Sunday, October 16, 2016

Diesel Engine Turboharger Fires

From what I can best determine from the comments on the videos below, when a turbocharger's seal or gasket fails on the air intake side, it lets crankcase oil into the air intake. So even if you turn off the fuel injectors, the engine gets more than enough oil to keep on running. The comments remind me that the title of a video is invented by the railfan that took the video, not a railroad or locomotive expert. Some of the comments claim that oil will not burn white and thus white exhaust indicates a failure that is allowing water into the combustion or exhaust chambers. But some of the videos start white, then go to black, and then catch fire. Perhaps a cylinder fails causing stress in the engine that causes another failure that leaks oil into the intake manifold.

The comments refer to an engine burning its crankcase oil as a "runaway engine." (From Locomotive Diesels, I learned the V12 engine in Amtrak's locomotives hold 390 gallons in their crankcase.) Note that only the first video stops the train. While watching the others, I wondered why they didn't stop when they had a major problem. Since they talk about a runaway engine over-revving and throwing a rod or even a piston, it later occurred to me that they would be better off running with the problem to keep the engine under load to keep the revolutions lower. And the first video shows that the only thing that can be done if you stop the train is cause the first-responders to hassle a lot of travelers by closing the road.

There is no valve in the air intake to stop the runaway by shutting off the air. Evidently the engine stops very quickly when it burns all of the crankcase oil otherwise it would be running with no oil on its bearings. If just the turbo fails, it seems that only the turbo needs to be replaced to fix the engine. If it ran long enough with no oil to burn the bearings, a lot more would have to be replaced.

This explanation from a trains thread makes it sound like the exhaust side of the turbo charger is more like a jet engine because extra fuel is added. I had thought the exhaust turbo was driven just by exhaust pressure.
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)

According to a comment, the flames at the end was oil in the exhaust pipes catching fire. Note the crewman calmly leaving the front of the engine at 1:53.

Skip to 2:07

Skip to 3:38

I recommend you turn off the audio on this video and watch it to at least 0:31 when it really flames out. But this fire burned out fairly quickly.

The ugly exhaust in this video is because it is a tourist line engine and normally runs slow and carbon builds up on the turbo blades. So an engineer is slightly applying the trains brakes so that he can run the engine in a higher notch. As a teenager, we used to kid about blowing the carbon out of the engine when we went too fast on the highway. Maybe we were not kidding.

The guy in this video is deliberately abusing the engine to try to make it backfire. He is using a special lever on the side that allows him to feed too much fuel to the engine. I believe the backfire is when you push enough unburned fuel through the engine you can get it to ignite in the exhaust pipe. Some of the comments were of the opinion that this crew member should be fired for this abuse of the equipment.

Heritage Railway Magazine posted
‎Omar Segovia‎[Comments agree that it is a failed turbocharger.]

Locomotives are not the only diesels that have turbo failures:

Volvo must add an intake air valve or something so that a runaway can be stopped.

These guys were periodically pulling hard on the throttle to cause turbo-lag to cause black smoke to put on a show for the camera. After the turbocharger catches up, they let it slow down so they can do another hard acceleration to top speed for another show. After a few pulls, they got a real show --- they blew the turbocharger!

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