[Diy_efi] Re: DIY-WB and methanol

Derek derek_obanion at yahoo.com
Sat Oct 12 17:29:32 GMT 2002


Reply to text by: Garfield Willis

> But think about what you're saying. You replaced up to half your petrol
> volume with a 50/50 mix of methanol (which has a stoich AFR of 6.5, well
> below half of petrol), and liquid water, which especially when expanded
> to water vapor in the exhaust is a MAJOR diluent of the total exhaust
> gas components (seriously dilutes the partial pressures of the things
> the O2 sensor is sensitive to), and yet is inert to the sensor. And
> there was no 'sudden jump' in the *indicated* AFR. I hope you understand
> what you're saying (or seeing).

Yes I do. I added enough 50/50 mix of methanol/water to allow a reduction of 20%
fuel from the injectors. That works out in terms of volume flow to be nearly the
amount of gasoline.

(6.45/14.7)*.5=21.9% (Meaning a 50/50 mix of meth/water has 21.9% of the fueling
capability as pure gasoline).

> Plus, I take it the last sentence above says that when you switch to
> pure methanol (total fuel stoich AFR now at more than HALF of petrol),
> you expect to see even "less inaccuracy"? Did I read that right? IOW,
> you're saying that if you switched from straight petrol, to a 50% 50/50
> mix of methanol+water, and didn't see much of a change in indicated AFR,
> then when you went to straight methanol, you'd expect even LESS of a
> change in indicated AFRs?

Less inaccuracy because as I understand it, it's the inert components that are
the real problem (IE water). All that water which was in the 50/50 mix is now
gone, replaced by a fuel.

I NEVER said you could use 50/50 meth/water as a primary fuel? Did you get that
impression? I'm spraying this stuff all supplemental, gasoline through the
injectors still does a majority of the WOT fueling duty. About 80-85% before,
60-70% when I start using pure methanol as the spray fluid.

On a pure methanol motor, widebands work fine, you just shoot for a .8-.85
lambda reading. On a pure gasoline motor, widebands work fine, you shoot for a
.8-.85 lambda reading. How should mixing the two change anything?

I hate the AFR numbers BTW, gets so confusing. Once you start thinking in lambda
you never want to go back (especially if you mix fuels like me). I'm getting
tired of explaning to people why you have to still shoot for about 12:1 reading
on their widebands with methanol, even though it has a stoich of 6.45:1. Because
that reading is just a translated lambda value. It been corrected for gasoline,
but doesn't actually tell you the ratios anymore once you mix fuels. A 6.45:1
mix on a methanol motor will display 14.7:1 on a wideband display set for
gasoline.



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