What causes this and how often does it happen?

Question

What causes this? How often does it happen?

http://members.cox.net/millermmail/rr/index_files/image017.jpg

Just curious, it's the only time I've seen that in person and was somewhat alarming since the lead engine was already under some nearby trees and this was heading that way...fortuniately it stopped before getting under the trees...

Answer 1

It happens more often than you think, but is more prevalent with older GE locos.

GE prime movers are four stroke engines while EMD uses a two stroke.  But more importantly, GE runs a true turbo-charger, running off the exhaust, while EMD uses a "hybrid," which is a gear driven roots blower up to and including run #5, after which a clutch disengages and the unit runs as a turbo charger.

And yes, they can start a fire...

Answer 2

Look like the turbo just went south...then again it could have been many things...ie, dropped valve, failed fuel nozzle, either way looks like its headed to a shop for repairs...trains set a lot of fires each year...costing railroads lots of cash....

Answer 3

For whatever reason, C39-8s do that a lot. I have very little experience with GE units, but I can imagine that the turbo is the culprit. In a turbocharged diesel, the exhaust gasses shoot through a turbine before blowing out the stack, and the turbine compresses air to be fed back into the cylinders. The result is higher compression, better combustion, and a lot more power. Turbochargers add hundreds of horsepower.

The problem with "true" turbocharged diesels, which isn't so much a problem with roots blown engines, is that compression is regulated almost entirely by the turbo. More fuel creates more exhaust, more exhaust drives the turbine faster, and as a result, the compression is increased accordingly. Alco engines are famous for turbo lag, and you'll see huge funnels of black smoke shoot out when they're powering up. Some guys get their jollies off by making smoke, but I'm not that big a fan.

Anyway, turbochargers wear out, and if that turbine fails, you'll get some pretty spectacular shows. If you think about it, there's an essential feedback loop missing. The engineer notches up, more fuel is shot into the cylinders, but the onslaught of exhaust gas doesn't trigger that increase in compression. The result is incomplete combustion, or in the case of your photo, really incomplete combustion. When the piston makes its final stroke and the exhaust valves open, there's still burning fuel.

There is a less technical cause, though, and that's low engine temperature. Sometimes you get into a pinch and you have to fire up a cold unit, and the engine doesn't get enough time to heat up. It's more a problem in the winter, obviously. But I've seen engines with seven feet of fire trailing over the cab, and I rode in a switcher that was shooting sparks. It's the same problem, just a lot easier to fix.

Answer 4

That's a typical problem with a Dash 8 GE locomotive.As a couple said it's mainly caused by turbo lag when throttling up a Dash 8.They normally only are bad at low throttle notches.I have had a few we had to shut down though because they wouldn't quit blowing fire.It's makes for quite a sight at night.As Albert said you never see an EMD do that because they are gear driven turbo's at notch 5 and below.