Water Injection Question

[DeltaDeltaDelta]

A couple of days ago, I saw a picture of a DC-8, i think, taking off,
trailing thick black smoke from the engines (they weren't on fire). The
description of the picture said that it was using water injection to give
more power for takeoff. I also came across this when reading about the P-47.
How does that system work? I presume it's different for pistons and jets.

Triple Delta

[Darkwing Duck \(The Duck, The Myth, The Legend\)]

"DeltaDeltaDelta" > wrote in message
...
> A couple of days ago, I saw a picture of a DC-8, i think, taking off,
> trailing thick black smoke from the engines (they weren't on fire). The
> description of the picture said that it was using water injection to give
> more power for takeoff. I also came across this when reading about the
P-47.
> How does that system work? I presume it's different for pistons and jets.
>
> Triple Delta
>
>

Doesn't this have something to do with methanol fuels and water? Supposedly
water increases HP in methanol.

[Scott Skylane]

DeltaDeltaDelta wrote:
> A couple of days ago, I saw a picture of a DC-8, i think, taking off,
> trailing thick black smoke from the engines (they weren't on fire). The
> description of the picture said that it was using water injection to give
> more power for takeoff. I also came across this when reading about the P-47.
> How does that system work? I presume it's different for pistons and jets.
>
> Triple Delta
>
>
Triple,

I am not sure about the jet physics. In the piston (large radial) world,
a water/alcohol mix is injected just downstream of the carburettor for
hight power operation. This has the effect of reducing combustion
chamber temperatures, thus allowing higher manifold pressures (i.e. HP)
without detonation. If you didn't inject water at these power settings,
the amount of excess fuel needed to keep the temps down would actually
flood the mixture, causing power loss.

The alcohol in the mix does virtually nothing to contribute to the power
output, it is there merely to keep the water fromm freezing at altitude.

Interestingly, Pratt & Whitney apparently stumbled upon this effect
while doing heavy rain water injestion tests in the early days.

Happy Flying!
Scott Skylane

[Scott Skylane]

Scott Skylane wrote:


> Interestingly, Pratt & Whitney apparently stumbled upon this effect
> while doing heavy rain water *injestion* tests in the early days.
>
> Happy Flying!
> Scott Skylane
>


Woops! Make that *ingestion*

[DeltaDeltaDelta]

Hmm...interesting. I always wondered about that MW50 (nethanol-water)
mixture used on some Luftwaffe WW2 fighters (most notably on the FW-190 and
derivatives)...Thanks for the info

Triple Delta

"Scott Skylane" > wrote in message
...
> Scott Skylane wrote:
>
>
> > Interestingly, Pratt & Whitney apparently stumbled upon this effect
> > while doing heavy rain water *injestion* tests in the early days.
> >
> > Happy Flying!
> > Scott Skylane
> >
>
>
> Woops! Make that *ingestion*
>

[Mike Rapoport]

Water injection cools the air both before and after combustion. The lower
temperatures allow more fuel to be burned (turbine) or allow more MP or
compression to be used without detonation (piston).

Mike
MU-2


"DeltaDeltaDelta" > wrote in message
...
> A couple of days ago, I saw a picture of a DC-8, i think, taking off,
> trailing thick black smoke from the engines (they weren't on fire). The
> description of the picture said that it was using water injection to give
> more power for takeoff. I also came across this when reading about the
P-47.
> How does that system work? I presume it's different for pistons and jets.
>
> Triple Delta
>
>

[Jim Baker]

"DeltaDeltaDelta" > wrote in message
...
> A couple of days ago, I saw a picture of a DC-8, i think, taking off,
> trailing thick black smoke from the engines (they weren't on fire). The
> description of the picture said that it was using water injection to give
> more power for takeoff. I also came across this when reading about the
P-47.
> How does that system work? I presume it's different for pistons and jets.
>
> Triple Delta
>
3D.....See Rapoports answer for the technical explanation. Aircraft such as
the B-52 models prior to the G and the KC-135A used water injection takeoff
thrust if the weight and weather demanded it. It was a tremendous boost in
thrust in the B-52G and when the water ran out, a big deacceleration. As
you noticed, water injected takeoffs caused a lot of smoke.

JB

[Jim Baker]

"Jim Baker" > wrote in message
...
>
> "DeltaDeltaDelta" > wrote in message
> ...
> > A couple of days ago, I saw a picture of a DC-8, i think, taking off,
> > trailing thick black smoke from the engines (they weren't on fire). The
> > description of the picture said that it was using water injection to
give
> > more power for takeoff. I also came across this when reading about the
> P-47.
> > How does that system work? I presume it's different for pistons and
jets.
> >
> > Triple Delta
> >
> 3D.....See Rapoports answer for the technical explanation. Aircraft such
as
> the B-52 models prior to the G and the KC-135A used water injection
takeoff
> thrust if the weight and weather demanded it. It was a tremendous boost
in
> thrust in the B-52G and when the water ran out, a big deacceleration. As
> you noticed, water injected takeoffs caused a lot of smoke.
>
> JB
>
Should be "...Aircraft such as...prior to the H and the..."

JB

[Don Hammer]

Water on the big round engines is called ADI. (Anti Detonation
Injection. It lowers the combustion temperature and accomplishes
exactly that.

A jet engine produces thrust by the amount of mass it can push out the
back end. By injecting water you have increased that mass and the
thrust increases without a cooresponding increase in internal
temperature. More fuel can be added also for the same internal
temperature withour the water.

The alcohol in the water is there to keep it from freezing and plain
water would accomplish the same thing as far as performance.

Water was/is only used on the older low bypass engines because their
low speed thrust is low and the metals used can't stand the
temperatures of modern engines. Modern engines have much better
low-speed thrust because of the high bypass fan and the ability to run
at a much higher temperature because of the metalurgy.



On Fri, 9 Jul 2004 16:42:42 -0700, "Jim Baker"
> wrote:

>
>"DeltaDeltaDelta" > wrote in message
...
>> A couple of days ago, I saw a picture of a DC-8, i think, taking off,
>> trailing thick black smoke from the engines (they weren't on fire). The
>> description of the picture said that it was using water injection to give
>> more power for takeoff. I also came across this when reading about the
>P-47.
>> How does that system work? I presume it's different for pistons and jets.
>>
>> Triple Delta
>>
>3D.....See Rapoports answer for the technical explanation. Aircraft such as
>the B-52 models prior to the G and the KC-135A used water injection takeoff
>thrust if the weight and weather demanded it. It was a tremendous boost in
>thrust in the B-52G and when the water ran out, a big deacceleration. As
>you noticed, water injected takeoffs caused a lot of smoke.
>
>JB
>

[steve]

Geez Scott,
I've got 5 textbooks that cover water injection and they dont even come
close to explainin git as well as you did..way to go
"Scott Skylane" > wrote in message
...
> DeltaDeltaDelta wrote:
> > A couple of days ago, I saw a picture of a DC-8, i think, taking off,
> > trailing thick black smoke from the engines (they weren't on fire). The
> > description of the picture said that it was using water injection to
give
> > more power for takeoff. I also came across this when reading about the
P-47.
> > How does that system work? I presume it's different for pistons and
jets.
> >
> > Triple Delta
> >
> >
> Triple,
>
> I am not sure about the jet physics. In the piston (large radial) world,
> a water/alcohol mix is injected just downstream of the carburettor for
> hight power operation. This has the effect of reducing combustion
> chamber temperatures, thus allowing higher manifold pressures (i.e. HP)
> without detonation. If you didn't inject water at these power settings,
> the amount of excess fuel needed to keep the temps down would actually
> flood the mixture, causing power loss.
>
> The alcohol in the mix does virtually nothing to contribute to the power
> output, it is there merely to keep the water fromm freezing at altitude.
>
> Interestingly, Pratt & Whitney apparently stumbled upon this effect
> while doing heavy rain water injestion tests in the early days.
>
> Happy Flying!
> Scott Skylane
>

[Dale]

In article >,
Scott Skylane > wrote:


> In the piston (large radial) world,
> a water/alcohol mix is injected just downstream of the carburettor for
> hight power operation. This has the effect of reducing combustion
> chamber temperatures, thus allowing higher manifold pressures (i.e. HP)
> without detonation.

Scott,

Are you guys using ADI on the -6?

And congrats on making First Officer!!

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

[Paul Sengupta]

"Don Hammer" > wrote in message
...
> A jet engine produces thrust by the amount of mass it can push out the
> back end. By injecting water you have increased that mass and the
> thrust increases without a cooresponding increase in internal
> temperature.

Ooo, a steam engine!

Paul

[Tom Sixkiller]

"Paul Sengupta" > wrote in
message ...
> "Don Hammer" > wrote in message
> ...
> > A jet engine produces thrust by the amount of mass it can push out the
> > back end. By injecting water you have increased that mass and the
> > thrust increases without a cooresponding increase in internal
> > temperature.
>
> Ooo, a steam engine!
>

PW, GE and Honeywell and going to merge with Stanley.

[DeltaDeltaDelta]

Thanks for all your replies. I understand it now. On the older big radials
equipped with some form of pre-charging, the charger itself would heat up
the air as it compresses it and have effect on the detonation point. Now it
makes sense :)

Triple Delta

[Scott Skylane]

Dale wrote:
/snip/
> Scott,
>
> Are you guys using ADI on the -6?
>
> And congrats on making First Officer!!
>

Dale,

Yes, we use it, generally for takeoffs above about 85,000 lbs. If
anyone's interested the fuel burn for an R2800 CB-16 is as follows:

Max Dry power (53" M.P. 2800 RPM 1950 HP) 1850 lbs/hr

Max Wet power (59.5" 2800 RPM 2400 HP) 1550 lbs/hr

And thanks for the congrats!! It sure beats working for a living ;)

Happy Flying!
Scott Skylane