Why doesn't rain effect a jet engine?

Answer 1

Turbine, (the most common of "jet" engines,) only burn about 25% of the air that flows through them. If you're dumb enough to be standing outside in torrential downpours, you can still breathe.

By the final stage of the compressor section of most jets, the air has already reached close to 400 Deg. C, so the rain is now steam. It takes a great deal of steam heading through the burner section to significantly reduce the efficiency of the engine.

On more modern engines, turbofans, a significant amount of the air pulled through doesn't even encounter the burner section.

Where I l trained as an A&P mechanic, we had an old J-34. During run ups, one of the tests was using a garden hose to see if we could kill the thing. Not only could we not manage to flood the thing out with anything short of a fire hose, the engine had been taken apart and reassembled so often that every seem in the engine's casing up to the burner section dripped water.

As noted in previous answers, it will degrade the efficiency, but modern engines with variable stators vanes can minimize the loss.

Water can damage compressor vanes on the first few stages of the engine in the same way that landing spray can damage the props of amphibious aircraft. The damage is neither as noticeable and much more easily repairable on turbine engines.

Look at any turbojet, or turbo fan, closely enough and unless it's brand new out of the crate, it has divots and depressions from overhaul shops filing down the compressor and fan vanes. What can be filed out of a compressor, fan or prop blade without causing vibration still amazes me sometimes.

JT

Answer 2

Most of the time you are flying above the weather or around the weather. But for the rain that does make it into the engine it has to go through many stages of compression and all those blades that make compression possible in a turbine. The temperature of this compressed air reaches well over 1500 degress F. before final compression, now you have water vapor by the time it reaches the burner section of the engine and all that water vapor dose is add gas density to the heated gasses in the engine that turn the turbine blades.
Most likely though the rain will never reach the core engine on most jet engines. Mojority of all commercial jet engines today are either low to medium bypass or high by pass engines, meaning most of the thrust produced comes from the initial fan of compression (the fan you see when you look into the ducting of a jet engine) and is flung out into the bypass gas stream that never gets used inside the core engine itself.
A neat thing is, if you are ever on an aircraft taking off from an airport at high altitude ground elevation, on a hot and dry day, they use water injection into the engines to help produce the thrust need from the lost of gas density in the ambient air.
Rain water has no long term negative effects on a healthy jet engine, they can't get certification if it does.

Answer 3

Lots of almost right answers.

Yes we switch to continuous ignition during flights through rain, but all ground engine runs are done in continous ignition too..... Just a hold over by the FAA from the old days (pratt J-47's?)

Why doesn't the water put out the fire. Take the SNECMA CFM-56 and the GE F101 as primary example of engines that external and internal duct the bypass air. By-pass means doesn't go through the combustion chamber.

The water enters the engine and goes through 3 stages of fan wich imparts a bit of cintrifugal force to the solid water drops and they get slung to the outside and wind up in By-Pass air.

The water that makes it to the 9 stages of compressor gets vaporized becuase the temp ramps up to 700 plus deg F. It's condensation removes some heat(physics) and makes the compressor charge more dense(B-52 J-57 water burners) and then more power(large quantities only).

A fire truck could snuff a jet engine, but not a rain storm. water burning jets are in between those two.

Volcanoes are a much bigger threat to engine operation than rain.

Retired USAF SNCO, ECS, Jets, Hydraulics, Electrical, Fuel Systems(All together- Aerospace Systems Branch- OK so I am old!)

Answer 4

Rain most certainly DOES effect jet engines. There have been two incidents wherein Boeing 737s have flown into heavy rain and suffered DUAL flame-outs, including the famous dead stick landing of a 737 on a levee near New Orleans. Because of that incident the CFM56 was updated with a 'coniptical' spinner, designed to sling rain and hail out around the booster inlet so as to prevent quenching of the burner. There have also been several flame-outs of Pratt JT8Ds due to rain.

The mechanism by which rain causes flame-out is the lowering of HP ('core') compressor discharge temperature below the threshold required to sustain combustion. As rain ingestion increases, more and more energy is extracted from the compressor to vaporize the water. This requires increased fuel flow. At some point the fuel flow limit is reached, no more energy is available to vaporize the rain, the discharge temperature starts to fall, and combustion ceases.

Answer 5

It does, and quite a lot in pure jets. Enough rain through the intake will put out the fire because everything that goes in the front goes through the engine. In modern high bypass turbo fan engines, only a small percentage of the air entering the front goes through the engine. The rest bypasses around the engine to produce a lot more thrust than a pure jet.

Answer 6

It does, to a degree. In heavy rain, the pilots can turn on continuous ignition, which functions alot like a spark plug so that in the event of a loss of combustion, it can be re-lit instantaneously. Rain ingestion is taken into consideration when designing the engine, so they usually protect the combustion chamber to the best degree possible.

Answer 7

What they said, and it would be affect, not effect, unless you asked What effect does rain have on a jet engine?

Answer 8

becasue with all the stage and rotor fans in the engine. the water is basically atomized by the time it reaches the combustion chamber. I know the old B-52 was all water injection and they used that to increase the thrust of the engines. the H model was the only one that wasnt water injection.

Answer 9

It does, but apart from take off and landing, the plane flies above the clouds, where there is no rain.