Chemical warfare

[Chris Conlon]

Hi everyone,

Greg wrote:

> Here I thought that only code heads did lots of caffeine and
> worked real late!!

Ahh, but these days writing code is what pays the bills around
here. Though come to think of it, late nights have always been
a way of life. So here's my Xmas contribution.


[reasons for power increase due to water injection]
> Don't be forgetting about the increase in net output due to
> absorbtion of heat (and consequent reduction in work done) during
> the compression stroke.

This is something I can understand but that I don't really have a good
feel for. I have to admit I've been very lazy about all this and
haven't done any of the calculations I should be doing. Yet. My
current hope is that high compression work is not a *terribly* bad
thing *as long as* your cylinder is insulated well enough that it
turns into expansion work a moment later, and not into heat lost
into the water jacket.

> In the real world, this means
> that the first thing to condense on a too cool engine surface will
> be rather strongly concentrated, highly corrosive acids. A seriously
> water injected engine might burn enough cooler to justify running a
> significantly hotter thermostat in order to help avoid acid
> condensation!

Hmm. I think sulfuric & sufurous acids will be the bigger problem
as far as water injection goes. Lean, hot conditions favor NOx,
and N2O5 + water is how you make nitric acid. Cooler, richer
conditions disfavor NOx, giving you less acids. (Also the BP of
nitric is way lower than sulfuric.) The path for sulfuric and/or
sulfurous acid production is similar, except that it depends
absolutely on the availability of sulfur in the gas, and less so
on lean conditions, and still less on hot conditions. I had read
that GDI was currently impractical on USA pump gas due to high
levels of sulfur... but have no real knowledge of this subject.

> I SUSPECT that this phenomenon may be the real root of corrosion
> troubles in alky motors, too.

Actually, I had meant to ask if anyone knew the exact chemical
path by which alcohols were so corrosive to engine parts. I have
some vague guesses, but would like to have a real answer.


Helene V. wrote:

> There is also something I have been wondering, what about the effects
> of minerals in water like Ca and Na? You would have to use distilled
> or at least demineralized water, right?

While I'm sure some people run tap water all day long, personally I'd
stick with distilled. It's still way cheaper than the gas that the
car uses in the same amount of time. I think Greg pointed out that
Ca and Mg will be the big troublemakers, their salts are less soluble
than Na or K. Here also sulfuric is more of a problem than nitric,
sulfates are often way less soluble than their nitrate equivalents.


> Well here I must say that just as with NOx, it is a question of
> whether you want to have performance "on motor" or "anything goes".
> It flatters my ego more to kick a** on motor and controllers alone
> because I know I can do it again and again provided I keep my car
> in good tune, whereas this guy is a bit embarrassed when the bottle
> peters out or the mixture

For me it's less about ego and more about afforability and
sustainability, and to a lesser extent crusing range. I want power
that the engine can sustain more or less continuously (assuming
infintite fuel and other consumables), and I want those consumables
to be relatively afforable, say no more than the 2x cost per mile
of 93 octane pump gas. I have nitrous, and it's fine for what it is,
but it doesn't fit this description. Water injection, OTOH, is fine
for me because I'm prepared to treat it just like gas, and fill up
every so often. But of course, to each their own.


Tom Sharpe wrote:

> I agree 100%.I would like to see a discussion of ammonium nitrate
> (fertilizer) and ??? injection. Would methanol/ethanol disolve it?
> Anything else??

I have some experience with liquid and semisolid explosives using ammonium
nitrate (AN) as one of the components. While I'm not gonna say it wouldn't
work (cos I'm sure it could be made to work) I'll point out a couple
engineering details to consider. AN loves water, and dissolves incredibly
well in it, but is much less soluble in nonpolar stuff. Solubility in
MeOH or EtOH is so variable with temp that (as a field technique) we
would use methanol and ice (or dry ice) to crudely recrystallize AN from
all the mud, etc, that it comes mixed with in fertilizer grade AN prills.
The blending octane is probably very low, but you probably can't use
too much anyway. IMHO it's pretty likely to deposit AN powder residue in
various places in your injection nozzles & engine, this will be "bad" if
it's let to sit as it will suck water from the air, form metal nitrates,
release ammonia, etc.


Robert Harris wrote:

> Acetone is always an option.

What's the octane number of acetone? I'd be scared that it, like most
small ketones and aldehydes, would be a strong pro-oxidant and prone
to detonation and/or doing nasty things to the insides of your fuel
system. But hey, simple theories are so often wrong.


Greg wrote:

> >Now if water/methanol formed a more stable azeotrope, in some ratio,
> >that might give a higher heat of vaporization than either one alone.
>
> Guessing here, but I bet on them forming the more stable azeotrope--it
> takes an awfully big (tall) tower to completely dry out alky, and alky and
> H2O have a really high affinity for each other--which is part of why
> methanol is such a good fuel tank dryer outer.

Yeah, I was thinking of the relative difficulty of drying out small
alcohols. (Instead of looking things up like I should). I'm not sure
you *want* such a high heat of vaporization unless you really do need
the charge cooling. Think the other way - imagine if you could inject
liquid freon or particulate dry ice into the cylinder. Since with those
materials you would not have to pay the high heat cost of vaporizing
water, there'd be more heat "left over" to raise the pressure. But of
course water has the 2 unbeatable advantages of being cheap, and not
requiring more oxygen to maintain stoich. (Since, except for a
monopropellant setup, oxygen is still one of the limits on generating
heat and thus power.)

But for the sake of something, consider:
Ethylene glycol, propylene glycol and glycerol as polyols capable of
sucking up a lot of heat of vaporization. Does anyone have octane
numbers for these puppies?

The headstrong may consider methyl nitrate, ethyl nitrate, and
propylene glycol dinitrate. #1 was used as rocket fuel in WWII, and
once upon a time I made some, but as I recall it was very liable to
detonate with increasing pressure, much more so than nitromethane.
("Under pressure" being anything above atmospheric.)  On the plus
side it has almost all the oxygen it needs to burn right in the
molecule. (Ethylene glycol dinitrate is even more dangerous, it's
one step short of nitroglycerin. On the plus side it undergoes
exactly stoich self-combustion. I never felt comfortable making
more than small amounts of this stuff at once.) "Propylene tri-ol
trinitrate" would be nitroglycerin, let's not go there. Propylene
glycol dinitrate might even be manageable, but I never had easy
access to PG and have never made it.

(Note: don't try this at home. But if you do, please put me in
your will.)

Someone mentioned hydraulic lock. That sure would suck, but it seems to
me that this could happen with the fuel even more easily, since a much
larger volume is being injected. As for corrosion, etc, many things are
solved cos you only inject water under higher loads, and remember to
run it at low load long enough to flush the water out nicely. (Like
cooldown on a turbo car, or using gasoline to flush out an alcohol
engine.)

One thing I rarely see mentioned is that the ignition system may need
some help with water injection. (My 10 year old stock one is marginal
right now, and totally loses it with a 50HP nitrous shot.) Certainly
the burn rate will change, which could easily mean you need a new
ignition timing curve for optimum power. Unfortunately I don't have
any practical info on this.

Ok, 'nuff bs from me for tonight. Happy Holidays everyone!

   Chris