QuickSilver2002

I just thought about something and was wondering if anyone here could provide some insight. It is a little confusing so please read carfully before responding.

Regular gasoline has a stiochiometric value of about 14.7:1, but methanol has a stioch value of about 7:1. My understanding is that stiochiometric results in the most complete combustion where all carbon becomes CO2, all hydrogen becomes H20, and all sulfur becomes SO2 (so there should be very little 02 left floating around on its own).

So here is where my confusion begins. How exactly does a WB give you accurate readings when you are mixing two different fuels?

My basic understanding is that an Oxygen sensor determines 02 content by using special materials that have a varying resistance that is proportional the amount of 02 it is being exposed to. The Controller then determines what the A/F ratio is based on the amount of resistance it is seeing in the circuit.

I understand that the stiochiometric output voltage should be the same for all fuels (eg 2.5v), but what happens when you start mixing fuels?

I ask this because I’m starting to question what the right target A/F is when spraying methanol. I was able to run the the motor way lean the other night (by most standards) without any problems and I’m just starting to think that the 11.5/12.0 target might be wrong with methanol.

Here is what I’m thinking in my head. Let’s say you have two glasses/beakers. One has pure 02 and one has gasoline. They are setup with a perfect 12.0:1 (PE type) ratio. Now, you remove half the gasoline and replace it with methanol. What is the ratio now (still 12.0:1)? I know that running it through the motor would not result in 12:0:1 on the WB, but is the ratio still ideal?

Anyone have any useful information on this subject? I know I’m just missing something simple.

Blackbird

there is a calculation out there. I think Steve knows it. basically though from my understanding, yes you will be running richer than your wideband indicates. I probably shouldn't be so lazy but with my water alky I just shoot for 11.8 - 12.0:1 and call it a day. I may be giving up some power but I figure I rather run it rich as a measure of saftey.

QuickSilver2002

Yea, I used to run alky/water and I did not notice a big change in what A/F the car liked. Now I'm pushing quite a bit of pure meth and it seems to tolerate and like being much leaner. My motor actually had other issues in the past, so my data from the past is a little inconsistent. It is almost funny, you make one change to these motors and the tuning game starts all over again.

QuickSilver2002

Ok, I think I figured this out. I knew I was missing something simple.

The physical ratio that the WB reads is no longer accurate when mixing fuels, but it is a valid index for tuning.

If you have 50% fuel and 50% meth and get a reading of 12:0:1 on the wb, you are not physically putting in 12 parts air to 1 part fuel. But it is still a valid index to say you are running a few points rich.

S_J_H

Both methanol and gas can run good at about 20% rich. Methanol runs good even richer.
The wideband display is just calibrated to show the Vout as a AF ratio for gas. For instance-
2.5 volts = 14.7-1 for gas and 6.4 for alcohol.
1.7 volts = 11.0-1 for gas and 4.08 for alcohol.
Since both fuels run well around 20% rich there is no need to worry about the combined effect. I would keep it at the very least 20% rich , which will show as 12.2 on the display.
I've constantly read from all sources that methanol can be run very rich with little or no power loss. But run it lean and it tends to detonate badly.
I would not want to test that last statement for myself.
Start

White_Hawk

iTrader: (3)

Most of the GN guys tune their alchy systems with an EGT gauge. They dial it in on Gas, start pumping the alcohol, then add boost and timing until they get back to roughly the same EGT as they were on gas. They mostly use isopropyl, though, so i can't say for sure that procedure would work for methanol. You need a good EGT with memory, too, which will record the highest reading it sees.

-Geoff