Quote:
Originally Posted by XfireZ51
A 10% ethanol gasoline blend drops stoich to ~ 14.3:1. That means you need a richer mixture to equal the same energy available from a 100% gasoline mixture. I change the Stoich number in the calibration. The ECM will use that to calc the pulsewidth required to achieve that. So, if I use straight gasoline while leaving the calibration at a 14.3 stoich, in closed loop the BLM will be based on achieving a 14.3 AFR but in fact motor will run slightly rich. There's nothing "hard-wired" about 14.7 AFR. That's why I can manipulate the O2 sensor voltages and basically re-define what the ECM considers a stoich condition.
|
Excellent explaination, Dom. I totally "get" what you've said and how you're manipulating the ECM to accomdate the 14.3:1.
(Looking forward to your "101" presentation at BG!)
Then the remaining question has to do with the readout of the wideband instrument itself when a % of oxygenated fuel (ethanol) is added:
Fact: Measuring exhaust gas content IS NOT a direct measurement of the actual air and fuel entering the motor! That (indirect) method for AFR reading is derived - estimated based on oxygen levels in the exhaust: two separte things - actual AFR and AFR "predicted", but based on other measurements.
So, with respect to exhaust gas analysis, it comes down to the truth or not of this simple statement:
Is the readout of the wideband exhaust sensors the same for a given oxygen % in the exhaust gasses, regardless of % of alcohol in the fuel?
If the answer is YES, then the next question is:
Will adding alcohol fueling to result in an AFR previously established with gasoline IN FACT result in a ACTUAL AFR comiserate with the alcohol percentage? In other words if the AFR was 14.7 on gasoline, will it now actually be approx 14.3 (using your number) even tho the wideband sensor is reading 14.7:1?
If that is true, then to set the actual fueling AFR in the ECM, to get an ACTUAL (say) 14.3:1 at the injectors, the same exhaust gas analysis wideband rig would have to display the original (say) 14.7:1 by indirect measurement, theoretically.
Granted, actual AFR might eventually need to deviate to accomdate other factors, e.g., water content, vapor pressure, etc . Case in point, the stoich for 100% gasoline might be 14.7:1 compared to 100% ethanol that is aprox. 9.1:1. This being the case, the 10% alcohol AFR calculates closer to 14.14, but conventional indications are ≈14.2 or 14.3 might work better.
(For a .54 AFR correction in closed loop, I suppose the ECM just handles it, no?)
Bottom line:
I'm pretty sure that if I use a wideband monitor and establish a particular AFR using some combination of pure gasoline or a mix (likely), that if for some reason the (alcohol) % changes, that tweaking my ECM's fueling to re-establish the original AFR measurement, that the new ACTUAL AFR into the motor will be essentially correct (allowing for minor tweaks, depending on other factors).
If I'm wrong with reguard to the actual AFR when using a wideband, then something else is afoot that I'd like to learn about.
P.
PS: Gotta run...no time to proof...will do later.