Lambda Reading off set by Exhaust pressure

[AbbeyMS]

We know the Link Can lambda when used with a exhaust pressure sensor (when lambda sensor is fitted in between engine and turbo) does anyone know the offset to the lambda values in relation to measured back pressure.

Thanks

[stammykins]

Not sure if this will help too much, but each lambda sensor has it's own pressure curve. There is some reading here that may help. Basically, you need to get the curve for your particular sensor to make a compensation map.

[dx4picco]

8 hours ago, AbbeyMS said:

We know the Link Can lambda when used with a exhaust pressure sensor (when lambda sensor is fitted in between engine and turbo) does anyone know the offset to the lambda values in relation to measured back pressure.

Thanks

I believe that the beauty of the can lambda is that this correction is made automaticaly as long as you have a sensor that has the exhaust pressure function.

The can directly sends it to the can lambda and correction is made

[AbbeyMS]

46 minutes ago, stammykins said:

Not sure if this will help too much, but each lambda sensor has it's own pressure curve. There is some reading here that may help. Basically, you need to get the curve for your particular sensor to make a compensation map.

Interesting reading thanks

 

 

12 minutes ago, dx4picco said:

I believe that the beauty of the can lambda is that this correction is made automaticaly as long as you have a sensor that has the exhaust pressure function.

The can directly sends it to the can lambda and correction is made

Yes this is good , I am looking for data that tells us what exhaust back pressure does to Lambda readings

 

[Adamw]

The pressure compensation is non-linear and applied to the pump current before conversion to lambda (also non-linear) so it is a fairly complex relationship, generally done with look up tables.  I suspect that RBR calulator linked above uses some simplified equation as it seems to give very optimistic results for the NTK sensor.  They are typically about 4 x more sensitive to pressure than the LSU4.9 in my experience. 

For the LSU4.9 there are a few slight variations of the pressure compensation curve but this is the one that is generally used from what I have seen:

So a couple of examples (not properly calculated, just eyeballed from graphs):

Observed lambda measured with un-compensated meter = 0.80.

If exhaust pressure was 150kpa absolute when measurement was taken then the actual lambda would have been about 0.81

If exhaust pressure was 250kpa absolute then actual lambda would be about 0.83