Thank you all very much for the detailed descriptions on the turbo’s. I really enjoy talking about this kind of stuff. It interests me greatly.
Justin
The road to to success is always under construction. _____________________________________________________________________________ When the going gets tough, the tough use duct tape.
Diesels are generally very fuel efficient and normally don't exhaust much unburned fuel. At normal temperatures blue foggy exhaust is cold unburned fuel and black exaust is hot partially burned fuel.
Unlike a gas engine that controls engine speed with an air valve (throttle body or carburator) diesel engines have a wide open intake. This is to always make sure there is enough compression heat to ignite the fuel when it is injected. Diesel engine speed is controlled by increasing the fuel pulse at the injector (mechanically "moving the fuel rack" or electronically varying an injector pulse duration)
Diesel engines usually have a governor to control engine speed. The governor controls the amount of fuel injected, adding more to speed up and less to slow down. The throttle just changes the governor "setpoint".
Turbochargers work by taking residual pressure in the exhaust and using it to drive a turbine. This in turn drives an impeller that pushes more air into the engine. This allows the engine to generate more horsepower.
When an Alco is powering up, the governor increases the fuel supply immediately driving the fuel to full rich until the engine can catch up to the new RPM setpoint, but increased air flow to burn this fuel efficiently doesn't happen until after the engine and turbocharger pick up RPM. As a result, for a few seconds the engine runs very rich creating lots of black smoke until everything evens out.
EMD's never had as much of a problem with this because their turbos are also driven by engine RPM through an overruning clutch. This allows some air boost during start up and at low RPM. It also makes sure that engine RPM is never limited by a lack of air, preventing it from running rich. The clutch drive is needed because a two cycle EMD diesel needs to have air pushed in to run and on start up and idle there isn't enough exhaust pressure generated to spin a free wheeling turbo effectively.
I don't know specifically how GE's avoid the ramp up smoke on their 4 cycle diesels, but methods include oversizing the turbo to always boost the air and using a blast gate to dump excessive air at high RPM, and electronically controlling the fuel system to match incoming air volume on ramp up to not get so rich.
Once in a while, usually on a cold start, raw fuel will build up in the turbo or exhaust passages and actually belch fire when the fuel ignites.
after viewing the first vid about the dyn. its the grill on top of the blower that goes flying off
When a turbo truly "lets go" the case will provide very little protection from shrapnal. The giant intercoolers on GE FDL's helped more with that. one of the many reasons we cannot be outside the cab when loadboxing a C45 is due to the turbos desire to come apart. (yes even with the "new and improved" turbos) an EMD turbo generally will be driven by the gear train until it gets to 85-90% load, then it starts to free wheel. even on GE's or most other engines the turbo really doesn't add much until you approch 30-35% load.
Quick and dirty...
Turbo's blow + more fuel suck = harder turbo blow and more bang for the buck.
Adrianspeeder
USAF TSgt C-17 Aircraft Maintenance Flying Crew Chief & Flightline Avionics Craftsman
There's a great discussion along the lines of turbos, etc, over on the Locomotives forum:
http://cs.trains.com/trccs/forums/t/162603.aspx?PageIndex=1
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Re Alco Turbo lag & smoke. Essentially what happens is this. In normal operation the turbo charger burns very hot(1200-2000 deg F ) & this burns any unburned fuel that comes out of the engine cylinders. The turbos on Alcos are very slow to spin up. As a result a lot of unburned fuel gets thrown in to the exhaust. Black smoke from the exhaust is unburned fuel. There was a pic of an RS 11 some years back pulling a train of empty auto racks throwing massive amounts black smoke out. This may have been a unit with a failed turbo that just was not burning anything.
What an exhaust turbo does is to take the air from the exhaust which is under considerable pressure, burn fuel in the combustion chamber and then route the pressurized air back into the intake manifold. The intake manifold normally is under a vacuum and pushing air into the intake boosts the pressure in the cylinder. (wish I know how to put a drawing into this)
Diesels are real ugly as far as the amount of unburned fuel that is in the exhaust. One of the big advantages of Turbos is that the turbo burns the unburned fuel(It was one of the reasons Santa Fe went to using GP-39-2's in the Denver area in the 70's) . Most of the better pollution control equipment for diesels tend to use turbos as the first stage of cleaning exhaust. The high pressure in addition to temperature goes a long way to cleaning up the exhaust.
The newer micro processor controlled engines specifically do not spin the engines up(ie add more fuel to the cyliners) until the turbo is spun up. I remember reading somewhere one of the bigger complaints of locomotive engineers is that the newer engines(specifically GE's) load up very slowly. This is understandable as turbines take longer to spin up then does the engine itself.
Also when a turbo blows(at least on a truck) it is very very loud, and produces considerable amounts of smoke. the smoke is engine oil burning in the combustion chamber(where the turbo core & blades used to be). Some years ago the turbo blew on my truck in the middle of traffic. Pulled to sided of the road & stopped the truck and made a quick inspection & was about to move truck to a safer location when the fire department & the police showed up. Firefighters told me that 911 got over 20 calls in less than a minute. Turbos blowing on a Railroad Locomotive is even better(their bigger). When you see a turbo charger the first thing you notice is how thick the metal is.(this is partly needed to contain the pressure & heat, it is also to contain damage when it blows)
Rgds IGN
PS my apoligies for being so long winded. I'll try to get back at some point and edit this down.
bubbajustinWhy did only Alco’s do that?
Hi all,
Thanks for the information. I really appreciate it.
Larry, I never dreamed that that was why Alco’s did that. Why did only Alco’s do that?
silicon212The explosion was the aft DYB fan and the thing that frisbee'd out was the fan itself.
The explosion was the aft DYB fan and the thing that frisbee'd out was the fan itself.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
IIRC correctly the SD40-2 turbo is gear driven in throttle 2-5, in throttle 6 the clutch disengages and it becomes "Free" and spins on exhaust pressure. Once in a while the clutch fails to work as intended, the engine will bog down from lack of air and black smoke results and eventually it dies. If you have ever seen a puff of smoke and heard a "Whoomp" sound, that is a turbo screen (located at end of exhaust manifold and turbo inlet) plugged up with carbon or spare parts. Usually happens in higher throttle positions and will clean itself out. If it doesn't, reduce throttle until the whoomp stops or isolate unit.
The first video shows what looks to be a hole in the side toward the rear of the brake grid blister. If both brake fans are not working you get a "Grid blower failure" and dynamic braking is locked out (until module reset) on that unit.
If a radiator fan blows off you keep going unless the radiators got damaged (soon to be out of water) by flying debris. If unit runs hot it will reduce to #6 throttle, if still too hot will shut down.
bubbajustinWhat role does the turbo play in a locomotive? I assume it is a very important one.
EMD didn't use a turbo early on - relying instead on the 'Roots Blower,' which, as I recall, is driven off the crankshaft.
I can tell you from personal experience that losing the turbo (or in the instance I had, the hose from the turbo) really takes the umph out of the engine.
The black smoke for which ALCO's (especially the early RS's) are famous was due to turbo lag - the turbo spooling up well behind the engine's demands.
corwinda In this case I think the brake grids frying was secondary to being hit by the broken fan. (Arcing across a crack.) Too soon for a meltdown IMO.
In this case I think the brake grids frying was secondary to being hit by the broken fan. (Arcing across a crack.) Too soon for a meltdown IMO.
I thought those DNBK’s would have to be whining pretty hard to start frying that quick.
What role does the turbo play in a locomotive? I assume it is a very important one.
Losing a fan is not as bad as having a turbo blow. When a turbo blows, there goes the engine it is "DOA". Blow a fan and the engine can still run for a while. The DB's may fry due to excess heat or the radiator may overheat, but the engine can keep going.
OK THAT’S WHAT THAT WAS!
That’s what I thought, but I wasn’t sure. That is what is sparking, and smoking isn’t it. So that means the train had it’s dynamic breaks on, and the fan blew.
What can cause that?
silicon212 The explosion was the aft DYB fan and the thing that frisbee'd out was the fan itself.
If you watch as and after the locomotive passes, you'll see the dynamic brake grids starting to fry.
bubbajustin http://www.youtube.com/watch?v=mCk21G2LR-M Here it is. The guy said it blew a turbo… Really? Also, It is a SD40-2 Another instance: http://www.youtube.com/watch?v=zGoQ8XaIeaA&feature=related Info? THX!
Here it is. The guy said it blew a turbo… Really? Also, It is a SD40-2
Another instance:
Info?
THX!
Justin,
I am curious too because I was never sure it was properly explained what happened in your first vidoe. I tend to think it was not a turbocharger explosion. Turbo disintegration leads to excessive smoke because the engine is suddenly starved for air compared to the amount of fuel being injected.
Isn't that frisbee-looking object a fan flange or ring. It appears as if the fan lifted off and took the ring and wire grill with it. But why would the fan launch like that? Don't all the fans pull air up? That would mean an unsupported fan blade would move downward. Would that be the dynamic brake fan that launched?
Blown turbos aren't all that uncommon. Here's another clip of a Pan Am Railways train doing the same thing. (Skip to 4:02) I believe the unit was out of service for a week while they put a new turbo in.
http://www.youtube.com/watch?v=LqrExWCVCXU
I saw a video on YouTube Where a locomotive (It looked like an SD40 something.) Was blistering along at about 15mph when a puff of smoke and some sparks came out of the DNBK blisters. Then, a disk looking thing went flying about 35 feet in the air and landed next to the train. The train passes the camera sparking, and smoking very lightly. Surprisingly the train just kept on rolling. (One of the comments said “That’s UP safety standards for you!”) What really happened here? What does each situation look like?
Thanks in advance!
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