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I must have stumped Bosch - O2 question.

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turboice

turboice

Automotive
Oct 1, 2003
27
I called Bosch and posed this question a while ago. The tech said it was interesting and since he didn't have an answer he would make sure they come up with one and get back to me in a few days. Not one to nag it has been a few months now.

Anyway to the question:

What would the expected impact be on a WBO2 reading from the injection of around 1% liquid water (leaving 99% as the normal air/fuel mixture) in the induction charge?

Would the error of the AFR calculation be of a magnitude of less than 0.1 AFR or would it be sufficient to completely invalidate the AFR reading?

I am not sure how to get to the effect, but the answer is of moderate importance to me since I discuss end result AFRs of tuning with water injection. I don't tune to a particular AFR (tuning to the maximum whp which happens to be between 12:1 and 13:1 AFR on all engines I have tuned) with water injection but I do monitor the resulting readings.

I was accused once that the AFR readings were completely invalid while I believe that if there is any error it is of a magnitude of less than 0.1 AFR.

Ed.
 
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Talk to Robert Schrader at Bridge Analyzers in Alameda Ca.
He can give you more info about a/f ratios, catalysts, and sensors than you will probably want to hear.
 
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Thank you Robert Schrader has been very kind and thorough in taking the time to respond and though not a specific definitive answer certainly has increased my understanding. As soon as I can absorb it sufficiently to summarize my understanding of his response I will post those thoughts.

Ed.
 
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The addition of water to the inlet shouldn't effect the lambda meter reading as it essentially measures free O2 not AFR (the lambda:AFR relationship changes depending on composition of the AFR components). As H2O is inert and provides no 'new' 02 to the system the lambda (rather than AFR) reading will still be correct. It's a bit confusing to mix up AFR and lambda as they are based on a different system of calculation, AFR is based on mass air(i.e. anything that isn't H or C based)/mass fuel (i.e. anything that isn't N2, O2, CO2, etc....) whereas lambda is a relationship between O2, H and C (and is therefore idependant of additional diluents such as H2O, CO2 etc...)
 
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I agree it doesn't change AFR - however the bosch wide band sensor is a lambda sensor and it is affected by partial pressures. The introduction of additional steam will dilute the partial pressures it senses. In effect the addtional steam will make the sensor think the mix is closer to 1.0 and the sensor reader as a result will read a closer to stoich AFR due to the calibration of the reader to the sensor.

At least this is my understanding based on my discussions with Bosch an Robert Schrader (who is immensely familar with and informative about lambda topics as toytech pointed out, if anyone ever needs to talk to someone on those topics).

Ed.
 
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Just to clarify everyone I have contacted about this agrees there would be an error unless the sensor reader was calibrated against a gas analyzer - but they also can not estimate for me what the error would be again unless compared against a gas analyzer.

Ed.
 
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Considering that water vapor displaces oxygen, I believe those who say that the reading will be in error. It is important to know the partial pressure for all gasses during calibration. This partial pressure calculation is skewed by the itroduction of water. I can't say how much as I would be a liar to tell you I know A: how to measure it B: how to do the maths

I would refer you to the document below however. Bruce is a genius and has explained his concerns quite well in the pdf. If not an outright answer to your question, perhaps it would put your mind at ease to know that your thoughts and methods (tuning for max power and use the O2 readings as a guide only) are validated by others?



Let us know if you ever hear back from the Bosch guys on this subject!

Craig
 
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