Flames out of exhaust

[.Taurus.]

Hello!

I think everbody knows the pictures of GE engines with a (major?) exhaust problem
here here here here here

But what is the problem exactly?
I think diesel fuel comes into the exhaust, but from where?
Has it to to with the turbocharger?
(But the turbocharger charges only air, the fuel will be injected later in the zylinder, so if there is a leak in the turbocharger there is no chance that fuel gets in the exhaust site of the turboloader)

Also what is to do with a engine that have this problem? Has it to shut down?

Greets

[Brad Smith]

Here is a thread from a while back that discussed the smoke and flame issues in GE's. It doesn't answer all you questions but you'll find it interesting.
http://www.railroad.net/forums/viewtopic.php?t=8831

[Petz]

I saw an interesting scene on a mexican Pentrex video. The engineer steadily switched between 0 and 4 or 5 to hold the speed up the montains (if i would be his chief i would have thrown him out of the running locomotive about this idiotic practice), in one such situation the engine was not able to ignit correctly anymore because of the high amount of fuel at too low speed (you could hear that clearely on the video) so first smoke comes out of the engine air intakes and unburned fuel reaches the turbo and the flames burn out of the stack.

Some diesels could turn her direction at too low speed without an announcement and you are wondering if the truck moves back in the first gear and forward in the reverse one.........i have experienced this on a big Iveco - truck.

[jgallaway81]

As a conductor on NS's harrisburg division, I had a set of GEs from Harrisburg to North Jersey, and ended up getting the same set back home the next nite.

Upon arrival on the HBR fuelpad, we shopped the power (the clean one needed 90-day inspection). The mechanical officer I talked to on the pad said that the most probable reason was due to the bearings on teh turbo charger going, causing the turbo to sieze up.

The diesel engine in that particular model NEEDED the turbo in notch 4 or higher, so when we throttled up, the fuel injectors were putting alot more fuel into the cylinders then what could be burned without the excess air from the turbocharger. This puts a lot of liquid fuel into the exhaust manifold. When the engine throttles up, and there is enough fuel in the stack, the exhaust will cause the fuel to ignite in the classic fireball.

[Petz]

@jgallaway81, this would explain exactly my observation. But i believe the problem is the turbocharger itself not its bearings.
If the charger has choosen too large it has no effect at the low notches, i found the similar problem on older Fiat and Lancia (same engines) tds car diesel engines.
When removing the turbo pressure measuring hose connecting with the injection pump the whole amount of fuel is injected and at low speed you can see smoke coming out of the air intake cause the burning cycle could not be finished by the engine, the only reasons no fire comes out of the exhausts is the use of a silencer and the length of the exhaust system.
In this case the amount of smoke behind the car remembers exactly on Alco engines and the drivers behind you should better use gas masks but it makes a lot of fun shocking other car drivers with this effect......

[amtrakhogger]

IIRC, EMD's utilize a clutch driven turbo-charger, could a GE loco
benefit from the same set-up to minimize turbo-lag, excessive smoke,
and stack fires?

[Petz]

@amtrakhogger, this would be one possibility but the more expensive one.
As far as i know EMD uses mechanical driven roots blowers. This system produces a constant pressure during the whole speed range so you have no turbo lag and no neccesity to adapt the amount of injected fuel in relationship to turbo pressure. In rare cases EMD had used a turbocharger too - for example in the SD24.
The turbocharger is a bit cheaper then a roots blower and less dirt sensible, this may be the reason most engine builders prefer to use a turbo.
All newer turbocharged engines (also in trucks and diesel cars) have a turbo related injection control to provide smoke screens.

[DutchRailnut]

Only NON-turbo charged EMD's have roots blowers like the 567 engines in F units and early GP/SD units.
The Turbo charger equiped EMD's indeed have a gear driven turbo with a clutch that will let the Turbo do its own thing when needed at higher power requirements.
The currently rebult MNCR P32acdm's like 202 and 203 have a much different turbo sound now, almost like an EMD.

[Petz]

@DutchRailnut, many thanks for the adding information.
In my opinion based on standard technical describtions a mechanical driven "turbo" isn´t one cause turbo means driven only by the exhaust gas - all other versions are blowers or (in the european definition) compressors.

[jgallaway81]

Petz... I'm a steam nut, so my understanding of diesels doen't extend much further then 'diesel engine turns generator to make electricity'. However in the US, there are two devices... one is a turbo charger, the other a supercharger, and then a third category is a blower. 'Chargers' use a more 'turbine' like means of creating compressed air.

Though I'm not sure which is which, one is driven from teh crankshaft, the other from the exhaust, and in GE's case, many models use independent electric motors.

[DutchRailnut]

The EMD turbo chargers run at low speed like Idle and low loads off the auxiliary output shaft, they drive the Turbo charger via a gearbox so the engine has more than just atmospheric air to use.
At higher speeds the clutch opens up, and the Turbo is driven by exhaust gas, like I said before the Turbo starts doing its own thing.
I know of no GE with electric powered blowers for engine combustion air.

[Typewriters]

Hmm...

SUPERCHARGING: The act of introducing pressurized air into an engine's cylinders at a pressure higher than atmospheric pressure.

SUPERCHARGER: A device that provides air to an engine's cylinders above atmospheric pressure.

TURBOSUPERCHARGER: A special variety of supercharger that employs a turbine, driven by engine exhaust gas as a means of power.

"TURBOCHARGER": Shortened version of the word "turbosupercharger" used for convenience.

"BLOWER": Slang term for a device that provides air to an engine, whether for scavenging air (as in a two-stroke engine) or else for supercharging effect.

I should note here that for many years, official materials of Baldwin Locomotive Works referred to their diesel engines as either normally aspirated or as supercharged; we all know, today, that when Baldwin said "supercharged" that this was actually being performed by a turbosupercharger. A supercharger, in the plain sense, is most often driven from the engine by belts or gears.

ROOTS BLOWER: A blower which employs lobed rotors which intermesh and provide a positive displacement air flow.

EMD units employ either Roots blowers (for scavenging air in the two-strokes) or else a centrifugal blower assembly that includes a turbine for exhaust drive, a centrifugal blower and an overrunning clutch. The clutch works in the same way that the drive on a bicycle works; if the rear wheel of a bike begins to spin faster than you're pedaling, it just spins faster! That's exactly what happens with the EMD turbocharger. Engine drive is direct through the clutch until there's enough energy in the exhaust gas to spin the rotor faster than it's being spun by the engine gear train. When that happens, it just outruns the engine gear train and provides even more boost pressure. This ensures proper scavenging at lower engine speeds and loads but provides actual useful work from the exhaust gas at higher exhaust manifold pressures.

As said, I also am not familiar with any locomotive engine that incorporated any kind of electrically driven intake air blower.

Finally, as an interesting aside, there were aircraft engines that used exhaust driven turbines which were connected to the engine crankshaft directly through fluid couplings. The otherwise-wasted energy was thus used directly to provide power, rather than having them drive blowers (which incidentally the engines also had). This was the Wright R-3350 Turbo-Compound engine.

-Will Davis

[Petz]

Thanks for your statements.
@DutchRailnut, thanks for reporting this very interesting system by EMD i´ve never read this details before.
Never heard of an electric driven turbo at GE locos too, this would require a heavy electric motor but provide troubles with the turbo lag.
I´ve seen some systems for cars at ebay (one uses a pc - ventilator impossible to bring any effects), another one was fitted with a 0,7 kw electric motor so it may have some affort but the electric generator of the car would not be very glad about this power consumption for longer times.

[jgallaway81]

I'll have to look into the lack of electrically driven turbochargers on the GE's. I had based that statement on the physical appearance of the engine, and what I assumed was the turbo charger... I'll see if I can find someone in Mechanical the next time I'm over at Juniata Back SHop to saee if someone can 'splain to me the means of supercharging the combustion air to the diesel.

Now, on the other hand, give me a boiler & a firebox, and I can field strip it and reassemble the unit to 49 CFR Part 230 regs.

[Paul]

As already explained, GE engines, along with most other four stroke cycle engines use turbo-supercharger to boost the inlet air pressures that are driven of the energy of the exhaust gasses. Under normal conditions, the turbo is not boosting until the load is such on the engine that the exhaust reaches a suitable temperature to spool up the turbo.

On two stroke cycle diesels such as EMD and F-M engines, a positive air charge must be maintained at all times in order to scavenge the exhaust out of the engine and to supply fresh air for combustion. On EMD engines just before the piston goes to bottom dead center the exhaust valves open up and relieves the pressure inside the cylinder. The pistons then reach near bottom dead center and uncover the intake ports and the fresh air forces the remaining exhaust gasses out of the valves, the exhaust valves close, then the air is slightly pressurized (only 3-5 pounds) and that is what is used for combustion. The mix comes in with higher horsepower EMD and the parasitic loss of horsepower by the blower. It takes horsepower to make horsepower. To get around this, EMD turbochargers are gear driven (again, all ready explained). At idle or low load conditions, the turbo is on the clutch providing positive air displacement for scavenging the exhaust. When the load conditions increase and suitable exhaust temps are achieved, the turbine compressor over spins on the clutch and free wheels driven entirely by exhaust temperature.

Since GE is a four stroke cycle engine, the air is drawn into the cylinders by vacuum-the effect of the intake valves open as the piston travels down the cylinder, then near the bottom of the stroke, the valves close and the air is compressed. Once again, under light loading or idle, the turbo isn't adding any boost until the engine is loaded. Now, you run the engine up to full RPM without a load ("governed no load") the engine will reach maximum RPM but the turbo will not boost as there isn't sufficient exhaust temperature to spool the turbo. Put the engine under full load ("governed load") then the exhaust temps will increase and spool the turbo up, usually, the turbo will start boosting around the sixth notch on a GE.

Now, in certain emergency standby power setups, (i.e., Nuke power plants, hospitals, etc.) the engines are required to start up, spool up and be at maximum horsepower in seconds. In these applications, generally, there is a large high pressure air line mounted to the exhaust manifold of a four cycle engine (such as GE's 7FD series and Alco 251s. During emergency start up, the compressed air force the turbo to spool up to full speed while the engine is started and coming on line. I have never heard of or seen any electrically driven positive displacement pump for huffing a medium speed diesel engine in locomotive service and I have over twenty years as a journeyman Machinist.

Now, back to the fire out the stack issue on GE engines.
Generally, one of four things has failed: Plugged turbo after-cooler, air manifold seals failed, hole in the air manifold, or a gang on injectors has failed electrically.
On EMD, one of three things has happened: Blower engine: Airbox fire, Turbo engine: plugged parts catcher, plugged after cooler. Generally, in the case of the turbo EMD, fire out the stack is detrimental to the turbo, and only lasts a few seconds before the turbo overheats and overspeed and destroys it's self.

I'll have my thirteen year old son read this to see if he understands what I posted. If he does, then I can be assured it will make sence to anybody else here.