Injecting methanol really complicates the tuning process. Complete combustion (stoich) for gas is about 14.7 A/F. For methanol it is about 6.3. Methanol has less fuel energy than gas, but adds considerable quantities of oxygen. Adding, 10% methanol, to gas creates a new unknown stoich value somewhere in between, maybe closer to about 13.8...who knows? The oxygen sensor is primarily measuring the very, very small amount of remaining oxygen from the combustion process. A sensor calibrated for gas will read leaner once significant alcohol is injected (more oxygen is available). The issue is calibration. "How do you know exactly what the A/F accuracy is with this new fuel mix?" Unfortunately, you don't.
It gets even more complex when using a rising rate of alcohol injection. My SMC hardware starts at about 6 psi boost with 70 psi injection line pressure, and ramps up to 100 psi by 16 psi boost. So, now you have not only a new fuel mix, it is also changing. Trying to tune using conventional wisdom with target A/F values is a bucket of worms that may have no practical solution. It's even tougher, when there is no access to an AWD dyno.
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11-02-2004, 01:49 AM
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