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Paul Workman · 03-03-2012

Wide band sensors: gasoline vs. alcohol =

The question comes up when ethanol is introduced to the fuel, and what accomodation if any is necessary, far as AF reading goes...

Down to cases:

Ethanol is oxygenated, and therefore requires less air to burn the fuel, i.e., given the "stoich" for gasoline is 14.7 parts air to 1 part fuel (14.7:1) , and for ethanol it is 9.1:1.

The O2 sensors measure free oxygen percentage in the exhaust gas (as I understand it). The oxygen is detected by the wideband sensor and then electronically analyzed and interpreted by a processor before being displayed as the AF ratio.

The thing making me

is that the wideband O2 sensor is an indirect reading; measuring O2 level in the exhaust, and not the actual air volume entering the engine. Adding or subtracting gasoline will result in a difference in the exhaust O2 %, which eventually results in an AF value readout - but based on gasoline fuel calibration, methinks.

But, suppose we were to switch the wideband sensor over to an exhaust pipe of a motor running on pure ethanol. Would the proper 9.1:1 (actual) AF mixture going into the engine be interpreted by the same exhaust O2% wideband equipment as a 14.7:1??

I think maybe so (based on what I think I know about the wideband sensors and their attendant processors/calibration). Put another way, the O2 percentage in the exhaust gas would have to result in a reading of 14.7:1 in order for the actual alcohol 9.1:1 stoich to be correct when interpreted by a wideband exhaust sensor calibrated for gasoline...NO?

One of you automotive engineering types prolly know, huh?

P.

03-03-2012	#1
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	stoichiometric vs. AF sensors Wide band sensors: gasoline vs. alcohol = The question comes up when ethanol is introduced to the fuel, and what accomodation if any is necessary, far as AF reading goes... Down to cases: Ethanol is oxygenated, and therefore requires less air to burn the fuel, i.e., given the "stoich" for gasoline is 14.7 parts air to 1 part fuel (14.7:1) , and for ethanol it is 9.1:1. The O2 sensors measure free oxygen percentage in the exhaust gas (as I understand it). The oxygen is detected by the wideband sensor and then electronically analyzed and interpreted by a processor before being displayed as the AF ratio. The thing making me is that the wideband O2 sensor is an indirect reading; measuring O2 level in the exhaust, and not the actual air volume entering the engine. Adding or subtracting gasoline will result in a difference in the exhaust O2 %, which eventually results in an AF value readout - but based on gasoline fuel calibration, methinks. But, suppose we were to switch the wideband sensor over to an exhaust pipe of a motor running on pure ethanol. Would the proper 9.1:1 (actual) AF mixture going into the engine be interpreted by the same exhaust O2% wideband equipment as a 14.7:1?? I think maybe so (based on what I think I know about the wideband sensors and their attendant processors/calibration). Put another way, the O2 percentage in the exhaust gas would have to result in a reading of 14.7:1 in order for the actual alcohol 9.1:1 stoich to be correct when interpreted by a wideband exhaust sensor calibrated for gasoline...NO? One of you automotive engineering types prolly know, huh? P. Last edited by Paul Workman; 03-03-2012 at 08:46 AM.