Turbo Stall

[asthpsw]

I've done a search on "Turbo Stall" but still don't understand the concept (so that I can prevent it happening to my TDI) what exactly is Turbo stall & what conditions create it ?

All I know is it is drastic if it happens.................hence want to prevent it ?

Paul

 

[GlanzaV]

Turbo stall or compressor stall/surge is when the compressor wheel of the turbo is operating outside it's compressor map (compressor map is defined by a number of "effieciency islands") outside of this is unstable flow inside the mechanical workings of the turbo.

This is either caused by the compressor wheel being incorrect for your application (too large) or in most cases that you'll hear on forums is when letting off you get "chatter" this is because the compressor wheel is still spining and generating boost even though as the throttle is closed and the intake pressure is "backing up" as it were -- this is usually remedied by having a BOV, and hence why removing your BOV promotes chatter/surge.

 

[asthpsw]

So if this back pressure is too much this put a strain on the compressor side of the turbo ? and in extreme cases could bend the compressor ?

To be honest I was thinking more of the opposite in that if someone had a too higher gear & opened it up there would be alot of boost requested but wouldn't be able to pull against the high gear !

What is a BOV ?.

 

[willives]

BOV = Blow Off Valve, aka Dumpvalve, aka Wastegate.

It releases the pressure in the turbo which causes it to stall.

TDI's don't require a BOV as they use a variable vane turbo which eliminates the problem.

 

[GlanzaV]

Oh good point... never noticed the TDi bit!

The damage will occur in the thrust bearings, doubt it would ever be enought to bend the compressor blades?

 

[asthpsw]

I did wonder about the "closed throttle bit" but I just thought it was a general statement about the back pressure building up against the compressor when there was no fuel being injected.

Which is why I had wrongly thought that if at low rev's/high gear a demand was made on the engine, more fuel injected, the VNT vanes opened up to increase boost but due to the low rev & high gear that extra boost was to much for an already "slow" running engine & hence pressure built up.


So This excess pressure actually can blow through the seals that contain the bearing & oil ? (& on the other side of the bearings is the Exhaust pressure ?)

 

[nightflight]

I always thought that the chatter on throttle lift was a good thing, as it meant that there was still pressure in the turbo ready for when you put the foot down again, whereas a dumpvalve dumps all the excess turbo pressure causing massive lag.

 

[GlanzaV]

I always thought that the chatter on throttle lift was a good thing, as it meant that there was still pressure in the turbo ready for when you put the foot down again, whereas a dumpvalve dumps all the excess turbo pressure causing massive lag.

Nope unfortunately. When you hear the chatter, that is your compressor blades chopping up the air as it has nowhere to go, which drastically reduces the rpm at which it is spinning, which means it'll take longer when you get back on throttle to get it back up to speed (for want of a better term)

So This excess pressure actually can blow through the seals that contain the bearing & oil ? (& on the other side of the bearings is the Exhaust pressure ?)

I don't quite get what you mean?

If you consider that the "reversed" air pressure or "Built up" air pressur is acting backwardly on the compressor wheel, this is what damages the bearing over time, it won't force though the bearing and oil until it's pretty much gubbed? The reason for this is the thrust is generally assumed to come from the Turbine side (ie the hot exhaust gas forcing the turbine wheel round which translates into a force on the turbine shaft)

 

[muddyboots]

Remember that diesels don't have a throttle