jet engines in rain conditions
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jet engines in rain conditions
Forgive me for the simplicity of this question but....
In heavy rain what happens to the water sucked into your turbofan engine?? Surely at the typical cruising speed of a passenger jet litres of water must get in during rain??
So does it make it as far as the compressor??? Does it involve a particle separator??
From a confused `internal combustion` fling wing student...
In heavy rain what happens to the water sucked into your turbofan engine?? Surely at the typical cruising speed of a passenger jet litres of water must get in during rain??
So does it make it as far as the compressor??? Does it involve a particle separator??
From a confused `internal combustion` fling wing student...
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I was once told that a departing Boeing 747 in a monsoon soaks up a volume of water about the size of your average olympic swimming pool. 
And nope, no particle separators here. Just continuous ignition.
In dry conditions, jet engines "diesel" along without needing a spark to ignite the mixture, but once the air has some water in it the continuous ignition comes on and the engine basically runs like your average gasoline car engine, with added sparks from big spark plugs in the conbustion chambers, operating continuously to prevent a potential flame-out from water ingestion.
The only aircraft turbine engines that use particle separators are on turboprop aircraft that operate in less-than-ideal conditions, like the Cessna Caravan.
And nope, no particle separators here. Just continuous ignition.
In dry conditions, jet engines "diesel" along without needing a spark to ignite the mixture, but once the air has some water in it the continuous ignition comes on and the engine basically runs like your average gasoline car engine, with added sparks from big spark plugs in the conbustion chambers, operating continuously to prevent a potential flame-out from water ingestion.
The only aircraft turbine engines that use particle separators are on turboprop aircraft that operate in less-than-ideal conditions, like the Cessna Caravan.
Avoid imitations
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Turbines don't "diesel along". They cannot provide the compression ratio (19 to 1 or higher) of a diesel engine. The process is continuous combustion, not really the same at all.
Quote: "The only aircraft turbine engines that use particle separators are on turboprop aircraft that operate in less-than-ideal conditions, like the Cessna Caravan". Unquote.
Not forgetting helicopter engines, of course. Long before the Caravan came along.
Quote: "The only aircraft turbine engines that use particle separators are on turboprop aircraft that operate in less-than-ideal conditions, like the Cessna Caravan". Unquote.
Not forgetting helicopter engines, of course. Long before the Caravan came along.
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Fanjet sel-separation?
Hmm. I was taught that on a modern fanjet engine, the fan acts as a pretty effective centrifugal separator, and that relatively little of the incoming rain makes it to the core. Is this in fact true?
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ShyTorque
I was referring to it as "dieseling" in terms of not needing an electrical spark to run, ofcourse it's not the same thing. Although some more "crude" turbines can run on anything from propane gas to diesel and whisky... try that with a reciprocrating engine 
And err.... "he-li-cop-ter".... never heard of it.... wot's that?
And err.... "he-li-cop-ter".... never heard of it.... wot's that?
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Not a problem to be dismissed lightly .. throw enough water into the intake and the flame might just go out ....
As a f'rinstance .. there were some problems with a well known engine on a well known Type around 15-20 years ago where this is precisely what happened ... on more than one occasion with, as I recall, at least one dead stick landing (?) ... ignitors notwithstanding.
Fix was to change procedural limitations so that minimum RPM requirements could address the problem .... never mind the problem in descent profile planning halfway down the slide when one needed to run the engines up to the relevant N1 upon encoutering unexpected heavy rain ....
As a f'rinstance .. there were some problems with a well known engine on a well known Type around 15-20 years ago where this is precisely what happened ... on more than one occasion with, as I recall, at least one dead stick landing (?) ... ignitors notwithstanding.
Fix was to change procedural limitations so that minimum RPM requirements could address the problem .... never mind the problem in descent profile planning halfway down the slide when one needed to run the engines up to the relevant N1 upon encoutering unexpected heavy rain ....
I'll start out with a simple explanation and some others may wish to add more detail.
The pressure rise and heat in the compressors pretty much turns the water to superheat and the combustion process having far more air than it really needs just purrs on ... up to a limit.
Each drop of water must be converted to superheat vapor so this does place a significant load on the engine cycle which if not compensated by an increase in fuel flow will drop the RPM (although the actual thrust may increase due to mass flow effect.).
Most engines were demonstrated to run without blowing out at conditions up to 10% water by airflow. This in itself can accomodate extreme water ingestion conditions if the engine is operating at high power. However at low flight idle conditions the spool down effect on the rotors could lead to a flame out (several event in the records),
Methods of accomodating water ingestion include using the fan spinner as well as the bypass itself to centrifuge the water away from the core compressors. As well as increasing flight idle to a point where the spooldown effect still remains in a stable operating envelop.
Most of todays engines are expected to accomodate all but a E-8 storm providing you follow recommendations
The pressure rise and heat in the compressors pretty much turns the water to superheat and the combustion process having far more air than it really needs just purrs on ... up to a limit.
Each drop of water must be converted to superheat vapor so this does place a significant load on the engine cycle which if not compensated by an increase in fuel flow will drop the RPM (although the actual thrust may increase due to mass flow effect.).
Most engines were demonstrated to run without blowing out at conditions up to 10% water by airflow. This in itself can accomodate extreme water ingestion conditions if the engine is operating at high power. However at low flight idle conditions the spool down effect on the rotors could lead to a flame out (several event in the records),
Methods of accomodating water ingestion include using the fan spinner as well as the bypass itself to centrifuge the water away from the core compressors. As well as increasing flight idle to a point where the spooldown effect still remains in a stable operating envelop.
Most of todays engines are expected to accomodate all but a E-8 storm providing you follow recommendations
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...not forgeting of course that some rather early turbojet (and turbofan) engines actually used water injection during takeoff, to provide more mass flow, so more fuel could be added...to increase thrust, all the while keeping EGT's in check.
Worked OK...except when the water stopped after about 2 and a half minutes, then it felt like the bottom dropped out, at least in the 707 water wagon.
Worked OK...except when the water stopped after about 2 and a half minutes, then it felt like the bottom dropped out, at least in the 707 water wagon.
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Heavy Rain
As it progresses through compressor, tempertures rise well over water boil temperature - say 60 celcius at medium altitude - and water changes to gas/water vapour. The change cools things a bit and allows for more fuel burn to maintain a desired TIT - Turbine Inlet Temp. All adds up to more mass flow and greater thrust. How much? Has anyone measured it?
Worse than Heavy Rain.
Biggest problem is copious water injestion during take offs from water logged runways when nose wheel tyres can throw big fire hose amounts into engine intakes. This can cause compressor surges and extreme discomfort to the pilot.
Cure here is usuallu specially chined tyres to deflect the water away from intakes.
Lots of cases where military A/C have landed wheels up disabling the fuel shut offs and fire crews have tried to stop the engine/s by hoses down the intakes. Rarely works and they have then to open fuel tanks and put water into the fuel system. This works.
As it progresses through compressor, tempertures rise well over water boil temperature - say 60 celcius at medium altitude - and water changes to gas/water vapour. The change cools things a bit and allows for more fuel burn to maintain a desired TIT - Turbine Inlet Temp. All adds up to more mass flow and greater thrust. How much? Has anyone measured it?
Worse than Heavy Rain.
Biggest problem is copious water injestion during take offs from water logged runways when nose wheel tyres can throw big fire hose amounts into engine intakes. This can cause compressor surges and extreme discomfort to the pilot.
Cure here is usuallu specially chined tyres to deflect the water away from intakes.
Lots of cases where military A/C have landed wheels up disabling the fuel shut offs and fire crews have tried to stop the engine/s by hoses down the intakes. Rarely works and they have then to open fuel tanks and put water into the fuel system. This works.
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Pratt & Whitney letter
There was a letter published by Pratt & Whitney in 1998 concerning this exact topic. I re-read the letter, which in some areas included some serious mathematical equations, and came upon a paragraph I had highlighted the first time I read the letter. Among other concerns, they included this small piece of information:
"The engine inlet size basically determines the capture area for water ingestion. However, the amount of air ingested depends upon aircraft and engine speed. At high aircraft speeds and low engine rpm more air is being forced into the inlet than the engines require. Thus air is spilled out of the inlet which effectively reduces the size of the column of air being ingested. The water droplets, being heavy, are not ejected and the result is an increased water/air ratio. On a typical high bypass ratio engine, this scoop factor during idle descent increases the water/air ratio by as much as 200%. Increasing engine rpm increases the airflow requirement while maintaining the same area for water ingestion. Reducing aircraft speed will also reduce air spillage around the inlet. This combination significantly reduces the water/air ratio as illustrated in Figure 3."
Figure 3 is nothing more than a visual of the above words.
I was not able to find a link to the article.
"The engine inlet size basically determines the capture area for water ingestion. However, the amount of air ingested depends upon aircraft and engine speed. At high aircraft speeds and low engine rpm more air is being forced into the inlet than the engines require. Thus air is spilled out of the inlet which effectively reduces the size of the column of air being ingested. The water droplets, being heavy, are not ejected and the result is an increased water/air ratio. On a typical high bypass ratio engine, this scoop factor during idle descent increases the water/air ratio by as much as 200%. Increasing engine rpm increases the airflow requirement while maintaining the same area for water ingestion. Reducing aircraft speed will also reduce air spillage around the inlet. This combination significantly reduces the water/air ratio as illustrated in Figure 3."
Figure 3 is nothing more than a visual of the above words.
I was not able to find a link to the article.
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How much? Has anyone measured it?
Why yes, as a matter of fact, many years ago.
JT3C-6 engine dry....10,600 pounds thrust (takeoff, MSL)
Same engine, same conditions...wet power, 13,400 pounds thrust.
A rather large increase.
JT3C-6 engine dry....10,600 pounds thrust (takeoff, MSL)
Same engine, same conditions...wet power, 13,400 pounds thrust.
A rather large increase.
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For the engineering types…On takeoff/climb in moderate/heavy rain, if in an “EPR” airplane, my assumption is that takeoff/climb thrust will be as indicated. On an N1 airplane, will takeoff/climb at a computed N1 result in a higher net thrust due to the “mass flow” phenomenon?
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The trident 2 used to use water glycol injected into the engine on take off to increase TOW.
Unfortunately the permitted increase was marginal compared to the technical costs of maintaining the system.
I recall there were several accidents due to finger trouble such as this one:-
http://www.super70s.com/Super70s/Tec...6(PanIntl).asp
Unfortunately the permitted increase was marginal compared to the technical costs of maintaining the system.
I recall there were several accidents due to finger trouble such as this one:-
http://www.super70s.com/Super70s/Tec...6(PanIntl).asp
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Way back circa 1973 was in cockpit of a USAF 707 tanker out of Hickham at max weight for met conditions.
Water methonol injection used for T/O and initial climb involving a wing tip almost scaping turn away from Honolulu.
Injection ran out progressively throuh the 4 engines readily felt by aircraft yaw.
We wouldn't have made it if the injection had not worked as rotation was VERY close to end. Indicated great reliance on the injection system.
Tanker supported F111s on direct flight to Australia.
Water methonol injection used for T/O and initial climb involving a wing tip almost scaping turn away from Honolulu.
Injection ran out progressively throuh the 4 engines readily felt by aircraft yaw.
We wouldn't have made it if the injection had not worked as rotation was VERY close to end. Indicated great reliance on the injection system.
Tanker supported F111s on direct flight to Australia.
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Milt,
Now you know why most folks (in the civvy world anyway) did not much appreciate the 'ole water wagons.
Only spent a brief time in these, before going on the the bigger JT4A-powered -320 series.
And even there, you got up close and personal with the far end of the runway, at heavy weights.
The fan-powered later models were much better.
Now you know why most folks (in the civvy world anyway) did not much appreciate the 'ole water wagons.
Only spent a brief time in these, before going on the the bigger JT4A-powered -320 series.
And even there, you got up close and personal with the far end of the runway, at heavy weights.
The fan-powered later models were much better.
The fan IS a good centrifugal seperator, but only for something that's attached to it (ice). Water and air just passes through.
Do a Hover - it avoids G
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Thanks to a lot of help from my friends you should be able to see the movie at
this link.
Its over 6Meg so you might want to right click the link and go Save Target as ...
this link.
Its over 6Meg so you might want to right click the link and go Save Target as ...
Last edited by John Farley; 20th May 2004 at 21:30.
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Until the 777 development there were no FAA standards concerning water injestion tolerance .. some engines like the CF-6 are naturally tolerant to water - other engines were very intolerant to water such as the CFM-56. However, the good old boys at Boeing solved this when it appeared on the 737 dual engine flame out - with their "cutback-splitter" fix documented in US patent 5431535 - " Foreign matter diverter systems for turbofan engines ". Since that time - the Airbus A320 & A340 have benefited from this technology as well - since they all use the same engine - more or less .. Today, this is wellunderstood and is further documented in the FAA's engineering design - certification compliance methods for turbomachinery ..