air fuel ration petrol and lpg

Interesting question!
I've an old Paj, running 100% of the time on LPG, open loop.

Your O2 sensor causes the ECU to make the AFR stoich, which is around 14.7 for petrol and 15.8 for LPG.

So your gadget reading out the AFR is actually looking at the output voltage of the O2 sensor and interprets an average of 0.45V as stoich. The voltage will actually swing rapidly between low and high (0 to 1.1V max), and if the average voltage is >0.45 the ECU will interpret this as rich and vice versa.

Since it's a closed loop system, the ECU will always try and maintain a 0.45V reading from the O2 sensor, regardless which fuel type is involved. But maybe your ECU is tuned for a slightly rich burn for LPG (>0.45 from the O2 sensor) which would show up as a lower AFR on your gadget, when on LPG.

Best regards, Peter

There we go, AFR 14.7 for both should make the mix stoich in both situations (although the real AFR for LPG will still be 15.8, it's just reported as 14.7 because you can't tell your gadget to display AFR for LPG and petrol differently I guess?)

I don't know if there would be anything to be gained by tweaking the AFR up or down for LPG?
From memory, I think it's better to err at the rich side because LPG lean burn is quite hot with a very quick flame front?
Maybe someone with a bit more LPG tuning experience will reply to this...

Best regards, Peter

NFI :-)

My head hurts.


Cheers
Glenn

Troppy

You were supposed to say that you can shift the reading sideways by applying a laplace transform in the time domain - effectively by adding a 100ms offset delay after the 02 sensor swings down - but just before it drops below 150 millivolts in practise.