Tired of bumping along to Oshkosh?

wrote:
Has anyone here been certified to actually work on a jet engine, how would
you keep from exceeding 620 degrees egt, the fuel control cant operate under
the avgas parameters in correcting the egt, the retired af person does not
appear to know anything about a jet engine. In a J-57 where you have 16
stages of compression prior to injecting the fuel in the combustion chamber
how would you bleed off enough air and still maintain power using avgas, the
combustion chambers and rest of the hot section can not take the extreme
heat of regular avgas, the flashpoint is too high compared to jp-4 or
similar fuel. How could the fuel control work properly when it is lubricated
by the jp-4. please tell me

Not all jet engines used jet fuel for lubrication, not all jet
engines are axial flow and if I recall correctly the USAF stopped using
JP-4 years ago. Ever heard of JP-5 or JP-8? The fact remains the B-36
and C-123 used avgas in their jet engines. I never worked on either but
I worked with men who did. The B-36 used four J47-GE-19 jet engines on
take off, high altitude and for dash speed. The C-123 used J-44R3 and
J-69 engines. In neither aircraft were there separate tanks for jet fuel.

As for jet engines while I was not a jet mech I worked the engine
instrumentations systems on C-130A, HC-130, AC-130, KC-135, C-141, T-33,
T-39, F-4E, UH-1P, HH-3, MH-53, UH-60, MH-60, several recips and a few
aircraft I will not mention.

As for your J-57 example I assume you have been looking at cut away
pictures. OK, let's do that. Take a look at the size of the inlet. It is
much bigger than needed to compress the air for combustion. Guess what,
that's done on purpose. It's done to take in a volume of air to cool the
engine.

Now tell me all about your experience with jet engines. Tell me all
about your vast experience that leads you to question my experience.


Dan, U.S. Air Force, retired

On Sat, 06 Aug 2005 13:57:33 -0400, Bryan Martin
wrote:

See: http://encyclopedia.laborlawtalk.com/Jet_engine

According to this article, modern turbine engines may achieve compression
ratios of as high as 44:1 at very high altitudes (very cold intake air). But
the compression ratio of a turbine engine can't be compared directly with
the compression ratio of piston engines due to the differences between
cyclic combustion and continuous combustion, among other things. He may have
been referring to fuel/air ratios with the 14:1 and 70:1 numbers, but they
still don't sound quite right.

In any case, just because gasoline is burned at a certain F/A ratio and
compression ratio in a piston engine has nothing to do with how you would
burn it in a turbine. Piston engines operate at near stoiciometric mixtures:
nearly all the oxygen and all the fuel react with each other leaving very
little of either in the exhaust. This can not be done in a turbine. No
matter what fuel is used it would result in melt-down of the hot section of
the engine. Most of the air passing through a turbine engine is used to keep
it cool. Only a small portion of the available oxygen is used to burn the
fuel. Theoretically, just about any fluid fuel could be used in a turbine as
long as you can produce a combustible mixture in the core of the combustor
and pump enough excess air through it keep it cool. You could probably burn
powdered solid fuels in a turbine if you could manage to feed a steady
stream of it to in the combustors and get it to mix properly.

Hmmm, a coal burning jet engine?

Or flour?

Bryan Martin wrote:
As I recall, the biggest problem with burning gasoline in a turbine is the
the TBO is shortened due to the lower lubricating qualities of gasoline over
jet fuel. The fuel pumps and injectors wear out quicker.

Another related durability problem is lead deposits on the turbine
blades. I'm not sure this was a significant problem with very early
jet engines run on avgas, since they didn't last thousands of hours
like nowadays.

Possible problems while running the engine could result from the
different fluid properties of the fuel. For example, gasoline is
thinner and evaporates at a lower temperature, so acceleration and
deceleration might be affected, vapor lock might occur.

Steady state the engine will run the same. Heat and pressure is what
drives the turbine, and it doesn't matter if the heat comes from Jet
A, 100LL, turpentine, or whatever.

To AF retired, my experience? I was a jet engine mechanic AF43250, so I know
what I am talking about. As far as the cold section of the engine it has
what is called a convergent-divergent duct system to compress the air to 70
parts oxygen to one part fuel, however the engine can't use all the air up
to approximately 80% power so it exhausts it thru the bleed valve on the
side of the engine.Again, check any engine guide and gasoline engines have
approximately 14 parts oxygen to 1 part fuel, doesn't matter how its
compressed. The fuel control controls the amount of fuel injected into the
engine but it relies on pressure sensors and temperature sensors to do that.
Using avgas the egt would go very high because of its quick burning
characteristics compared to kerosene or other jets fuels therefore the
pressure and temperature sensors would send that information to the fuel
control for adjustment. The fuel control also is lubricated by jet fuel and
would soon fail without this lubrication ( it is so critical that we had to
submerge the fuel control in jet fuel for 24 hours prior to installation and
then if we manually moved the controls more the three times prior to
installation we had to send it back for rebuilding. Incidentally, I also
worked on F-102.T-33,B-57,T-39,C-130,C-133,F-101,all the aircraft had the
same requirements for fuel. Perhaps the more modern engine have more
tolerant materials , however when talking to recent jet engine mechanics
they say the requirements are the same. As I understand it the aircraft you
flew on used the jets for takeoff and at times at altitude only, if that's
truly the case the engine may be able to operate on avgas at those times and
those times only.

"Jim Carriere" wrote in message
...
Bryan Martin wrote:
As I recall, the biggest problem with burning gasoline in a turbine is
the
the TBO is shortened due to the lower lubricating qualities of gasoline
over
jet fuel. The fuel pumps and injectors wear out quicker.

Another related durability problem is lead deposits on the turbine blades.
I'm not sure this was a significant problem with very early jet engines
run on avgas, since they didn't last thousands of hours like nowadays.

Possible problems while running the engine could result from the different
fluid properties of the fuel. For example, gasoline is thinner and
evaporates at a lower temperature, so acceleration and deceleration might
be affected, vapor lock might occur.

Steady state the engine will run the same. Heat and pressure is what
drives the turbine, and it doesn't matter if the heat comes from Jet A,
100LL, turpentine, or whatever.

wrote:
To AF retired, my experience? I was a jet engine mechanic AF43250, so I know
what I am talking about. As far as the cold section of the engine it has
what is called a convergent-divergent duct system to compress the air to 70
parts oxygen to one part fuel, however the engine can't use all the air up
to approximately 80% power so it exhausts it thru the bleed valve on the
side of the engine.

J-33s had bleed air? Please explain to me the J-33 used "convergent -
divergent" air flow.


Again, check any engine guide and gasoline engines have
approximately 14 parts oxygen to 1 part fuel, doesn't matter how its
compressed. The fuel control controls the amount of fuel injected into the
engine but it relies on pressure sensors and temperature sensors to do that.
Using avgas the egt would go very high because of its quick burning
characteristics compared to kerosene or other jets fuels therefore the
pressure and temperature sensors would send that information to the fuel
control for adjustment. The fuel control also is lubricated by jet fuel and
would soon fail without this lubrication ( it is so critical that we had to
submerge the fuel control in jet fuel for 24 hours prior to installation and
then if we manually moved the controls more the three times prior to
installation we had to send it back for rebuilding.

The lead in AvGas would have acted as a lubricant long enough to get
where you were going.

Incidentally, I also
worked on F-102.T-33,B-57,T-39,C-130,C-133,F-101,all the aircraft had the
same requirements for fuel.

When you get a chance look at the -1 TOs for those aircraft. They
list substitute fuels. A lot has changed since you were in, I'm assuming
1960ish, but fuel characteristics.

You worked on all those aircraft in less than 6 years in the USAF? It
took me 20 to do the aircraft I listed.



Perhaps the more modern engine have more
tolerant materials , however when talking to recent jet engine mechanics
they say the requirements are the same. As I understand it the aircraft you
flew on used the jets for takeoff and at times at altitude only, if that's
truly the case the engine may be able to operate on avgas at those times and
those times only.

Do us both a favour and do some research on the subject, OK? Try
Google. Telling me I don't know what I am talking about doesn't quite
make for civil discourse. BTW, I never said I flew on B-36s or C-123s.

Dan, U.S. Air Force, retired

The J-33 is not a axial flow engine, it is centrifical flow with one stage
of compression, AF I suggest YOU are the one who needs to read up on the
subject and not me, btw do you believe everything that google returns as the
factual information, I suggest you keep in your line of expertise and don't
go outside of either apg or flt engineer, you definitely aren't experienced
enough to debate jet engines and their feeding.

"Dan, U.S. Air Force, retired" wrote in message
news:QvnJe.71991$FP2.65700@lakeread03...
wrote:
To AF retired, my experience? I was a jet engine mechanic AF43250, so I
know what I am talking about. As far as the cold section of the engine it
has what is called a convergent-divergent duct system to compress the air
to 70 parts oxygen to one part fuel, however the engine can't use all the
air up to approximately 80% power so it exhausts it thru the bleed valve
on the side of the engine.

J-33s had bleed air? Please explain to me the J-33 used "convergent -
divergent" air flow.


Again, check any engine guide and gasoline engines have
approximately 14 parts oxygen to 1 part fuel, doesn't matter how its
compressed. The fuel control controls the amount of fuel injected into
the engine but it relies on pressure sensors and temperature sensors to
do that. Using avgas the egt would go very high because of its quick
burning characteristics compared to kerosene or other jets fuels
therefore the pressure and temperature sensors would send that
information to the fuel control for adjustment. The fuel control also is
lubricated by jet fuel and would soon fail without this lubrication ( it
is so critical that we had to submerge the fuel control in jet fuel for
24 hours prior to installation and then if we manually moved the controls
more the three times prior to installation we had to send it back for
rebuilding.

The lead in AvGas would have acted as a lubricant long enough to get
where you were going.

Incidentally, I also
worked on F-102.T-33,B-57,T-39,C-130,C-133,F-101,all the aircraft had the
same requirements for fuel.

When you get a chance look at the -1 TOs for those aircraft. They list
substitute fuels. A lot has changed since you were in, I'm assuming
1960ish, but fuel characteristics.

You worked on all those aircraft in less than 6 years in the USAF? It
took me 20 to do the aircraft I listed.



Perhaps the more modern engine have more
tolerant materials , however when talking to recent jet engine mechanics
they say the requirements are the same. As I understand it the aircraft
you flew on used the jets for takeoff and at times at altitude only, if
that's truly the case the engine may be able to operate on avgas at those
times and those times only.

Do us both a favour and do some research on the subject, OK? Try
Google. Telling me I don't know what I am talking about doesn't quite make
for civil discourse. BTW, I never said I flew on B-36s or C-123s.

Dan, U.S. Air Force, retired

wrote:

The J-33 is not a axial flow engine, it is centrifical flow with one stage
of compression, AF I suggest YOU are the one who needs to read up on the
subject and not me, btw do you believe everything that google returns as the
factual information, I suggest you keep in your line of expertise and don't
go outside of either apg or flt engineer, you definitely aren't experienced
enough to debate jet engines and their feeding.

You never made the distinction between types of engines. You said
"As far as the cold section of the engine it as what is called a
convergent- divergent duct system to compress the air to 70 parts oxygen
to one part fuel, however the engine can't use all the air up to
approximately 80% power so it exhausts it thru the bleed valve on the
side of the engine."

Try saying what you actually mean.

I told you what my job was and it certainly wasn't a flight engineer.

If you really were in the Air Force it wasn't very long since you
never went beyond 5 level. How does that compare with my 20 years?

As for Google I never said I believed everything or anything, I
simply suggested you try using it instead of insulting me.

Since you refuse to be civil this discussion is closed.

Dan, U.S. Air Force, retired and damned proud of it



"Dan, U.S. Air Force, retired" wrote in message
news:QvnJe.71991$FP2.65700@lakeread03...

wrote:

To AF retired, my experience? I was a jet engine mechanic AF43250, so I
know what I am talking about. As far as the cold section of the engine it
has what is called a convergent-divergent duct system to compress the air
to 70 parts oxygen to one part fuel, however the engine can't use all the
air up to approximately 80% power so it exhausts it thru the bleed valve
on the side of the engine.

J-33s had bleed air? Please explain to me the J-33 used "convergent -
divergent" air flow.


Again, check any engine guide and gasoline engines have

approximately 14 parts oxygen to 1 part fuel, doesn't matter how its
compressed. The fuel control controls the amount of fuel injected into
the engine but it relies on pressure sensors and temperature sensors to
do that. Using avgas the egt would go very high because of its quick
burning characteristics compared to kerosene or other jets fuels
therefore the pressure and temperature sensors would send that
information to the fuel control for adjustment. The fuel control also is
lubricated by jet fuel and would soon fail without this lubrication ( it
is so critical that we had to submerge the fuel control in jet fuel for
24 hours prior to installation and then if we manually moved the controls
more the three times prior to installation we had to send it back for
rebuilding.

The lead in AvGas would have acted as a lubricant long enough to get
where you were going.

Incidentally, I also

worked on F-102.T-33,B-57,T-39,C-130,C-133,F-101,all the aircraft had the
same requirements for fuel.

When you get a chance look at the -1 TOs for those aircraft. They list
substitute fuels. A lot has changed since you were in, I'm assuming
1960ish, but fuel characteristics.

You worked on all those aircraft in less than 6 years in the USAF? It
took me 20 to do the aircraft I listed.



Perhaps the more modern engine have more

tolerant materials , however when talking to recent jet engine mechanics
they say the requirements are the same. As I understand it the aircraft
you flew on used the jets for takeoff and at times at altitude only, if
that's truly the case the engine may be able to operate on avgas at those
times and those times only.

Do us both a favour and do some research on the subject, OK? Try
Google. Telling me I don't know what I am talking about doesn't quite make
for civil discourse. BTW, I never said I flew on B-36s or C-123s.

Dan, U.S. Air Force, retired

It would appear as though we have another "wood species expert" in our
midst.

In the first place, your original post used the term "compression ratio",
not air-fuel ratio. I doubt you know what you are talking about.

PLONK.


Jim



" wrote in message
...
To AF retired, my experience? I was a jet engine mechanic AF43250, so I
know what I am talking about.

Sorry Dan, Very true that I was in the Af in the 60's, however the 5 level
in 43250 indicates expert rating, 43270 would be inspections level. I worked
on that many aircraft because in the 60's they didn't have as many jet
engine mechanics as perhaps they have today, also as I was assigned to the
flight line I had to be proficient on multiple aircraft as many different
types visited Andrews afb, and the Clark afb. I apologize if I got feisty,
it just seemed with some of the comments from everyone that some doubted my
expertise and I attempted to explain what was reality versus logical with
jet engines.


"Dan, U.S. Air Force, retired" wrote in message
news:8joJe.73553$FP2.30579@lakeread03...
wrote:

The J-33 is not a axial flow engine, it is centrifical flow with one
stage of compression, AF I suggest YOU are the one who needs to read up
on the subject and not me, btw do you believe everything that google
returns as the factual information, I suggest you keep in your line of
expertise and don't go outside of either apg or flt engineer, you
definitely aren't experienced enough to debate jet engines and their
feeding.

You never made the distinction between types of engines. You said "As
far as the cold section of the engine it as what is called a convergent-
divergent duct system to compress the air to 70 parts oxygen to one part
fuel, however the engine can't use all the air up to approximately 80%
power so it exhausts it thru the bleed valve on the side of the engine."

Try saying what you actually mean.

I told you what my job was and it certainly wasn't a flight engineer.

If you really were in the Air Force it wasn't very long since you never
went beyond 5 level. How does that compare with my 20 years?

As for Google I never said I believed everything or anything, I simply
suggested you try using it instead of insulting me.

Since you refuse to be civil this discussion is closed.

Dan, U.S. Air Force, retired and damned proud of it



"Dan, U.S. Air Force, retired" wrote in message
news:QvnJe.71991$FP2.65700@lakeread03...

wrote:

To AF retired, my experience? I was a jet engine mechanic AF43250, so I
know what I am talking about. As far as the cold section of the engine
it has what is called a convergent-divergent duct system to compress the
air to 70 parts oxygen to one part fuel, however the engine can't use
all the air up to approximately 80% power so it exhausts it thru the
bleed valve on the side of the engine.

J-33s had bleed air? Please explain to me the J-33 used "convergent -
divergent" air flow.


Again, check any engine guide and gasoline engines have

approximately 14 parts oxygen to 1 part fuel, doesn't matter how its
compressed. The fuel control controls the amount of fuel injected into
the engine but it relies on pressure sensors and temperature sensors to
do that. Using avgas the egt would go very high because of its quick
burning characteristics compared to kerosene or other jets fuels
therefore the pressure and temperature sensors would send that
information to the fuel control for adjustment. The fuel control also is
lubricated by jet fuel and would soon fail without this lubrication ( it
is so critical that we had to submerge the fuel control in jet fuel for
24 hours prior to installation and then if we manually moved the
controls more the three times prior to installation we had to send it
back for rebuilding.

The lead in AvGas would have acted as a lubricant long enough to get
where you were going.

Incidentally, I also

worked on F-102.T-33,B-57,T-39,C-130,C-133,F-101,all the aircraft had
the same requirements for fuel.

When you get a chance look at the -1 TOs for those aircraft. They list
substitute fuels. A lot has changed since you were in, I'm assuming
1960ish, but fuel characteristics.

You worked on all those aircraft in less than 6 years in the USAF? It
took me 20 to do the aircraft I listed.



Perhaps the more modern engine have more

tolerant materials , however when talking to recent jet engine mechanics
they say the requirements are the same. As I understand it the aircraft
you flew on used the jets for takeoff and at times at altitude only, if
that's truly the case the engine may be able to operate on avgas at
those times and those times only.

Do us both a favour and do some research on the subject, OK? Try
Google. Telling me I don't know what I am talking about doesn't quite
make for civil discourse. BTW, I never said I flew on B-36s or C-123s.

Dan, U.S. Air Force, retired

Bryan,
a jet engine does use all the air it intakes after 80% throttle, prior to
80% the engine bleeds the part of the air not needed to the atmosphere thru
a valve mounted on the side of the engine called a bleed valve. You are
right about physics however the kerosene needs much more air then gasoline
to achieve proper combustion.

"Bryan Martin" wrote in message
...
Gasoline fueled reciprocating engines may use a 14:1 oxygen to fuel ratio
but this is totally irrelevant when discussing jet engines. Reciprocating
engines combine all the oxygen they take in with the fuel, jet engines do
not. You may have been a really good jet mechanic but you obviously don't
know much about the physics involved.

in article , at
wrote on 8/7/05 8:14 AM:

what is called a convergent-divergent duct system to compress the air to
70
parts oxygen to one part fuel, however the engine can't use all the air
up
to approximately 80% power so it exhausts it thru the bleed valve on the
side of the engine.Again, check any engine guide and gasoline engines
have
approximately 14 parts oxygen to 1 part fuel, doesn't matter how its
compressed.