Fire coming out of diesels

[Anonymous]

QUOTE: Originally posted by SILVERCHAMPION

[8D]Why do I see fire coming out of diesels locos

As mentioned before, stack fires from turbo engine'd diesel locomotives, is most generally a result of the failure of the turbo bearing's oil seal. Mostly, nothing else will cause this condition.

Apparently, GE locomotives suffer this condition more often than EMDs, which would indicate a design problem with GE's prime mover's turbo oil seal.

A stack fire is not to be confused with fire out of the stack of a naturally aspirated diesel engine'd locomotive. Two entirely different happenings.

Jim - Lawton, NV MP 236

[Randy Stahl]

QUOTE: Originally posted by SP9033

QUOTE: Originally posted by SILVERCHAMPION

[8D]Why do I see fire coming out of diesels locos

As mentioned before, stack fires from turbo engine'd diesel locomotives, is most generally a result of the failure of the turbo bearing's oil seal. Mostly, nothing else will cause this condition.

Apparently, GE locomotives suffer this condition more often than EMDs, which would indicate a design problem with GE's prime mover's turbo oil seal.

A stack fire is not to be confused with fire out of the stack of a naturally aspirated diesel engine'd locomotive. Two entirely different happenings.

Jim - Lawton, NV MP 236

In 20 years of working on locomotives I've never seen a stack fire as a result of turbo seal failures. I have covered parking lots full of vehicles in lube oil, had to repaint some trackside houses, but never had a fire because of lube oil out the stack. Bottom line is the lube oil coming out the stack isn't any where near it's flashpoint. There is no design problem with the GE turbo seal.
Randy

[Anonymous]

QUOTE: In 20 years of working on locomotives I've never seen a stack fire as a result of turbo seal failures. I have covered parking lots full of vehicles in lube oil, had to repaint some trackside houses, but never had a fire because of lube oil out the stack. Bottom line is the lube oil coming out the stack isn't any where near it's flashpoint. There is no design problem with the GE turbo seal.
Randy

Randy,

I think you are right on this, and I was wrong. Having driven a diesel truck during a turbo seal failure, I do remember the oil coverage on the following trailer that I was pulling. But then again I seem to remember witnessing a real turbo fire.

Flashpoint is really the wrong term to apply when talking about this subject, the right term is autoignition, from what I've read after your posting. As I now understand it, flashpoint has to to with transportation standards and autoignition has to do with engine fuel combustion.

From time to time I pick-up at Globe Turbo, I think I'll ask one of the engineers at that place this question. Globe Turbo is the OEM source for turbos for Alco locomotives.

This is very much subjective, but I've never seen photos of a turbo'd EMD stack fires, but lately there are many photos of GE turbo'd stack fires being posted on the web. What's going on here? Can you explain?

Jim

[mudchicken]

One of those four cycles isn't......Also, the GE Cooper Bessemer design has gone about as far as it can go. The newer engines out of Erie have their Alco-like teething problems. (the more things change, the more they stay the same)

[Overmod]

Some little points that Randy might confirm in better detail:

In order for a stack fire to occur, you have to have two things -- just one of these things will cause interesting results, but not a fire:

Excessive fuel or soot in the exhaust-gas stream, sufficient to support combustion,

and

A source of ignition -- something that is above the transition temperature for the reaction between fuel and oxygen at the conditions in the exhaust stream.

If you have the former, but not the latter, you will either see the famous blue smoke from revving FM OPs, or the voluminous clouds of inky black smoke seen in some pix of GE units -- where was that famous picture of a "sick UP GE" a few weeks ago? That was essentially a stack fire without ignition...

As mentioned in the old MILW threads... that blue FM smoke will ignite nicely into plumes if there's a hot source of some kind, including chunks of carbon, etc. that act as 'flameholders', But absent that, you'd be surprised at how much unburned fuel can be volatilized into thick, stinking clouds without ignition... but will produce enormous WHUMPs of flame if even a tiny source lights them off. (I've seen it firsthand in the Hamptons with friends trying to speed up the lighting of charcoal fires by spritzing lots of lighter fluid on relatively cold coals...)

You can have ignition hotspots in GEs all the time -- remember the flame that licks out of U34CH stacks on hard acceleration? Part of that is residual carbon, not burned during the power stroke, that is still glowing and reacting with oxygen a foot or more above the exhaust stack outlet -- you can easily understand that it is at least that hot back down the exhaust tract, and that there are characteristics in the engine that allow EGTs to reach that level. Blow turbocharger oil out a leaking seal into that exhaust gas, which effectively carburetes the oil, or into the intake tract where it effectively overfuels the cylinder (remember this is a four-stroke engine family) and you shouldn't be surprised if your excessive black carbon flashes more conveniently. Doesn't help if the leaking turbo seal either reduces expected boost pressure or effectively drops it to "normally-aspirated" levels.

Your basic EMDs, on the other hand, are using the turbo to pressurize the crankcase. Excess oil or fuel here are somewhat more likely to produce crankcase explosions than fires out the stack; the purge air is likely to drop exhaust temps well below what would be expected from a four-stroke of comparable net output. You might get white smoke galore... something I used to see all the time on old PC FL9s trying to accelerate out of Harmon with harrumphing and sighing as the engineers pumped them up to where they'd hold power... but as Randy points out, even if there were to be a short burst of flame in the rich exhaust, it would go out as soon as there was excess air in the exhaust.

I leave it up to the Alco boys to tell whether the black smoke from 244s (et al.) via turbo lag could be ignited long enough to cause big problems -- my guess would be that any flaming exhaust would go out once the turbo came up to speed and provided adequate combustion-air mass flow for the commanded fuel setting.

Randy (et al.) -- tell us more, more, more...

[Anonymous]

Originally posted by Overmod

Some little points that Randy might confirm in better detail:


Your basic EMDs, on the other hand, are using the turbo to pressurize the crankcase...

I'm a little slow here...So for my benefit lets consider GE's locomotive prime movers 4 stroke diesels engines and EMD's locomotive prime movers a 2 stroke diesel engine(which was the rule, to about 4 or 5 years ago).

A turbo uses exhaust gases to drive a compressor (the turbo) that compresses air so that more oxygen reaches the combustion chamber of whatever type of diesel. The compressor/turbo has two main inlets and outlets.

The drive inlet and outlet of a turbo/compressor is driven by the engines exhaust gases. When the diesel engine exhausts through a port or valve to the exhaust manifold it spins a compressor blade in the turbo. Inlet for the turbo from exhaust is small, outlet of the turbo is large.

This exhaust driven compressor blade in the turbo compresses the incoming air so the engine can burn more fuel, thus creating more horsepower. A turbo on either a 2 or 4 stroke diesel has little or no affect on pressures to the crankcase in a simple understanding. Flow of the air is exactly reverse from the exhaust. Inlet air is carried from a large hole and pushed through a small hole.

This turbine blade in the turbo/compressor, rotates very fast, so to make sure this doesn't overheat it is lubricated via a wet bearing, oil coming from the engines lube oil. If the seal fails on the exhaust side, a person calls a crew to clean oil off of stuff like Randy states.

If the seal fails on the inlet side, a nice stack fire happens. Gosh, Mr Smart, my high school shop teacher, thanks for the basics, you let me figure this out through writing it out.

Randy, its apparent you have never seen a turbo seal failure on the intake side! Now, I remember watching a turbo fire. Its just like the GE stack fires pictured recently, these not happening in EMD's, so it must be a design flaw with the GE's!

Jim Bryant - Lawton, NV MP 236

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