Turbo Bark
12-26-2006 | 11:08 AM
#3
Registered User
Joined: Dec 2003
Posts: 14,672
Likes: 9
From: Montana
You should avoid barking by letting off the throttle slowly. While I've only seen a couple of turbo shafts snap in half from it I've seen many factory airbox lids and BHAFs blown off from it.
Sort of a sick feeling opening the hood finding your air filter in the wrong place and realizing you've been sucking in dirty air for who knows how long.
Sort of a sick feeling opening the hood finding your air filter in the wrong place and realizing you've been sucking in dirty air for who knows how long.
12-26-2006 | 12:46 PM
#5
Registered User
Joined: Apr 2004
Posts: 8,234
Likes: 1
From: Texas/Oklahoma Border
It's basically a compressor stall, which puts a heavy reverse load on your shaft, while it's spinning over 100,000 rpm.
Some major forces are involved, IMO.
As Bill says, not a lot of shafts get reported as breaking, but still, should be avoided as much as possible.
RJ
Some major forces are involved, IMO.
As Bill says, not a lot of shafts get reported as breaking, but still, should be avoided as much as possible.
RJ
Trending Topics
12-26-2006 | 11:08 PM
#8
Registered User
Joined: Jul 2003
Posts: 122
Likes: 0
You can get a turbo guard which BD Performance sells or other brands that protect from turbo bark. Bds sell for around 6 bills. And yes it is bad to have it bark. Usually you can get away with it but it can break things also. A couple af years ago there were some threads on guys making their own. the turbo guards are basically a popoff valve that relieves the pressure at pre deremined settings
12-27-2006 | 05:55 PM
#10
Muted User
Joined: Jan 2005
Posts: 640
Likes: 0
A blow off vavle will not stop what people on here are calling turbo bark. Since there is no throttle on a diesel there is no rapid rise of compressor pressure like there is on a gasser when you get out of the throttle.
What diesel folks are calling turbo bark is nothing more than the turbo rapidly decellerating. When you get out of the accelerator pedal, there is immediate cessation of fuel burn in the engine and thus there is a rapid drop in the turbine power output due to the dropped EGT, pressure and volume of exhaust gas flow, and since the turbine no longer is supplying enough power to operate the compressor at high speeds, the turbo rapidly decelerates due to the great resistance of the compressor operating at speed. And there is no torque reversal either, its in the same direction.....
Kp
What diesel folks are calling turbo bark is nothing more than the turbo rapidly decellerating. When you get out of the accelerator pedal, there is immediate cessation of fuel burn in the engine and thus there is a rapid drop in the turbine power output due to the dropped EGT, pressure and volume of exhaust gas flow, and since the turbine no longer is supplying enough power to operate the compressor at high speeds, the turbo rapidly decelerates due to the great resistance of the compressor operating at speed. And there is no torque reversal either, its in the same direction.....
Kp
12-27-2006 | 06:57 PM
#11
Registered User
Joined: Feb 2004
Posts: 629
Likes: 0
From: south west, Michigan
12-27-2006 | 11:35 PM
#12
Muted User
Joined: Jan 2005
Posts: 640
Likes: 0
Well if its controlled by a device looking at the accelerator pedal position, then it would work ! Didnt know they were making them like that. Thought they were just pressure operated like the gassers.....
my bad...But, I must still say, that the bark is not a bad thing on a diesel. I believe this myth got started when guys were breaking HX40 shafts.... Stock HX40 shafts tend to break in a high boost applications, and with high boost you get loud barks, and so the breakage got associated with the bark.... There is no torque reversal on the turbo shaft with a bark...
Kp
12-28-2006 | 12:52 AM
#13
Registered User
Joined: Jul 2006
Posts: 511
Likes: 0
A blow off vavle will not stop what people on here are calling turbo bark. Since there is no throttle on a diesel there is no rapid rise of compressor pressure like there is on a gasser when you get out of the throttle.
What diesel folks are calling turbo bark is nothing more than the turbo rapidly decellerating. When you get out of the accelerator pedal, there is immediate cessation of fuel burn in the engine and thus there is a rapid drop in the turbine power output due to the dropped EGT, pressure and volume of exhaust gas flow, and since the turbine no longer is supplying enough power to operate the compressor at high speeds, the turbo rapidly decelerates due to the great resistance of the compressor operating at speed. And there is no torque reversal either, its in the same direction.....
Kp
What diesel folks are calling turbo bark is nothing more than the turbo rapidly decellerating. When you get out of the accelerator pedal, there is immediate cessation of fuel burn in the engine and thus there is a rapid drop in the turbine power output due to the dropped EGT, pressure and volume of exhaust gas flow, and since the turbine no longer is supplying enough power to operate the compressor at high speeds, the turbo rapidly decelerates due to the great resistance of the compressor operating at speed. And there is no torque reversal either, its in the same direction.....
Kp
Also keep in mind that the net thrust on turbo shafts is relatively small. That is because of the equal thrust aplied by the compressor in one direction and the thrust of the turbine in the other direction. The wheels are balanced so that these respective thrusts are equal and mostly counter act each other out. Push a compressor into stall almost instantly and its component of the thrust goes away almost instantly. Now the only thrust felt on the shaft is from the turbine. When the compressor comes out of stall, the whole process gets repeated in the opposite direction. These radical changes in thrust direction and magnitude have to be absorbed by the bearings.
As far as breaking shafts there could be significant torque type forces on the shaft in relation to the compressor and turbine ends. As the compressor blades go in and out of stall, they conversely go in and out of a loaded / unloaded condition. Unloaded during the stall, loaded (overloaded) recovering from the stall. From the turbine end, the shaft would get rotationally loaded and fulling unloaded almost instantly. You can see how this would cause pretty severe and rapid rotational torque as well as longitudenal thrust surges on the shaft itself. As well the probability of some really rapid RPM changes both acceleration and deceleration as the load / unload process occurs. My guess is that the shaft would most likely snap during a rapid deceleration, at high RPM, as the compressor suddenly is able to "bite" into the air again when it comes out of stall.
Jim
12-28-2006 | 03:45 AM
#14
Registered User
Joined: Dec 2005
Posts: 74
Likes: 0
From: Europe - Finland
Compressor stall and surge is an interesting phenomena. The net is full of explanations and studies over this issue. Here are just few links.
--
"Experts in 'compressor surge'Definition:
A disturbance occuring in gas compressors, especially centrifugal compressors, due to excessive pressure across the compressor in which the compressor blades stall and air flow suddenly drops. The flow can fluctuate and the compressor be damaged. It is the point of instability at which a compressor surges across, trying to reestablish its point of stability. "
http://www.intota.com/multisearch.as...mpressor+surge
--
http://www.airforce.forces.gc.ca/dfs...05/Jan05_e.pdf
http://en.wikipedia.org/wiki/Compressor_map
--
"Experts in 'compressor surge'Definition:
A disturbance occuring in gas compressors, especially centrifugal compressors, due to excessive pressure across the compressor in which the compressor blades stall and air flow suddenly drops. The flow can fluctuate and the compressor be damaged. It is the point of instability at which a compressor surges across, trying to reestablish its point of stability. "
http://www.intota.com/multisearch.as...mpressor+surge
--
http://www.airforce.forces.gc.ca/dfs...05/Jan05_e.pdf
http://en.wikipedia.org/wiki/Compressor_map
12-28-2006 | 11:30 AM
#15
Muted User
Joined: Jan 2005
Posts: 640
Likes: 0
I believe that RJ was refering to thrust reversal not torque reversal. This is cause primarily by the reversal in direction of the air flow from the high pressure in the manifold back through the compressor into the air filter. I am going to guess that the stall cavitation forces and the flexation forces on the compressor blades could be pretty significant under certain conditions. Especially if the turbo is already at or over rated RPM. Do it enough times and a blade or a bearing might fail.
Also keep in mind that the net thrust on turbo shafts is relatively small. That is because of the equal thrust aplied by the compressor in one direction and the thrust of the turbine in the other direction. The wheels are balanced so that these respective thrusts are equal and mostly counter act each other out. Push a compressor into stall almost instantly and its component of the thrust goes away almost instantly. Now the only thrust felt on the shaft is from the turbine. When the compressor comes out of stall, the whole process gets repeated in the opposite direction. These radical changes in thrust direction and magnitude have to be absorbed by the bearings.
As far as breaking shafts there could be significant torque type forces on the shaft in relation to the compressor and turbine ends. As the compressor blades go in and out of stall, they conversely go in and out of a loaded / unloaded condition. Unloaded during the stall, loaded (overloaded) recovering from the stall. From the turbine end, the shaft would get rotationally loaded and fulling unloaded almost instantly. You can see how this would cause pretty severe and rapid rotational torque as well as longitudenal thrust surges on the shaft itself. As well the probability of some really rapid RPM changes both acceleration and deceleration as the load / unload process occurs. My guess is that the shaft would most likely snap during a rapid deceleration, at high RPM, as the compressor suddenly is able to "bite" into the air again when it comes out of stall.
Jim
Also keep in mind that the net thrust on turbo shafts is relatively small. That is because of the equal thrust aplied by the compressor in one direction and the thrust of the turbine in the other direction. The wheels are balanced so that these respective thrusts are equal and mostly counter act each other out. Push a compressor into stall almost instantly and its component of the thrust goes away almost instantly. Now the only thrust felt on the shaft is from the turbine. When the compressor comes out of stall, the whole process gets repeated in the opposite direction. These radical changes in thrust direction and magnitude have to be absorbed by the bearings.
As far as breaking shafts there could be significant torque type forces on the shaft in relation to the compressor and turbine ends. As the compressor blades go in and out of stall, they conversely go in and out of a loaded / unloaded condition. Unloaded during the stall, loaded (overloaded) recovering from the stall. From the turbine end, the shaft would get rotationally loaded and fulling unloaded almost instantly. You can see how this would cause pretty severe and rapid rotational torque as well as longitudenal thrust surges on the shaft itself. As well the probability of some really rapid RPM changes both acceleration and deceleration as the load / unload process occurs. My guess is that the shaft would most likely snap during a rapid deceleration, at high RPM, as the compressor suddenly is able to "bite" into the air again when it comes out of stall.
Jim
This was very refreshing to read through a subject matter on here and get some good technical explanations for things rather than listen to unsubstantiated wives tales.
Bravo!!! Jim and RJ!!
Kp