wideband A/F with alcohol injection

[EclipseTurbo]

Anyone really given thought about what the A/F mean when you run a mixture of gasoline and alcohol together?

I mean, gasoline stoich at 14.7:1 and methanol stoich at 6.4:1

so if a wideband reads 11:1 from a car running alky injection, what the hell does it really mean? Does it mean maybe the gas is running rich and alky is running lean?

 

[bruce]

Originally posted by EclipseTurbo
Anyone really given thought about what the A/F mean when you run a mixture of gasoline and alcohol together?

I mean, gasoline stoich at 14.7:1 and methanol stoich at 6.4:1

so if a wideband reads 11:1 from a car running alky injection, what the hell does it really mean? Does it mean maybe the gas is running rich and alky is running lean?

A WB reads O2 content.
The calibration normally used is for reading gasoline. Run some other fuel, and then you need to refer that chemistry. Run a combination fuel, and then you have to figure out what the new Stoich Ratio, really is.

If 2.5v output on a WB is stoich, then 2.5 is stoich for whatever fuel your running. So when you run mixture fuels, you just have to ignore the ratios involved, and look to how far from Stoich you are.

An easy trap to fall into is tuning to get a AFR rather then what the engine runs best with. It's a slight difference, but critical.

 

[Razor]

Trick is to maintain stable AFR while spraying the medium, and use an EGT meter to montor engine temps as to your tune. EGT doesnt care what is being used, it only reports temp.

Example, if you run 11.5:1 AFR on gasoline and as soon as the alky sprays you drop to 9.0:1 then obviously there is a problem with the amount being sprayed.

Whereas if you kept 11.5:1 AFR throughout your RPM band with or without alky..then your a lot closer than the 9.0:1 run. this is the inherent problem with injection systems that spray "X" volume at a certain boost level. Once you hit "X" PSI and the system turns on, it dumps fuel into the motor cuasing the major drop in AFR.

I do have a customer with a WB O2 on a SC 383 SBC and he's able to keep flat 11.7:1 AFR throughout his entire boost curve using the progressive. Maybe on alky the tune should be lower, and 11:7 may be lean.. but if the motor is happy and doesnt knock..EGT's are not through the roof.. and he's happy..what else is there? Yes there is tuning involved..

My .02