Whys and Hows of Water Injection on Jet Engines

From:         hclack@pyrolab.ME.Berkeley.EDU (Herek Clack)
Date:         16 Feb 96 04:33:24 
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Recently while making an analogy to one of my research advisors,
I mentioned that the earliest jet engines sometimes used water
injection to increase thrust for takeoff.  My advisor, being a
chemist specializing in combustion, initially scowled at the
notion.  He has since consulted a couple of other chemist/
combustion types, who all have different ideas of why this was
done (cooling the exhaust stream vs. increasing exhaust mass flow)
and exactly how it was done (injection before combustion vs. after).

Can anyone authoritatively shed some light on what the actual
logic was for water injection in jets?  Clearly there were
fluid dynamic, thermodynamic, combustion and operational/maintenance
issues that were factors, but can anyone provide the *main*
considerations for the practice and the ways in which it was
implemented back then?

As a die-hard lurker on this list, I'll gladly take private email
responses if this is a no-brainer.....