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Quoting BALandorLivery (Reply 2): Wonder if anyone on these forums has used it in anger. |
Quoting Qantas744ER (Reply 1): Roughly speaking, the concept of water injection (with or without methanol) in a gas turbine is to reduce the temperature of the air entering the combustion zone. |
Quoting kl671 (Reply 6): The water cools the flame temperature (not the incoming air temperature) thus reducing the turbine inlet temperature. |
Quoting tdscanuck (Reply 7): Water cools the flame temperature *by cooling the incoming air*. |
Quoting tdscanuck (Reply 7): Flames are a gaseous reaction, they don't "see" liquids. |
Quoting tdscanuck (Reply 7): The only way for water to interact with the flame (at the quantities we're talking about) is to vapourize. This sucks a ton of heat out of the air, lowering the air temperature. |
Quoting tdscanuck (Reply 7): The temperature rise due to combustion is also pretty fixed |
Quoting tdscanuck (Reply 7): |
Quoting kl671 (Reply 8): |
Quoting Qantas744ER (Reply 1): Also the water has mass, which is accelerated through the engine increasing mass flow. |
Quoting kl671 (Reply 8): Quoting tdscanuck (Reply 7): Water cools the flame temperature *by cooling the incoming air*. Wrong. Water injection into a combustion chamber is used to cool exhaust gasses, not intake air. |
Quoting kl671 (Reply 8): Quoting tdscanuck (Reply 7): Flames are a gaseous reaction, they don't "see" liquids. Injecting water into a combustion chamber results in steam. Steam is a gas at the temperatures and pressures found in a combustion chamber. |
Quoting kl671 (Reply 8): Quoting tdscanuck (Reply 7): The temperature rise due to combustion is also pretty fixed Not when you inject water to lower the temperature rise. |
Quoting kl671 (Reply 8): I stand by ny statement. "The water cools the flame temperature" |
Quoting jetmech (Reply 9): The question is where would the best location be to inject the water? |
Quoting jetmech (Reply 9): I suppose this can be done in the compressor or diffuser section, or directly in the combustion chamber (CC). Nonetheless, wouldn’t the overall effect be the same? |
Quoting jetmech (Reply 9): I wonder whether it is an increase in mass flow, or the increased acceleration (or both?) that provides the additional thrust? |
Quoting jetmech (Reply 9): Water in the gas phases occupies much more volume compared with the liquid phase. This rapid and significant expansion would surely be beneficial, as the expansion of the working fluid is a key to improving the performance of a jet engine. |
Quoting BALandorLivery (Thread starter): BALandorLivery |
Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this. |
Quoting kl671 (Reply 6): any water injection systems (Other than industrial applications) where water is used to cool air entering the combustion chamber |
Quoting tdscanuck (Reply 7): Flames are a gaseous reaction, they don't "see" liquids. The temperature rise due to combustion is also pretty fixed (the water injection doesn't alter the fuel/air ratio much). The only way for water to interact with the flame (at the quantities we're talking about) is to vapourize. This sucks a ton of heat out of the air, lowering the air temperature. You've now got colder air participating in the combustion reaction...colder inlet air with constant temperature rise means colder outlet products. |
Quoting tdscanuck (Reply 10): Mostly, yes. The farther you put it upstream, the greater the intercooler effect in the compressor, but I suspect that's pretty small compared to the bulk temperature drop's impact on turbine inlet temperature. |
Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this. |
Quoting DocLightning (Reply 17): So what did it feel like to take off with one of these systems? |
Quoting DocLightning (Reply 17): So what did it feel like to take off with one of these systems? |
Quoting Longhauler (Reply 18): The passengers likely couldn't't tell. The wet takeoff was used under heavy or hot conditions. More likely the passengers would notice if it weren't used! As it would be a slow lazy takeoff. |
Quoting 747classic (Reply 19): Especially after selecting the waterinjection off and setting CLB thust it became very quite in the aircraft, so sometimes the captain warned the passengers before take off, that after take off the engines were only retarded and not shut off !!!! |
Quoting TravelAVNut (Reply 20): Did all the KL 747 classics have water injection or only the early ones? I was always convinced that only the very early turbojets/fans required water injection. |
Quoting Longhauler (Reply 18): The passengers likely couldn't't tell. The wet takeoff was used under heavy or hot conditions. More likely the passengers would notice if it weren't used! As it would be a slow lazy takeoff. |
Quoting 747classic (Reply 19): In my memory passengers could hear the difference. |
Quoting DocLightning (Reply 22): Could those aft of the wing see the steam? |
Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this. |
Quoting tdscanuck (Reply 10): The only way to get more mass flow is to increase velocity, which requires the spools to spin faster, which means higher pressure ratio, which means more acceleration. |
Quoting 747classic (Reply 12): |
Quoting tdscanuck (Reply 10): This increases the outlet velocity of the engine (same flow area, more volume flow rate), hence the thrust hike. |
Quoting LTC8K6 (Reply 26): The gaseous form of water, water vapor, is invisible. |
![]() Photo © Miguel Snoep | ![]() Photo © Walter Van Bel |
Quoting 747classic (Reply 12): Conditions : Static test stand, sealevel, 29.92 "Hg, OAT 26.7 degr C, no bleed, no accessory power extraction, Take -off power. |
Quoting 747classic (Reply 12): Remarkable is the lower N2 RPM in wet condition (typo ?) or somebody can explain this. |
Quoting okie (Reply 13): Decreased working pressure from the additional fuel/water in the combustion area? |
Quoting DocLightning (Reply 27): Quoting LTC8K6 (Reply 26): The gaseous form of water, water vapor, is invisible. But i'd figure that it would tend to condense to visible steam pretty quickly on exiting the rear of the engine, especially on a cold day. |
Quoting bri2k1 (Reply 14): just before the throttle body |
Quoting BALandorLivery (Reply 2): Just heard the BAC 1-11 had an option for it? |
Quoting Starlionblue (Reply 34): On the 747-200, was all the water used, or simply as much as would be needed until the "set climb power" point? |
Quoting Starlionblue (Reply 34): Is there a time limit on wet power, similar to the time limit on take-off power? |
Quoting Starlionblue (Reply 34): Assuming it was not all used, how much would be left? Was this a safety margin? |
Quoting Starlionblue (Reply 34): Say you're doing a wet take-off and one engine fails just as you climb out. Would all the water then be used in order to get all possible power out of the engines? |
Quoting 747classic (Reply 32): The issue was freezing of the water in the watertanks |
Quoting Larshjort (Reply 33): Does anyone know why it is allowed to use 110% torque on a TPE331 installed on a Metro when using water injection? We used a lot of time to discuss it ay my module 15 turbine ngine course. |
Quoting 747classic (Reply 35): Sometimes the two water quantity indicators (Left for engine 1&2, Right for engine 3&4) approached zero BEFORE reaching the 2.30 minutes time limit. |
Quoting moose135 (Reply 40): Was the system on the 747 split between left and right? On the KC-135, the water came out of one tank (in the starboard main gear well) but one pump fed the inboard engines and one pump fed the outboards. Apparently, when first designed, one pump handled engines 1&2, the other 3&4, but after a few incidents where they lost water on one side (and at least one crash, I believe) the system was changed to inboard/outboard. |