I'm struggling with something, as i am prone to do. I understand why the right side of the map matters, that's fairly cut and dry. Overspin a turbo, and bad things happen. The end.
But as for the left side. Let's say you could go off the map on the left side without exceeding RPM limits. (Whether everyone thinks it's possible or not, i don't care, i still want to know)
Can pressure alone kill a turbo? If so, how is that number figured?
You'll notice that the top of the map is usually defined by the maximum RPM line, so going off the top of the map would be spinning the turbo past its design RPM. I suspect RPM would get it first. But if you got a turbo to fail from overpressure, this could take the form of a burst housing, broken shaft, or bent vanes on the turbine or compressor wheel.
Going off the surge line at the left would mean the turbo equivalent of water hammer, if that was also part of the question.
I imagine bearings would fail or that the pressure would find another way to escape then through the side of the turbo if you really got the boost up.
I think that sortof answers it... but in the case of the map above, we see that the max the turbo will flow under any circumstance is ~35lbs.
Are we saying that no matter how terribly the motor the turbo is attached to flows, the RPM limits will be exceeded at the point that the pressure ratio "outruns" the chart?
Swank Force One wrote: I think that sortof answers it... but in the case of the map above, we see that the max the turbo will flow under any circumstance is ~35lbs. Are we saying that no matter how terribly the motor the turbo is attached to flows, the RPM limits will be exceeded at the point that the pressure ratio "outruns" the chart?
Max flow could be RPM or even cavitation limited. Cavitation can do some real interesting things.
Going past the left side is compressor surge.
Compressor surge under no load like when you let off the throttle is harmless and sounds kinda cool in an 80s kind of way (I repeat myself)
Compressor surge under load breaks things. Quickly.
http://www.youtube.com/watch?v=nCj6Spwl1CU
Thanks, Ben, for the next week I'm going to read "turbo" as "turblo".
Spend time here - Garrett turbo learning...
Let's say you could go off the map on the left side without exceeding RPM limits. (Whether everyone thinks it's possible or not, i don't care, i still want to know)
Oh, you totally CAN. It's called having a E36 M3-flowing motor that only flows 10lbs/min even at 20psi of boost. 
I think surge is rare in real life because most aftermarket or custom setups have the turbine sized so that it's impossible to get into the surge zone. In general i think any time someone is going into surge it's because they should be running a bigger turbine and don't realize it. Just my .02.
Turbo's generally fail due to lack of oil, ingestion of a F.O. or overspeed issues. (mostly lack of oil)
In Surge you are effectively stalling the compressor.
Do this enough and with enough force you could get HCF or LCF of the turbine or compressor blades.. But what usually happens in the pressure balance around the wheel changes so drastically that an imbalance occurs, usually do to wheel nut slip... When that happens.. shaft motion goes to E36 M3 and the compressor cover and wheel touch at high speed.
Compressor and Turbine covers will not fail due to high pressure, full stop. They are tested to contain over speed blade out conditions that result in very violent disintegration of the comp or turbine wheels. You'd need some insane ammount of pressure to create a crack in a compressor cover.
Been too many years since I designed those things.
Ohh Forgot about hot shutdowns.. In the trucking and construction equipment applications, they are a turbo killer. I've seen oil coking that would make your eyes pop.
From what i understand, the way surge kills turbos is by cracking the turbo shaft right where the diameter goes down to fit inside the compressor wheel.
Vigo wrote: From what i understand, the way surge kills turbos is by cracking the turbo shaft right where the diameter goes down to fit inside the compressor wheel.
shaft breakage usually starts as one of two things.. Oil starvation leading to the seizure of the bearings and/or an imbalance issue.
Diagnosing a broken shaft is difficult, but what usually happens is the turbo loses balance first, contacts the cover, comes to an abrupt stop and then you snap the shaft. Usually you get a box of parts back, two busted wheels and an irate customer.
I used to do this for a living for Holset a while ago.... nearly 10 years now.. ugh.. I'm old.
Does anyone have a good description of what compressor surge actually entails? And what does it mean when a compressor stalls? Are these similar or totally different scenarios? Does it mean the compressor wheel is fighting against too much pressure in the inlet manifold, such that the compressor wheel is quickly made to stop by the air wanting to go back out the way it came due to the high pressure differential? I'm having trouble picturing what happens, hope someone can explain.
Yep, that's exactly it. Here's a video:
http://youtu.be/nCj6Spwl1CU
http://www.turbobygarrett.com/turbobygarrett/compressor_surge
Gotta remember that turbos aren't air movers like leaf blowers, they compress air by accelerating it at a curved wall like riding the Rotor. Corollary to that, a turbo has to spin fast enough to throw the air hard enough at the wall. (Note that on a turbo map, turbo speed mainly affects pressure ratio, not airflow. At least not until you go past the meat of the efficiency)
If the turbo isn't flowing enough air for a given speed, the flow will stall. If it's just barely not flowing enough, then the flow will stall, then restart, then stall... and then you get the video that SFO (and I) posted. And as pointed out elsewhere, you generally have to do some funky things with your compressor/turbine matching to get into that range.
Fueled by Caffeine wrote: PRODUCTION Compressor and Turbine covers will not fail due to high pressure, full stop. They are tested to contain over speed blade out conditions that result in very violent disintegration of the comp or turbine wheels.
Edited - Race housings OTOH that are designed for weight savings and not containment look like a bomb went off inside them though.
That's not gone well!
DILYSI Dave wrote:Fueled by Caffeine wrote: PRODUCTION Compressor and Turbine covers will not fail due to high pressure, full stop. They are tested to contain over speed blade out conditions that result in very violent disintegration of the comp or turbine wheels.Edited - Race housings OTOH that are designed for weight savings and not containment look like a bomb went off inside them though.
never worked with race housings.. but have worked with turbo's with 2Kg compressor wheels. Cast Iron compressor cover it is.
If a race housing couldn't contain the wheel that would mean the wheel itself would breach the outside of the cover. That's a pretty scary situation... Like throwing a disc in a Jet engine.
Swank Force One wrote: That's not gone well!
neither of those were cover failures. I have pulled wheels from off roof's and in farmers fields from behind factories. I have also set engine test cells on fire due to massive oil leaks.
Oh i know... it was just some impressive turbo carnage. Figured i'd share.
Swank Force One wrote: Oh i know... it was just some impressive turbo carnage. Figured i'd share.
my favorites is when the intake gets choked off and compressor sucks oil from the center section into the engine.. Then the engine runs away until it explodes....... At which point the turbo runs out of oil and both wheels pop off..
Fueled by Caffeine wrote:
my favorites is when the intake gets choked off and compressor sucks oil from the center section into the engine.. Then the engine runs away until it explodes....... At which point the turbo runs out of oil and both wheels pop off..
I guess you know how to design a reliable turbo system.
Mr_Clutch42 wrote:Fueled by Caffeine wrote:my favorites is when the intake gets choked off and compressor sucks oil from the center section into the engine.. Then the engine runs away until it explodes....... At which point the turbo runs out of oil and both wheels pop off..
I guess you know how to design a reliable turbo system.
nope. Just had to deal with bluebird buses, and their inability to utilize a torque wrench.
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