RE: Water injection!
 

I believe the methanol is used with the water to prevent freezing at altitude or cold weather.

RE: Water injection!
 

Water/alch. was used on recip engines to lower the inlet temp to avoid pre-detonation with superchargers. It was also called adi. Aniti detonation injection. The water injection on the jets was used only on takeoff, and so would not freeze at altitude. We used to dump water on the B-52 when the temp got below 40 deg, and on the tanker, below 20. Alert takeoff run was figured with 6 engines wet, or 8 dry on the Buff. The tankers were going to have to dump fuel at the end of the runway if temp was too low for injection. They could not get off 4 engines dry with our normal 188000 pound fuel alert load. Interesting note. The original set up for the KC-135 water system was left wing on one system, and right wing on another. After losing a few aircraft due to asymetric thrust with water failure, mods were made to put both inbd engines on one system, and otbd on another.

RE: Water injection!
 

I can't speak for the jets (yet), but for reciprocating engines.... I crew for some teams who race at Reno and we use variations of water or water/alcohol both for spraying onto the outside of the engine, and also into the supercharger intakes to allow us to produce more power. My non-professional (and therfore possibly flawed) understanding is that due to the fact that the two liquids evaporate differently, varying the mixture allows for some fine-tuning of the benefits.

I may be crewing in the jet class this year too (if my pilot's aircraft gets its problems sorted out in time), in which case I will try to find out whether the same principle applies to the jets.

Gordon

RE: Water injection!
 

Gordon,
My lay opineon about water injection is that to some degree the water plays an active role in the chemistry of combustion. This is also the only contribution it makes in piston engines on top of cooling I think. In jets there is a secondary effect of increasing gas production. More gas means higher exhaust velocity at the same internal pressure. Injecting some water into the intake of a compressor will increase compressor pressure delivery due to the higher density effect of the air/water mix together with a lower inlet temp. Now mass flow times velocity = thrust on a pure turbojet and more torque on a powershaft engine. The excess heat of combustion is absorbed by the water and turned into "steam" which has of course a much higher volume. The further benefit results from lower EGT which in turn means more fuel can be burned while keeping the engine stress acceptable.
The idea that it increases massflow only may not be entirely correct except for the actual increase caused by the water itself being added to the air massflow. However this increased massflow now leaves the engine at a much higher velocity. But I could be wrong. Would love to hear a more scientific explanation.
Groete uit die Kaap,
Andre

RE: Water injection!
 

thanks!

RE: Water injection!
 

Hi Gordon.
But what is happening when the ECU tells the engine not to exeed 120K rpm???
This question is the BIG one for me.
Due to the much higher pressure, the turbine wheel would turn faster, but then again the ECU will reduse the kerosene flow to keep it under the 120k?..?..
Thuesday is the day to see what happens.
Do the fullsize have a similar system, and if they have, is this disabled then the water is injected? Or is the injection just a big GO for the engine?

Regards

Gudmund

RE: Water injection!
 

I think it will perform like it it is in cold weather.......

freezing cold day, it eats more fuel, and has more thrust.

Very hot day, gives less fuel, and less thrust...

RE: Water injection! THE TEST!!
 

Hi all.

Me and my friend Trond Hoseth performed a water-test today.

A half full Cokebottle ressurized to 10 Barg, and a Saab 900 ozzilating injection needle was strapped to the elctrostarter.
A fishingweight was the measurer to verify the change in performance.
At 10 Barg, the water was making a very fine mist, and a lot of it too.

The engine spooled up to full throtlle, and the water was at first gently supplied.:)
No reaction..[:-] Moore water, still no reaction.:eek:
Still at full throttle, the rest of it was just soaked into the compressor.
BUT THERE WAS NOT THE SLIGHTEST SIGN OF DIFFERENSE IN PERFORMANCE!![:-][:-]:D:D[:o]

Sean, you was right about beeing a sceptic![8D]. Our conclusion is as follows:

1. The amount of water needed to make any difference, isn`t nearly justified to the drawback of carrying it.. Using several litres of water to make a 20-30 sek boost, is not practical in our terms.

2. Our test showed surprisingly no drop in temperature. This points to the enormeous amounts of water needed to do so.

But we have reached one goal. And this was to find out what happened, and have the experience. :)
So, the gain was not worth it, and we can continue using our engines, fully aware of their allready optimized performance. In fact, I`m happy about the result. It most likely prevented some major modifications to my models.


Regards

Gudmund

RE: Water injection!
 

See my PM ;) !

Ya, it's simple math to me. If you consider the size of our turbines in terms of scale to full scale, and size of airplane in percentage to full scale, this technology would hardly make a difference.

I doubt even a full blown afterburner would make a noticeable difference in flight, even if it could be measured on the ground.

I'll bet it was a fun project though!!

RE: Water injection!
 

Yes, it really was. A very exiting moment, indeed!!
But this is what I like about this hobby too. Any theoretically good idea has to be tested to find out how, why and what.

Regards

Gudmund