Jumo 004 flameouts?
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- Start date
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mikewint
Captain
The original BMW003 engines both failed on their first test flight. The pilot survived because only because the aircraft also had a prop engine in the nose. The Jumo004 engins were only marginally better. By the summer of 1943 the Jumo004A engines had passed several 100 hour tests with overhaul times of 50 hours BUT the engine could not be mass produced because of its weight and use of very scarce metals (Ni, Co, Mo) to make the turbine blades sufficiently heat resistant.
Enter the Jumo004B with all high heat resistant parts changed to mild steel. The engines now required an overhaul after 25 hours and a maximum life span of 35 hours. In addition the engines were fitted with a air bleed system to cool the now delicate turbine blades.
The engines were now VERY susceptible to failing if the throttles were increased or decreased to rapidly.
The problem with the Jumo004B is the fuel injection control mechanism, which is operational only when the engine is above a specific rpm (6000 or 7000, depending on sources).
Once above that rpm, you can move the throttle forward and backward as quick as you like, the automatic fuel injection will take care of keeping the combustion chamber within its operational parameters.
Below that rpm however, you have to manually adjust the amount of fuel matching the current engine's rpm, which is just a narrow band of applicable settings, hence in order to increase or decrease speed, you have to move the throttle slowly, otherwise one of the following will happen:
Flameout in case you move back the throttle too quickly.
This happens because the engine runs at relatively high rpm and according to your quick fuel reduction, the mixture inside the combustion chamber becomes too lean to keep the fire going.
Since the flameout will also stop further energy on the turbine, your engine will quickly die.
This is particularly critical since the restart of a Jumo004 is a lottery game where you only win when New years eve and Easter fall on the same day.
Oversaturation, causing unburnt fuel to spill into the jet pipe, where uncontrolled ignition occurs.
This is generally less critical and it's often seen in old movie footages, especially when the Jumo004 gets started: You see some flames coming out of the bottom of the jet's tailpipe.
It's okay unless it stays like that for too long or it becomes too severe.
If it does become too severe, it can lead to a flameout from oversaturation. In effect your engine keeps burning, but not where it should.
Oversaturation to a point where fuel is spilled into bleed air pipes.
The background here is the metallurgy of the blades:
Since the Germans couldn't produce stainless steel in required quantities, the serial production Jumo004B hollow turbine blades were produced from folded and welded Cromadur alloy (12% chromium, 18% manganese, and 70% iron) and cooled by compressed air "bled" from the compressor..
When the engine gets massively oversaturated, fuel will spill back into the air bleeds, making it into the cooling air of the turbine blades.
It's easy to guess what happens when you manage to run a flammable fuel/air mixture through hot blades where it's supposed to cool down the blades:
It will deflagrate, rupture the blades and eventually catch fire.
Now you have a burning, disintegrating turbine and that's a REALLY BAD thing.
Jumo tried a variety of compressor blades, beginning with solid steel, later hollow sheet metal ones, welded on the taper, with their roots fitted over
Enter the Jumo004B with all high heat resistant parts changed to mild steel. The engines now required an overhaul after 25 hours and a maximum life span of 35 hours. In addition the engines were fitted with a air bleed system to cool the now delicate turbine blades.
The engines were now VERY susceptible to failing if the throttles were increased or decreased to rapidly.
The problem with the Jumo004B is the fuel injection control mechanism, which is operational only when the engine is above a specific rpm (6000 or 7000, depending on sources).
Once above that rpm, you can move the throttle forward and backward as quick as you like, the automatic fuel injection will take care of keeping the combustion chamber within its operational parameters.
Below that rpm however, you have to manually adjust the amount of fuel matching the current engine's rpm, which is just a narrow band of applicable settings, hence in order to increase or decrease speed, you have to move the throttle slowly, otherwise one of the following will happen:
Flameout in case you move back the throttle too quickly.
This happens because the engine runs at relatively high rpm and according to your quick fuel reduction, the mixture inside the combustion chamber becomes too lean to keep the fire going.
Since the flameout will also stop further energy on the turbine, your engine will quickly die.
This is particularly critical since the restart of a Jumo004 is a lottery game where you only win when New years eve and Easter fall on the same day.
Oversaturation, causing unburnt fuel to spill into the jet pipe, where uncontrolled ignition occurs.
This is generally less critical and it's often seen in old movie footages, especially when the Jumo004 gets started: You see some flames coming out of the bottom of the jet's tailpipe.
It's okay unless it stays like that for too long or it becomes too severe.
If it does become too severe, it can lead to a flameout from oversaturation. In effect your engine keeps burning, but not where it should.
Oversaturation to a point where fuel is spilled into bleed air pipes.
The background here is the metallurgy of the blades:
Since the Germans couldn't produce stainless steel in required quantities, the serial production Jumo004B hollow turbine blades were produced from folded and welded Cromadur alloy (12% chromium, 18% manganese, and 70% iron) and cooled by compressed air "bled" from the compressor..
When the engine gets massively oversaturated, fuel will spill back into the air bleeds, making it into the cooling air of the turbine blades.
It's easy to guess what happens when you manage to run a flammable fuel/air mixture through hot blades where it's supposed to cool down the blades:
It will deflagrate, rupture the blades and eventually catch fire.
Now you have a burning, disintegrating turbine and that's a REALLY BAD thing.
Jumo tried a variety of compressor blades, beginning with solid steel, later hollow sheet metal ones, welded on the taper, with their roots fitted over
Last edited:
- Thread starter
- #3
(my bold)
Mike, I'm after information, not after disinformation. Turbine blades were made hollow, not compressor blades. Please edit the post.
fubar57
General
Mike copy/pasted that from here...Me 262 engine fire Post #4
- Thread starter
- #5
But how? Why? He never does that.
fubar57
General
I know....I was stunned....stunned I tells ya
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