Matt S

I've got a Stage 3 Garrett 3788 awaiting install. I'm told there's problems with this type of turbo surging. What is surging?

omaharam

Surging is when the speed of the compressor wheel is too high in relation to the amount of air the engine wants to take in. The turbo is then fighting itself on building boost and stalling due to nowhere for the air to go. Your boost gauge will flutter violently as the turbo fights itself.

CamperAndy

Not exactly.

Surge is the reversal of air flow through the compressor. The most common cause (in our trucks) is the rapid deceleration of the turbo due to loss of drive pressure to the turbine when you go from WOT to no pedal. Normally this is announced by what is often referred on here as "compressor bark", that sound is the rapid dump of air from the inner cooler back out the turbo compressor and out the inlet filter. Does not hurt the engine but can be VERY bad for the turbo and inlet filter.

Stall is more of what you are describing. Stall occurs when the compressor is right at its max pressure DP for a given compressor speed.Stall may not be audible but will normally present itself as a rapidly fluctuating intake pressure (maybe only a couple of pounds) and a rapid sharp rise in EGT. Not real bad for the turbo but real bad for the engine.

omaharam

Um, no. I was correct. Here is some reading for you. Surge is what I described and will ruin a turbo - as will "barking" a turbo. I had this problem and ruined a turbo. I am very familiar with it - unfortunately.

http://www.turbobygarrett.com/turbob...o_tech103.html

White97GTVert

Omaha is correct.

KNUCKLEMOVER

So, Lets Hear About The Results/fall-out Of Said Condition..

trx

One member on this forum had issue (olywrench) have not heard of any others. Matt if you already have this turbo then throw it in and let us know how it works out for you.

omaharam

Destroyed thrust bearing. Luckily I pulled it before it came apart.

CamperAndy

If you had a failure does not mean you understand the term to describe the condition that caused the failure. The definition on the Garrett link for surge glosses over the stall line that occurs before surge. Thus your description was not 100% correct to the condition that was asked about and I guess none of us have answered for his specific turbo.

The following quote is from a well known data base on the web and is a bit more detailed in explaining what occurs in a compressor stall and surge. The company I work for (see avatar) and have a wee bit if time with built the first turbine engine and I feel that on this particular aspect of turbo compressor operation my posted definition is correct (first post was abbreviated but concise, this post has a more detailed description) and if you really feel I am missing an important point please let me know but you cant just say you are right because you failed a turbo.

Qoute -

There are two severities of compressor stall.

"Rotational stall" is a local disruption of airflow within the compressor which continues to provide compressed air but with reduced effectiveness. "Rotational stall" arises when a small proportion of aerofoils experience aerofoil stall disrupting the local airflow without destabilising the compressor. The stalled aerofoils create pockets of stagnant air (referred to as "stall cells") which, rather than moving in the flow direction, rotate around the circumference of the compressor. The stall cells rotate with the rotor blades but at 50%-70% of the speed, passing to the next aerofoils around the rotor. Stable local stall can also occur which cover the complete circumference (axisymmetric) but only a portion of the radius of the compressor with the remainder of the passage continuing to pass normal flow.

A rotational stall may be momentary, resulting from an external effects, or may be steady as the compressor finds a working equilibrium. Local stalls substantially reduce the efficiency of the compressor and increase the structural loads on the aerofoils in the region affected. In many cases however, the compressor aerofoils are critically loaded such that the original stall cells affect neighbouring regions and rapidly grow to a complete compressor stall.

"Axisymmetric stall" more commonly known as "Compressor Surge" is a complete breakdown in compression resulting in a reversal of flow and a violent expulsion of the previously compressed air out the intake, due to the compressor's inability to maintain pressure. An axis-symmetric stall will occur when a compressor either experiences conditions which exceed the limit of its pressure rise capabilities: or is highly loaded such that it does not have the capacity to absorb a momentary disturbance. In this case, a rotational stall will quickly propagate to include the entire compressor. The compressor will recover to normal flow once the pressure ratio reduces to one that the compressor is capable of sustaining stable airflow. If, however, the off-design conditions that induced the stall remain, the return of stable airflow will quickly reproduce the other conditions at the time of surge, and the process will repeat.[1] Such "Locked-in" stall is particularly dangerous, with very high levels of vibration causing accelerated engine wear and possible damage.

omaharam

That is exactly what I said - just in layman's terms. I said the turbo is fighting itself. And why do the two occurrences happen that you quoted above? It has to do with engine rpm, exhaust production, and intake ability. Your quote even calls it "surge" in the second paragraph. That is what he was asking about and what I was referring to. See the part I changed to red.
Also, I never said I was right because I ruined a turbo. When I was personally having this trouble I did a lot of research to identify the problem. That is what I based my statement on.

CamperAndy

Well if that is the way you interpret what you wrote, fine but it is as clear as mud to me and I have no need for layman's terms. So I would hate to see how well the rest of the board interpret what you wrote.

To answer the question you asked directly. Why does stall and or surge happen?

1 - poor design, very wide answer but it covers items such as
a - too much tip clearance
b - Miss match in turbine to compressor performance
c - operator modifications (i.e. capping waste gate)
2 - Dirty compressor, this causes loss of efficiency and will push the delta off the map towards the stall and surge line.
3 - Loss of drive pressure to maintain the required compressor speed for a given compressor delta.

j-fox

CamperAndy you are correct.Surge happens when the drive pressure suddenly falls and the shaft violently stops and reverses direction. As you know, it can snap the shaft on some turbos.
Ususally it is a turbo design that has a large compressor on it.

omaharam

It's nice to know that you don't want things in layman's terms. What about everyone else?

omaharam

Only in certain applications. You could have a turbo function perfectly fine on one truck and put it on another truck and have it surge, stall, bark, whatever.

So if I had not replied to the original question at all, what would your reply to him have been?

KNUCKLEMOVER

This Is A Constant Condition In My Rig...
The Needle On My Boost Gauge Is Rarely Stable.
In Most Cases It Fluttering In A 1-2 Lb Increment At Blur Speed
@ Cruising Speed , Under Hard Accel Ect..
Turbo "bark Is A Common Occurrence As Well

Something To Worry About>?