Locomotive Clag

[Titan]

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

 

.

 

They were also a popular fit for buses too, so they must have been OK for stop/start conditions as well.

[jjb1970]

Black smoke of the sort in this thread is down to poor combustion. In extreme cases like these it is engine condition rather than engine design. Some engines do issue a bit of smoke when increasing speed as a result of turbo lag but it should be more of a puff than a sustained discharge and will be more of a black whisp, it shouldn’t blot out the sun. Poor combustion can be down to a huge number of reasons. The actual problems are either inadequate compression, incorrect injection or timing. Sometimes it is bad fuel but that tends to cause degradation of the engine which results in poor combustion rather than being the cause of smoke in itself unless something catastrophically wrong has happened in the fuel. Engine power is a function of how much fuel you can burn in the cylinder which is in itself a function of how much air you can get in the cylinder hence why it’s a bit senseless to make an engine of any size without pressure charging (either turbos or mechanical super chargers). So engines have to pump fuel to the cylinder, inject it as precisely the right time, in the right quantity and correctly atomised and with the right fuel – air ratio. The theoretical ideal would be to combust fuel at a stoichiometric air ratio but that is impractical so there is always excess air. This is very high precision stuff and requires very highly engineered fuel systems operating within very tight tolerances and timing. On a modern common rail engine the fuel pressure can be 1000Bar+ and the actual injection can pulse so that rather than a single “squirt” to have a serious of vanishingly short and very tightly controlled pulses. Some engines use very high pressure super charging (eg. Two stage turbo charging or high pressure mechanical super chargers) with pressures of circa. 7Bar, pushing engines onto a Miller cycle. Most people think gas turbines are fancy and exotic but in many respects gas turbines are quite agricultural compared to a reciprocating engine. Smoke happens when any of this goes wrong and can be caused by problems such as:

 

• Engine timing incorrectly set up or adjusted, worn cams etc

• Linked to timing, on a modern electronic engines the control system may go for a walk (failure of an input sensor, earthing of a sensor cable etc)

• Fouled fuel injector nozzles or poor nozzle sealing

• Incorrect fuel for the engine set up (fuel is a whole subject in itself and much more complex than normally recognised)

• Failed injector (unlike fouling or poor sealing where the injector still functions, albeit less than greatly which is a part of wear and tear, failure is if a nozzle breaks completely)

• Worn, sticking or broken piston rings causing poor compression

• Excessive cylinder lubrication and/or poor oil control

• Worn or damaged inlet/outlet valves

• Fouled turbo charger

• Constricted air supply, such as blocked air handling filters

• Accumulation of oil or unburnt fuel where it shouldn’t be (this can make quite heavy smoke but it should be a brief blow which clears quickly as the oil burns off)

 

There are other reasons too, however I would say that if an operator continues running an engine in the condition seen above then it is grossly irresponsible on environmental and safety grounds and pretty dumb in that the engines are probably on their last legs. In the UK you’re risking prosecution operating an engine like that, and quite rightly so. Combustion does tend to be less than ideal when starting up from cold but again we’re talking about a bit of a whisp, not the sort of sun blocking mess in the images above.

There are other causes, regeneration of a dpf has already been mentioned but that is a different smoke characteristic and shouldn’t be anything like these images, it is usually a periodic, relatively short discharge and again should be discolouration rather than heavy black or white clouds. Traditionally, mechanical engines were much less controllable than a modern electronic engine, on a modern electronic engine combustion is monitored and fuel injection can be fully controlled in real time without being pre-determined by mechanical cam adjustment, spacers and linkages as on older engines (although some mechanical engines offered some level of control, Sulzer had some good sytems). Modern engines also have far more advanced controls in terms of load control, load ramps etc which should avoid the sort of puffs of smoke typical of older engines caused by speeding up quickly.

A touchy subject is maintenance. Engines will work well if properly operated and maintained. A problem with more modern engines especially is that it is not uncommon to find the control systems beyond the capabilities of operators own resources or to see old timers treating engines in completely inappropriate ways because that’s what they did with engines in the old days.

A subtler but in some ways serious problem is if the engine is just not suitable for the intended application. Engines are designed around duty cycles, a key part of this is their suitability to change load quickly (or otherwise) and if the engine makes smoke every time the load changes then it probably indicates that the engine selection was not ideal. Maloperation is a possibility, but again if the engine can be maloperated to be smokey it raises more questions about engine selection really.

These days engines are almost designed around the emissions strategy, so rather than the emissions being whatever you get as a result of wanting an engine of a defined power and size, the power and size of the engine are now the result of what you have to do to achieve emissions compliance. On ships and in power plant applications this increasingly means downstream emissions abatement such as SCR and scrubbing, but it can also mean using techniques like EGR and fuel emulsification. Again if these things go wrong it can affect the exhaust.

Apologies this is a bit long winded but hopefully it gives some back ground on smokey engines.

[The Stationmaster]

JJB you expertise has of course hit the nails on the head but one very telling point comes near the end in this sentence - 'A subtler but in some ways serious problem is if the engine is just not suitable for the intended application.'  And that, of course is exactly the case with the Hymek that started this thread in that powerful locos designed and engined for rigorous mainline work have to be operated in a totally different way on a heritage railway with limited loads and numerous drastic restrictions of speed.  As a consequence the engines are working to a very different cycle, and far lower power demand, than they were designed for - spending much more of their time in traffic at, or little above, idling speed with extended periods of standing completely idle between their occasional use,

[Andy Kirkham]

 I don't remember Hymeks smoking like this when they were in service.

 

It was not unknown

SEP 73 19. 7001 near Twyford with the 15:05 Paddington-Hereford, August 1, 1973 by Andy Kirkham, on Flickr

[jjb1970]

'A subtler but in some ways serious problem is if the engine is just not suitable for the intended application.'  And that, of course is exactly the case with the Hymek that started this thread in that powerful locos designed and engined for rigorous mainline work have to be operated in a totally different way on a heritage railway with limited loads and numerous drastic restrictions of speed.  As a consequence the engines are working to a very different cycle, and far lower power demand, than they were designed for - spending much more of their time in traffic at, or little above, idling speed with extended periods of standing completely idle between their occasional use,

 

Engines often get blamed for the poor performance of engines when the problem is not so much that the engine is bad but more that a perfectly good engine has been used in an inappropriate application. And as pointed out by the stationmaster, engine use can change dramatically over the life of a locomotive so the correct engine when a locomotive is new may not be the right engine later in its life. Heritage railways will always be a problem for diesels I think, at least as long as the funds and spares are there to run them, personally I'm very sceptical about the long term future of many preserved diesels as supplies of critical spares dry up and the knowledge base to keep them working fades away. It should also be said that sometimes the engine builders are often to blame in the case of new installations for selling the engines in the full knowledge of their design and the operating environment of the application. This is an especial problem for some American mass produced engines which are sold from the factory are bare engines to regional agents who package the engine and manage the application side of things. Some packagers are very good and very capable, but some are clueless.

[ejstubbs]

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.

 

Regeneration burns off the filtered particulates - mostly soot from incomplete combustion, which is close to pure carbon - and turns them in to CO2, which is a gas.  Hence the particulate filter is still doing its job: reducing/preventing the emission of particulates, which are known to be carcinogenic and to cause diseases like emphysema.  The fact that burning off the filtered particulates causes a small, and temporary, increase in the engine's greenhouse gas emissions is basically the lesser of two weevils: environmental damage vs direct impact on people's health.  (Note that exhaust catalytic converters also cause an increase in greenhouse gas emissions, by turning carbon monoxide - which is directly toxic - in to CO2.)

 

The bottom line is: despite lean-burn technology and all the other clever stuff that is being done to improve fuel consumption and thus reduce CO2 emissions - by the 'simple' expedient of burning less hydrocarbon fuel to get the same amount of useful work out of the engine - until someone comes up with a method of sequestrating CO2 within the exhaust system, you aren't going to eliminate greenhouse gas emissions from ic engines.  So a small amount of additional CO2 is seen as an acceptable price to pay in exchange for effective controls over the various other noxious substances that ic engines emit, and that kill people more or less directly (ie rather than indirectly, and slowly, by gradually making the planet they inhabit overall less conducive to the survival of large organisms).

[jessy1692]

Wonder how old that clip is as 7076 was fitted with an engine salvaged from a scrap yard in York that had apparantly been a stand by generator at a hospital and when it was first fitted it was very smokey before afjustment. 7076 was running very well at the autumn event, but if clag but no where near as much as this

Cheers

James

[Davexoc]

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

Pretty much spot on. At the bottom of the drivers power handle is a pneumatic valve which varies the air pressure in the control pipe. For multiple working this is the hoses on the buffer beam with white ends/handles. If the driver opens up quickly the air pressure in the control pipe rises quickly causing the engine governor to open the fuel rack. As the turbo(s) are not really doing much you briefly get maximum fuel for very little charge air, resulting in thick black smoke. As the exhaust gas speed increases the turbo spins faster and increases the charge air pressure reducing the smoke as you get nearer to optimum fuel/air ratio. The clip of D1015 shows that quite well.

Also watch something like a pair of class 37s and you can see that the lead loco will clag first and more than the second due to the air pressure in the control pipe taking longer to get to the slave loco.

Don't forget that in order to accelerate you always need to overfuel slightly, its down to how heavy your foot is, or in this case how vigorously you move the power handle.

 

Dave

[jjb1970]

The main issue with many rail engines is the engines are antiquated. The EE units are 1950's and 60's tech, to put that into perspective imagine the performance of a car engine from that era with a modern engine. Even the EMD 710 engine of the class 66 is old technology. Modern engines manage turbolag effectively and are better in just about every way by a large margin. Something that is not immediately obvious is that the production life of a basic engine platform has been dropping, until the 90's a platform could remain in production for over 40 years, albeit continuously updated. That is now more like 10 - 20 years outside of US rail engines.

[bike2steam]

Memories of train-spotting in the 'transition' period at Kings X, where, on departure, Deltics could make more smoke than any pacific.  Probably where the term 'bloody strokers' came from.

[Davexoc]

The main issue with many rail engines is the engines are antiquated. The EE units are 1950's and 60's tech, to put that into perspective imagine the performance of a car engine from that era with a modern engine. Even the EMD 710 engine of the class 66 is old technology. Modern engines manage turbolag effectively and are better in just about every way by a large margin. Something that is not immediately obvious is that the production life of a basic engine platform has been dropping, until the 90's a platform could remain in production for over 40 years, albeit continuously updated. That is now more like 10 - 20 years outside of US rail engines.

I remember when the 59s first arrived and were being tested. I was shown around one of the 59/0s and I think the American technician accompanying it told me the engine block design was from 1938, the original being normally aspirated. As with alot of old kit, it was so over engineered in the day that it could withstand the over 3x increase in power output over the years without much modification. 

As for turbo lag on these engines, there isn't any as such due to the fact that they have an engine driven super-charger for low revs, disconnecting via torque convertor when the turbo-charger is has spun up to speed.

 

Dave

[TheSignalEngineer]

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.  

I remember a shot of one at Worcester in the mid 1960s when it virtually obliterated Shrub Hill Station.

[jjb1970]

The EMD 645 engine was an evolutionary development of the older 567 engine, the 645 itself would later form the basis of the 710 engine. To say the 645 engine is a 1930's design is not quite correct as that engine was launched in the mid-60's, it is however fair to say that it's lineage goes back to the 567 engine of the 1930's. The use of mechanically driven superchargers to support low load operation is not uncommon and on big diesel engines (by which I mean the big slow speed engines which are in a different world from the sort of medium and high speed engines most would recognise) the engine cannot operate without pressure charging. Well, they can run, but they sound dreadful, can't go beyond about 25% power and won't last very long. Detroit were big advocates of using both roots blowers and turbochargers on their engines, many years ago I was on a Maersk ship with a pair of V16 Detroit harbour generators each of which had a roots blower and twin turbochargers. They were very highly rated for their size but screamed in service, burned lube oil at a prodigious rate, were quite maintenance intensive and very inefficient. We hardly ever used them as usually the ship ran on two shaft generators, one on each shaft and with CPPs we could leave the shafts running if we were only alongside for an hour or two.

EMD produced a very solid, dependable engine for the most part (although they tried to push the 645 too far and the version used for the SD50 let the side down, as did some of the V20 versions) but dependability was bought using conservative, evolutionary development that also left them way, way behind other similarly sized engines designed in Europe and Asia in terms of fuel consumption. When they decided that their classic 2 stroke had been taken about as far as it could go they designed a new 4 stroke engine, the H, which was a complete lemon and effectively a failure. They've improved it and now sell an improved version as the 1010 but I always think the failure of the H engine was a large part of why EMD were left behind by GE after they'd dominated the US rail market for so many years.