I was wondering, why don't they design a locomotive that shuts down its diesel engine while the locomotive is descending a long grade in dynamic braking mode. It seems like that would save fuel. Or is reality more complicated than that?
- Rails West
It would be more efficient to store the electrical energy being created by both the prime mover and the dynamics in a battery that would then be used to assist the train ascend the next hill. The GE hybrid locomotive stores the dynamic brake energy in batteries that are located between the frame rails, but I'm not sure if it also stores the electrical energy from the prime mover.
I had an idea to also store the energy in batteries from non-hybrid locomotive to allow locomotives as old as SD40-2s to operate as hybrids. I did a patent search and I learned that GE already holds this patent but to my knowledge this has never been developed.
Locomotive engines aren't little 4-banger gas engines like you would find in hybrid automobiles. There is a lot of weight moving around, and getting it restarted takes a while. The Smart Start systems I deal with have a delay from auto-restarting of about a minute before the engine will respond to throttle commands. This enables the oil pressure to stabilize, etc. Many times running a train you would come out of dynamics right into power, to start up the next hill, or what have you. If you are waiting for the engine to restart, if it restarts, at best you might stop, at worst you might scatter the train all over the countryside.
Most EMDs built after 1978 or so have a two-step dynamic card. These units stay in idle until about 500 amps or so of dynamic effort is requested. Then they rev up a bit to help with cooling.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
Right, you still gotta run the traction motor blowers otherwise the motors turn into a pile of melted copper.
Randy
One of the features of older EMD's is "slow idle". If the reverser switch is in "neutral" the prime mover idle is low. That saves some fuel on the SPD-40 that the Osceola and St. Croix Valley RR operates.
In addition, we can adjust the speed of the diesel in dynamics. Since we only use a small range of dynamics we speed up the engine to run 2 in dynamic braking. This provides enough power for the fans and traction blowers.
Fuel is obviously a large cost and even locomotives from the '60's were built to conserve fuel.
There is a thread somewhere about a shutdown switch located where the engineers foot might bump it. It seems to me there was a major accident when a loco was accidentally shut down and the train lost most of the dynamics and derailed. Can somebody refresh my memory?
UP Runaway accident on Cima Hill in California 1997 or 1998. Train ran into an Intermodal train ahead of it. Top speed reached 118 mph. The Intermodal train Engineer tried to out run the Runaway Tie train, but his overspeed tripped. The cause was the Engineer bumped the switch on UP SD60M 6205 shutting down all the locomotives on the tie train . Solution was to relocate the switch and install a guard. The problem was known, but the first solution of installing a guard was being done only as affected locomotives came in for regularly scheduled maintenance with enough shop time. Locomotives involved were all SD60Ms with the 3 window cab on UP, and BNSF. Soo Line's SD60Ms had already completed a modification of the switch location and had a guard installed at the time of the accident.
Dunno which accident you meant to describe, but the tie train that overtook the TOFC train allegedly at 118 mph was in the 1980s, and AFAIK the switch in question wasn't involved (the tie train had an SD40-2).
timz Dunno which accident you meant to describe, but the tie train that overtook the TOFC train allegedly at 118 mph was in the 1980s, and AFAIK the switch in question wasn't involved (the tie train had an SD40-2).
Your right, I confused two runaway accidents. The shutdown runaway happened January 12, 1997 and involved UP Extra 6205 West with 3 locomotives and 75 covered hoppers of corn. The crew was lucky the drawbar between the last locomotive and the first car broke, followed by most of the train derailing.
Yes, "it's really more complicated than that." One reply correctly pointed out the need to keep the traction motor blowers running. In general, it's nice to keep the auxiliaries going. But, the biggest "need" is that to have dynamic braking you need excitation (which is true whether DC or AC traction) and that requires that the engine be turning the generator/alternator.
The details are beyond the scope of this discussion thread, but that's the basic reason.
Dave Phelps
Sounds like a good argument for gensets in larger road locomotives.
Jim
The AR-10 will make plenty of excitation current and voltage in low idle, the maximum actually.
A running engine is required to operate the dynamic brakes. Actually, locomotives are a lot more fuel efficient than you might think. When you figure the total amount of gallons a locomotive consumes to move the tonnage involved over the distance traveled it is rather small.
Tim G
NS Locomotive Engineer
Anybody think of this: When using dynamics and having power generated by them, why not reverse the prime mover generator in a motor and use that to keep the cylinders spinning? Very similar to engine braking on a diesel truck - that way you can cut off the fuel going into the cylinders have saving fuel but keep the engine spinning, so your oil pressure and everything else is kept up and as soon as you need power just re-introduce fuel and you are good to go.
jscheef Sounds like a good argument for gensets in larger road locomotives. Jim
Nope
Gensets are an advantage in things like local and switching service because you rarely need maximum power and spend much of your time at idle or using a fraction of the unit's horsepower, so having multiple engines that allow partial shutdown under those circumstances is an advantage.
Out on the road on a mainline freight, you'd often be using all the power you have available. And the most fuel efficient way to provide that is with a single diesel engine in each locomotive. Gensets get away with less fuel efficient powerplants because the majority of the time they're operating, they're only using a fraction of the total horsepower available to the unit.
So a three engine Genset, like Railpower's RP20BD, rarely will actually have all three engines online. When it does have all three engines operating and outputing 2000hp, it's less fuel efficient than a modern, single engined, 2000hp locomotive.
The advantage comes from the fact that most of the time due to the type of service they're in, a 3 engine Genset will just have 1 or 2 of it's engines operating. That's where the efficiency comes from. A large road locomotive wouldn't benefit since it would spend much of it's time with all engines online burning more fuel. So if we see any changes, it's going to be a shift towards things like GE's Evolution hybrid prototype that captures previously wasted dynamic braking energy in a bank of batteries that then gets used when the engineer throttles up to increase fuel efficiency.
There was a bad derailment on the Southern pacific in California either in the 80's or 90's where a train loaded with pot ash derailed. ff I remember right it had over 100 cars and they all derailed. The locomotives and many cars ended up demolishing peoples houses around a curve.
From what I remember many of the locomotives overheated and automatically shut down. When the locomotives shut down they lost the dynamic braking and could not stop it on air alone. I believe that train was going close to 100 mph when it hit that cure.
Shutting down a locomotive going down a hill would be a good idea as there are some very long hills(the Moffat route in Colorado is all almost all downhill from the Moffat tunnel to Denver). There is one big problem though,and that is locomotives drive the air compressor with the engine(I believe they have electric air compressors on locomotives now that are not driven by the engine but I am not sure).
With out the engine running you would not be running a air compressor and it wouldn't take long to lose your air and lose control of your train. Even with dynamic braking it can only take so much of a load over a period of time before you start to melt the traction motor cables. So it's best to count on your air brakes as your primary means of stopping a train.
On a side note when the Milwaukee road used to coast their electric locomotives down a big hill,they turned their electric motors into generators pumping electric right back into the grid. People used to say "a train going down a hill is powering another one coming up the hill".
Thomas 9011,
The derailment you are thinking of was commonly known as the "Duffy Street Incident" in San Bernadino, CA. Wikipedia has an informative article titled " San Bernardino train disaster". The cargo was listed as "Trona", I don't know how, or if Trona differs from potash. the trains weight was mis-calculated, and of 6 locomotives only two had working dynamic brakes, which was unknown to the engineer.
Doug
May your flanges always stay BETWEEN the rails
So it's best to count on your air brakes as your primary means of stopping a train.
If STOPPING your train is your concern, then the air brakes are your only option, as dynamic brakes will only SLOW a train, NOT stop a train.
Leo_Ames jscheef: Sounds like a good argument for gensets in larger road locomotives. Jim Nope Gensets are an advantage in things like local and switching service because you rarely need maximum power and spend much of your time at idle or using a fraction of the unit's horsepower, so having multiple engines that allow partial shutdown under those circumstances is an advantage. Out on the road on a mainline freight, you'd often be using all the power you have available. And the most fuel efficient way to provide that is with a single diesel engine in each locomotive. Gensets get away with less fuel efficient powerplants because the majority of the time they're operating, they're only using a fraction of the total horsepower available to the unit. So a three engine Genset, like Railpower's RP20BD, rarely will actually have all three engines online. When it does have all three engines operating and outputing 2000hp, it's less fuel efficient than a modern, single engined, 2000hp locomotive. The advantage comes from the fact that most of the time due to the type of service they're in, a 3 engine Genset will just have 1 or 2 of it's engines operating. That's where the efficiency comes from. A large road locomotive wouldn't benefit since it would spend much of it's time with all engines online burning more fuel. So if we see any changes, it's going to be a shift towards things like GE's Evolution hybrid prototype that captures previously wasted dynamic braking energy in a bank of batteries that then gets used when the engineer throttles up to increase fuel efficiency.
jscheef: Sounds like a good argument for gensets in larger road locomotives. Jim
The new PR43C units that NS is buying from Progress Rail are, in fact, "Road Gensets" but most of the power comes from the large (3600 HP) primary engine/alternator with a smaller 700 HP genset providing power only at higher loads as well as for hostling with the "big engine" shut down..
http://en.wikipedia.org/wiki/Progress_Rail_PR43C
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
I use dynamic brakes to stop my train everyday. Hi-Adhesion Extended Dynamic Brakes will bring a train to a complete stop unless conditions warrant otherwise.
Thanks,
Tim
To provide air for the brake system, as well as other things, the air compressors, direct driven or motor driven. must run. You could use an auxiliary engine driven air compressor that would use less fuel but diesel fuel consumption at idle or low notch positions is so low it hardly seems worth it. On a gas turbine powered locomotive the separate air compressor would be a natural solutions since turbine idling fuel consumption is high. A gas turbine can be shut downwithout consequence and full power can be attained in 90 seconds on restart.
It's my understanding that the PR43C isn't built to really be working alongside things like NS's Dash 9 and GEVO fleets in heavy duty road service. But rather, for things like road duty on secondary lines, serving as heavy power in local services, etc. All situations where you frequently wouldn't need all 3600 or 4,300 hp online and could get by with just 700hp online a substantial amount of the time.
I believe that the manufacturer even labels this model as a "medium" duty locomotive.
Don't you need the engine block to power the air compressor for air braking?
A running diesel engine is not required to operate the air compressor, or any other "parasitic" loads, with an appropriate locomotive design. With Brookeville Locomotive's CoGeneration (2100 hp) locomotive, all energy generated by the traction motors in dynamic braking mode is available to power any/all loads on the locomotive, including the air compressor. So I believe that this locomotive could qualify for the thread title, " a loco that shuts off its engine while going down hill." You can read more about this locomotive here:
http://www.brookvilleequipment.com/pdffiles/CoGenerationBrochure.pdf
So where does the excitation of the traction motor fields come from?
Jerry PierA gas turbine can be shut downwithout consequence and full power can be attained in 90 seconds on restart.
OH would UP disagree with you there!
If you don't have turning gear and USE IT, shaft sag will turn your pretty turbine into a mass of expensive scrap in a comparatively short time -- and as I recall UP found this out by experience.
Thermal cycling of the burners and cans, and clearances inside the engine, will not benefit from random startup and shutdown, even if you follow the 'recommended' autostart procedure. (Not to mention what happens if you're using heavy oil and the lines to the turbine were'nt properly purged with diesel at shutdown, and things have cooled off a bit...)
I think Jerry was referred to "aero derived" gas turbines as opposed to industrial turbines. Airliners typically shut their engines down when arriving at the gate and I don't recall seeing any jet engines equipped with turning gears (which are mandatory for large steam turbines). IIRC, the turbines used in the Big Blows were based on stationary gas turbines and not cores from jet engines (i.e. aero derived).
- Erik
Rails West I was wondering, why don't they design a locomotive that shuts down its diesel engine while the locomotive is descending a long grade in dynamic braking mode. It seems like that would save fuel. Or is reality more complicated than that?
I think what you are getting at is why should the engine idle during periods of time when it could be shut down?
That is exactly what RRs do. In fact, some have installed auto-start and APUs to allow the diesel engine to shut down when it's not needed.
However, while the train is moving, you pretty much need the diesel engine running - for a whole bunch of reasons, most of them already discussed.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
episette It would be more efficient to store the electrical energy being created by both the prime mover and the dynamics in a battery that would then be used to assist the train ascend the next hill. The GE hybrid locomotive stores the dynamic brake energy in batteries that are located between the frame rails, but I'm not sure if it also stores the electrical energy from the prime mover. I had an idea to also store the energy in batteries from non-hybrid locomotive to allow locomotives as old as SD40-2s to operate as hybrids. I did a patent search and I learned that GE already holds this patent but to my knowledge this has never been developed.
Railpower also holds similiar patents and there were some "Green Goat" slugs that operated on the principal you describe but IINM, they were all withdrawn from service due (like all green goats) to battery issues..
oltmanndThat is exactly what RRs do. In fact, some have installed auto-start and APUs to allow the diesel engine to shut down when it's not needed.
Don, I think you might want to make clear that the engine HAS to be running when the locomotive is in DB. The 'regenerated' current is not used in the fields or controllers (or, at least in my experience, the fans) -- all of it goes to the resistance. That is why you have to advance the throttle to a specified notch when in DB...
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