I overheard a conversation between a crew and their carrier's "Diesel Doc" over the radio regarding the HP rating of a locomotive. This unit had been derated according to the Diesel Doc but the company's TE guidelines reflected the older, higher HP rating. This conversation led me to some questions.
I am of the impression that derating a locos HP saves on maintenance and fuel usage. For sake of argument 3900 HP to 3500 HP. I'm thinking of a B39-8 specifically here. How much of a difference might that make? Could/would it make sense to use such a derated engine to replace, say, a GP40-2LW?
Dan
Most de-ratings involve removal of the turbocharger on an older locomotive that has been demoted to less demanding service, such as SD40-2's as hump pushers or GP40-2's in local freight and transfer service. The derating in these instances is usually from 3000 to 2000 HP.
I'm not too sure about the advantages of minor de-ratings that seem to involve resetting the fuel racks or reprogramming the microprocessor.
CSSHEGEWISCH Most de-ratings involve removal of the turbocharger on an older locomotive that has been demoted to less demanding service, such as SD40-2's as hump pushers or GP40-2's in local freight and transfer service. The derating in these instances is usually from 3000 to 2000 HP. I'm not too sure about the advantages of minor de-ratings that seem to involve resetting the fuel racks or reprogramming the microprocessor.
The advantages of derating a locomotive by changing out control modules are primarily fuel savings. This is what CSX has done with SD50's to derate them to 3,000 HP and B40-8s which are derated to 2,000 HP..
De-turbocharging an EMD is more complicated that it may seem as the turbo has to be replaced with a Roots blower. I recall reading that there have been some EMD units derated in recent years by "pinning" the turbocharger clutch so it can't spin freely which means that it then becomes more like a roots blower and is driven by mechanical linkage.
GE FDL engine's can't operate without the turbocharger so the only way to derate them is to change engine and fuel settings..
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
carnej1 CSSHEGEWISCH: Most de-ratings involve removal of the turbocharger on an older locomotive that has been demoted to less demanding service, such as SD40-2's as hump pushers or GP40-2's in local freight and transfer service. The derating in these instances is usually from 3000 to 2000 HP. I'm not too sure about the advantages of minor de-ratings that seem to involve resetting the fuel racks or reprogramming the microprocessor. The advantages of derating a locomotive by changing out control modules are primarily fuel savings. This is what CSX has done with SD50's to derate them to 3,000 HP and B40-8s which are derated to 2,000 HP.. De-turbocharging an EMD is more complicated that it may seem as the turbo has to be replaced with a Roots blower. I recall reading that there have been some EMD units derated in recent years by "pinning" the turbocharger clutch so it can't spin freely which means that it then becomes more like a roots blower and is driven by mechanical linkage. GE FDL engine's can't operate without the turbocharger so the only way to derate them is to change engine and fuel settings..
CSSHEGEWISCH: Most de-ratings involve removal of the turbocharger on an older locomotive that has been demoted to less demanding service, such as SD40-2's as hump pushers or GP40-2's in local freight and transfer service. The derating in these instances is usually from 3000 to 2000 HP. I'm not too sure about the advantages of minor de-ratings that seem to involve resetting the fuel racks or reprogramming the microprocessor.
Derating or Downrating a diesel engine saves on more than just fuel, it reduces all engine stresses, lengthening the time between engine overhauls, and reduces the likelihood of premature engine component failures. Norfolk Southern had all of the GE Dash-9 and ES40DC and EMD SD70M-2 locomotives delivered with an output of only 4000 hp. for just that reason. With the delivery of their new AC locomotives NS feels that the AC Drive will allow those locomotives to productively use the extra horsepower and so has not chosen to have them downrated. The change is done with different engine control software. CP's AC4400CWs and ES44ACs will limit horsepower to 4000 hp. if the locomotive is traveling faster than 25 mph, but if the locomotive is traveling slower the software will allow the full 4400 hp to be available., a different variation on downrating a diesel.
When switching in a yard you would want a non turbo charged locomotive. Turbo charged locomotives tend to load up fast and get moving fast and take longer to back the engine RPM's down. When kicking cars in a yard this would be working against you since you really just want to give the cars a bump or a short push at low speed. With higher horsepower and turbo charged locomotives it is harder to get that low speed crawl you want since they load up faster and tend to get the whole train moving at faster than walking speed which makes more work for the engineer because he has to use the brakes a lot more to slow it down. With a low horsepower locomotive such as a SW-1200 you can just throttle up and down and keep the train moving at walking speed with out even using the brakes.
Turbocharged locomotives in rail yards do work good for hump service where you need some good horsepower when pushing a entire train over the hump.
Thomas 9011 When switching in a yard you would want a non turbo charged locomotive. Turbo charged locomotives tend to load up fast and get moving fast and take longer to back the engine RPM's down. When kicking cars in a yard this would be working against you since you really just want to give the cars a bump or a short push at low speed. With higher horsepower and turbo charged locomotives it is harder to get that low speed crawl you want since they load up faster and tend to get the whole train moving at faster than walking speed which makes more work for the engineer because he has to use the brakes a lot more to slow it down. With a low horsepower locomotive such as a SW-1200 you can just throttle up and down and keep the train moving at walking speed with out even using the brakes. Turbocharged locomotives in rail yards do work good for hump service where you need some good horsepower when pushing a entire train over the hump.
We just use what we have. SD40-2s work fine for switching. When kicking I usually go right to 6 (about 2000 hp, same as a GP38, just more axles), then if more push is needed up to 8. Some SD40s won't go right to 8, they stall out.
For hump service tractive effort is the requirement, so many outfits use slugs. Splitting the 3000 hp to 12 axles gives a lot more push at the speeds needed. Also helps with stopping.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
Wait, I'm confused by the above post indicating the Turbo needed to be replaced with a roots blower.
It was my understanding that all EMDs are roots blown regardless of if they had a turbo installed or not. The blower is a requirement for the 2 cycle engine design. It MUST be there.
You can of course have a Super charger and a turbo charger on an engine, so I assume no reason not to on a Locomotive.
SO deturboing a 40 series should not involve replacing the turbo with a roots blower, the blower is already there.
YoHo1975 Wait, I'm confused by the above post indicating the Turbo needed to be replaced with a roots blower. It was my understanding that all EMDs are roots blown regardless of if they had a turbo installed or not. The blower is a requirement for the 2 cycle engine design. It MUST be there. You can of course have a Super charger and a turbo charger on an engine, so I assume no reason not to on a Locomotive. SO deturboing a 40 series should not involve replacing the turbo with a roots blower, the blower is already there.
I am not a professional railroader or a specialist on large medium speed diesel engines so I'm certain that there are other folks on the forum who can answer this better than I..
My understanding is that all turbocharger equipped EMD engines use a system whereby at low speeds the turbocharger is mechanically driven via a clutch system off the prime mover and acts as a supercharger. At higher speeds the linkage de-clutches and the Turbo spins from the force of the exhaust gases,thus acting as a conventional turbocharger. I am read that there have been some rebuildings of older EMD turbocharged units where the turbo was "pinned", meaning it no longer would spin from the exhaust gases and acts as soley as a Roots blower..
Like I said, I bet someone else can provide a better explanation of this..
The EMD turbo is different from everybody else's in that at low power operation it is driven off the no. 2 idler gear through an over riding clutch, through a 18 to 1 speed increaser planetary gear train. At higher engine output the exhaust gases pick up the load through the turbine wheel until it "over speeds" and the clutch releases. At full power the turbo is turning about 2000 rpm faster than it would on the clutch. The turbo is much more expensive to maintain than a blower set up and in switching service to engine is running at the low end of the power range anyway. The differences use to be that the power assemblies on blower engines had 16:1 compression ratio and 14.5 for turbo equipped engines. Since then both can be run with newer type P/A's at 18:1. There were differences in fuel injector, water pump, lube oil pump sizes also so I don't know what they change to de-turbo an engine.
I'm copying this from another forum, they are not my words, but they are my understanding.
EMD's that are turbocharged still have the roots blower that is crankshaft driven, but have an overrunning clutch that also allows them to be driven at higher speeds by an exhaust turbine as a turbo. At low RPM/loads and when starting, the roots blower is driven by the crankshaft to supply scavenging air just like all 2 cycle EMD's. But at higher throttle settings when there is enough exhaust flow, the turbine in the exhaust will produce enough power to spin the blower faster than it normally would spin if driven by the crankshaft. The overrunning clutch will let the blower run faster, supplying more air and thus making more horsepower. Most engines that have a turbocharger or supercharger have just one or the other; EMD is somewhat unique in having a combination of the two on their "Turbo" models.
The Roots Blower is there and by removing or locking the turbine, the engine will behave just as if it is a roots blown engine.Obviously other parts, as mentioned may be different to support the higher pressure and HP, but there is no removing the Turbo and installing the blower. The blower is always there.
My understanding is that the blower on turbocharged EMD two cycle engines use the same basic style of centrifugal compressor that almost all turbochargers use. This is much better suited to the RPM range produced by an exhaust driven turbine than a roots blower.
The overrunning clutch on the EMD engines was a subject of a couple of "On-line with Verna" column in Nuclear News some 20 or so years ago. At some load factors, the overrunning clutch would be cycling between driven and free-wheeling which greatly reduced its life.
- Erik
A roots blower is a positive displacement device having 2 interlocking paddle like devices in a figure 8 shaped housing. The EMD 12 and 16 cylinder engines have two, one each side discharging into it respective airbox. A turbocharged EMD engine has no blower but uses a centrally placed CENTRIFUGAL i.e.: non positive displacement fan that discharges into two ducts going to each side of the engine. Since the turbo at high power generates relatively high airbox pressure the heat of compression is absorbed by radiator like aftercoolers placed right where the blowers are normally found on blower engines. Since its a 2 stroke engine and since it doesn't have any other way to scavange the engine at start up an at low load they use the clutch speed increase gear set up to replace the engine driven blower.
All other 2 strokes ( FairBanks Morse OP, Detroit Diesel 52,71,92, and 149's, Cleveland Diesel 498's and the largest Sultzer with electrically drive fans) use the 2 stage system with a turbo discharging into the blower and etc.
YoHo1975 I'm copying this from another forum, they are not my words, but they are my understanding. EMD's that are turbocharged still have the roots blower that is crankshaft driven, but have an overrunning clutch that also allows them to be driven at higher speeds by an exhaust turbine as a turbo. At low RPM/loads and when starting, the roots blower is driven by the crankshaft to supply scavenging air just like all 2 cycle EMD's. But at higher throttle settings when there is enough exhaust flow, the turbine in the exhaust will produce enough power to spin the blower faster than it normally would spin if driven by the crankshaft. The overrunning clutch will let the blower run faster, supplying more air and thus making more horsepower.Most engines that have a turbocharger or supercharger have just one or the other; EMD is somewhat unique in having a combination of the two on their "Turbo" models. The Roots Blower is there and by removing or locking the turbine, the engine will behave just as if it is a roots blown engine.Obviously other parts, as mentioned may be different to support the higher pressure and HP, but there is no removing the Turbo and installing the blower. The blower is always there.
EMD's that are turbocharged still have the roots blower that is crankshaft driven, but have an overrunning clutch that also allows them to be driven at higher speeds by an exhaust turbine as a turbo. At low RPM/loads and when starting, the roots blower is driven by the crankshaft to supply scavenging air just like all 2 cycle EMD's. But at higher throttle settings when there is enough exhaust flow, the turbine in the exhaust will produce enough power to spin the blower faster than it normally would spin if driven by the crankshaft. The overrunning clutch will let the blower run faster, supplying more air and thus making more horsepower.Most engines that have a turbocharger or supercharger have just one or the other; EMD is somewhat unique in having a combination of the two on their "Turbo" models.
We're describing the same system slightly differently, the Blower meaning the compressor that pressurizes intake air and the "turbine" being the system that converts exhaust gases into mechanical energy to turn the compressor at higher RPMs..it all makes sense now..
A lot of times that the AC44CW'c & the EVO'S derate themselves is the EGU (electric govenor unit) senses a problem with the cooling,fuel problem, so it derates it's self for protection to protect it's self against major engine problems, I work at Alyth diesel shop in Calgary Alberta for CP rail & I had a EVO that derated it's self to 2300 HP because of a cooling system problem & a air to air fan #2 not operating, the DID screen said it was working but it was not. It took a while to figue it out but I got it & now shes back to 4400HP
CNW 6000 carnej1: CSSHEGEWISCH: Most de-ratings involve removal of the turbocharger on an older locomotive that has been demoted to less demanding service, such as SD40-2's as hump pushers or GP40-2's in local freight and transfer service. The derating in these instances is usually from 3000 to 2000 HP. I'm not too sure about the advantages of minor de-ratings that seem to involve resetting the fuel racks or reprogramming the microprocessor. The advantages of derating a locomotive by changing out control modules are primarily fuel savings. This is what CSX has done with SD50's to derate them to 3,000 HP and B40-8s which are derated to 2,000 HP.. De-turbocharging an EMD is more complicated that it may seem as the turbo has to be replaced with a Roots blower. I recall reading that there have been some EMD units derated in recent years by "pinning" the turbocharger clutch so it can't spin freely which means that it then becomes more like a roots blower and is driven by mechanical linkage. GE FDL engine's can't operate without the turbocharger so the only way to derate them is to change engine and fuel settings.. Thanks for the responses folks. Are the options for derating a prime mover such as the FDL "user definable" or a limited set of options from GE? How much of a difference would the 3900 HP to even a 2500 HP change make in fuel usage?
carnej1: CSSHEGEWISCH: Most de-ratings involve removal of the turbocharger on an older locomotive that has been demoted to less demanding service, such as SD40-2's as hump pushers or GP40-2's in local freight and transfer service. The derating in these instances is usually from 3000 to 2000 HP. I'm not too sure about the advantages of minor de-ratings that seem to involve resetting the fuel racks or reprogramming the microprocessor. The advantages of derating a locomotive by changing out control modules are primarily fuel savings. This is what CSX has done with SD50's to derate them to 3,000 HP and B40-8s which are derated to 2,000 HP.. De-turbocharging an EMD is more complicated that it may seem as the turbo has to be replaced with a Roots blower. I recall reading that there have been some EMD units derated in recent years by "pinning" the turbocharger clutch so it can't spin freely which means that it then becomes more like a roots blower and is driven by mechanical linkage. GE FDL engine's can't operate without the turbocharger so the only way to derate them is to change engine and fuel settings..
Thanks for the responses folks. Are the options for derating a prime mover such as the FDL "user definable" or a limited set of options from GE? How much of a difference would the 3900 HP to even a 2500 HP change make in fuel usage?
Depends how and why you are doing it. If you are derating because you just don't need all that HP, then you'd slow the engine down proportionately to the top HP you'd need. Think about this like limiting a GP40 to notch six if you only want to use it for local service. There is almost no impact on fuel efficiency doing this.
If you are trying to save the engine some mechanical grief, you might derate the engine by slowing down the engine speed schedule. The SD50 derate programs did this, dropping the 950 rpm N* engine speed down a bit and dropping the HP proportionally. There is almost no impact on fuel efficiency doing this.
If you do it by dropping the fuel, but keeping the speed schedule - you WOULD reduce the fuel efficiency. You would still have all that parasitic and aux load that goes up with speed squared (think pumps and blowers) but would be dropping just traction power. You might do this to try to lessen the oomph per power stroke to save some wear and tear on the engine. Conrail did this to some of the SD45-2s (with little noticeable effect on maintenance costs....probably a bad idea.)
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
creepycrank The EMD turbo is different from everybody else's in that at low power operation it is driven off the no. 2 idler gear through an over riding clutch, through a 18 to 1 speed increaser planetary gear train. At higher engine output the exhaust gases pick up the load through the turbine wheel until it "over speeds" and the clutch releases. At full power the turbo is turning about 2000 rpm faster than it would on the clutch. The turbo is much more expensive to maintain than a blower set up and in switching service to engine is running at the low end of the power range anyway. The differences use to be that the power assemblies on blower engines had 16:1 compression ratio and 14.5 for turbo equipped engines. Since then both can be run with newer type P/A's at 18:1. There were differences in fuel injector, water pump, lube oil pump sizes also so I don't know what they change to de-turbo an engine.
The theory of turbocharger removal saving money was sound... but never really played out. the roots blowers have their own maintanance headaches and in reality with current maintanance standards end up costing about as much or more to maintain then a turbocharger unit.
you are exactly right, it is not near as simple as remove turbo and drive system and install blowers, the crankcase is the same, not 100% sure about the air box, IIRC the blower throat mounts a little different than the air ducting with the turbo. even the load regulators are different, hence the process usually winds up being a complete rebuild, rather than a parts swap.
On the WC we derated the 20 cylinder engines to 3200 HP to save a few crank shafts.
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