Effect of water injection on UEGO sensor
Effect of water injection on UEGO sensor
(OP)
We are making plans to set up an air cooled opposed 6 cylinder engine with digital electronic fuel control. As the target bmep is about 25 bar, the heat load on the engine exceeds the typical air cooling function, and we plan to use water injection to help cool the cylinder head and prevent detonation. (Some racers call the fluid ADI, but it does more than just prevent detonation.)
I am looking for advice from someone with experience using O2 sensor to help calibrate injector drive signal, and specifically the impact of water injection (upstream of intake valve) on the operation of the O2 sensor. Maximum water injection (at full power) is expected to be about 0.04 lbm water / lbm air.
Will this injection have an impact on the O2 sensor signal?
Once the fuel injectors are calibrated, we will switch the ADI from water to 50MW (50/50 water methanol (by weight)). But we will do the calibration work using just water, so that we do not introduce additional combustibles into the mix when considering O2 sensor feedback.
Thanks for your comments.
I am looking for advice from someone with experience using O2 sensor to help calibrate injector drive signal, and specifically the impact of water injection (upstream of intake valve) on the operation of the O2 sensor. Maximum water injection (at full power) is expected to be about 0.04 lbm water / lbm air.
Will this injection have an impact on the O2 sensor signal?
Once the fuel injectors are calibrated, we will switch the ADI from water to 50MW (50/50 water methanol (by weight)). But we will do the calibration work using just water, so that we do not introduce additional combustibles into the mix when considering O2 sensor feedback.
Thanks for your comments.





RE: Effect of water injection on UEGO sensor
RE: Effect of water injection on UEGO sensor
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Effect of water injection on UEGO sensor
RE: Effect of water injection on UEGO sensor
je suis charlie
RE: Effect of water injection on UEGO sensor
Of course the combustion itself is also affected by humidity, like any inert diluent. My experience is specifically with Otto cycle engines, so I can't speak for diesel; but we had to correct our combustion recipe for absolute humidity. So after correcting the UEGO signal, there were lookup tables for compensating spark timing, to normalize the start of combustion, and compensating target lambda, to normalize rate of heat release. The objective of all this was to normalize BSNOx, BMEP, and BSFC. It wasn't perfect, but a whole lot better than no correction.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Effect of water injection on UEGO sensor
je suis charlie
RE: Effect of water injection on UEGO sensor
Regarding humidity effects, what I can further tell you is that well qualified engineers at Cummins, using information from well qualified engineers at NGK, devised and implemented an ambient humidity correction algorithm for the UEGO sensor raw signal, as part of the air-fuel ratio control for the B-, C-, and L-Gas Plus on-highway products of the 2000's.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Effect of water injection on UEGO sensor
When the air/fuel mixture is rich, the reference cell produces a high Vs voltage (above 0.450 volts). The Precision Wideband Controller reacts to produce a pump current (Ipump) in one direction to consume the free fuel. The pump cell requires a "negative" current that goes from zero to about 2.0 milliamps when the air/fuel ratio is near 11:1.
When the air/fuel mixture is lean, the reference cell produces a low Vs (lower than 0.450 volts). The Precision Wideband Controller sends the pump current in the opposite direction to consume free oxygen. The pump cell requires a "positive" current that goes from zero up to 1.5 milliamps as the mixture becomes "free air".
When the air/fuel mixture is 14.7:1 (the stoichiometric ratio for gasoline), the pump cell requires no output current. Since the free oxygen or free fuel has been neutralized by the pump current, the Vs feedback signal goes to about 0.450 volts (the same as the Vref value).
Regarding humidity. It is absolutely true that humidity levels have an effect on ambient oxygen content and fuel rates will need to be adjusted if the desired AFR must be achieved. Water vapour in the combustion air is however a diluent - AFAIK lambda and UEGO sensors respond only to reactants (oxidation and reduction components).
If this is not correct and humidity does affect the sensor output, I would be interested to hear the mechanism. Perhaps the oxygen concentration in the "air-side" of the sensor has an effect?
je suis charlie
RE: Effect of water injection on UEGO sensor
But you could be onto something with the air side idea. At any rate, the effect is quite small, and unless you're splitting EPA emission hairs, probably can be ignored.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz