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CA SMOG, HIGH NOx

My fuel Rail has a vac regulator as well as two lines, towards the front of the Jeep.

I will pull a few plugs tonight and report back..

Pete

LOL, pull them all, else the one you don't pull will be the droid we were looking for!!!:D

I thinking just one cylinder might be running lean, and show the signs on the plug?
 
I disagree on two points (possibly typos?), one is the theoretical zero O2. I suspect it takes a good bit of excess O2 to reach the 14.7 stoich number, since that is not an excessively high rich burn number. I have also seen test data showing multiple percent excess O2, but that may have been tailpipe 6X dilution numbers on the O2, so the data is not always on equal footing. I could be wrong on that?

The other I think is a typo: " CO2 is going to be fairly low because it's almost naturally low enough to be considered a "trace gas".

The O2 is replaced by CO2, so if O2 goes from 21% to zero, the CO2 will go way up as the O2 is replaced by CO2. I have seen CO2 numbers average around 14% in many reports, which would suggest 6% remaining O2, but there is a huge increase in H20 gas that dilutes them all that is not measured or reported, and I have seen O2 numbers reported well below 1% on many reports (which is why the O2 numbers running from 6% to under 1% have always puzzled me so far. Only thing I can figure is the O2 reported is sometimes a diluted O2 due to tester differences, and the huge increase in CO2 and H20, from fuel combustion, dilutes the N2 and remaining O2....)

Hm.

As I understand it, "stoichiometric combustion" means there's enough oxygen to combust all fuel, there's enough fuel to consume all oxygen, and there's none of either left. Most of the "ash" from combustion of hydrocarbons is actually water vapour (there's far more hydrogen than carbon in a hydrocarbon chain - although it has been some time since I took O chem...) and measuring humidity of exhaust gas RT ambient air would be illustrative. Theoretically, you should have zero oxygen remaining in an unaltered hydrocarbon combustion system, running properly with an effective feedback loop in place.

And, that addresses both the O2 and CO2 (IIRC, seeing 12-18% CO2 is a marked increase over general atmospheric content - but it's still going to be relatively low, else we'd have asphyxiated ourselves years ago as a result of combustion of hydrocarbons in general.)

Looking at the composition of the atmosphere (Wiki chart - http://en.wikipedia.org/wiki/Atmospheric_chemistry) it can be noted that CO2 is indeed a trace constituent of the biosphere - Hell, there's more argon in the atmosphere than there is CO2 (and argon is and remains chemically inactive, being a noble gas.) (For those who don't want to read through the link, or lack intermediate chemistry to understand the numbers, here's a link directly to a graphic representation of the issue - http://upload.wikimedia.org/wikipedia/commons/1/14/Atmospheric_composition_Langley.svg. It also features a raw percentage breakdown - CO2 comprises not quite 0.04% of ambient air...)

So, reading CO2 of over ten percent in the exhaust stream very much is a marked increase in content, and makes sense.

However, if combustion in the engine is truly stoiciometric (~14.7:1AFR) and the feedback loop is effective, accurate, and the information followed, then it stands that remaining %m O2 should be zero, and %m HC should be likewise zero (stoichiometry simply refers to the combustion of hydrocarbons and the oxygen available in relation to that - CO is partial combustion, and therefore still "combustion" in se. Ergo, CO is not measured as a byproduct to indicate that stoichiometry is not followed, it is measured to ensure that combustion is total.)

The provision of excess O2 available to combustion means that combustion will not follow stoichiometry, by definition, that results in a "lean burn" condition (there's not enough fuel available to the quantity of oxygen provided,) and can result in elevated combustion temperatures. This relationship will continue until the LBL (Lean Burn Limit) is reached, and the chain reaction of combustion can no longer be supported (I don't recall the LBL for gasoline, but I think it's up around 20-22:1) Lean burning is typically characterised by an absence of HC and CO, the presence of exhaust gas O2, and an increase in NOx (due to elevated combustion temperatures)

Going the other way, we run into having excess fuel available, which is a "rich" burn condition. This has the effect of lowering combustion temperatures, and excessively rich combustion can cause "washdown" where the oil remaining after the oil control rings wipes the sides of the cylinder bore gets literally washed off of the metal. This accelerates ring wear (in addition to the increased HC and CO emissions.) This will continue until the RBL (Rich Burn Limit) is reached - again, I don't recall exactly, but I'm thinking it's about 7-8:1. Rich burn conditions are indicated by the absence of O2, increased HC and CO, and depressed NOx (excess heat is absorbed in finishing the job of vapouorising the fuel.)

It's interesting to note that, despite all of the fuss over reaching stoichiometric burning, it's actually not an "ideal state" for engine operation!

"Best cruise operation" is typically slightly lean, running at about 15.2:1.

"Best power operation" is typically slightly rich, usually about 12.8-13.0:1

Go figure.
 
LOL, as usual the EPA likes to redefine things, like stoich, LOL!!!

True chemist stoich is where all of A reacts with all of B to make nothing but compound AB. If the product is A-2B, then you need 1A + 2B => A-2B so the stoich ratio is 1:2

Everything I have read says 14.7:1 is a rich ratio which is the number EPA likes, so how can it be a true chemists stoich ratio if it is on the rich fuel side of a true stoich?

But there is more too it than that. In order to run the system rich, so that there is enough excess fuel to heat the Cat converter, the engine must be run rich (excess fuel), but in order to burn all the fuel, 100%, meaning all the H goes to H2O, and all the C goes to CO2, you need excess oxygen, and some of the oxygen turns into NOx, so you need even more excess O2.

Got a head ache on that one yet? :banghead:LOL

Frankly I have no idea why they use the term stoich except to define that it IS a fuel to O2 (or O2 to fuel?) ratio, even if it is not a true chemists stoich?

I Googled the hell out of it one week, and never found anything solid anywhere on the internet in writing that nailed down the BS of what the real numbers are and what they really mean!!!!

I did run across some info that said that the PD process control of the ECU and O2 sensor, where it rapidly oscillates from slightly rich to slightly lean, is designed to pulse feed excess fuel to the cat converter to keep it hot enough to work. so there is a pulse oscillation process going on there!!!!

IIRC the Cat converter is a surface adsorpion, conversion-reaction, desorption process that generates its own heat!!!! Add in the pulse wave of the O2 sensor PD control of the ECU swings, and the pulse waves of the engine valves opening and closing and it gets real interesting!!!!!! Long story short, even at cruise there is a wave cycle superimposed on a wave cycle going on the PD control and 2 step combustion (step one the engine, step two the Cat converter).

To a chemist, stoichimetric ratio is a fixed number, it does not change, from a rich stoich to a lean stoich ratio, it is what is, a fixed mol ratio for complete reaction of a A and B to make AB.
 
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LOL, as usual the EPA likes to redefine things, like stoich, LOL!!!

True chemist stoich is where all of A reacts with all of B to make nothing but compound AB. If the product is A-2B, then you need 1A + 2B => A-2B so the stoich ratio is 1:2

Everything I have read says 14.7:1 is a rich ratio which is the number EPA likes, so how can it be a true chemists stoich ratio if it is on the rich fuel side of a true stoich?

But there is more too it than that. In order to run the system rich, so that there is enough excess fuel to heat the Cat converter, the engine must be run rich (excess fuel), but in order to burn all the fuel, 100%, meaning all the H goes to H2O, and all the C goes to CO2, you need excess oxygen, and some of the oxygen turns into NOx, so you need even more excess O2.

Got a head ache on that one yet? :banghead:LOL

Frankly I have no idea why they use the term stoich except to define that it IS a fuel to O2 (or O2 to fuel?) ratio, even if it is not a true chemists stoich?

I Googled the hell out of it one week, and never found anything solid anywhere on the internet in writing that nailed down the BS of what the real numbers are and what they really mean!!!!

I did run across some info that said that the PD process control of the ECU and O2 sensor, where it rapidly oscillates from slightly rich to slightly lean, is designed to pulse feed excess fuel to the cat converter to keep it hot enough to work. so there is a pulse oscillation process going on there!!!!

IIRC the Cat converter is a surface adsorpion, conversion-reaction, desorption process that generates its own heat!!!! Add in the pulse wave of the O2 sensor PD control of the ECU swings, and the pulse waves of the engine valves opening and closing and it gets real interesting!!!!!! Long story short, even at cruise there is a wave cycle superimposed on a wave cycle going on the PD control and 2 step combustion (step one the engine, step two the Cat converter).

To a chemist, stoichimetric ratio is a fixed number, it does not change, from a rich stoich to a lean stoich ratio, it is what is, a fixed mol ratio for complete reaction of a A and B to make AB.

Correct as far as it goes.

However, stoich != AFR (or FAR,) and is is the AFR/FAR that varies, not stoich. The stoichiometric ratio of a fuel is immutable and unchanging - you can't alter it without either altering the oxygen content of the atmosphere (oxygen enrichment, another planet) or altering the fuel (at which point, you're not dealing with gasoline anymore, are you?)

It's still goofy because it's generally defined using octane (either n-octane or i-octane) and there ain't that much octane in gasoline, but it's workable. Besides, true stoich isn't even 14.7:1 - that's just a convenient number (I think it's about 14.68...:1)

And, the catalytic converter reaction heat is self-sustaining once it gets going, but the catalyst has to reach "light-off" temperature in order to kickstart the reaction. Once it's lit, it will stay "lit" as long as the engine is running (which has much to do with why startup AFR is closer to "best power" mix during open loop operation.)

As far as the EPA? We all know about them - what the EPA does bears little on actual reality, methinks. "Best Power" and "Best Cruise" were determined by experimentation - read Taylor and Ricardo for more information on that, as their works are definitive.

As far as oscillation of AFR, tht's more a product of the narrowband HEGO (NHEGO) sensors commonly used. The NHEGO has a very sharp response curve running from about 12.5:1 to about 16:1 - beyond that range, response is bloody flat (this applies to both titania and zirconia type NHEGO sensors.) I still don't understand why wideband HEGO sensors aren't in common use - they don't cost that much more than NHEGO units, give much finer response over a much wider range (it's predictable and responsive through the range between RBL and LBL,) and with a small alteration in programming, it can be used for much finer feedback control over fuel delivery and trim. I think they're finally coming into use on some higher-end vehicles, I'm informed that MBZ and BMW are starting to have OEM six-wire HEGO sensors, but I only believe those are WHEGO units (it's a bit odd, because I believe the typical WHEGO sensor is a four-wire unit. I'm not sure why offhand, I haven't checked. Probably to get the finer signal, a self-grounding sensor isn't useful anymore?)

Frankly, I don't think the EPA gets even close to using "stoichiometric" to define anything - as you've noted, any time they used it would be likely to be incorrect anyhow. And, how much of EPA regs really have any useful basis in actual science - apart from known toxic effects of a substance, or something similar? Very few EPA (or CalEPA) regs I've seen are based on practicality or science, and their use of language bears as much on "common English" as "mess hall food" bears in "fine dining." (I've had mess hall food, I've had fine dining. Not even close...)

But you are entirely correct in your basic presumption - however, combustion is rarely stoichiometric, for a number of reasons.
 
5-90, if you ever find a citation that confirms what the units are for this mythical 14.68:1 ratio, I would like to see it.

I searched for a week, and never found any one that confirms the units, like lbs:lbs, gallons:cu. ft, or mols:mol......

If it once was Mols:Mols, 10% ethanol tossed that ratio out the window, as the C and H mol count is no where close to the C and H count in octane, LOL!
 
5-90, if you ever find a citation that confirms what the units are for this mythical 14.68:1 ratio, I would like to see it.

I searched for a week, and never found any one that confirms the units, like lbs:lbs, gallons:cu. ft, or mols:mol......

If it once was Mols:Mols, 10% ethanol tossed that ratio out the window, as the C and H mol count is no where close to the C and H count in octane, LOL!

Correct - I'm quite sure that the actual stoichiometric ratio has changed - and probably continues to change, due to the uses of ethers and alcohols in fuels (the EPA keeps screwing things up for no very good reason. We were better off when it was "motor spirit" and still a mix of straight hydrocarbons...)

However, turn your research toward The Internal Combustion Engine in Theory and Practice (two volumes, Charles Fayette Taylor) and The High-Speed Internal Combustion Engine (Sir Harry Ricardo.) The detailed information is a bit dated - Taylor was written in the 1960's, and Ricardo even earlier. However, the principles have not changed.) More detailed information can probably be found in The Bosch Automotive Handbook - which is at least on its 6th edition, since that's what I have on the shelf (Bosch 6th is copyrighted 2004.)

Various texts on fuels should be available at your local library, and you can do more detailed research at any university that has a School of Engineering or an Organic Chemistry programme. (It may be covered under inorganic chemistry, but I'm sure it will be under O chem.) I would suggest the use of a textbook that deals with alternative fuels as a start, as it would have to cover more recent blends of gasoline as basic material.

However, Bosch 6th gives a theoretical air mass requirement of 14.7-14.8kg per kg of fuel (so my head was a bit off. Bosch, 6th Ed. p. 324.)

Taylor is available from MIT Press.
Ricardo takes some looking.
Bosch is available from Bentley Press.
 
5-90,

"However, Bosch 6th gives a theoretical air mass requirement of 14.7-14.8kg per kg of fuel (so my head was a bit off. Bosch, 6th Ed. p. 324.)"

Thanks, I always suspected it was a mass based number, which is not something Chemists would normally do, LOL. (Did you forget I am a bio-chemical engineer?) While I don't work in combustion engineering, I work in other areas like toxic industrial waste water treatment, and air emissions, industrial....and lab work...permitting, etc. So I work on the fringes of it.

I think the real key is ECU process control, the feed back control loop, and measured rate of oxygen depletion as the control. I wonder if an aftermarket header has any issues with O2 sensor locations? He might need to tweak his MAP sensor, or other sensors to force it a little richer to compensate if the aftermarket header O2 sensor and combustion scrubbing changes are causing his higher NOx? If the aftermarket header is the problem, I also wonder if boosting the oxygenated fuel concentration, or using a colder plug for the inspection would help? Or a colder T-stat for the inspection?


I wonder if our OP has pulled the spark plugs yet? Photos????
 
5-90,

"However, Bosch 6th gives a theoretical air mass requirement of 14.7-14.8kg per kg of fuel (so my head was a bit off. Bosch, 6th Ed. p. 324.)"

Thanks, I always suspected it was a mass based number, which is not something Chemists would normally do, LOL. (Did you forget I am a bio-chemical engineer?) While I don't work in combustion engineering, I work in other areas like toxic industrial waste water treatment, and air emissions, industrial....and lab work...permitting, etc. So I work on the fringes of it.

I think the real key is ECU process control, the feed back control loop, and measured rate of oxygen depletion as the control. I wonder if an aftermarket header has any issues with O2 sensor locations? He might need to tweak his MAP sensor, or other sensors to force it a little richer to compensate if the aftermarket header O2 sensor and combustion scrubbing changes are causing his higher NOx? If the aftermarket header is the problem, I also wonder if boosting the oxygenated fuel concentration, or using a colder plug for the inspection would help? Or a colder T-stat for the inspection?


I wonder if our OP has pulled the spark plugs yet? Photos????

I'd thought you were some variety of chemist.

Yah, chemists typically work in moles rather than straight mass - but with the variable composition of atmospheric air and the varying content of hydrocarbons, ethers, and alcohols in gasoline, it probably makes more sense to work in mass. And it's been a mass ratio for as long as I care to remember - using the mass of ambient air with typical partial pressures of component gasses vice an absolute ratio of fuel:eek:xygen (although that's what it eventually comes out to be.)

So, have we derailed the original intent of the thread enough yet? :doh::wow::lecture:
 
Well if the "CA SMOG, HIGH NOx" was not making it fuzzy enough to derail things, by lowering the OP's visibility, no doubt we have done so by now, LOL!!!!

How about it, where is our OP and his problem now???
 
Its cool, you guys were having interesting chemistry talk while i was gathering data :) The tech in me doesn't mind at all !! :laugh2:

I was able to measure the Manifold Air Temp Sensor and Coolant Temp sensor at cold/warm condition and the value's checks out on the Resistance Table.

Spark Plug #2:

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Spark Plug #4:

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What do you folks think, next thing to do or check ?

Pete
 
Do all 6 plugs look the same?

How many miles on those?

If they have many miles on them they look way too clean for normal operation.

What is the fully warmed up operating coolant temp? Still might try a 180 F t-stat fot for the E-tests?

I wonder if a dirty air filter might help, LOL!!!

I am still thinking the aftermarket header might be part of the problem. If so, running more oxygenated fuel additives (like acetone or methanol added to the tank for the inspection), or switching to premium for the E tests, might be enough to get you under the NOx numbers.

Some how you need to get it to run cooler and or richer in the combustion chamber.

Can you run an analog volt meter (high impedance meter) test on the O2 sensor (back probe) while running the engine hot?
 
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It was pretty cold last night, but i will try to pull a few more plugs to take a look if they are all the same. They were replaced ~6months ago during my last tune up, so i would expect them to look pretty decent, no clue on the number of miles on them though..

Under normal operation as mentioned, the jeep operates dead smack in the middle as far as temp, if i am at a stop light on a hot summer day or climbing a hill it goes over but the efan brings it back down.

Some food for though that just hit me, not sure if it has bearing on these numbers, but after my last smog check which i passed, i had the jeep re geared to 4.56 with the same tires (32" BFG AT's) ? ?

I will also try to get a hold of a analog multimeter and get those O2 numbers as well.

Pete
 
If you have a good 5000 miles on those plugs they should have a tint of a tan color on them by now. Bright white I think is a too lean sign, I think, but I am not the expert on plug color here.

Sorry but, "jeep operates dead smack in the middle as far as temp" is not a temperature, LOL!!!! Give us some numbers in degree F please!!!

I have read smog post from the Denver (MidWest chapter? guys, IIRC) where they had to swap the tires to small tires to pass smog tests!!!! Something about gearing and tire diameter and the PCM/ECUs not being able to compensate on the smog engine RPM & vehicle speeds required during the tests???

So you may be onto something there for sure!!! IIRC the Chapter president was a good source about it.
 
High NOX is caused by high combustion temps as others have stated. One way to lower combustion temps is to use a colder spark plug. You can determine a spark plugs heat range by how much the porcelain and electrode is sticking past the threaded part of the plug. That plug you pulled out is an extremely hot plug. I tried to find the ones I pulled out last time but I bet they weren't as hot as those. I would get a plug one heat range colder and I bet it would pass. It is quite hard to find a parts person at any chain parts store who can figure out how to look up colder then recomended plugs (most can't find you anything if the computer doesn't find it for them) so you might want to go to the manufactures website and find the part number yourself.
 
I was wondering about that, those are a lot longer porcelain tips than mine are. I used the Autolite single platinum tip plugs and the porcelain is very short and stubby compared to those. 5-90 already suggested colder plugs, and now I agree, it is worth a look see!!! And cheap part to try!!!
 
Actually, the "heat range" of a plug is the distance from the tip of the porcelain insulator to where it makes contact with the plug shell - which happens somewhere inside the shell proper, and is generally not visible. If you want to figure out where this point is, a fine solid wire can get you close (a little trig will get you the exact point.)

The visible porcelain past the end of the shell is the "reach" of the plug, and has nothing to do with heat range (two plugs may have identical reach, but widely differ in heat range.)

General Characteristics of Spark Plugs (from The Bosch Automotive Handbook, 6th Ed.):

Per the Bosch numbering system, these are the basic variables of spark plugs as used in gasoline-fuelled, spark-ignition engines. We will use Bosch P/N WR7DTCX for our example breakdown (since that's what at the top of the chart. The application is not listed...)

W - Indicates M14-1.5 thread, washer seat, with 21m/m wrenching hex
R - Has suppression resistor (to reduce RFI/EMI in other vehicle electronics)
7 - Heat Range of the plug (as discussed above.) In the Bosch numbering system, this may be one or two digits, but the chart in Bosch doesn't say which direction is hotter or colder. Bosch's spark plug catalogue should explain this, but I don't have it to hand.
D - Indicates length of thread and spark gap position. The washer seat has a 19m/m length of thread for the washer seat. Also, the spark gap is 3m/m from the end of the threaded shell (if this were a taper seat plug, the thread would be 17.5m/m long, but the spark gap would be in the same place.)
T - Electrode version. No character here would indicate a standard single ground - this part number has three ground electrodes, arranged equally about the shell. Bosch plugs will have one (standard,) two (180* apart,) three (120* apart) or four (90* apart) ground electrodes.
C - Electrode material, the "C" indicates copper. May also be platinum ("P",) Silver ("S",) or a nickel-yttrium compound (yttrium is a rare earth metal, it gets stiffened up with nickel for durability. This is indicated by an "E")
X - Version type. There are several of these, the "X" indicates that the spark gap is nominally 1.1m/m

Bosch has probably the highest resolution in their numbering system - Autolite uses three or four numerical digits, followed with a "P" for a platinum centre post, or a "PP" for a platinum centre post and platinum pad on the ground "finger." Most characteristics are covered under the application (the first two or three numerical digits,) and the heat range is the last numerical digit. Champion uses a combination of letters and (usually) one number - the number is indicative of heat range. Some manufacturers have plugs get hotter as the heat range digit increases, some have them get colder.

As far as "nominal gap" - always check! Plugs may get gapped at the factory, but they get knackered about in shipping, and even with the little cardboard or plastic sleeves on the end, the gap can get closed up in transit. Always check.

And thus closes this lesson on intermediate spark plug tech (Gawd, I spent far too much time behind a parts counter...)

Another oddity would be aircraft-style spark plugs - the shell is turned inward at the sparking end to form an annular ground electrode, and gapping is literally not necessary (it can't close up, unless the plug gets contaminated.) This also heavily delays the effects of HV gap erosion, since the spark will jump the shortest gap possible once variations start to take place. These plugs were developed for Rotax and Lycoming engines, and got adapted for use in automotive engines (starting with Mazda's Wankel rotary - using four ground electrodes.)
 
I have been looking for the last couple hours for a colder plug for the 4.0 but haven't had much luck. I did see a thread on Jeepforum where people were saying the V8 grand cherokee plugs were a step colder direct bolt in..Autolite 3923.. but I'm not too sure about trying that. I am an NGK guy anyway and from what I can tell they don't make a colder plug. I believe I need fr6-1 but I don't think they make one. But if you get bored 5-90 I wouldn't mind if you checked for me.

If someone does find a colder plug please post parts numbers. I am going to smog on saturday and last time It passed NOX by a hair so I am a bit worried.
 
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