[Diy_efi] DIY-WB and methanol

[Geddes, Brian J]

Good info.  What if we take the nitrous out the equation, and talk =
about
just injecting extra fuel of a type other than petrol?  Propane, =
methanol
and good old denatured alcohol seem to be the popular applications I've =
seen
floating around recently.  From an off-the-cuff-been-years-since-chem =
point
of view, it seems to me that propane (being a petroleum derivative) =
would
have a pretty minimal effect on readings.  Denatured alcohol and =
methanol
might muddy things up more, since they're not as "chemically similar".  =


I'm in the process of building a couple of DIY WB units, and currenly =
am
running propane injection at high boost with possible future plans for =
water
and/or alcohol.  I'm very curious to see where this discussion leads...

- Brian

> -----Original Message-----
> From: steve ravet [mailto:sravet at arm.com]
> Sent: Tuesday, October 08, 2002 1:54 PM
> To: diy_efi at diy-efi.org
> Subject: Re: [Diy_efi] DIY-WB and methanol
>=20
>=20
> steve ravet wrote:
> > > My question is fairly simple:  Will the DIY-WB provide=20
> accurate A/F ratio
> > > information when a mixture of gasoline and methanol is=20
> present, oxidized by
> > > nitrous oxide?
>=20
> Here's what I found in my Trash folder (there's more good info in =
that
> thread):
>=20
> Subject: Re:    [Efi332] Nitrous and WBO sensing
> Date:    Wed, 24 Jul 2002 16:45:19 -0700
> From:    Garfield Willis <garwillis at msn.com>
>=20
> The only good way to deal with questions like this is to=20
> understand the
> fundamentals about how the sensor "senses" AFR. Especially in the =
case
> of mere oxygenates (like N=B2O-NOS, which is just oxygen in a compact
> form, tied to some nitrogen; the nitrogen isn't combustible), it DOES
> seem like it should be intuitive that nothing is altered in the AFR
> sensing. After all, we're just adding more Os, and attempting=20
> to supply
> the correct amount of fuel corresponding to those added Os, right? So
> that's probly everyone's (including mine) intuition at first glance;
> it's not a different FUEL per se, we're still just running straight
> petrol, just that we're getting more "air" into the engine, and then
> adding more fuel, so the AFRs should still be "petrol" AFRs, right?
>=20
> Right, they *should*. And if our NTK sensors we all use to=20
> read AFR were
> a type that counted molecules of O2 and molecules of CxHy,=20
> and gave us a
> ratio, that would be that. Unfortunately, life isn't that simple, and
> the sensors we're stuck with at present don't work that way.
>=20
> The problem arises because our sensors only pick up "partial=20
> pressures"
> of the gases they're sensitive to, in the exhaust stream. That's why
> even mere diluents like water injection, have to be accounted and
> corrected for in use. Because they end up in the exhaust stream, and
> dilute the partial pressures of the "active ingredients" our sensors
> actually measure. Soooo ANYTHING that alters the assumed background
> constituents of the exhaust gas, upon which the sensor's calibration
> curve is based, will affect the AFR readings and produce errors.
>=20
> Some of you will already be saying, Geezus what a mess, I'm=20
> outta here.
> Too complicated. Yeah, I sympathize. Especially when none of the =
other
> AFR vendors have bothered to attempt to raise the level of=20
> consciousness
> on this key issue (remind you at all of those similar EBP issues? :)
>=20
> But for those intrepid enough to hang in there, here are the =
salients:
> in any combustion process, there are 3 components from our =
proformance
> standpoint. (1) Fuel, combustibles, hydrocarbons that burn, (2)
> oxygenates, molecules or partial molecules that contain=20
> oxygen that can
> feed the fire along with the O2 injested via inducted air, and (3)
> diluents, anything in the inducted or injested mix that is=20
> neither 1 or
> 2. Nitrogen in the air that's inducted is a diluent, atomized water
> inducted into the chambers is a diluent, and the nitrogen in=20
> NOS is also
> a diluent, because it ends up as elemental . Diluents are, well,
> diluents (or dilutents, not really a word, but you get the idea),
> because they're inert *to the chemistry of the combustion=20
> process*, but
> they may be either unavoidable, in the case of the 73%N=B2 in =
inducted
> atmospheric air, OR they may be advantageous directly, like=20
> water, as a
> coolant, or piggybacked onto an oxygenate, and thereby unavoidable, =
as
> in N=B2O/NOS. Actually, since NOS is in liquid form and cools on
> expansion, it's ALSO an advantageous coolant.
>=20
> OK, so got the taxonomy? Fuels, Oxygenates, Diluents. EVEN=20
> with straight
> petrol combustion, normally aspirated, all THREE are in play.=20
> The petrol
> is a straight fuel (usually :), the air is a mixture of oxygenates =
and
> diluents. They all get weighed going in, and coming out, and presto,
> AFR!  NOT...heh, they all go in, turn into gases and vapors, some of
> which our sensor is sensitive to, others not, and out they come in =
the
> exhaust tract.
>=20
> The calibration curve many are familiar with, for AFR vrs. Ip or Vout
> for these NTK sensors, is based on an ASSUMED ratio of all these
> byproducts ONLY for straight petrol combustion with ordinary earth
> *air*. IOW, that calibration curve is based on there being a certain
> percentage of Nitrogen in air (a mere diluent), and ALSO a certain
> percentage of h2o vapor present in the exhaust as a result of the
> combustion (so-called 'wet' exhaust gases), again a mere diluent.
>=20
> The reason these percentages of mere diluents is important=20
> isn't because
> the sensor is sensitive to them (it isn't), but because what=20
> the sensor
> IS going to be picking up is the partial pressures of the gases =
(H=B2,
> HC/VOC, CO, O2) that it is sensitive to, BUT these partial pressures
> will be 'diluted' or relative to the amount of inert gas components
> they're mixed with.
>=20
> To put this in perspective, let's say you plan to go one step further
> than water injection, and outdo all your buddies at the track; you're
> going to inject liquid nitrogen!! You've found nirvana and a way to
> store LN=B2, cheaper, easier, and lighter than water. You're out =
there
> tuning away with your AFR meter, wondering if the readings=20
> you'd expect
> with straight petrol will apply with your inert coolant=20
> injection. They
> WON'T! Why not, it's inert!? you say. And true it is, BUT you've just
> added an unexpected diluent into the exhaust stream, and your=20
> AFR sensor
> is going to see that as a decrease in the partial pressure of =
whatever
> gases it's sensing. You haven't changed the number of O2 molecules
> combining with your hydrocarbon molecules, and infact, as far as the
> *air* in AFR is concerned, you haven't even changed that!=20
> BUT, if you're
> running on the lean side of stoich, it's going to indicate richer =
than
> you really are, and if you're running on the rich side of stoich, =
your
> uncorrected AFR instrument is going to indicate you're leaner than =
you
> are.
>=20
> --=20
> Steve Ravet
> steve.ravet at arm.com
> ARM,Inc.
> www.arm.com
>=20
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://www.diy-efi.org/mailman/listinfo/diy_efi
>=20

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