO2), then you end up with fewer moles.

N2 + 2O2 --> 2NO2         (3 moles --> 2 moles).

And, thus the formation of NOx would actually reduce the energy.

Assuming it is mildly endothermic, that means lower temperatures, and less energy too.

Breaking down the NOx, would produce more moles of product, and more kinetic energy.
 

Offline peppercorn

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For Nitric oxide (NO), you start with dimers and end with a dimer, so you end up with no net change in moles.
N2 + O2 --> 2NO
But, if instead you are making Nitrogen Dioxide (NO2), then you end up with fewer moles.
N2 + 2O2 --> 2NO2         (3 moles --> 2 moles).
And, thus the formation of NOx would actually reduce the energy.
Assuming it is mildly endothermic, that means lower temperatures, and less energy too.
Breaking down the NOx, would produce more moles of product, and more kinetic energy.
I'm sure your analysis is correct but is it purely a matter of counting moles for working out if there is an increase in volume? (I mean for a steady temperature that this is almost certainly not).

Can you also explain why, as mentioned earlier, advanced timing (in relation to a 'traditional' advance) will give a better, more complete burn?
 

Offline CliffordK

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Uhhh....
It has been too many years since I've studied "Science"   [xx(]

But, from the Ideal Gas Law:

pV = nRT

pressure * volume = moles * Constant * Temperature

R = 8.314472 J/Kˇmol

So...
I think the pressure is independent of WHAT it is, but only dependent on how much you have (in moles) and what the temperature is.

So, anything that would reduce the temperature (endothermic reaction) or would reduce the moles, would also reduce the pressure.

----------

I'm not an expert on things like Engine Timing.
I need to get one of those exhaust gas gizmos for playing with  ;)

I think advancing the timing increases the time for combustion...  and thus I would expect a more complete burn.
But, perhaps there are other influences.

I'm sure there is more technical info on the web somewhere.

 

Offline Geezer

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I think advancing the timing increases the time for combustion...  and thus I would expect a more complete burn.

I believe that's it. The ignition timing is not fixed for that reason. It varies with engine speed. In ye olden days we had mechanical distributors that had a centripetal advance mechanism. Presumably these have been superceded by fiendishly complicated electronics (and firmware even!) to discourage people like me from doing my own repairs.

I changed the spark plugs on my car recently, and I was slightly surprised to discover that the entire operation took well over two hours! The actual removal and replacement of the plugs only took about fifteen minutes. The rest of the time was spent disassembling and reassembling a load of kit that looked like it belonged more properly in a CRT type TV set  :D
 

Offline peppercorn

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I think advancing the timing increases the time for combustion...  and thus I would expect a more complete burn.
Maybe I was unclear in my inquiry. Perhaps if I were to ask why you think that, in traditionally set-up engine, having the timing set for a burn that ends later than the ideal - will reduce NOx formation.
Or is it more to do with purposely leaving some CO/HC to oxidize at the Cat and drive the thermal dissociation of NOx's?

In ye olden days we had mechanical distributors that had a centripetal advance mechanism. Presumably these have been superceded by fiendishly complicated electronics
Those old points systems do wonder pretty horribly around the timing though. Anyone who's ever used a timing-light on an old car, esp. with a few decades ware in the dissy will have seen this.  As I'm sure you know really, electronic ignition has much to be said for it.

The rest of the time was spent disassembling and reassembling a load of kit that looked like it belonged more properly in a CRT type TV set
I'm sure there is an element of keeping the buyer from fixing their motor too easily (or at all!), but having coil-packs, etc is a really neat advance in autos IMO.
 

Offline CliffordK

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Remember that NOx is a combustion byproduct that is essentially opposite from Carbon Monoxide (CO), Hydrocarbons (HC), and Particulate Matter (PM).

Think of NOx as too much oxygen, and too much combustion.
CO, HC, PM, are essentially too little Oxygen, and too little combustion.

Thus graphs of NOx often go opposite the others.

A quick web search indicates suggestions of advanced timing increases NOx, and retarded timing decreases it.

--------------------------------

A little aside,
NOx can also be used as an oxidizer.

So, if you took: Dinitrogen tetroxide, (N2O4)

N2O4 --> N2 + 2O2 (1 mole --> 3 moles).  Also, one gets a higher oxygen/nitrogen mix than one would normally have in air.  Being Exothermic, it would also increase the combustion temperatures (and also increase cylinder pressures).

So, while producing NOx in the engine and releasing it into the exhaust takes away power.  Adding excess NOx to the intake increases power (and likely also causes a significant amount to be released in the exhaust).  But, if your goal is maximum acceleration, adding some NOx into your intake might just give you the edge you need.

(all based on the Ideal Gas Law which should more or less apply).
pV = nRT

(Note for the "topic police".  Sorry if we are rambling a bit.  But a rough understanding of emissions is critical to any discussion of decreasing them, or otherwise managing the emissions.)
 

Offline peppercorn

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Remember that NOx is a combustion byproduct that is essentially opposite from Carbon Monoxide (CO), Hydrocarbons (HC), and Particulate Matter (PM).

Think of NOx as too much oxygen, and too much combustion.
CO, HC, PM, are essentially too little Oxygen, and too little combustion.

Thus graphs of NOx often go opposite the others.

But too much oxygen is also a prerequisite of 'lean-burn'. Unfortunately localised high temperatures can be difficult to avoid with lower fuel vaporisation cooling of lean-burn and may lead to NOx formation.


A quick web search indicates suggestions of advanced timing increases NOx, and retarded timing decreases it.

I suggested the reason for this: 'Is it more to do with purposely leaving some CO/HC to oxidise at the Cat and drive the thermal dissociation of NOx's?'
So it is an indirect effect....
 

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