Propane/water/alcohol injection and O2 sensors

[Axel Rietschin]

Joel,

It's not like your exhaust will suddenly be freezing cold, more like it will
be 1000C instead of 1100C, still warm enough to fry a sensor and a cat or
two. By the way, the water to fuel ratio might be around 1:10 or 1:5, at the
end this is not so much water.

--Axel

----- Original Message -----
From: "Eck, Joel" <Joel.Eck at COMPAQ.com>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, April 09, 2002 5:23 PM
Subject: RE: Propane/water/alcohol injection and O2 sensors


>
> I understand the desire to inject water in an attempt to stave off
detonation, especially under high boost, advanced timing, etc. However,
something bothers me about it.
>
> 1. If the water vapor cools the exhaust gas temps, then how bad (overall
bad, that is) will that be for the whole combination? By cooling the
exhaust, you are inhibiting the O2 sensor from reaching it needed
temperature (unless you're using a heated one, and then, does the cooling
effect of the water vapor then pose any problem to the actual heating of the
sensor?), so will the O2 sensor read right?
> 2. Also, the cooling of the exhaust gases will keep the cat from reaching
its proper temps also, so how will that be affected?
> 3. On top of all that, I've also been told that for optimal performance of
the exhaust system, you want to keep the temperature of the exhaust gases as
high as possible; otherwise, the gases (somewhat) condense, thereby flowing
through the tubing slower and creating more backpressure. By cooling the
gases indirectly with the water vapor's presence, does this mean that one
would end up with more backpressure by virtue of using the water injection
so they could tweak the system a little beyond what they would normally feel
safe with, and, does the benefit of the added power from not backing off the
timing or boost just a little outweigh the detriment of the added
backpressure?
>
>
> -----Original Message-----
> From: Garfield Willis [mailto:garwillis at msn.com]
> Sent: Sunday, April 07, 2002 3:11 PM
> To: diy_efi at diy-efi.org
> Subject: Re: Propane/water/alcohol injection and O2 sensors
>
>
> On Fri, 29 Mar 2002 11:37:27 -0800, "Geddes, Brian J"
<brian.j.geddes at intel.com>
> wrote:
>
> >I'm contemplating a propane injection system for my car, but don't know
how
> >O2 sensors (Wideband and standard) will react to the presence of propane
in
> >the exhaust mixture.  Will a gasoline/propane mix influency the
> >accuracy/lifespan of O2 sensors?  I have the same concerns about
> >water/alcohol injection and the O2 sensors.  Any experience or theories
> >here?
>
> No problem with either propane or alcohol, you will just have to
understand the
> difference in AFRs you see, since the stoich AFR value of these fuels is
of
> course different from petrol. Indeed, the NTK WBO2 sensor currently in
vogue is
> also widely used in natural gas furnace combustion monitoring. So no,
these
> fuels inNof themselves don't pose a hazard to lifespan; they are both
> non-contaminating to the sensor. Also, I doubt if running either of them
> continuously on the rich side is any more wearing on them than the same
done
> with petrol. Long-term rich running does *age* these sensors faster than
> near-stoich running, which is why in racing & proformance tuning (unlike
the
> original OEM usage), you DO need a way to track this aging.
>
> But another thing about your question puzzles me; you ask "will a
petrol/propane
> mix influence ...?". It's the word "mix" I'm wondering about; I'm going to
> assume you just mean alternating between these fuels? I trust you don't
mean
> actual mixing of petrol & propane as a compound fuel? Or do you? Inquiring
minds
> wanna know.
>
> Water injection is a bit of a different animal (in a way), since altho
it's not
> a fuel that's going to change your stoich AFR values because of different
> combustion properties, it WILL affect the off-stoich AFR values simply
because
> now significantly increased amounts of water vapor in the exhaust affects
the
> partial pressures of all the other combustion byproducts. And it's the
partial
> pressures of mostly O2, CO, & HC that these sensors are actually sensing.
In
> fact, whenever pro people do gas calibrations, they will either create a
"wet"
> testgas mixture (using a thing called a "bubbler"), OR use a "dry" testgas
> mixture & adjust for the absence of normal exhaust gas water vapor (a
normal
> product of combustion but often not included in testgas formulation, for
obvious
> reasons). This is the same sort of issue, except that NOW you're really
adding
> prodigious amounts of water vapor beyond just the normal products of
combustion.
> BTW, it's not water *vapor* that's a hazard for the WBO2s, but
*liquid-phase*
> water, which can shock-cool the sensor elements or heater, and cause them
to
> crack.
>
> The stoichiometric calcs to include the effect of added moles of water
vapor in
> the overall products of combustion, to correct your measured AFRs, isn't
all
> that involved, but "beyond the scope of this post", sotaspeak. You may
even be
> able to find a chemistry exercise or two on the net that shows these
calcs. Just
> do a search on "stoichiometry" and "vapor" or some such. There's actually
a ton
> of good stuff online regarding stoichiometry, if you're really curious
about all
> this (ask me how I know :). I'm hoping to get a whitepaper written up for
our
> website that goes thru these exercises, including alternate fuels, but
judging
> by how I'm doing so far on the rest of the site, I wouldn't want to
suggest
> anyone hold their breath. :)
>
> All that said, I have to interject (ahem :), I'd personally be VERY
interested
> in monitoring the EGTs when it came to water injection. Increasing the
thermal
> capacity of your engine is primarily what you're after with H2O injection,
so
> seeing these effects first-hand via EGT measurement would be *must-have*
> sensing, IMO.
>
> HTH,
> Gar Willis
> Principal Engineer (actual engineer, not make-believe/fairy-tale engineer)
> EGOR Techno
> www.egortech.com
>
> ----- End of forwarded message from owner-diy_efi at diy-efi.org -----
> --------------------------------------------------------------------------
--
> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the
quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org
>
> --------------------------------------------------------------------------
--
> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the
quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org
>

----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org