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How Does a Lambda Sensor Work in a Common Rail Diesel

rapport25

Go Kart Champion
Location
Midlands
Hi Guys,

Have a read of this link.

Quote from
http://www.autospeed.com/cms/articl...Rail-Diesel-Engine-Management-Part-2&A=108105

Closed Loop Oxygen Sensor Control

As with petrol management systems, diesel management system use oxygen sensor closed loop control. However, in diesel systems a broadband oxygen sensor is used that is capable of measuring air/fuel ratios as lean as 60:1. This Universal Lambda Sensor (abbreviation in German: LSU) comprises a combination of a Nernst concentration cell and an oxygen pump cell.

Because the LSU signal output is a function of exhaust gas oxygen concentration and exhaust gas pressure, the sensor output is compensated for variations in exhaust gas pressure. The LSU sensor output also changes over time and to compensate for this, when the engine is in over-run conditions, comparison is made between the measured oxygen concentration of the exhaust gas and the expected output of the sensor if it were sensing fresh air.

Any difference is applied as a learned correction value.

Closed loop oxygen control is used for short- and long-term adaptation learning of the injected fuel quantity. This is especially important in limiting smoke output, where the measured exhaust gas oxygen is compared with a target value on a smoke limitation map. Oxygen sensor feedback is also used to determine whether the target exhaust gas recirculation is being achieved.

Rappy:cool:
 

mds1256

Passed Driver's Ed
Location
Durham
Thank you for stating how a lambda sensor works, I am sure I could have googled it myself, what is the point of this thread?
 

rapport25

Go Kart Champion
Location
Midlands
Thank you for stating how a lambda sensor works, I am sure I could have googled it myself, what is the point of this thread?

No worries :eek::eek:

If you follow my posts, you will see in another thread a debate on how the lambda sensor works. I was called foolish :mad:

I explained it worked the same as a petrol car. And was called foolish as my understanding was incorrect.

I didn't want to get into a debate, in fact showing that I was clearly correct. So I thought I would open a new thread, clearly showing what I had said was indeed factual.

Rappy:D
 

chrismc

Passed Driver's Ed
No worries :eek::eek:

If you follow my posts, you will see in another thread a debate on how the lambda sensor works. I was called foolish :mad:

I explained it worked the same as a petrol car. And was called foolish as my understanding was incorrect.

I didn't want to get into a debate, in fact showing that I was clearly correct. So I thought I would open a new thread, clearly showing what I had said was indeed factual.

Rappy:D

Oh dear.

There is/was no debate on how a Lambda works.

I know how it works, whereas you are convinced a tuning box will end up reverting to reduced/stock output which is completely incorrect. That is the 'could appear foolish' bit.

Please see what you wrote below:

'So a lambda sensor constantly measures the fuel, air mixtute & boost'. By adding a tuning box it fools all these variables. But the Lambda sensor will send these high readings back to the ecu & it will readjust to over come the tuning box.'


As per your link above it is referring to 'Closed loop' control. Another term you should google along with Open Loop- specifically on a modern Diesel engine.

This should then help you understand why the tuning box won't cause power to tail off over time.

How many posts exist on the web from disgruntled DTUK owners whose cars have returned to stock power? I can't find any
 
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MrPotatoHead1

Passed Driver's Ed
Location
Northumberland
 

rapport25

Go Kart Champion
Location
Midlands

Nothing to see here, move along:D.

Being told by the subject matter expert that the GTD Lambda sensor is open loop & infact it's closed loop the same as the petrol:rolleyes::rolleyes:

Just wanted clarify I was indeed not foolish:p.

I will no longer post on his threads, as I cant be bothered.

I have a remap that runs a tweaked closed loop system. Mr "Subject Matter Expert" runs a tuning box that is fighting the standard factory settings.

The End!!!

Rappy:cool:
 

chrismc

Passed Driver's Ed
Nothing to see here, move along:D.

Being told by the subject matter expert that the GTD Lambda sensor is open loop & infact it's closed loop the same as the petrol:rolleyes::rolleyes:

Just wanted clarify I was indeed not foolish:p.

I will no longer post on his threads, as I cant be bothered.

I have a remap that runs a tweaked closed loop system. Mr "Subject Matter Expert" runs a tuning box that is fighting the standard factory settings.

The End!!!

Rappy:cool:

Clueless!!��

'the GTD runs open loop Lambda' Where exactly have I said that???

Stick to being happy with your remap rather than trying to lecture other users on the technical aspects & making foolish claims...
 
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rapport25

Go Kart Champion
Location
Midlands
Clueless!!��

'the GTD runs open loop Lambda' Where exactly have I said that???

Stick to being happy with your remap rather than trying to lecture other users on the technical aspects & making foolish claims...

Post 26 in your thread....

I quote I'm well aware how a Lambda works Rappy.

It doesn't measure fuel, air mix & boost.

What it does do is sense oxygen content within the gas stream. Crucially on a modern diesel, unlike a petrol engine Lambda it isn't used to maintain a given air/fuel ratio in closed loop.

:rolleyes::rolleyes:
 

chrismc

Passed Driver's Ed
Post 26 in your thread....

I quote I'm well aware how a Lambda works Rappy.

It doesn't measure fuel, air mix & boost.

What it does do is sense oxygen content within the gas stream. Crucially on a modern diesel, unlike a petrol engine Lambda it isn't used to maintain a given air/fuel ratio in closed loop.

:rolleyes::rolleyes:

I.E WHILST it's in closed loop it doesn't aim to maintain a given AFR (as per a petrol lambda)

NOT it doesn't work in closed loop whatsoever!!!!!

You have totally misinterpreted what has been written. I have absolutely NOT written 'the GTD runs open loop' so please do not quote me as having done so.
 
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fastlane1

Passed Driver's Ed
Location
Sweden
A Lambda sensor for a diesel must work the same way as it does in a petrol engine? or am I so clueless when it comes to diesels?

In a petrol car A Lambda measures air mixture to see if it need too compensate the fuel air ratio. it does not read boost. It is usually one wide band lambda before catalysator and one small band after the catalysator. the car can operate in open loop (using MAF/MAP whatever sensor) or in some driving situation closed loop and only work with feed back from the lambda readings.

In an NA car you will see around lambda 1 when you cruse in same speed,letting of the gas pedal or at stand still and maybe lambda ~0,85-0,88 at full gas. Turbo cars usually atleast tuned goes lower (more fuel) at full gas.

I know Diesels have a little bit different lambda table but not so mutch.

I guess without better knowledge about diesels that its do exactly the same thing only we have a DPF also.
 

chrismc

Passed Driver's Ed
Correct. A Lambda does not 'read' boost in any application. There is a boost pressure sensor that does. Rappy is/was incorrect.

I don't know how modern we are talking here but generally petrol applications use 2 lambdas- both narrowband. Pre- cat aims to keep Lambda 1 (14.7:1 AFR) when in closed loop (idle/fixed throttle cruising) then goes to open loop when accelerating/heavy demand.

The post cat sensor is there to monitor the cat is working efficiently.

With the diesel, it uses a wideband probe as a derv has a much wider variation of Air/Fuel ratios that the probe 'sees' (a derv generally runs much leaner than petrol.

This allows for very fine tuning of injector durations during fixed & light throttle conditions. This is where the ECU will sense lambda readings & can 'fine tune' injector durations to suit. Modern diesel injectors inject in 'stages' for a better combustion process.

With a diesel much of this Lambda control is all about NoX & smoke emission control as opposed to constantly striving for Lambda 1 (stoichiometric) as on a petrol.

When under high load a diesel, same as petrol, will disregard lambda, (open loop) & use look up 'maps' for fuelling (combined with many other parameters). These are the maps that are re-written (adjusted) on remapped cars!

To make more power on a diesel, more fuel is required (& is combined with more boost) to produce a bigger bang. This is fact.

As Lambda is only really used on part/fixed throttle it doesn't see the 'extra' fuel under heavy load that contributes to the extra power!!!

This is why a mapped (or tuning box) car WILL NOT suffer a reduction in power due to Lambda readings. Rappy was wrong in his understanding.

Apologies for long-winded explanation but hope this helps explain!
 
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