jscheef Sounds like a good argument for gensets in larger road locomotives. Jim
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.
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.
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
The AR-10 will make plenty of excitation current and voltage in low idle, the maximum actually.
Randy
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
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).
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.
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.
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?
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.
Right, you still gotta run the traction motor blowers otherwise the motors turn into a pile of melted copper.
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
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.
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
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