IEP for beginners

Discussion in 'Traction & Rolling Stock' started by nickshanks, 14 Jan 2013.

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  1. sprinterguy

    sprinterguy Established Member

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    I have no idea how you come to that conclusion: The 5-car Bi-mode IEP trains will have distributed traction, a similar power output to a 4-car Voyager and a lower weight than either a 5-car Super Voyager or a hypothetical 5-car Pendolino. It is well known that the Voyagers completely trounce HST timings and that distributed traction is superior when it comes to acceleration. And of course the Bi-mode trains will be running on electric power for the greater part of their journeys, instantly setting up power outputs, rates of acceleration and journey times that leave a diesel powered HST in the dust.
    --- old post above --- --- new post below ---
    According to the published figures, the 5-car Bi-mode trains will have a power to weight ratio of 11.325hp/tonne when running on diesel. This compares with 13.25hp/tonne for a 5-car class 221. There are no published figures (that I know of) for the weight of the 9-car bi-mode trains that will be used on the East Coast, but some rough calculations suggest that the power to weight ratio will be similar to that of the 5-car Bi-modes.
    --- old post above --- --- new post below ---
    Yes, electricity use is costed separately. In the current CP4 period, overhead electricity use is charged at 1.13 pence per vehicle mile for passenger trains.
     
    Last edited: 24 Jan 2013
  2. RAGNARØKR

    RAGNARØKR Member

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    I admire your trust. And what was Armstrong about? One-size fits all has an irresistible appeal to the collective Civil Service mind. It has been the same story with defence procurement for decades - the weapon or military vehicle that can do everything is a familiar story.
     
  3. sprinterguy

    sprinterguy Established Member

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    To add to this, according to the published figures, even the Bi-mode IEP trains are going to be comparable in weight to a Pendolino, and as another poster has said with longer carriages their will be fewer axles per train to meet the same passenger capacity provided by, say, an 11-car Pendolino.
     
  4. RAGNARØKR

    RAGNARØKR Member

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    So it will be a gas-guzzler in diesel mode.
     
  5. sprinterguy

    sprinterguy Established Member

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    With each engine delivering 700kW, this would be likely. However it will still consume considerably less fuel than a solely diesel powered train, be it an HST or some sort of long distance DMU, running for hundreds of miles under the wires on a London to Aberdeen or Inverness run. I can't see fuel consumption being much worse than that of a 3000hp diesel locomotive, and these are high speed Intercity trains after all.
     
  6. Dave1987

    Dave1987 Established Member

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    Current emission regs which IEP will have to comply with means that a loco will be far far more fuel efficient than underfloor diesel engines. Also a loco would have 2,800kW if it were a class 68 or similar, far more power than the underfloor engines so it will have far better acceleration than bi-mode. It will also cause less track damage.
     
  7. sprinterguy

    sprinterguy Established Member

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    I doubt that. Class 67s have truly appalling acceleration when hauling any sort of a load, and a loco only has four axles available to transmit power at the railhead, compared to twelve on a 5-car IEP Bi-mode or twenty on a 9-car set. For the same reason I can't see how an 80 tonne locomotive carried on four axles will cause less track damage than a 40 - 45 tonne IEP carriage carried on the same number of axles. I don't know of any UK locomotive design that accelerates as fast as a comparable multiple unit formation.
     
  8. RAGNARØKR

    RAGNARØKR Member

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    Yes but a diesel train running all the way to London would use no electricity! However, power consumption is to some extent a function of how the train is driven, its acceleration rates and cruising speeds. What is the difference in efficiency between several underfloor engines and the same power in a single locomotive?

    A further question relates to traffic levels, which are lower beyond the end of the wires. Splitting avoids running a half empty train. A train with a bi-mode portion and an electric-only portion would help get round both problems, would it not? ie the bi-mode portion proceeds to the final destination, whilst the electric portion turns round and goes back to London.
    --- old post above --- --- new post below ---
    Perhaps it needs to be a six-axle loco? However, acceleration is gas guzzling, and there is also the issue of the constant power curve to be taken account of. But loadings north of eg Edinburgh are lower than south so it is not necessary for the entire train to go all the way to eg Aberdeen.
     
  9. sprinterguy

    sprinterguy Established Member

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    There are economies to be had from only specifying a larger fleet of one train type (A Bi-mode one) rather than two smaller fleets of electric and Bi-mode trains. Having only Bi-mode 5-car trains also makes unit diagramming easier, as all the trains can be used indiscriminately on or off the wires. Having said that however the East Coast will have a mix of electric and Bi-mode 5-car sets.
    --- old post above --- --- new post below ---
    Six axle locos introduce their own problems of track wear that are disproportionately higher than those associated with a four axle loco, due to the different dynamics of a three axle bogie, particularly their behaviour in curves.
    --- old post above --- --- new post below ---
    Just because the rate of acceleration of a loco will be lower than that of a comparable multiple unit does not mean that the loco is consuming fuel at a slower rate. It means that the loco is less efficient at applying power at the railhead.
     
  10. tbtc

    tbtc Veteran Member

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    A loco would cause more track damage, hence the reason that a loco faces much higher track access charges (if you remember the GEML thread...).

    No loco on one engine could out-accelerate a Voyager with distributed engines. And good acceleration would be required on the regular stopping patterns you get "beyond the wires".
     
  11. The Ham

    The Ham Established Member

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    OK, my mistake, I must of miss understood that.

    Anyway 1.13pence per vehicle mile for passenger trains sounds very good value and noticeably cheaper than diesel.
     
  12. tbtc

    tbtc Veteran Member

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    ...which is why the idea of running diesels under the wires all the way from London to Edinburgh seems a bit silly to me (but not to RAGNARØKR)...
     
  13. RAGNARØKR

    RAGNARØKR Member

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    I seem to recall the class 37s on the Crewe-Holyhead services got way pretty smartly with four mark 1s. And I wonder how an 8P such as the Duke of Gloucester would perform with a load of only 200 tons?
     
  14. tbtc

    tbtc Veteran Member

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    We've gone from discussing Voyager/ IEPs (i.e. up to 130m) to discussing hauling just eighty metres of coaches?

    Moving the goalposts again?
     
  15. Dave1987

    Dave1987 Established Member

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    I totally disagree. A 200 tonne train would be nothing for for a class 68 when they are build. On GEML a class 90 can accelerate very quickly. Plus because you are transmitting the torque through only four axles instead of 12+ the track damage would be less. I believe that Porterbrook publication stated this as well. Fuel efficiency on a loco would be far greater on a loco than underfloor engines due to exhaust back pressures on underfloor engines. That is the reason class 172's are not as efficent as one might expect.
     
  16. AndyLandy

    AndyLandy Established Member

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    Do you have any citations or evidence for this? I only ask because it goes against everything I had previously understood about diesel/electric/centralised/distributed traction.
     
  17. RAGNARØKR

    RAGNARØKR Member

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    It was you made the unqualified assertion. There is obviously a locomotive or pair of locomotives available which can match the performance of a set of between six and ten self-powered vehicles. Whether that is a better option is another matter.
    --- old post above --- --- new post below ---
    What a pity the Railway Technical Centre is not more. I think these arguments are going to rumble on because it is going to be very difficult to establish the truth. On the face of things it would seem reasonable to suppose that distributed traction would cause less wear and tear on the track, and also that it would give better acceleration in the low speed range but the differences would even out at higher speeds.

    I recall the Deltics were very slow at getting away but the acceleration kicked in hard at 30mph. That might be a clue to what is going on.
     
  18. Dave1987

    Dave1987 Established Member

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    From what I gather the more rotationally stiff axles you have the more track damage is caused. Underfloor engines also cause extra vibrations bad noise they also cannot meet emission regs without sacrificing fuel efficiency. Add that to the waste of energy under the wires then bi-modes are a thoroughly bad idea. My idea would be to just electrify the whole lot and just run emus all the way and then this bi-mode argument would be irrelevant.
     
  19. AndyLandy

    AndyLandy Established Member

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    Again, this seems counter-intuitive to my understanding of how these things work. Wikipedia cites UK emission standards as up to 400 kg CO2/MWh. It seems apparent to me that by making more efficient use of the fuel, you'd be better off emissions-wise. I freely admit I'm no expert though, so if someone has evidence to the contrary, I'd be fascinated to see it and understand.

    On that point, we agree. But I genuinely don't believe that's realistically achievable before we need to be looking at new trains. That's largely the reason why I'm in support of bi-modal trains. They're a stopgap measure to be more efficient than plain diesel-under-the-wires, until we can finish the wiring.
     
  20. 455driver

    455driver Veteran Member

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    That is because of the gearing.
     
  21. HSTEd

    HSTEd Established Member

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    People.... the 1.13p per vehicle mile is nothing to do with the price of electricity.

    That is the charge that is introduced to account for wear on the overhead wiring by pantographs.

    The price of traction electricity and the established metrics for each traction type are listed in another document.
     
  22. 455driver

    455driver Veteran Member

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    Basically there is a huge catalytic converter in the exhaust converting the harmful emissions into less harmful ones, this catalytic converter is very restrictive so the engine has to work harder (using more fuel in the process) to push the exhaust out.

    It isnt actually a reduction in all emissions (in fact it increases most of them) just the harmful ones.

    It is much more complicated than that but thats the jist of it.
     
  23. Dave1987

    Dave1987 Established Member

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    It is far easier to comply with the emissions regs on a loco that with underfloor engines due to exhaust back pressure. So under current regs its more fuel efficient with a loco.
     
  24. tbtc

    tbtc Veteran Member

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    Agreed.

    But the reality is that HSTs aren't going to last (in number) for much beyond another decade and we've already seen some CP5 plans pushed into CP6 (Sheffield won't see electrification until half way through CP6 now), so there's no chance of finding extra resources to wire in CP5.
     
  25. HSTEd

    HSTEd Established Member

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    SCR will probably help with the emissions issues.

    And as to the electrification issue.

    We will never see the resources neccesary to achieve total electrification without purchase of bi mode units for intercity work and if the bi mode units are ordered the justification for electrification of the extremities of the intercity network dissapears.

    Bi-mode IEP will kill the electrification programme essentially.
    (Since the electrification of the extremities of the network is best justified as eliminating under-wires diesel running).
     
  26. jimm

    jimm Established Member

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    Again, I have to ask, do you ever read what anyone else posts? I dealt with this ages ago and really can't be bothered to trawl for it, so I'll just restate it again. Maybe it will stick this time...

    1. Traffic levels are not always lower beyond where the wires will end. As I have pointed out before, several peak HSTs on the Cotswold Line with 500 seats - or more if it's a super-HD set with a mini-buffet - arrive at Oxford from the west in the morning, or leave the other way in late afternoon full up. Cheltenham and Gloucester peak services can also be very busy west of Swindon - well beyond the capacity of a five-car train.

    2. If you had a formation of a five-car bi-mode and a five-car electric and the bi-mode breaks at Oxford or Swindon, you have to cancel the entire service. Two bi-modes mean you can still operate the train through to its destination. Or you could have a big loco and shunting engines pottering about adding and removing coaches instead...

    So when is XC ordering its fleet of new bi-modes then, since there is no hope of wiring beyond Sheffield or on Derby-Birmingham-Bristol on the basis of that assertion?

    Meanwhile, back in the real world where the railways have to operate... how are you going to pay for your idea?

    Or is this just another question you're going to ignore, like explaining all the waste involved in running diesel locos for miles under wires to get to a depot under your other strategy for not having bi-modes, because they are so wasteful?
     
  27. HSTEd

    HSTEd Established Member

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    Why order bi-modes when you can just keep the Voyagers? :P
     
  28. Dave1987

    Dave1987 Established Member

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    I have answered your point jimm or have you not bothered to read it?:roll:
     
  29. D365

    D365 Established Member

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    So that trains can actually use the OHLE that is being put up. What a shame about eVoyager...
     
  30. AndyLandy

    AndyLandy Established Member

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    You'd need something to replace them on CrossCountry first. Perhaps I might suggest some kind of "bi-modal" train? :lol:
     
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