IFEMaster
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Clouds & Engines

Wed Jun 28, 2006 12:16 am

When an aircraft flies through a cloud, the disruption in airflow is evident by the turbulence felt in the aircraft.

I also know there have been some occasions when an engine has experienced a flame out because of water ingestion (though not necessarily while flying through cloud).

My question is what is the effect on an engine when flying through a cloud? Does the humidity/moisture affect the efficiency of the engine?
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SlamClick
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RE: Clouds & Engines

Wed Jun 28, 2006 12:36 am

Quoting IFEMaster (Thread starter):
an engine has experienced a flame out because of water ingestion (though not necessarily while flying through cloud).

The most famous event was probably Southern 242, a DC-9-31 that crashed at New Hope GA in 1977. You should know that the intensity of the rain was such that you could not duplicate the water ingestion in a test cell using a fire hose. The cloud in this case was irrelevant. It was the rain shaft that did the damage.

I will leave the rest of the answers to my academic superiors as it might get pretty technical. Empirically speaking I have never seen the slightest effect on engine performance in all the cloud and all the rain I've ever flown in, from the Arctic to the Equator over forty years.

Cloud is water droplets or ice crystals. Water in the intake air can improve the expansion, probably by a sort of steam effect. Turbulence associated with certain cloud forms might have some effect but it is usually momentary and would have to be extreme to have any significant effect.

Recips have an intake scoop that usually leads to a plenum which stabilizes the air under some pressure, while taking the velocity out of it. A momentary disruption at the lip of the intake is probably not going to translate to a blip on the pressure at the throttle.

Jet engines are subject to some effects from disruption at the intake but, again, such disruptions are truly momentary - measured in thousandths of a second, perhaps. The compressor section may feel the disruption but remember that the flame itself is in a 'flame holder' in the combustion section, downstream from a diffuser that, again, maintains the pressure while taking out some of the velocity of the airflow.

Of course most PHs call for ignition to CONTINUOUS in severe turbulence. Maybe in such cases we might get momentary flameouts, but it lights right back up again.

That's my experience with it.
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Starlionblue
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RE: Clouds & Engines

Wed Jun 28, 2006 12:41 am

As Mr Click explains, ops are typically not affected by rain. It takes a pretty powerful downpour for enough water to be present to make a difference. Just think of it like this: Is there enough water present in the air on a rainy day to make breathing difficult? Not really.

Having said that, part of engine certification involves running it on a stand and pouring zillions of liters of water into the intake to see what happens.
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kaddyuk
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RE: Clouds & Engines

Wed Jun 28, 2006 3:25 am

http://100.rolls-royce.com/facts/view.jsp?id=217

Hope that gives you a good insight...  Smile
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SlamClick
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RE: Clouds & Engines

Wed Jun 28, 2006 3:26 am

Quoting Starlionblue (Reply 2):
As Mr Click explains

That's 'captain' Click if you please.
I didn't spend eight years in flight training to be 'Mister' Click, thank you very much.  Smile

(cue the psychedelic scene change)
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Starlionblue
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RE: Clouds & Engines

Wed Jun 28, 2006 3:47 am

Quoting SlamClick (Reply 4):
Quoting Starlionblue (Reply 2):
As Mr Click explains

That's 'captain' Click if you please.
I didn't spend eight years in flight training to be 'Mister' Click, thank you very much. Smile

(cue the psychedelic scene change)

Ok then. Captain Click it is. Big grin
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IFEMaster
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RE: Clouds & Engines

Wed Jun 28, 2006 4:33 am

Quoting Kaddyuk (Reply 3):
http://100.rolls-royce.com/facts/view.jsp?id=217

Hope that gives you a good insight...

That's very interesting. Thanks for the link.
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CosmicCruiser
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RE: Clouds & Engines

Wed Jun 28, 2006 6:12 am

Quoting SlamClick (Reply 1):
The most famous event was probably Southern 242, a DC-9-31 that crashed at New Hope GA in 1977. You should know that the intensity of the rain was such that you could not duplicate the water ingestion in a test cell using a fire hose. The cloud in this case was irrelevant. It was the rain shaft that did the damage.

Hey SlamClick, if I remember those poor souls hit the absolute heaviest part of the line and actually suffered lots of hail damage including cracked windshields and damaged inlets and compressor blades. That's the reason they never got one started even after they exited the storm cell.
 
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RE: Clouds & Engines

Wed Jun 28, 2006 7:27 am

Quoting CosmicCruiser (Reply 7):
damaged inlets and compressor blades.

I've had good briefings on that accident by two different parties, including Pratt & Whitney. I no longer remember all the details but, yes that is correct. Compressor stalls began at about the 13th stage and were so severe that they flexed compressor blades forward 'til they hit the stators ahead of them. Not any real chance of saving it but they did pretty well getting it down on a narrow road. It could even have been worse.

Flew into a 'radar shadow' if I remember, an area of no returns behind an intense cell which was returning the entire radar signal. The area held an even worse cell.
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777wt
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RE: Clouds & Engines

Wed Jun 28, 2006 7:55 am

 
Oryx
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RE: Clouds & Engines

Wed Jun 28, 2006 10:17 pm

I think a theoretical engine optimized for moist air would even have better performance than for dry. Thermodynamically compressing water is nearly a free lunch and the higher mass flow rate and heat capacity should increase the power output or EGT margin.
 
CosmicCruiser
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RE: Clouds & Engines

Wed Jun 28, 2006 10:32 pm

Quoting Oryx (Reply 10):
I think a theoretical engine optimized for moist air would even have better performance than for dry.

That's why some turbine engines have water injection. I flew the YS-11 for a while that used "injection" t/os alot in the summer.
 
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Starlionblue
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RE: Clouds & Engines

Wed Jun 28, 2006 10:36 pm

Quoting Oryx (Reply 10):
I think a theoretical engine optimized for moist air would even have better performance than for dry. Thermodynamically compressing water is nearly a free lunch and the higher mass flow rate and heat capacity should increase the power output or EGT margin.

Indeed. Which is why many older jets like the early 747s used water injection at take-off to achieve higher thrust and smoke trails.
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Aaron747
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RE: Clouds & Engines

Thu Jun 29, 2006 12:04 am

^
Surely you didn't mean that they were making a deliberate attempt to produce smoke of a more thick and dense nature

[Edited 2006-06-28 17:24:16]
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SlamClick
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RE: Clouds & Engines

Thu Jun 29, 2006 12:18 am

Quoting Starlionblue (Reply 12):
Which is why many older jets like the early 747s used water injection at take-off to achieve higher thrust and smoke trails.

Ahh, yes, the waterwagons.

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darkblue
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RE: Clouds & Engines

Thu Jun 29, 2006 1:54 am

Quoting Oryx (Reply 10):
I think a theoretical engine optimized for moist air would even have better performance than for dry. Thermodynamically compressing water is nearly a free lunch and the higher mass flow rate and heat capacity should increase the power output or EGT margin.


Quoting CosmicCruiser (Reply 11):
That's why some turbine engines have water injection. I flew the YS-11 for a while that used "injection" t/os alot in the summer.



Quoting Starlionblue (Reply 12):
Indeed. Which is why many older jets like the early 747s used water injection at take-off to achieve higher thrust and smoke trails.

Be careful not to confuse the performance impact of water injection with the impact of humidity or "moist air". Humid air will actually hurt engine performance by increasing engine temperatures. This is because as the air comes through the inlet, the water vapor condenses which releases heat (heat of condensation). You generally see this at high power / low airspeed (takeoff conditions).


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Now, as for water injection, the cooling comes from water evaporation in the compressor and combustor. A liquid water spray is introduced to the flow, and when it evaporates heat is removed from the flow (heat of evaporation). Reducing engine temperatures improves component life and reduces NOx emissions (which are heavily dependent on combustor temperature). The other option is to trade off the reduced engine temperatures for increased thrust performance.

[Edited 2006-06-28 18:57:32]
 
Tristarsteve
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RE: Clouds & Engines

Thu Jun 29, 2006 2:13 am

Quoting DarkBlue (Reply 15):
Now, as for water injection, the cooling comes from water evaporation in the compressor and combustor. A liquid water spray is introduced to the flow, and when it evaporates heat is removed from the flow (heat of evaporation). Reducing engine temperatures improves component life and reduces NOx emissions (which are heavily dependent on combustor temperature). The other option is to trade off the reduced engine temperatures for increased thrust performance.

I thought that the idea of water injection was to restore max power at high temps. We used to operate BAC111 with water injection in the Gulf and IIRC it was only used when the temp was above the flat rating temp to move the rating temp up. But with the Spey512-14 which was rated at 24degC and OAT of 35degC it didn't go far enough!
There were Spey 512-14W and 512-14DW. Do you know what the difference was?
 
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RE: Clouds & Engines

Thu Jun 29, 2006 2:47 am

Quoting Aaron747 (Reply 13):
Surely you didn't mean that they were making a deliberate attempt to produce smoke of a more thick and dense nature

What, that wasn't the purpose?  Wink

Quoting DarkBlue (Reply 15):
Be careful not to confuse the performance impact of water injection with the impact of humidity or "moist air". Humid air will actually hurt engine performance by increasing engine temperatures. This is because as the air comes through the inlet, the water vapor condenses which releases heat (heat of condensation). You generally see this at high power / low airspeed (takeoff conditions).

Now, as for water injection, the cooling comes from water evaporation in the compressor and combustor. A liquid water spray is introduced to the flow, and when it evaporates heat is removed from the flow (heat of evaporation). Reducing engine temperatures improves component life and reduces NOx emissions (which are heavily dependent on combustor temperature). The other option is to trade off the reduced engine temperatures for increased thrust performance.

Thx for clarification.
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CosmicCruiser
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RE: Clouds & Engines

Thu Jun 29, 2006 3:19 am

Quoting Starlionblue (Reply 17):
Now, as for water injection, the cooling comes from water evaporation in the compressor and combustor. A liquid water spray is introduced to the flow, and when it evaporates heat is removed from the flow (heat of evaporation). Reducing engine temperatures improves component life and reduces NOx emissions

I don't think reducing eng. temp is the real purpose. As you stated the water evaporates and cools the air therefore making it denser therefore providing more power. Like taking off on a cooler day.
 
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RE: Clouds & Engines

Thu Jun 29, 2006 4:19 am

Quoting TristarSteve (Reply 16):
I thought that the idea of water injection was to restore max power at high temps. We used to operate BAC111 with water injection in the Gulf and IIRC it was only used when the temp was above the flat rating temp to move the rating temp up. But with the Spey512-14 which was rated at 24degC and OAT of 35degC it didn't go far enough!
There were Spey 512-14W and 512-14DW. Do you know what the difference was?



Quoting CosmicCruiser (Reply 18):
I don't think reducing eng. temp is the real purpose. As you stated the water evaporates and cools the air therefore making it denser therefore providing more power. Like taking off on a cooler day.

Careful with your quotes...  Smile

Correct, water injection is usually done to increase takeoff thrust. Adding water reduces compressor temperatures which then allows you to increase power without increasing turbine temperatures.
 
CosmicCruiser
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RE: Clouds & Engines

Thu Jun 29, 2006 5:31 am

Quoting DarkBlue (Reply 19):
Careful with your quotes...

Correct, water injection is usually done to increase takeoff thrust. Adding water reduces compressor temperatures which then allows you to increase power without increasing turbine temperatures

When the water/coolant is sprayed into the compressor inlet, the temperature of the air is reduced, increasing the density of the compressor inlet air, and consequently, the thrust is increased.
This is from purdue univ. C.C.
 
Oryx
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RE: Clouds & Engines

Thu Jun 29, 2006 8:57 pm

I must admit that I wasn't sure about how it all sums up. I thought of clouds where the water part is already condensed. Nevertheless there is still the higher mass flow and the higher heat capacity. But as you said the negative effect of the heat release of the condensing steam in the compressor my be larger.
 
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Jetlagged
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RE: Clouds & Engines

Thu Jun 29, 2006 11:44 pm

Quoting CosmicCruiser (Reply 20):
When the water/coolant is sprayed into the compressor inlet, the temperature of the air is reduced, increasing the density of the compressor inlet air, and consequently, the thrust is increased.

In addition because the air temperature is reduced, more fuel can burnt without exceeding combustion temperature limits. So when water is injected extra fuel is also metered. Consequently there is higher mass flow and more thermal energy, both of which will result increased thrust.
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Tristarsteve
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RE: Clouds & Engines

Fri Jun 30, 2006 4:40 am

Quoting CosmicCruiser (Reply 20):
When the water/coolant is sprayed into the compressor inlet,

On the Spey, the water was sprayed into the combustor. It went down a separate tube in the fuel spray nozzle.
 
SlamClick
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RE: Clouds & Engines

Sun Jul 02, 2006 2:13 am

Quoting Oryx (Reply 10):
I think a theoretical engine optimized for moist air would even have better performance than for dry. Thermodynamically compressing water is nearly a free lunch and the higher mass flow rate and heat capacity should increase the power output or EGT margin.



Quoting CosmicCruiser (Reply 11):
That's why some turbine engines have water injection.

Recips too; read on.

Quoting DarkBlue (Reply 19):
Correct, water injection is usually done to increase takeoff thrust.

All of this had my memory searching old dusty files. Then I ran across this picture:

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Photo © Neville Murphy-Aviation Images Australia


This plane is a Lockheed P-2V Neptune with 'two turning and two burning' meaning two Wright R-3350 recips and two smallish auxilliary jets for takeoff and some maneuvering.

Notice the dual manifold pressure gauge at the top left of the center instrument panel. The green arc ends and the yellow arc begins at about 50" hg. Then there are two red radials, one at about 54.5" hg and one at about 59.5" hg.

I'm not qual'd in the Neptune (taxiied one once) but I'm going to guess that these represent 'dry' and 'wet' takeoff manifold pressure limits.

Anyone here fly 3350s who can confirm or correct?

If I'm correct, the upper manifold pressure limit is only available with the use of ADI or Anti-Detonation [water] Injection.
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