Hi Norbs,
Yes, I know it's confusing when you are thinking in AFR. For people thinking in Lambda it's crystal clear.
The LM-1, like all widebands, measures Lambda, not AFR. For display purposes it then multiplies the measured Lambda value with the programmed AFR value. On many widebands, that multiplier is fixed at 14.7. In the LM-1 it's programmable.
For example:
Assume you tuned your engine to 0.85 Lambda. That would be 12.5 gasoline AFR (0.85 * 14.7 = 12.5). This is 15% rich. If you are running blended fuel, the engine will still produce max power at 15% rich, independent of the fuel. But, because the fuel has a lower stoich value (14.13) you need more of it to get to that 15% rich operation. If you leave the AFR multiplier at 14.7 for stoich, 15% rich from 14.7 is still 12.5. So, if your engine is running 15% rich with the blended fuel, the AFR displayed would still be 12.5 (0.85 * 14.7 = 12.5).
Only if you reprogrammed the AFR multiplier to 14.1, 15% rich would now be 12, not 12.5.
If you had your fuel maps set all correctly to run a perfect 12.5 on straight gasoline, blended fuel would now show a leaner AFR (~13) and Lambda. The reason is that there's not enough fuel to get to 15% rich because lower stoich AFR means more fuel for a certain richness %.
All this means is that if you don't care about the stoich AFR value (for mass flow calculations for example), leave it alone and tune to the SAME AFR as with unblended fuel. Alternatively, screw the entire AFR metric and use Lambda.
Hope I did not confuse you more. :biggrin:
BTW: In closed loop operation (wether WB or narrowband) you don't have to worry about it, as the computer targets a certain Lambda and increases the fuel flow to reach it. That's true even IF you have programmed a target AFR, because that is again just Lambda multiplied with a stoich factor.
Regards,
Klaus
