178 replies to this topic

[McGuire]

Quote

Originally posted by gruntguru
That might have been the question at one stage and quite easy to answer.

We now have a new question. Does a lambda sensor track closer to oxygen concentration or AFR? So I am trying to devise a test to help find out what the sensor does when presented with two exhaust streams having the same AFR yet different oxygen concentrations.

The background for my assertion that a lambda sensor responds primarily to AFR is this -

Logic suggests that combustibles (HC and CO) remaining in the exhaust will tend to react with free oxygen on the hot platinum electrode so after all possible reactions occur only one of the two types (combustibles or oxidants) will remain and the oxygen concentration will be generally dependent on AFR alone and not on combustion efficiency alone (except for gross combustion inefficiencies eg misfire).

There are any number of conditions in which the O2S signal value and the AFR diverge and head off in opposite directions, but if the O2S value and O2 content diverge there is a problem.

The O2 sensor has no significant gas-catalyzing function.

[gruntguru]

Quote

Originally posted by McGuire
The O2 sensor has no significant gas-catalyzing function.

What would you define as "significant"?
eg.
If 80% of possible catalytic reactions on the surface of the anode were to occur it would be an insignificant proportion of the total exhaust stream, yet this would have a very significant effect on the oxygen partial pressure at the anode and therefore on the sensor output voltage.

[gruntguru]

Quote

Originally posted by McGuire
There are any number of conditions in which the O2S signal value and the AFR diverge and head off in opposite directions

Apart from cold sensor (sensor inoperative) and grossly incomplete combustion (eg misfire) I can't think of any. Are there any that occur with the sensor operating normally?

[McGuire]

Quote

Originally posted by gruntguru
What would you define as "significant"?
eg.
If 80% of possible catalytic reactions on the surface of the anode were to occur it would be an insignificant proportion of the total exhaust stream, yet this would have a very significant effect on the oxygen partial pressure at the anode and therefore on the sensor output voltage.

The sensing (exhaust) side has a Spinell coating over the platinum electrode. (A sort of glass.) It's porous, just like the platinum, so the zirconia will be exposed to exhaust gas. The coating is there to protect the sensor from erosion, mainly particulates.

BTW, the amount of platinum in an O2 sensor is nearly infinitesimal. If you cut a sensor apart and have a look, it's more of a watery platinum wash. Platinum is selected for its resistance to tarnishing, and is only there to collect the voltage potential and conduct it to the terminals. Meanwhile, only half this teensy amount of platinum is on the sensing side. The other half is on the reference (atmospheric) side. Not very much platinum there at all. The unit cost of an O2 sensor is a couple of bucks. Meanwhile, there is enough platinum and other metals in a catalytic converter to make them worth stealing. When metal prices were up there were roving bands of crooks with Makita saws harvesting cats city blocks at a time. Everyone on the street goes out to start their cars in the morning and Vroooom, WTF.

Another interesting item: If the reference side becomes contaminated with various substances found around an engine, a sensor can actually work backward, producing a negative potential relative to the ECU. Thus sensors are typically well-shielded against atmospheric instrusions, with a steel or "rubber" sheath. Early on there were two-wire O2 sensors, with floating low reference circuits aka isolated grounds.

[McGuire]

Quote

Originally posted by gruntguru
Apart from cold sensor (sensor inoperative) and grossly incomplete combustion (eg misfire) I can't think of any. Are there any that occur with the sensor operating normally?

Anything that takes the system into open or modified loop, for starters.

[NTSOS]

I have had to re-adjust/upgrade my thinking....."think of squish/quench in terms of quench as well as squish". I also noticed that the intake ports have wings to help promote "mixture motion" and from your description, the piston design complements the process.....a complete package.......good stuff mac!

BTW, I stumbled across this interesting video:

Operating Combustion Chamber

The Jumbo Crate Motor Comparo Of Death

I read the entire ordeal and watched the interview with Mike Copeland..........btw, he looks like me......I have got to cut back on the Budweiser.

Excellent piece and the amount of work involved was excruciating to imagine.......truly an epic!

IMO, the most amazing motor for the price was the LS327..........best run was a 12.354 at 105.67 mph, not bad for what, 323 or so cubic inches?

Anyway, I was going to look on the gmperformanceparts website for the LS9, but never got around to it........the availability of the LS9 can't be a good thing for me.....like you said of the LS7........"The whole deal plugs together like Xmas lights, fires up instantly, and idles like a dream."

Ah jaysus, here we go again!

Oh, I forgot............chevy needs to fix the red line in their catalog!



Thanks man!

John

[NTSOS]

Quote

Originally posted by cheapracer


Ahh someone with taste, Ozians drool over 57's and 55's in order but seldom mention the 56 which I happen to prefer.

Me too, me too!

This may be a criminal act, but I am seriously thinking of getting this '56:

1956 Post

...and then swapping out the chassis and running gear with mine, but keeping everything else exactly as it appears externally and also use the stock interior.......except for maybe black 18" steel wheels with small chevy hub caps.

It would actually save me quite a bit of money as the body/paint/interior are perfect!

John

[penske1414]

Quote

Originally posted by McGuire


Two words for you: frog legs.

HA!! i'll buy that.

[gruntguru]

Quote

Originally posted by NTSOS
Oh, I forgot............chevy needs to fix the red line in their catalog!

The yellow one needs a tune-up (tune-down?) too.

[gruntguru]

Quote

Originally posted by McGuire


Anything that takes the system into open or modified loop, for starters.

How does that make the sensor output diverge from AFR?

[McGuire]

Quote

Originally posted by NTSOS

Oh, I forgot............chevy needs to fix the red line in their catalog!

Good eye. Here is one not invented by a graphic artist:

[McGuire]

Quote

Originally posted by NTSOS



Excellent piece and the amount of work involved was excruciating to imagine.......truly an epic!

A project of that scale needs a lot of committed partners, which usually means many different agendas, i.e. too many cooks in the soup. But for some reason everyone just climbed on board and let it roll. Good thing it all worked out or mcg would be hanging from a post somewhere.

[McGuire]

Quote

Originally posted by penske1414


HA!! i'll buy that.

I imagine that somewhere in Luigi Galvani's lab notes is the observation, "not bad, tastes like chicken."

BTW, Galvani's findings are said to be a partial inspiration for Mary Shelley when she wrote Frankenstein, or, the Modern Prometheus.

[phantom II]

I drove 600 miles over the weekend. Sebring (Corvette Coral), Sarasota and back to the east coast. I put gas in 4 times and averaged 14mpg. 5 Vettes drove to Sebring and basically cruised at the speed limit except for an occasional blast. Coming back from Sarasota was a steady 80mph. The same trip in a stock Z06 would give 24 mpg and steady cruise sections would be 28 mpg. Before the dealer 'fixed' it, it was getting 10-12mpg.

Quote

Originally posted by McGuire


Yep, that's me and my face. Hard to say what is wrong with your 1 except it does sound rich. For the record I can't do anything with your VIN, not a GM employee. What kind of mpg are you getting?

[phantom II]

Technical writers of this caliber are worth their weight in gold.

Quote

Originally posted by McGuire
If people would actually read the link posted above the discussion would already be over. Here it is again:


http://www.motorcraf...df/OBDSM704.pdf

[cheapracer]

Quote

Originally posted by phantom II
I drove 600 miles over the weekend. Sebring (Corvette Coral), Sarasota and back to the east coast. I put gas in 4 times and averaged 14mpg.

Good for you, the A-Rabs are bit light on cash this year!

[McGuire]

Quote

Originally posted by cheapracer


Good for you, the A-Rabs are bit light on cash this year!

You're just trying to wind him up, aren't you?

[McGuire]

Quote

Originally posted by phantom II
I drove 600 miles over the weekend. Sebring (Corvette Coral), Sarasota and back to the east coast. I put gas in 4 times and averaged 14mpg. 5 Vettes drove to Sebring and basically cruised at the speed limit except for an occasional blast. Coming back from Sarasota was a steady 80mph. The same trip in a stock Z06 would give 24 mpg and steady cruise sections would be 28 mpg. Before the dealer 'fixed' it, it was getting 10-12mpg.

I believe the ZR1's ratings are 14 city/20 hwy, so at least you are in the neighborhood of the ballpark. I would want to drive the car and have a look at the scan data. Due to the blower I don't think the ZR1 will ever pull the great hwy numbers like the Z06, but it ought to be better than 14 mpg, I would think.

[cheapracer]

Quote

Originally posted by McGuire


You're just trying to wind him up, aren't you?

I think I'm becoming too transparent ;)

[gruntguru]

Quote

Originally posted by McGuire
That is not its physical function. It can only measure O2 content and allow AFR to be inferred from there.

Did you say I have egg on my face in this thread? Your statement above was repeated several times in this thread. You have a lot of facts and knowledge in your head McGuire but you wouldn't recognise an original thought if it was surgically implanted. I haven't bothered obtaining the full text of the paper below - the abstract says enough.

Quick question Fonz. Were you . . . . . . . . wrong?


"Operating characteristics of zirconia galvanic cells (lambda sensors) in automotive closed-loop emission control systems
Bozek, John W | Evans, Richard | Tyree, Clifford D | Zerafa, Kenneth L
SAE Special Publications , no. 910, pp. 1-17. 1992

Simple tests were performed to investigate the operating characteristics of zirconia galvanic cells (lambda sensors) in automotive closed loop 'three-way' emission control systems. Commercially available cells were exposed to typical gaseous components of exhaust gas mixtures. The voltages generated by the cells were at their maximum values when hydrogen, and, in some instance, carbon monoxide, was available for reaction with atmospheric oxygen that migrated through the cells' ceramic thimbles in ionic form. This dependence of galvanic activity on the availability of these particular reducing agents indicated that the cells were voltaic devices which operated as oxidation/reduction reaction cells, rather than simple oxygen concentration cells. Such operation explains why a cell that is used as a lambda sensor in a closed-loop control system exhibits a sixfold or greater decrease in voltage output when the exhaust gas composition changes from a slightly rich condition (lambda identical with 0.995) to a slightly lean condition (lambda identical with 1.005). It also explains why the voltage of a cell that is located downstream of a properly operating catalyst normally remains at a low level as the air/fuel ratio oscillates around the stoichiometric value but increases to a high level when ignition misfire occurs at a rate that exceeds a certain value."

[McGuire]

Quote

Originally posted by gruntguru
Did you say I have egg on my face in this thread? Your statement above was repeated several times in this thread. You have a lot of facts and knowledge in your head McGuire but you wouldn't recognise an original thought if it was surgically implanted. I haven't bothered obtaining the full text of the paper below - the abstract says enough.

Quick question Fonz. Were you . . . . . . . . wrong?

[/i]

Not that I can see. Your two points were: 1) that an oxygen sensor is actually an "air/fuel ratio sensor" as it were; and 2) the platinum plating on the O2 sensor has a gas catalyzing function.

#1 is wrong because the O2 sensor does not measure AFR. It measures exhaust gas oxygen content, what with being situated in the exhaust pipe and all. It will never see A/F mixure, let alone measure it. The A/F mixture goes into the engine; exhaust is what comes out. So if the sensor were measuring AFR it would have to be located in the intake manifold, wouldn't it? (Early on there were such sensors as Bendix and others attempted to beat the Bosch patents.)

#2 is wrong because the platinum electrode has a glass-like coating to resist erosion and is thus not exposed to the exhaust stream. Also, the quantity of platinum is miniscule...which is the reason for the coating.

I am familiar with the paper you cited, which does not support your positions in any way. This is one of your specialties: expanding and diffusing your arguments by any means necessary. In other words, you will argue endlessly about anything whether you understand it or not or if you even care. Blah, blah, blah.

[gruntguru]

Quote

Originally posted by McGuire
Not that I can see. Your two points were: 1) that an oxygen sensor is actually an "air/fuel ratio sensor" as it were; and 2) the platinum plating on the O2 sensor has a gas catalyzing function.

#1 is wrong because the O2 sensor does not measure AFR. It measures exhaust gas oxygen content, what with being situated in the exhaust pipe and all. It will never see A/F mixure, let alone measure it. The A/F mixture goes into the engine; exhaust is what comes out. So if the sensor were measuring AFR it would have to be located in the intake manifold, wouldn't it? (Early on there were such sensors as Bendix and others attempted to beat the Bosch patents.)

This is a typical piece of dodging via lunatic rant. 99% of AFR measuring devices on planet earth, do so by analysing exhaust gas. If this is impossible there are going to be a lot of disappointed people out there. Perhaps you are confusing mass fraction AFR with dimensionless AFR? Of course all exhaust based AFR measurement will only give the dimensionless value which must then be multiplied by the stoichiometric ratio of the fuel in use, if you need the mass fraction AFR.

[gruntguru]

Quote

Originally posted by McGuire


Not that I can see. Your two points were: 1) that an oxygen sensor is actually an "air/fuel ratio sensor" as it were; and 2) the platinum plating on the O2 sensor has a gas catalyzing function.

#1 is wrong because the O2 sensor does not measure AFR. It measures exhaust gas oxygen content, what with being situated in the exhaust pipe and all. It will never see A/F mixure, let alone measure it. The A/F mixture goes into the engine; exhaust is what comes out. So if the sensor were measuring AFR it would have to be located in the intake manifold, wouldn't it? (Early on there were such sensors as Bendix and others attempted to beat the Bosch patents.)

#2 is wrong because the platinum electrode has a glass-like coating to resist erosion and is thus not exposed to the exhaust stream. Also, the quantity of platinum is miniscule...which is the reason for the coating.

I am familiar with the paper you cited, which does not support your positions in any way. This is one of your specialties: expanding and diffusing your arguments by any means necessary. In other words, you will argue endlessly about anything whether you understand it or not or if you even care. Blah, blah, blah.

#1 is correct because
". . . .rather than simple oxygen concentration cells. Such operation explains why a cell that is used as a lambda sensor in a closed-loop control system exhibits a sixfold or greater decrease in voltage output when the exhaust gas composition changes from a slightly rich condition (lambda identical with 0.995) to a slightly lean condition (lambda identical with 1.005). This sentence is saying that the step response of the lambda sensor occurs - not at some mystical oxygen concentration - but at a precise AFR between 0.995 and 1.005.

#2 is correct because
"This dependence of galvanic activity on the availability of these particular reducing agents indicated that the cells were voltaic devices which operated as oxidation/reduction reaction cells, rather than simple oxygen concentration cells." This sentence is saying that oxidation/reduction reactions are occurring in the sensor.

And finally, whether I was right or wrong, the paper you are familiar with (but clearly don't understand) has proven YOU wrong - as follows.


McGuire
No, an O2 sensor works by directly measuring the oxygen content in the exhaust.

quote:Originally posted by gruntguru
I agree that gross changes in oxygen content (eg misfire) will have the effect described. However for reasonably combusted exhaust gas (no misfire), the lambda sensor is also responding to unburned fuel products in the exhaust (CO, HC).

McGuire
No, the sensor is only capable of responding to O2. It cannot detect HC or CO at all.

McGuire
The O2 sensor is (make a note of this) positioned in the exhaust stream. It is not exposed to air/fuel mixture, only exhaust gas, and the only exhaust component it can effectively measure is O2.

McGuire
There are any number of conditions in which the O2S signal value and the AFR diverge and head off in opposite directions, but if the O2S value and O2 content diverge there is a problem.

McGuire
The O2 sensor has no significant gas-catalyzing function.

All contradicted by this
"The voltages generated by the cells were at their maximum values when hydrogen, and, in some instance, carbon monoxide, was available for reaction with atmospheric oxygen that migrated through the cells' ceramic thimbles in ionic form. This dependence of galvanic activity on the availability of these particular reducing agents indicated that the cells were voltaic devices which operated as oxidation/reduction reaction cells, rather than simple oxygen concentration cells.

[McGuire]

Gibberish. You haven't even read the paper you are citing. In the first place, the effect is not a result of catalysis but simple oxidation and reduction. Congratulations, you have discovered that CO and H react with O2.

[gruntguru]

Quote

Originally posted by McGuire
Gibberish. You haven't even read the paper you are citing. In the first place, the effect is not a result of catalysis but simple oxidation and reduction. Congratulations, you have discovered that CO and H react with O2.

Not without an ignition source + combustible proportions or a catalyst they don't. Otherwise exhausts would be much cleaner with just an air pump (which won't work at the same low temps a lambda sensor will).

Besides - whether the platinum acts as a catalyst or not, I was correct in saying that reducing agents have a key role in the sensor function and output, that the sensor output is better described as a Lambda sensor than Oxygen sensor and that you were wrong in your insistence that the sensor "only responds to oxygen" as quoted below (I guess this is the part of my previous post that you were referring to as "Gibberish")

McGuire
No, an O2 sensor works by directly measuring the oxygen content in the exhaust.

quote:Originally posted by gruntguru
I agree that gross changes in oxygen content (eg misfire) will have the effect described. However for reasonably combusted exhaust gas (no misfire), the lambda sensor is also responding to unburned fuel products in the exhaust (CO, HC).

McGuire
No, the sensor is only capable of responding to O2. It cannot detect HC or CO at all.

McGuire
The O2 sensor is (make a note of this) positioned in the exhaust stream. It is not exposed to air/fuel mixture, only exhaust gas, and the only exhaust component it can effectively measure is O2.

McGuire
There are any number of conditions in which the O2S signal value and the AFR diverge and head off in opposite directions, but if the O2S value and O2 content diverge there is a problem.

McGuire
The O2 sensor has no significant gas-catalyzing function.

All contradicted by this
"The voltages generated by the cells were at their maximum values when hydrogen, and, in some instance, carbon monoxide, was available for reaction with atmospheric oxygen that migrated through the cells' ceramic thimbles in ionic form. This dependence of galvanic activity on the availability of these particular reducing agents indicated that the cells were voltaic devices which operated as oxidation/reduction reaction cells, rather than simple oxygen concentration cells."

[gruntguru]

Quote

Originally posted by McGuire
#2 is wrong because the platinum electrode has a glass-like coating to resist erosion and is thus not exposed to the exhaust stream.

So the electrode is insulated? How then does it function as an electrode if the oxygen ions cannot make contact with the platinum?

[McGuire]

Quote

Originally posted by gruntguru
So the electrode is insulated? How then does it function as an electrode if the oxygen ions cannot make contact with the platinum?

We need the zirconia exposed to the oxygen ions. The zirconia substrate is porous so its lattice is exposed to oxygen ions. So the platinum layer must be applied very thin -- as I said, a runny wash, like watercolor if you will -- so as not to seal the porosities. This very thin coating of platinum is sufficient as an electrode for while the potential is in the one volt range, the current is miniscule.

The type of spinnell coating employed is a significant variable in sensor operation, interestingly enough. ECU programming typically employs some means to compensate for sensor degradation over time, adjusting ECU response to O2S value according to the tested degradation rate of the sensor. Bosch and Delco/Delphi etc sensors employ a nearly identical spinnell coating so in that regard they are interchangeable in application. However, Asian rim sensors employ a different spinnell composition with smaller microporosities that plug up at a faster rate, so the falloff is steeper. So you get a mismatch between the degradation rate the ECU expects to see and actual. It's nowhere near enough to affect driveability, especially in the first half of the sensor's life cycle, but it is enough to fail a car in long-term emissions standards. And it has happened. (Fun project, I made some $$$ on that one.) One practical takeaway from this otherwise useless minutiae is to be careful about universal, one-size-fits-all O2 sensors at the local parts store.

BTW, in the paper you cited (SAE 92089) the effect described applies only to thimble sensors, varies significantly among sensor manufacturers, and is only significant above 850 C. It's not a first-order characteristic in other words. It might be helpful to know the context of this work. The paper is around 20 years old, when it was hoped that exhaust O2 value might be employed to detect cylinder misfire, thus enabling embedded diagnostics for same. But it never worked out, as you can see. That diagnostic routine is typically performed by monitoring the crankshaft's translational velocity. Which is interesting info as you can imagine.

[gruntguru]

Quote

Originally posted by McGuire
We need the zirconia exposed to the oxygen ions. . . Blah. . . Which is interesting info as you can imagine.

Not your usual inflammatory response McGuire? No ideas yet on whether you might have been wr. . . wr. . . .wr. . . . in error?

The platinum itself needs to be exposed to the oxygen ions for current to flow. The zirconia is simply the electrolyte, the platinum forms the electrodes. If the oxygen ions can access the platinum , so can the H and CO. I think I will stick to my belief that the reduction reactions on the negative electrode are primarily the result of catalytic action of the platinum.

[McGuire]

Quote

Originally posted by gruntguru
Not your usual inflammatory response McGuire? No ideas yet on whether you might have been wr. . . wr. . . .wr. . . . in error?

The platinum itself needs to be exposed to the oxygen ions for current to flow. The zirconia is simply the electrolyte, the platinum forms the electrodes. If the oxygen ions can access the platinum , so can the H and CO. I think I will stick to my belief that the reduction reactions on the negative electrode are primarily the result of catalytic action of the platinum.

Nope, the zirconia can only conduct O2 ions through its lattice, not H or CO, while the spinnell coating goes over the platinum, not between the zirconia and platinum. The O2 ions in the zirconia apply a charge to the platinum electrode and a current goes up the wire.

I do wish you would do a little research instead of simply tossing out one harebrained theory after another.

[gruntguru]

Quote

Originally posted by McGuire
Nope, the zirconia can only conduct O2 ions through its lattice, not H or CO, while the spinnell coating goes over the platinum, not between the zirconia and platinum. The O2 ions in the zirconia apply a charge to the platinum electrode and a current goes up the wire.

I do wish you would do a little research instead of simply tossing out one harebrained theory after another.

Still sounds like just your interpretation McGuire (insults have returned too). The oxygen ions need to contact the platinum to give up their negative charge and pair up to form an oxygen molecule, then continue through to the exhaust stream. If this is so, the H and CO molecules can get to the platinum too. Plain logic and understanding of how the system works. If you have unearthed research that contradicts this - quote it and I will retract (an act you are obviously incapable of as apparent in this thread)

e.g. - deny this.

1. Lambda sensors respond to reducing agents in the exhaust as well as oxygen.

2. The response of a lambda sensor is more closely related to AFR than it is to exhaust oxygen content since the "switch" in output occurs at an AFR of 1.0 rather than some particular value of oxygen concentration.

[McGuire]

Quote

Originally posted by gruntguru
Still sounds like just your interpretation McGuire (insults have returned too). The oxygen ions need to contact the platinum to give up their negative charge and pair up to form an oxygen molecule, then continue through to the exhaust stream. If this is so, the H and CO molecules can get to the platinum too. Plain logic and understanding of how the system works. If you have unearthed research that contradicts this - quote it and I will retract (an act you are obviously incapable of as apparent in this thread)

From the same paper you cited above -- page 5, paragraph 2:

"The thimble is fabricated from zirconium oxide which contains a small amount of lower valent oxide, such as yttrium oxide. The dispersion of trivalent yttria within the tetravalent zirconia crystalline lattice results in valence "holes" which allow oxygen ions to migrate through the zirconia wall of the thimble but prevent such migration by any other kind of ion, atom, or molecule. The specificity of the zirconia porosity in regard to oxygen ions is similar to that in other kinds of "ion selective" solid materials that have been developed."

[gruntguru]

Quote

Originally posted by McGuire
From the same paper you cited above -- page 5, paragraph 2:
"The thimble is fabricated from zirconium oxide which contains a small amount of lower valent oxide, such as yttrium oxide. The dispersion of trivalent yttria within the tetravalent zirconia crystalline lattice results in valence "holes" which allow oxygen ions to migrate through the zirconia wall of the thimble but prevent such migration by any other kind of ion, atom, or molecule. The specificity of the zirconia porosity in regard to oxygen ions is similar to that in other kinds of "ion selective" solid materials that have been developed."

This still doesn't state that other species don't have access to the -ve electrode or that catalysis doesn't occur in a lambda sensor.

Regardless - catalytic action is a minor point. Whatever the process, it is clear that reducing agents play a crucial role in lambda sensor operation and my original descriptions were far more accurate than your aggressive rebuttal e.g.
Post 2
"its response is more closely related to AFR than exhaust oxygen content"
Post 4
"the lambda sensor is also responding to unburned fuel products in the exhaust"

These 2 points were the essence of my position and were both fiercely disputed by yourself, even to the point where - with no supporting evidence - you claimed in another thread that I had "egg on my face". Both of these points are supported by this paper which you claimed to be "familiar with".

[McGuire]

Quote

Originally posted by gruntguru
This still doesn't state that other species don't have access to the -ve electrode or that catalysis doesn't occur in a lambda sensor.

The zirconia cannot admit them so the effects are ternary at best. Obviously there is catalytic action, but net catalysis is zero. All this is rather like debating the catalytic properties of a platinum spark plug: amusing... to a point.

[gruntguru]

Quote

Originally posted by McGuire
The zirconia cannot admit them so the effects are ternary at best. Obviously there is catalytic action, but net catalysis is zero. All this is rather like debating the catalytic properties of a platinum spark plug: amusing... to a point.

The spark plug case is very different. While no one would claim that catalysis in the lambda sensor is directly reducing emissions, any catalysis at the -ve electrode would have an effect on the oxygen partial pressure at that electrode and consequently a pronounced effect on the sensor output around stoichiometric and richer AFR's.

[cheapracer]

Quote

Originally posted by gruntguru
The spark plug case is very different. While no one would claim that catalysis in the lambda sensor is directly reducing emissions.

Why just the other day having a beer with a friend from Nippon, Mr Denso, I claimed that emissions were directly reduced via catalysis in the lambda sensor. He remarked that he thought I had a lead there and I replied "yes and at the end of that lead there is a bright spark".

I worry about him lately, he mentioned he was under pressure and may be fired but he didn't expand on it, exhausting really.

[gruntguru]

Quote

Originally posted by cheapracer
Why just the other day having a beer with a friend from Nippon, Mr Denso, I claimed that emissions were directly reduced via catalysis in the lambda sensor. He remarked that he thought I had a lead there and I replied "yes and at the end of that lead there is a bright spark".

I worry about him lately, he mentioned he was under pressure and may be fired but he didn't expand on it, exhausting really.

I will rephrase then. "Apart from Cheapy and Mr Denso (bit thick that boy) no one would claim that catalysis in the lambda sensor is directly reducing emissions."

[McGuire]

Quote

Originally posted by gruntguru


Regardless - catalytic action is a minor point.

I fully agree that catalysis is not an issue here -- as I have said all along. I will take that as the retraction you promised.

But there is still a huge non sequitor in your thinking. How is the sensor's response more closely related to AFR than to exhaust oxygen content, as you say? The sensor is placed in the exhaust stream, not the intake stream, and the zirconia can only conduct ionized O2, not whole fuel hydrocarbons or air. H and CO are not "unburned fuel products" but partial combustion products. Thus your catalyst argment did not support your point in the first place, but without it you have no point at all.

Obviously there is catalytic action wherever O2 and Pt meet, but here net catalysis is zero. Molecular O2 is disassociated and sequentially ionized, each atom gaining two electrons. Monatomic O2 anions (aka oxides) enter the zirconia substrate only to yield the two surplus electrons applying their charge to the collector, spontaneously reassociating as diatomic O2. Null change in chemical state. Molecular O2 in, molecular O2 out. Ion exchange to produce an electrical current, galvanic process. As the paper's title indicates.

All this is covered in the paper you cited. Not trying to be a wise guy in any way, with all due respect etc, but clearly you have not read it. Why don't you read it so we can have a pleasant and intelligent discussion instead of this one? I see you repeatedly quoted only from the abstract, which suggests that the text of the paper is not available to you. If that is the case I will be glad to send you a copy, or other papers that may be of interest.

[cheapracer]

Quote

Originally posted by cheapracer




I worry about him lately, he mentioned he was under pressure and may be fired but he didn't expand on it, exhausting really.

Did anyone notice I got the whole Otto cycle in the one sentance?

I didn't think so, oh well I guess it's back to the 160+ forum

[gruntguru]

Quote

Originally posted by McGuire
But there is still a huge non sequitor in your thinking. How is the sensor's response more closely related to AFR than to exhaust oxygen content, as you say? The sensor is placed in the exhaust stream, not the intake stream,

The basis of my assertion is this
1. The only useful part of the lambda sensor signal is the "switching" point where the outut rapidly transitions from low to high.

2. This switching point occurs at a particular AFR (1.00) and not at some particular exhaust oxygen concentration.

Point 1 is widely acknowledged and point 2 is confirmed in the abstract of the above mentioned paper.

[gruntguru]

cheapracer, on Apr 29 2009, 11:04 PM, said:

Did anyone notice I got the whole Otto cycle in the one sentance?

I didn't think so, oh well I guess it's back to the 160+ forum

I can see it now that you mention it but I can only count 3 strokes. You may have had a sharp intake of breath immediately before uttering the sentence, but it doesn't appear on the screen I hope you realise.

[cheapracer]

gruntguru, on Apr 30 2009, 05:51 AM, said:

I can see it now that you mention it but I can only count 3 strokes. You may have had a sharp intake of breath immediately before uttering the sentence, but it doesn't appear on the screen I hope you realise.

umm that explains why they kicked me down to the 100 and struggling IQ threads then at the 160+ Forum, darn it.

[Joe Bosworth]

I don’t know why I am jumping into this discourse now except that I can’t stand watching people bicker over technical details and scientific matters, splitting the meanings of words and possibly confusing those who are reading this and seeking knowledge.

I will try to provide a view that has a 100% factual scientific basis and incontestable by anyone in the combustion technology field. There will be a couple of areas where I provide informed opinion and will advise when such pop up at the end of this.

All combustible fuels consist of virtually only carbon and hydrogen molecules combined in variously shaped complex long and short strings. This is true of all types of coals, gasses, fuel oils and petrols (gasolines). In the process of combustion air is taken in and the 21% (+/-) oxygen contained therein is utilised to oxidise the C and H molecules.

There are only three chemical equations that apply; H + 2O = H2O and C + 2O = CO2 or 2C + 2O = 2CO.

All three reactions are exothermic, that is heat is given off. The heat given off by these reactions is the energy form used in the process we are using when we burn the fuels.

It would be good if I can explain the next part with a graph but I will not sign up with a hosting group that I will use only for things like this. I will provide via email for those who might want one or is willing post such here on the behalf of this discussion.

However, let me paint a word picture. When very rich, (fuel surplus). CO2 in the combustion products are close to nil, CO is very high and O2 is zero. As the air:fuel ratio becomes less rich and moves to stoichemetric the CO2 in exhaust gasses rise, CO percent falls and O2 percent stays at zero. At the point of stoichemetric ratio we have the theoretical situation in the exhaust products of:
CO is zero
O2 is zero
CO2 is at a max with the percentage depending on the number of C molecules in the fuel. This varies from about 13% to about 18%.

Then as the air:fuel ratio goes leaner, (air/O2 surplus) the CO2 starts to fall, CO stays at zero and the percentage of O2 in the exhaust starts rising.

There are a lot of very sophisticated pieces of equipment available that allows one to read the percentages of O2, CO and CO2 in exhaust gasses. A Lambda sensor is one of the less sophisticated in some respects, it just happens to be cheap, accurate and long lived, though does not provide the whole picture directly or indirectly. But perfect for automotive use!

All of these pieces of equipment do not measure A/F ratios. They provide information relative to percentages of constituents in the exhaust gasses.

The good news is that the boffins can calculate A:F ratios from these percentage figures. Since boffins can do so, so can computers; it is all mathematically fixed.

Now let me go from the theoretical to the practical. When you have large combustion spaces and long burn times the theoretical picture of products in exhaust gasses is accurate. But automotive applications have very restrictive combustion spaces and very short combustion times. Theory flies out the window and practice strolls in the door. Rather than very clear percentage delineations at the stoichemetric point we find very small amounts of O2 present while still a little bit on the rich side. (We also find very small amounts of CO present while a little bit on the lean side. But the relationships remain constant. Lower O2 equals higher CO and v-v.)

Now I am not going to say I am a Lambda expert but I do believe that the Lambda sensor only reads O2 in exhaust gasses by electrically reacting to O ions. The fewer the ions (lower O2 percent - richer the mixture) the higher the voltage output.

Lambda reading devices read the voltage signals from the sensors and goes through the process I previously described to read out some output representing A:F ratio for use by ball including the ECU. The output can be meaningful as compared to unity, A:F ratio or an ideal voltage, all the samo-samo.

I am absolutely on solid ground up to the last two paragraphs. If you are going to fight over all of this do so within the confines of the last two.

Regards

[Tony Matthews]

gruntguru, on Apr 30 2009, 06:51 AM, said:

I can see it now that you mention it but I can only count 3 strokes. You may have had a sharp intake of breath immediately before uttering the sentence, but it doesn't appear on the screen I hope you realise.

Well I'll be sucked, squeezed, banged, blown and knocked down with a Lamda sensor! How's that? Yes, purile, I know...

[cheapracer]

Joe Bosworth, on Apr 30 2009, 10:59, said:

Now I am not going to say I am a Lambda expert but I do believe....

Regards

I don't know about you others but when I saw this I saw 2 hungry wolves snapping at each other and a stray lamb (da) just wandered off into the woods and into their sights ......

Edited by cheapracer, 30 April 2009 - 13:19.

[gruntguru]

Joe Bosworth, on Apr 30 2009, 20:59, said:

Now I am not going to say I am a Lambda expert but I do believe that the Lambda sensor only reads O2 in exhaust gasses by electrically reacting to O ions. The fewer the ions (lower O2 percent - richer the mixture) the higher the voltage output.

Lambda reading devices read the voltage signals from the sensors and goes through the process I previously described to read out some output representing A:F ratio for use by ball including the ECU. The output can be meaningful as compared to unity, A:F ratio or an ideal voltage, all the samo-samo.

I will start by clarifying that the disagreement in this thread relates specifically to narrow band lambda sensors as used in road cars with 3-way catalysts. Some of your comments appear to refer to broad-band lambda sensors.

McGuire and I both agree that the lambda sensor output is generated only by migration of oxygen ions from the atmospheric electrode to the exhaust electrode and that this output is determined by the difference in oxygen concentration on these two electrodes. Where McGuire (and possibly yourself) is wrong is his assertion that reducing agents (CO, HC, H, and C) in the exhaust, have no effect on the sensor output. The fact is these agents will (if present) combine with oxygen molecules (if present) in the vicinity of the exhaust electrode. This will of course reduce the oxygen concentration at the exhaust electrode and alter the sensor output.

The outcome of this is that the "step" response of the sensor output (which occurs at the transition from "excess oxygen" to "excess reducing agents") will occur precisely at the stoichiometric AFR. Thus the lambda sensor is indeed a very accurate (0.5%) AFR switch which is ideal for precisely identifying stoichiometry to a control system which has stoichometry as its setpoint.

Edited by gruntguru, 01 May 2009 - 10:56.

[McGuire]

gruntguru, on May 1 2009, 13:39, said:

McGuire and I both agree that the lambda sensor output is generated only by migration of oxygen ions from the atmospheric electrode to the exhaust electrode and that this output is determined by the difference in oxygen concentration on these two electrodes. Where McGuire (and possibly yourself) is wrong is his assertion that reducing agents (CO, HC, H, and C) in the exhaust, have no effect on the sensor output. The fact is these agents will (if present) combine with oxygen molecules (if present) in the vicinity of the exhaust electrode. This will of course reduce the oxygen concentration at the exhaust electrode and alter the sensor output.

It's not that I disagree so much as I don't even care. It's not relevant here. It's not a significant factor in a properly functioning O2 sensor and it doesn't support your argument anyway.

gruntguru, on May 1 2009, 13:39, said:

The outcome of this is that the "step" response of the sensor output (which occurs at the transition from "excess oxygen" to "excess reducing agents") will occur precisely at the stoichiometric AFR. Thus the lambda sensor is indeed a very accurate (0.5%) AFR switch which is ideal for precisely identifying stoichiometry to a control system which has stoichometry as its setpoint.

Two problems with that:

1. The ECU does the "switching," not the O2 sensor. The sensor can only respond to O2 content, and its useful sensitivity range lies in a very narrow band around stoich. So the ECU must constantly retrim fuel delivery to keep the O2S value with the band -- otherwise the O2 value will quickly drift out of the sensor's range. Indeed, in the experiment you proposed earlier there is no O2S "switching" at all. The sensor maintains a constant ~450 mv because it has no "switching" function of its own.


2. Lambda is a dimensionless equivalence value represented by unity. However, O2 content at lambda may represent an equivalent AFR of ~14.7:1 or it may not. That is entirely dependent on the stoichiometric value of the fuel. Here in the USA we have engine control systems that successfully accommodate fuels with stoich values from ~9.7:1 with E85 to ~15.7:1 with propane. (All with the same O2 sensor part number.) So obviously, the O2 sensor does not detect or determine AFR but only oxygen content. The ECU determines the AFR accordingly. More importantly, since the sensor operates in a narrow band around stoich, it cannot effectively measure exhaust content when the mixture is significantly above or below stoich. If, as is often the case, an AFR of 12.5:1 for acceleration or 16:1 for economy are required, a narrow-band O2 sensor cannot measure an equivalent exhaust O2 content for them. In fact, the sensor cannot measure or determine AFR at any time or in any case, only exhaust O2 content.

[cheapracer]

Did you know what my favorite movie is?

"Silence of the Lamb(da)'s".

[Joe Bosworth]

I will further try to narrow the scope for arguments on this subject:

Grunt advises,”Where McGuire (and possibly yourself) is wrong is his assertion that reducing agents (CO, HC, H, and C) in the exhaust, have no effect on the sensor output.”

I can state absolutely and categorically that based on thousands of samples I have taken with very sophisticated equipment that within the range of stoichemetric mixtures that we are discussing that 0.0000....0000% HC, H or C will exist. None, zero, zip, nada, it ain't there. period. Please trust me on this. CO does exist in the very small band being discussed but it actually does not bias the results that I have measured. Don't ask me why CO doesn't have any practical effect, For that matter I don't know why it should have an effect. I said I am no expert at that level. And I am not going to waste my time figuring out the whys, when I know the practical result.


Mac talks about:
“1. The ECU does the "switching," not the O2 sensor. The sensor can only respond to O2 content, and its useful sensitivity range lies in a very narrow band around stoich. So the ECU must constantly retrim fuel delivery to keep the O2S value with the band -- otherwise the O2 value will quickly drift out of the sensor's range. Indeed, in the experiment you proposed earlier there is no O2S "switching" at all. The sensor maintains a constant ~450 mv because it has no "switching" function of its own. “

He is quite correct and particulalrly relative to the very narrow band around Stoich. As I explained, it is only i the very narrow band that O2 exists on the rich side of stoich and then only because of the short burn time and very confined space. If this weren't true then the Lambda could not be used as it is.

Mac goes on,”2. Lambda is a dimensionless equivalence value represented by unity. However, O2 content at lambda may represent an equivalent AFR of ~14.7:1 or it may not. That is entirely dependent on the stoichiometric value of the fuel. Here in the USA we have engine control systems that successfully accommodate fuels with stoich values from ~9.7:1 with E85 to ~15.7:1 with propane. (All with the same O2 sensor part number.) So obviously, the O2 sensor does not detect or determine AFR but only oxygen content. The ECU determines the AFR accordingly. More importantly, since the sensor operates in a narrow band around stoich, it cannot effectively measure exhaust content when the mixture is significantly above or below stoich. If, as is often the case, an AFR of 12.5:1 for acceleration or 16:1 for economy are required, a narrow-band O2 sensor cannot measure an equivalent exhaust O2 content for them. In fact, the sensor cannot measure or determine AFR at any time or in any case, only exhaust O2 content.”

This squares exactly with my earlier post and is quite correct and gets into better detail than I bothered to present on movable stoich ratios..

Keep debating and I will help close the gaps between you.

Regards again

[gruntguru]

Joe Bosworth, on May 2 2009, 05:06, said:

Grunt advises,”Where McGuire (and possibly yourself) is wrong is his assertion that reducing agents (CO, HC, H, and C) in the exhaust, have no effect on the sensor output.”
I can state absolutely and categorically that based on thousands of samples I have taken with very sophisticated equipment that within the range of stoichemetric mixtures that we are discussing that 0.0000....0000% HC, H or C will exist. None, zero, zip, nada, it ain't there. period. Please trust me on this. CO does exist in the very small band being discussed but it actually does not bias the results that I have measured. Don't ask me why CO doesn't have any practical effect, For that matter I don't know why it should have an effect. I said I am no expert at that level. And I am not going to waste my time figuring out the whys, when I know the practical result.

Are you saying that there are no HC emissions at stoich? If so, I recommend you get your HC analyser checked right now. I have never seen an engine with zero HC emissions at stoich except post cat so no - I aint gonna trust you on that one.

Joe Bosworth, on May 2 2009, 05:06, said:

Mac talks about:
“1. The ECU does the "switching," not the O2 sensor. The sensor can only respond to O2 content, and its useful sensitivity range lies in a very narrow band around stoich. So the ECU must constantly retrim fuel delivery to keep the O2S value with the band -- otherwise the O2 value will quickly drift out of the sensor's range. Indeed, in the experiment you proposed earlier there is no O2S "switching" at all. The sensor maintains a constant ~450 mv because it has no "switching" function of its own. “

He is quite correct and particulalrly relative to the very narrow band around Stoich. As I explained, it is only i the very narrow band that O2 exists on the rich side of stoich and then only because of the short burn time and very confined space. If this weren't true then the Lambda could not be used as it is.

I will respond directly to McGuire's post on that one.

Joe Bosworth, on May 2 2009, 05:06, said:

Mac goes on,”2. Lambda is a dimensionless equivalence value represented by unity. However, O2 content at lambda may represent an equivalent AFR of ~14.7:1 or it may not. That is entirely dependent on the stoichiometric value of the fuel. Here in the USA we have engine control systems that successfully accommodate fuels with stoich values from ~9.7:1 with E85 to ~15.7:1 with propane. (All with the same O2 sensor part number.) So obviously, the O2 sensor does not detect or determine AFR but only oxygen content. The ECU determines the AFR accordingly. More importantly, since the sensor operates in a narrow band around stoich, it cannot effectively measure exhaust content when the mixture is significantly above or below stoich. If, as is often the case, an AFR of 12.5:1 for acceleration or 16:1 for economy are required, a narrow-band O2 sensor cannot measure an equivalent exhaust O2 content for them. In fact, the sensor cannot measure or determine AFR at any time or in any case, only exhaust O2 content.”

This squares exactly with my earlier post and is quite correct and gets into better detail than I bothered to present on movable stoich ratios..

This is all generally accepted stuff I consider waffle irrelevant to the point of contention.

Joe, did you read the abstract I posted. Here it is again.

"Operating characteristics of zirconia galvanic cells (lambda sensors) in automotive closed-loop emission control systems
Bozek, John W | Evans, Richard | Tyree, Clifford D | Zerafa, Kenneth L
SAE Special Publications , no. 910, pp. 1-17. 1992

Simple tests were performed to investigate the operating characteristics of zirconia galvanic cells (lambda sensors) in automotive closed loop 'three-way' emission control systems. Commercially available cells were exposed to typical gaseous components of exhaust gas mixtures. The voltages generated by the cells were at their maximum values when hydrogen, and, in some instance, carbon monoxide, was available for reaction with atmospheric oxygen that migrated through the cells' ceramic thimbles in ionic form. This dependence of galvanic activity on the availability of these particular reducing agents indicated that the cells were voltaic devices which operated as oxidation/reduction reaction cells, rather than simple oxygen concentration cells. Such operation explains why a cell that is used as a lambda sensor in a closed-loop control system exhibits a sixfold or greater decrease in voltage output when the exhaust gas composition changes from a slightly rich condition (lambda identical with 0.995) to a slightly lean condition (lambda identical with 1.005). It also explains why the voltage of a cell that is located downstream of a properly operating catalyst normally remains at a low level as the air/fuel ratio oscillates around the stoichiometric value but increases to a high level when ignition misfire occurs at a rate that exceeds a certain value."

Joe Bosworth, on May 2 2009, 05:06, said:

Keep debating and I will help close the gaps between you.

What - and ruin our fun?

Edited by gruntguru, 02 May 2009 - 04:58.

[cheapracer]

I like ice cream.