Volcanic ash and the Jet Engine

This is more of a specific jet engine question than just an F-16 one, but it does apply to the F-16 no matter the power plant. I'm looking for the intelligent answer here so I'm hoping "that engine guy" will wade in with the assist.
The question is: What "specifically" is the cause of jet engine shutdowns when exposed to volcanic plumes?

To quantify the question, I understand about the potential for long term exposure, what I am looking for is what was the causes of jet engine "flameouts" related to plume ingestion.

Read about the 747 flight that had all four flame out multiple times.. tons of info

The cloud is a mixture of carbon particle sizes consisting anywhere from larger soot that acts as an abrasive to ultra fine particles that when combined with high working pressure and extreme heat are prime for growing diamond crystals. I have a feeling that has potential to add undesirable weight to the moving parts let alone sandblasting them and creating localized areas of hotspots. Think instant dirty engine conditions on the grand scale. Remember, these clouds have, in the worst case scenario, potential to circulate in the atmosphere for years.

NATO: F-16 fighters damaged by volcanic ash

Source and full story.
http://www.google.com/hostednews/ap/art ... wD9F63E6G4

Earth scientists and engineers have warned us that much of this ash is a type that is particularly dangerous to aircraft. Supposedly much of the dust resembles microscopic shards of glass and can be very abrasive, as this dust enters the hot section of the engine the microscopic shards of glass can melt and condense on engine components changing the engines characteristics. The added weight can change the performance of the engine. The coating can change the size of engine components which can essentially change the compression ratio and can cause parts to interfere, vibrate and can change the thermal properties which can make the parts overheat easier. In addition the glass coating from the ash can clog cooling holes in the components (an additional reason the components overheat under such circumstances).

Mechanical and aeronautical engineers already know and have stated that volcanic ash is extremely harmful for jet engines. So that should put the ball of responsibility in the court of meteorologists and Earth scientists. There is little doubt that politicians, the general public and airlines will probably pressure the meteorologists and Earth scientists to rush to judgment to push to get the airways open back up, ; and/or the powers that be may ignore/override the advice of meteorologists, scientists and engineers; then if things go wrong they will be looking for people to point fingers at.


Most jet engines are fairly vulnerable to sand and volcanic ash ingestion. The only exception I can think of at the moment is small gas turbo shaft engines for the likes of small combat and SAR helicopters. Some of these small engines are designed with what is essentially a centrifugal filter that helps cast off heavier than air objects. These centrifugal filters are pretty good at casting off small caliber bullets, small limbs, sand, gravel, volcanic ash and sea water spray. There is some performance loss, increase in weight and increase of expense. However these filters are only practical on smaller gas turbine engines.

It’s not only the engines that are vulnerable on aircraft. I suspect that sensors like pitot tubes can be harmed by volcanic ash. The airliner that almost crashed from volcanic ash years ago, had to make a nearly blind landing because the volcanic ash abraded the windscreen so badly that it essentially was frosted like a privacy window, in addition to scratched the surface of the windscreen allowed dirt to adhere better further obstructing the vision. The possibility of having multiple sensor failures occur in quick succession on a flyby wire aircraft is very scary to me.

Some of the consequences from sand and ash damage is not always immediately noticeable. Some of the damage is very insidious, such as the sand can abrade airframe and cause premature and accelerated corrosion that can lead to secondary fatigue cracks and possible catastrophic failures. Even if airframe abrasion is caught before failure and the danger is circumvented; the cost can often be very expensive to make the aircraft flyable again. I think in some cases the damage is so severe that it is cost prohibitive to do a repair; so the aircraft is scrapped.

More than 500 additional aircraft are awaiting repairs…The aviation reset project is now estimated to cost $1.2 billion…Maintainers in Iraqi Freedom removed 35 pounds of sand from under a radio console in one Black Hawk. Rotor blades in the desert commonly suffer significant sand erosion. Abrasive sand also clouds windshields, and grains caked between panels by field washing ultimately cause corrosion.

Source and full story
http://www.allbusiness.com/public-ad.../327956-1.html

There are some engines that are more robust to sand and volcanic ash but that does not mean that they are not damaged under such circumstances.
http://www.youtube.com/watch?v=IMIkk-ZqUzM


If you scroll through some of these photos at this link you’ll see some of the damage from volcanic ash. You will notice that there are holes deliberately manufactured into the hollow bades/fins. The bades/fins have relatively cool air blown into them to help keep the bades/fins cool. When those orifices get clogged by volcanic ash and the resulting glass it causes the bades/fins to overheat.

A jet flew into an ash cloud:
http://www.techeblog.com/elephant/photo ... 0#prevnext

Jet engines were optimized to fly in 78% nitrogen, 21% oxygen & some trace gases, not underground.

When the ground comes up to the flying jet engine, all bets are off.

OL

Yes, F-16s have limits in their flight manuals that cover flight into ash plumes. (different for the F100 and F110 but both are covered) It is in the 'adverse operation' section of the manual, and simply states in the first paragraph to avoid ash plumes to prevent damage, but 'if you have too...' and details instructions specific for each engine type.

Crash has it right, and Outlaw's comments are valid as well.

The biggest thing is that the melting temperatures of the fine 'glass like' ash is below the operating temperatures of most modern gas turbine engines. (F100/F110, commercial, what have you...)

The ash enters the engine, melts inside the combustion chamber, then enters the turbine in a molten state. The blades/vanes of the turbine are much cooler than the air, (otherwise they would melt too) so the ash sticks to their cooled surfaces. By reducing the vane flow, you're creating back-pressure on the combustion and compressor, which can induce compressor stalls. With this you also have an increasing operating temperature (that the FADEC tries to deal with) due to clogged vane cooling passages and choked flow. Downstream damage to the rotating hardware can also occur if the weight of the material exceeds the strength of the blades, or 'breaks off' and creates FOD within the turbine.

The ash also contaminates the small sensor openings that feed the control system, as well as get into the fuel/oil systems that will foul filters.

You have to remember the amount of air (and ash) an F-16 would swallow in only a few seconds. The buildup on the turbine could start almost immediately and cause the engine to compressor stall/flame out in very short order depending on the ash density. Jet engines are very close tolerance machines, just a few thousands of an inch in restrictions or clearances can cause massive flow distortions and interferences within the engine.

Sand can have the same effects depending on type. There are places in the world that have sand that act similar to volcanic ash. Most sand does not have the same melting effects as ash, and will not affect an engine so rapidly or badly.

And, as OL stated, 21% O2 is needed. After all the government calls them 'engine, gas-turbine, internal combustion, aviation' (Key word COMBUSTION) Without the proper fuel/air ratio the flame in the engine will stop. Engine control systems are based on the 78/21% spit of air. All work on density which is temperature versus pressure. What the FADEC, (or hydro-mechanical fuel control) doesn't realize, as the mixture it's measuring may only have 17% O2. So the 'density' of the air may be the same, but if you fly into a ash-cloud, it may contain more of the 'trace gasses' like methane, or the like. The engine still sees x pounds of air, not knowing it is 4% short on oxygen, and flame out; Or the sudden change in density can cause a stall/flame out. (Like flying through hot exhaust at 32K feet) Reducing altitude into cleaner air, or more dense air will allow the engine(s) to start again. Hopefully...

Read Boeing's comments here: http://www.boeing.com/commercial/aeroma ... story.html

Was that what you were looking for Falconrep?

Keep 'em flyin' (in 'safe' air...)
TEG

...
Last week, two Finnish Air Force F-18 fighter-bombers suffered similar damage while flying through the ash plume that has paralyzed air traffic over much of Europe.
http://www.google.com/hostednews/ap/art ... wD9F63E6G4

More info about that with pretty pictures in here:

http://www.ilmavoimat.fi/index_en.php?id=1152

Wow, that stuff is NASTY.

IMAO A more reputable source calls into question the validity of the sources and content of the above article that I had posted and linked.

NATO unsure on F-16 damage claim
http://www.flightglobal.com/articles/20 ... claim.html

It might be Standard OPSEC - The affected Air Forces might not want the number or units affected to become public knowledge.
The combustion process uses very high temps so "glassing over" the turbine cooling holes is a known problem.
(Great explanation by TEG). In this case, I still think your article is valid.

Excellent points outlaw162 and That_Engine_Guy; ones I neglected to cover. Volcanoes spew all kinds of nasty things besides volcanic ash. IE: Carbon dioxide, methane gas, sulfur dioxide and many others.

I saw an excellent documentary debunking the tendency for supernatural explanations of losses in the Bermuda triangle. The point of the documentary was largely to demonstrate that more natural phenomena was probably more likely than supernatural explanations.

Some scientists hypothesized that some of the disappearances can be explained by methane and methane hydrate deposits under the ocean that can sometimes massively or catastrophically release. The supernatural cult culture largely denied that ships and aircraft could be adversely affected by methane venting.

To demonstrate the validities of the scientists hypothesis; the scientists used a large model or small boat on the water and aerated the water under the test subject, and the test subject sank because the density of the water was reduced by the aeration. (For this test they substituted air for methane; because of the explosion hazard, logistics and expense of using methane)

Another more topic related demonstration that they did; is they took an old fashion radial engine much like what was on many of the aircraft that have been lost in the Bermuda triangle, and put the engine on a test stand and rigged it so that they could add and regulate methane into the intake while the engine was running. They started up the engine and ran it up and warmed up and stabilized the engine, then they slowly started to add methane into the air intake. I forget the exact numbers but it didn’t take very much percentage of methane to cause the engine to sputter and stall.

I think that last test can be extrapolated into volcanic eruptions and engine performance. The gases that are released from a volcanic eruption can change the gas ratio in the local atmosphere that can interfere with the combustion mixture (air to fuel ratio) of engines which can cause loss of performance and/or engine stalls.

Thanks TEG, I get all of the erosion stuff, but these are (even in the terms of the airflow) longer term effects than a flameout, and in all situations, I found, the engines restarted (one didn't accelerate and subsequently reshut down) but this precludes that there was suffifient airflow blockage that was causing the flame-out. In fact in some of the pictures I found, ther were turbine blades (incorrectly identified as Fan blades) thaa looked pretty nice. Turbine parts often look so nasty, and in fact I have personally seen 1st stage turbine blades eroded to nubs appoximately a third of their orignal length still operating.
Blocking cooling holes, galssing over of airfoils are all life debits. But these don;t shut down hte engine. I think the best answer here is the change in combustible gases and either an engine die out or the abrasives attacking the tip aberadables, which results in decreased compressor operating margin, with an ensuing stall and stagnation.
The fine particualte will prevail in the atmosphere for years, this will result in a lot of airframe damage to paints along the leading edges of the aircraft, filters will need to be changed more often, and engine maintenance due to leading edge fan and compressor wear, and potential bearing and seal wear.

Thanks TEG, I get all of the erosion stuff, but these are (even in the terms of the airflow) longer term effects than a flameout, and in all situations, I found, the engines restarted (one didn't accelerate and subsequently reshut down) but this precludes that there was suffifient airflow blockage that was causing the flame-out. In fact in some of the pictures I found, ther were turbine blades (incorrectly identified as Fan blades) thaa looked pretty nice. Turbine parts often look so nasty, and in fact I have personally seen 1st stage turbine blades eroded to nubs appoximately a third of their orignal length still operating.
Blocking cooling holes, galssing over of airfoils are all life debits. But these don;t shut down hte engine. I think the best answer here is the change in combustible gases and either an engine die out or the abrasives attacking the tip aberadables, which results in decreased compressor operating margin, with an ensuing stall and stagnation.

IMAO I think that is somewhat myopic (I think you‘re somewhat oversimplifying). All factors are important. The damaged blades and compromised sensors can confuse engine control computers and that can alter the fuel ratio. As I often say in a simple metaphor “the computer gets confused” by the erroneous sensor input and the changes to the components. Sometimes the altered feel ratio is the cause, sometimes it's the effect.

Sometimes under some circumstances when things are not right on some engines the computer will reduce the power of the engine or take it to idle or even shut it down. The lower power or idle settings is an emergency mode that I often use the metaphor “limp in mode”. The low power mode is an attempt to save the engine long enough to find the nearest runway. The idle mode is a last-ditch effort to try to keep hydraulics and electrical system powered.

Some scientists hypothesized that some of the disappearances can be explained by methane and methane hydrate deposits under the ocean that can sometimes massively or catastrophically release.

I think that guy worked in my office, ATFS!?

fisk

Ok, so broken jet engines are a very bad thing but does anyone know what happens if we humans breathe this stuff in? Would we all get lung problems or would it be harmless? Sounds like nasty stuff.