Locomotive Clag

[Robert]

At the weekend, I was browsing YouTube and came across this film (as one example of many):

 

 

Now, don't get me wrong I like to see Locomotives working hard as well as the next person but I don't remember Hymeks smoking like this when they were in service.  Which makes me wonder what the reason is.  I can't believe that it is down to the engines being long in the tooth because firstly, the engineering staff on the preserved railways do an excellent job of maintaining many of the preserved locomotives - plus, having recently seen a V200 here in Germany with engines of a similar type and vintage which was only producing a very light blue haze.

 

"Clag" seems to be popular - so is it down to driving style, or are some locomotives "adjusted" to over fuel?

 

By the way - my intention isn't to start an environmental debate - I am purely interested from a technical point of view!

 

[Fat Controller]

I suspect that at least part of the problem is that these engines are not used anything like as intensively as they were when in BR service, so that oil has a chance to build up. I spent a lot of times around diesel-operated railways (some on  lines with very steep gradients, others with heavy trains) in the 1960s and '70s, and rarely, if ever, saw muck like that coming out of the exhaust. It was almost always just a faint haze, except when starting with a load. Anything chucking out crap like that would be going for a looking-over at the nearest depot very quickly. It's not the diesel that's causing it, but lube oil getting where it shouldn't.

I do remember getting clouds like that out of my car, but only after putting Redex in the carburetor to clean the system out.

[Jenny Emily]

Excessive smoke on any engine could mean one of many things, none particularly healthy. Black smoke is excessive fuel (or limited oxygen when, for example, the air filter is cloggd). Blue smoke is oil getting burnt, though in a healthy engine oil should not get burnt in any great quantity. White smoke is water vapour, which if an engine continually puts out clouds as it runs means that usually there is a water leak into the engine innards. I have an old car that puts out a haze if revved after a period of idling. It's done 250,000 miles and it is probably the valve stem oil seals. A second rev in quick succession doesn't repeat this. If it smokes every time it is revved, then worn rings are more likely to be the issue; not scraping the oil from the cylinder walls on the down stroke and leaving it to be burnt perhaps. Burning oil doesn't half soot up the valves and exhaust manifold though. 

[Welly]

Clag is a sign of either a faulty engine or a design flaw in the engine. The white exhaust smoke of the Deltics is a result of a design flaw in the Napiers allowing unburnt lube oil to accumulate in the exhaust manifold.

 

Thick black smoke from steam locos were frowned on during revenue earning steam days.

[ThePipersSon]

Two thoughts on the original clip -

 

1 - it suddenly started clagging - either a failure or the driver did something

 

2 - that campsite at the track side looked like travelers!!

[The Stationmaster]

The original clip needs to be listened to as much as watched.  The sound indicates the engine was probably at or near idling speed until the Driver opened the controller - hence the cylinders then got a good dousing with unburnt fuel which had collected in the fuel system and injectors and that fuel was duly heated, not thoroughly burnt, and ended up as thick black smoke.

 

The problem is most prevalent on the preserved railways where speeds are limited and for a lot of the time engines are working well below their normal power capability but when there is a need to open up you get a smokescreen (or flames in the worst examples).  A similar effect could be observed sometimes even in BR days when engines were revved up from idling.

[petethemole]

IMHO it looks as though the clag (and tones) were pre-arranged for the video. As I'm ignorant of the inner workings of diesels I don't know how. The caravans are on a proper site with marked pitches etc. I just checked on Google Maps and it's Burrs Country Park Caravan site.

 

Edit: was typing while The Stationmaster's explanation came up.

[Arthur]

 

 

That it's just unburned fuel and lube oil flooding in following a spell of idling is borne out by the exhaust cleaning up considerably by the time the loco exits stage right.

 

Very common phenomena on Diesel engines, particularly older examples.

[Arthur]

 

Sadly we still lag behind Soviet era technology when it comes to clag generation;

 

 

Similar advanced technology seems to be installed in the Admiral Kusnetsov, well, its recent passage through the channel would suggest so.

[keefer]

some Indian Railways locos too (a lot of clips seem to be ALCOs, don't know if that's relevant or not)

 

[Zomboid]

Any excuse for some Alco action. They are known for being a bit claggy.

That Russian one isn't healthy though. The flames can't be normal, and it's only from one of about 4 exhaust ports.

[Jenny Emily]

Black smoke and flames could also be a sign that seals in the turbocharger have expired, which would allow lube oil to be drawn into the cylinder. In the worst case scenario this can lead to a runaway where the engine starts burning its own lube oil and revs higher and higher resulting in catastrophic failure of the engine unit through massive over revving and eventual seizure. In such circumstances, it can be very hard to shut down the unit once it has runaway - I've seen truck engines do this and when some-one shoved a rag into the air intake to block it, the engine just sucked it clean in and kept on revving.

[keefer]

I think I've heard that referred to as 'priming' - it's scary enough on a car engine, it would be really something on a loco!

[Arthur]

 

Plenty of Diesel runaway action on YouTube. Two here, both old Detroit diesels and both stopped by cutting off the air supply with rags. On the first the turbo can clearly be seen as it's not linked to any ducting or filter. Not sure throwing a rag into it would do it much good

 

 

 

 

[Phil Bullock]

Turbo lag is often the cause of clag - driver wishes to accelerate, opens controller, fuel rack delivers more fuel but until engine accelerates exhaust gases do not drive turbo charger fast enough for air supply to match fuel supply - hence black smoke

 

Is it somewhat puerile to glorify clag? Oh what the heck.... 

 

https://www.youtube.com/watch?v=uEDD_MyMPzU

 

Phil

[ColinK]

Hymek is almost certainly playing for the camera. It's at the most popular lineside spot on the ELR; they sometimes have photo specials there.

 

One winter I stayed on the Caravan Club campsite because they had early morning run pasts arranged for photographers (yes, I paid my share). Out of bed, filming 5 mins later. Excellent.

[Holmesfeldian]

Two thoughts on the original clip -

 

2 - that campsite at the track side looked like travelers!!

 

 

Burrs Country Park - I enjoyed a most convivial weekend there during the recent diesel gala.

[newbryford]

Modern diesels can easily clag.

Class 70s when opened up are quite good for clag

https://www.youtube.com/watch?v=_o-O6WKyX94

 

They even do it when idling.

https://www.youtube.com/watch?v=9EERoJO3G_w

 

I have a one year old Fiesta (and Mrs has a three year old version) that can chuck out some clag when clearing it's throat when the pedal is pressed enthusiastically when the engine/exhaust hasn't been given chance to get hot enough for a prolonged period.

 

As with the 70, it's something to do with preventing carbon/soot build up in the particulate filter. (Regeneration?)

 

I know b*gger all about the workings of a diesel engine apart from it's a compression ignition engine, but jjb1970 on here is very informative about these things. Hopefully he'll pick it up.

 

Cheers,

Mick

[Derekstuart]

Burning lubricant will usually come out as a dirty white to mid grey colour. Black is un-burned diesel.

 

What you are describing with blocked intake is causing the turbo to 'suck' whatever it can from wherever it can, which is invariably the bearing seal- once it breaks the seal then it can run away with the lub oil as you describe.

 

However, that Hymek isn't doing that as if it was you would have heard the clatter as it threw its pistons out.

Black smoke and flames could also be a sign that seals in the turbocharger have expired, which would allow lube oil to be drawn into the cylinder. In the worst case scenario this can lead to a runaway where the engine starts burning its own lube oil and revs higher and higher resulting in catastrophic failure of the engine unit through massive over revving and eventual seizure. In such circumstances, it can be very hard to shut down the unit once it has runaway - I've seen truck engines do this and when some-one shoved a rag into the air intake to block it, the engine just sucked it clean in and kept on revving.

 

 

Rough guide to smoke:
black= partially burned fuel (poor combustion usually down to charge air issues, can also be caused by faulty injectors, low compression)

white= un burned fuel (a gaseous vapour. Can be down to faulty timing (retarded injection), serious compression issues, faulty injectors)- not be be confused with steam from CH failure

blue to dirty grey= burning lubricant. Colour will vary depending upon where it is leaking and temperature of engine.

 

The above is a very crude analysis and is my experience of road diesels, gen-set and marine. Only worked on a couple of railway diesels but principle the same.

[MarkC]

Plenty of Diesel runaway action on YouTube. Two here, both old Detroit diesels and both stopped by cutting off the air supply with rags. On the first the turbo can clearly be seen as it's not linked to any ducting or filter. Not sure throwing a rag into it would do it much good

 

 

 

 

I had the misfortune to sail on one ship fitted with 3 Detroits as gensets - we referred to them as "Destroyed Diesels". 1800rpm, 2 stroke, fitted with both a Rootes Blower and a turbocharger. You couldn't get them to anything like their rated running hours between overhauls - a couple of standbys with two engines on low load (you have spare 'spinning reserve' when in confined waters  in case of problems) and even a freshly overhauled engine was fouled up - gummed up piston rings, carbon deposits in the exhaust etc. This was one reason, of course, why the Co-Bos were a disaster, except on the Condor service, where they ran for long periods at high power settings. Low loads are bad news for any diesel, but 2-strokes in particular.

[MarkC]

Turbo lag is often the cause of clag - driver wishes to accelerate, opens controller, fuel rack delivers more fuel but until engine accelerates exhaust gases do not drive turbo charger fast enough for air supply to match fuel supply - hence black smoke

 

Is it somewhat puerile to glorify clag? Oh what the heck.... 

 

https://www.youtube.com/watch?v=uEDD_MyMPzU

 

Phil

 

Exactly. Modern diesels, if there's a compressed air supply, sometimes have a system where compressed air is used to speed up the turbocharger quickly if there's a sudden high load demand.

 

[Robert]

Thanks to everyone for the answers.  I suppose at the end of the day, we are talking about equipment that is over half a century old, and technology has moved on.

 

I always thought that a diesel kicking out that much black smoke must be a sign of something seriously wrong, but as has been said there are reasons for it.

 

I must admit, I have never really understood the benefits of diesel particle filter regeneration.  Surely, if you burn off the deposits in the filter, then they are released into the atmosphere, which is exactly what the filter is designed to stop happening.

[Classsix T]

Is it somewhat puerile to glorify clag? Oh what the heck....

 

Phil

When we were running 56040 we "won" the Clagging Cup at the Battlefield line, there's also a shot of 56301 at the Swanage Gala doing a convincing impression of Vesuvius.

Neither of which I or the C56G engineering team should be particularly proud of if I'm brutally honest (though the Cup is just a bit of fun). Indeed, I asked the question of 301 if someone had been d***king about with the injectors...tsk.

 

C6T.

[russ p]

That loco looks to be getting worse. I drove it last year and it was claggy but not that bad. They also don't appear to have fixed the high tone on the horn

[Arthur]

where they ran for long periods at high power settings. Low loads are bad news for any diesel, but 2-strokes in particular.

Interesting. Detroit 2 strokes were a very common fit in US trucks for many years. I think environmental regulations have seen them off in recent years.

 

We did have the Commer 2 stroke here in the 50s & 60s and Detroit 2 strokes were an option in Scammell Crusaders, and probably others, in the 70's. There were certainly a few about but they were never that common.

 

Maybe the opportunity to drive for hours across the highways at a constant load better suited them to US conditions.

 

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