Water Injection. What do we agree on so far?

[Danny Barrett]

OK Gents. This discussion has happened a few times before, if we look in the
archives, and to what I can tell, not once has a definitive answer been
obtained as to whether water injection would/should work in normally
aspirated engines. We should all know that it is very valuable as an
anti-knock agent in turbo/supercharged engines - it has been used for years.
I think that we obviously have some very intelegent people here, and I
believe that we should be able to come up with an answer to this problem, so
that if the subject comes up again by newly registered people to this
mailing list we can give them the one true and final answer (if possible),
and tell them to look it up on the archives (and, yes, I'm actually the
guilty party for bring up the topic this time, as I have a certain amount of
knowledge, but I want to know the absolute answer).

What do we all agree on? Who agrees/disagrees with the following?



It has been shown that the water injected will vaporise before TDC, and
remain vaporised throughout the compression/power strokes.

For economy and power in normally aspirated engines, to reduce the amount of
energy lost due to latent heat of evaporation, the water should be heated by
the exhaust manifold to say 90 deg C (194 deg F), so that it is still a
liquid, and not simply another inert gas.

If the anti-knock properties are needed (ie. Turbo, and Supercharged
engines), however, the water should be injected cold to make use of the
latent heat of vaporisation (Note, this has been a known, tried and true
method for possibly longer than many of us have been around).

For fuel economy in normally aspirated engines, a small amount of water may
help, but it should not be used in quantities remotely resembling those used
in turbo/super charged engines.



Questions yet to be answered in gaining the absolute answer:

Are the expansion properties of steam better than those of N2, O2 (ie.
excess O2 in the charge), CO2 and NO (produced at least in small quantities
due to the heat of the reaction in the cylinder)?

If so, what quantity of water, at what temperature should be injected so
that the benefit of extra horespower (without extra fuel) is maximised
(considering water's tendancy to "put out" the combustion process)?

Also, If water injection (without an increase in fuel used) gives more
power, would this equate to more fuel efficiency if your driving habits do
not change?

If water injection is viable (as far as increased power/efficiency is
concerned, without the use of extra fuel), how (or should) we
de-chlorinate/de-floridate the water? Should we use a vehicle mounted
charcoal filter? Or should we filter the water before it is put into the
vehicle?


If you have any other questions/points, feel free to add them...

Danny Barrett.