[Shivank]

Originally Posted by Rehaan

Nowhere have i said that. I have steered clear of that whole part of the discussion! Am only interested in the technical aspects here.

Personally though, i think its a good thing that TSi engines are being brought it. However, i also think its a good thing that we are being educated about the finer points of their functioning.

I love the 1.8TSi.

Hey, I didn't mean you in particular. I was just referring to the thread-starter and other among us who believe the TSi is simply useless for our country. It needs a thorough research before leaping to such conclusions.

Nevertheless, I too find the thread of great knowledge. If not all I have been able to learn a few things on stratified engines through these tech-talks...

[Rehaan]

Originally Posted by Sutripta

Considering that OBD was legislated for emission compliance, I'm sure these modes will show up on a scangauge. Someone willing to do the experiment?

Great! Thats EXACTLY what my next question was going to be.

I have an ELM 327. Who has a TSI?

cya
R

[vina]

Originally Posted by Sutripta

In the context of this thread, the reaction with sulphur of the NOx adsorber is an undesirable sideeffect. As long as the sulphur in the fuel is not zero, it will happen. And will have to be taken care of. By regeneration. As stated, regenration from the N compounds takes seconds, from the S compounds minutes.
...

I little tangential to the topic, but how does NOx absorption help reduce pollution if you are going to release it later anyway during regeneration?

Doesn't the regeneration process cause NOx to react with the fuel to generate N2 + CO2?

[Aroy]

Originally Posted by vina

I little tangential to the topic, but how does NOx absorption help reduce pollution if you are going to release it later anyway during regeneration?

Doesn't the regeneration process cause NOx to react with the fuel to generate N2 + CO2?

You convert the NOx to Nitrogen and Water, using catalyst. The sulfur in fuel can inhibit this especially in a very lean burn.

here are some links
Catalytic Converter NOx Emmissions
"
Case Study
" I'm working on a 1992 3.1-liter Chevrolet that failed in the test lane. The results were very good for HC and CO—nearly zero—but it failed for NOx. The converter seems to be operating properly and the engine is running okay. What's causing the problem?"
Answer: Because this application, like many others, does not have an EGR adjustment, there's little the technician can do to "tweak" the engine's performance to bring it into compliance. It's clear the engine is running overly lean. A lean engine operating condition produces more NOx than usual, and the lean exhaust chemically interferes with the converter's ability to clean NOx (remember that excess oxygen is good for cleaning HC and CO, but bad for NOx)."

SmogTips.com - How Does A Catalytic Converter Work? CAT. Faulty Catalytic Converter, Catalytic Converter System, CAT failure, Defective CAT, Defective Catalytic Converter, Find CAT, Burned CAT, Plugged CAT, plugged catalytic converter, Reduction CAT
"The catalytic converter only begins working after exhaust has exited the engine's combustion chambers. When hot exhaust gases are forced through the catalytic converter, they contact the catalyst substrate. This causes a rapid increase in temperature, thus burning the exhaust gases even hotter and more thoroughly, ultimately reducing emissions. In the Three Way CAT, once the HC and CO reduction has occurred by extreme heating, a NOx reduction substrate separates the harmful pollutant known as nitrogen oxides into nitrogen and oxygen.
Catalysts are designed to function for a limited time, and require replacement. How long a vehicles CAT will last depends on how completely the engine burns fuel before presenting it the to the CAT and also on the quality of the CAT."

Selective Catalytic Reduction - SCR - Diesel NOx Reduction
"Selective Catalytic Reduction (SCR) is a method of converting harmful diesel oxides of nitrogen (NOx) emissions, by catalytic reaction, into benign nitrogen gas and water. SCR can deliver near-zero emissions of NOx, an acid rain and smog-causing pollutant and greenhouse gas, in modern highway clean diesel engines."

[vina]

so does converter work by:

NOx + heat --> N2 + O2

or is it:

NOx + fuel + heat --> N2 + CO2 + H2O + more heat

?


Also what is the meaning of "storage type catalytic converter" then?

[Sutripta]

Originally Posted by vina

I little tangential to the topic, but how does NOx absorption help reduce pollution if you are going to release it later anyway during regeneration?

Doesn't the regeneration process cause NOx to react with the fuel to generate N2 + CO2?

What we are talking about is an accumulator/ convertor. Which is separate from, and downstream of the primary cat.

It is a three stage process:
Accumulate
Remove
Convert

Engine is run briefly in rich mode so that there are reducing agents (like H2, HCs, CO). The Barium Nitrate is first converted to BaO and NO. The NO is then converted to N2 and H2O or CO2.

(I can guess your next question! If I'm correct, I'll pat myself on the back!)

Regards
Sutripta

[Neil.Bhujbal]

Since my knowledge is limited I can't answer all the questions asked :(

Doesn't mean any info I have posted is wrong I hope this thread will atleast tell the basics of the principals on which these engines work. (Stratified mode & homogeneous mode)

[vina]

Originally Posted by Sutripta

What we are talking about is an accumulator/ convertor. Which is separate from, and downstream of the primary cat.

It is a three stage process:
Accumulate
Remove
Convert

Engine is run briefly in rich mode so that there are reducing agents (like H2, HCs, CO). The Barium Nitrate is first converted to BaO and NO. The NO is then converted to N2 and H2O or CO2.

(I can guess your next question! If I'm correct, I'll pat myself on the back!)

Regards
Sutripta

So are you saying that the unit in the car will accumulate most of the NOx till it is full, then during servicing the accumulator will be taken away to some special setup where the NOx will be reduced using some fuel (hydrocarbons, alcohol or something similar - given you talk of H2O and CO2)

[sgiitk]

Let us face it. In the good (bad!) old leaded days 5* in the UK was 100RON. My plain Jane Ford Escort needed 4* or 97RON. All this is history now.

Unleaded reduced the RON across the board. Of course cats and the like were unheard of then.

[Sutripta]

Originally Posted by vina

So are you saying that the unit in the car will accumulate most of the NOx till it is full, then during servicing the accumulator will be taken away to some special setup where the NOx will be reduced using some fuel (hydrocarbons, alcohol or something similar - given you talk of H2O and CO2)

NO.
When the accumulator is full (detected by increasing NOx downstream of the accumulator), the engine enters regeneration mode.

Remember, the reason for excess NOx originally is the lean burn nature (excess O2) of SCSI. But this also means there are no reducing agents in the exhaust. (NOx has to be reduced.) So the normal primary cat cannot deal with the NOx.

For regeneration, the engine shifts to HCSI, and in fact a rich one. This introduces the reducing agents in the exhaust. (The ignition might also be retarded to increase exhaust temp.) This starts the regeneration process. For just NOx, it just takes a few seconds. Then the engine shifts back to SCSI.

Regards
Sutripta

[vina]

Originally Posted by Sutripta

NO.
When the accumulator is full (detected by increasing NOx downstream of the accumulator), the engine enters regeneration mode.

Remember, the reason for excess NOx originally is the lean burn nature (excess O2) of SCSI. But this also means there are no reducing agents in the exhaust. (NOx has to be reduced.) So the normal primary cat cannot deal with the NOx.

For regeneration, the engine shifts to HCSI, and in fact a rich one. This introduces the reducing agents in the exhaust. (The ignition might also be retarded to increase exhaust temp.) This starts the regeneration process. For just NOx, it just takes a few seconds. Then the engine shifts back to SCSI.

Regards
Sutripta

Well in that case, how is it different from catcon in a diesel vehicle?

Even the catcon in a non-TSI petrol vehicle basically does the same thing -"accumulation" mode lasts much shorter though. The stoichiometric ratio is 14.7 on an average (taken over a few seconds), not all the time.


Also how does the ECU figure out that the catcon is full? Is it some conductivity measurement of the substrate?

And while we are at it, one other question - assuming sulphate formation happens on the accumulator - how would the recution happen then?

[Sutripta]

Originally Posted by vina

Well in that case, how is it different from catcon in a diesel vehicle?

Not really different. Running a diesel rich has other problems. So research moving in different directions, like NH3 for reduction.
This is a rapidly changing field.

Even the catcon in a non-TSI petrol vehicle basically does the same thing -"accumulation" mode lasts much shorter though. The stoichiometric ratio is 14.7 on an average (taken over a few seconds), not all the time.

Reduction, yes. Accumulate, release, reduce, no.

Also how does the ECU figure out that the catcon is full? Is it some conductivity measurement of the substrate?

NOx sensors downstream of the accumulator.

And while we are at it, one other question - assuming sulphate formation happens on the accumulator - how would the recution happen then?

Same process as Barium Nitrate regeneration. Except that happens at higher temp, for much longer. And (AFAIK), the SO2 produced is not treated. Only care being taken that H2S is not produced.

Regards
Sutripta

[thoma]

Originally Posted by Sutripta

For regeneration, the engine shifts to HCSI, and in fact a rich one. This introduces the reducing agents in the exhaust. (The ignition might also be retarded to increase exhaust temp.) This starts the regeneration process. For just NOx, it just takes a few seconds. Then the engine shifts back to SCSI.

Sorry for the layman-ish question. Can we read that for better emissions, the engine momentarily runs on richer mixture for the same load conditions? So, would there be a slight decrease in FE (and thus more emissions; might not be NOx) for better NOx emissions?

[antz.bin]

Originally Posted by thoma

Sorry for the layman-ish question. Can we read that for better emissions, the engine momentarily runs on richer mixture for the same load conditions? So, would there be a slight decrease in FE (and thus more emissions; might not be NOx) for better NOx emissions?

As far as my understanding goes, The car runs a mixture which is leaner by 60% than required for 95% of the time. And runs a slightly richer mixture for the rest of the 5% in regeneration mode. This is only for the low load + low throttle conditions. So regeneration mode is required only if you do not press the throttle at all for over 3-3.5 minutes. Or else, it will be taken care of by a 30 second burst at regular mixture (at greater throttle input).

[Neil.Bhujbal]

I hope people don't kill me after reading the below information

It also proves TSI, TSFI, FSI, CGI Engines are useless in India.
(By useless I mean the stratified charge technology and not direct injection which is a part of it.)

Yesterday in workshop I had a chance to service a C-200 CGI. When I took it up on ramp I was surprised to find a normal exhaust rather than a complicated one with 2 catalytic converters, 4 sensors, bypass pipe etc which we had studied about.

So to cut it all in short these are just normal direct injection petrol engines running normal AF ratios.
They don't run on stratified mode (crazy lean mode) for which they are actually designed.

Reason : low octane fuel , they need atleast 95 Ron fuel.

Countries which have high octane fuel available have these engines running what they are designed for.

Don't know about other manufacturers but Mercedes in India won't sell the direct injection petrol engines with the name CGI. They won't have the CGI logo on trunk.

And all these pages we were discussing how are various manufacturers compensating for bad fuel when running on stratified mode LOL