Just speaking theoreticly, could you
realize some thrust benefit by
injecting a fine spray of water into the
exhaust which would turn to steam
and increase thrust? Of course, you'd
have to refill your huge water tank
just like a steam locamotive, so it
wouldn't be practical. Just wondering.
Brian Trubee
I think so. If it works for a combined
cycle gas turbine it should work
for jet exhaust. Both devices work on
similar principles.
Paul Lamar
I definitly DO NOT believe so. The
operating theory and cycle of a steam
bottoming cycle is worlds away from just
dumping water into the exhaust.
Efficiency in any thermal cycle consists
of bringing the working fluid up
to a higher pressure, then heating it
(possibly through a phase change),
before expanding it for useful work.
That is a long way from just
squirting it in by the turbine. In a gas
turbine there is limited gain
from injecting water to act as sort of
an intercooler in the compressor,
just as there is some gain in positive
displacement engines (piston/rotor)
as anti detonation fluid. I am afraid
that most of these schemes belong
in a J C Witney catalog along with the
magnets on a fuel line.
USEFUL expansion is the magic bullet
for improved efficiency.
Mechanically varying compression ratio
as an inverse function of
load has been done - heavy, complicated,
expensive.
Turbocompounding works well AT DESIGN
POINT altitude, near full
power etc.
The most efficient thermal engine ever
built is the Space Shuttle Main
Engine
actually in the 90 percent range at
altitude E
XPANSION! - Vance.
I don't thing Brian was advocating
squirting it into the turbine Vance. Did
you get
my messages on the Merlin exhaust stack
thrust? I think he was talking
about squirting it into the exhaust
expanding it into steam and
adding to the mass flow for the jet
effect. Hopefully it would not affect the
overall temp to significantly reduce the
kinetic energy. No turbine involved.
I agree with you if you squirt plain water
upstream of the turbine that will
cool the gas defeating the purpose. Making
steam with the left over exhaust
heat and then squirting the steam back
into the gas turbine does indeed work.
I have lots of papers on the subject from
the ASME Journal of Engineering
For Gas Turbines and Power. Don't make me
scan them in and upload them :)
BTW what struck me about NACA Report 786
was the scaling of the turbo
compound concept. The R3350 TC at 2800 HP
got the same percentage
of HP recovery that an R1350 550 HP engine
got. Namely 21% at high altitude
and 9% at sea level. Apparently they both
had the same ratio of kinetic energy
to heat energy in the exhaust. Surely the
scaling will hold true down to 200 HP.
In NACA Report 765 the rule of thumb for
kinetic mass flow contained in the exhaust
appears to be .002 pounds per second per
main engine HP. So the 200 HP rotary would
have
.4 pound per second mass flow in the form
of kinetic energy to work with.
That is 24 pounds per minute. That seems
to be right in the ball park for a
Garrett GT35R turbine which is similar in
size to a TO4 which I don't have
a turbine map for yet.
Paul Lamar
The older model B-52G and KC-135's with
the J-57 engines all used Water Injection
(900 to 1100 Gallons if I remember right)
to get off the ground in the summer time.
By the way dose anyone have the logo that
chrissy made. "Less Cubes, More Balls" I
would love to have it again made a great
Background for my desktop.
Allen Ervin
Scorpion472@comcast.net
Spokane, WA
PS just started a new yahoo group for
Spokane area Rotorheads.
http://autos.groups.yahoo.com/group/spokan
erotorheads/
