Locomotive haulage vs. multiple units

[mike57]

One thought on all this wrt DMUs, maintenance. I would have thought a single large engine would be simpler to maintain than multiple smaller ones. The benefits may not be enough to get a return to loco haulage however.

 

[Dr Hoo]

One thought on all this wrt DMUs, maintenance. I would have thought a single large engine would be simpler to maintain than multiple smaller ones. The benefits may not be enough to get a return to loco haulage however.

Don’t smaller engines have the benefit of usually being more mass produced for automotive, marine, mobile plant, etc.? This tends to lead to easier spares availability, wider fitter skills, earlier de-bugging and so on.

 

[MarkyT]

The wheels limit the low floor more than the motors. Talgo completely does away with bogies on passenger vehicles so need the power cars to move.

Even without Talgo split axles, The wheelrim tops of trailing axles under passenger cars can be very close to or even slightly higher than general floor height without ramps as long as the gangway can clear the axles between them. I think Stadler can do level floor at ~760mm across their articulated bogies on FLIRTs. 550mm floors need ramps over the axles. Clearly the bodyshells and bogie need to be specially designed to allow the passageway through at the desired height, with some wheelboxes penetrating the saloon at the car ends which is why those seats are sometimes raised a little even if the gangway isn't. More room for beefier braking components might be needed at higher speeds which could narrow the passageway, although that would also be a challenge with Talgos and the Avril manages 360kph. Either method doesn't leave much room for motors and gearboxes, especially high power HS ones. On Flirts, power bogies on short sets are at the trains' extremes alone, with high floor cabs and equipment cubicles above them that the public can't access. Where additional power is required on a longer set, a back to back power section exists at a mid-train pair of non-articulated bogies, again topped by equipment cubicles and a higher level walkway across the motor bogies with necessary ramp or step access for the public (note I'm not talking about the diesel power pod here).

Also, most multiple units have unpowered vehicles.

True but I'd say there's a trend toward greater centralisation of traction equipment since the low floor revolution began. Many thought the trend was towards ever greater distribution within unit trains, with Alstoms AVG the concept's European poster child. Now Alstom claim the Avelia concept is lighter and more efficient overall, far less complex and thus more reliable. Above all, it's cheaper. Concentrating modern lighter weight traction gear into their new especially short power cars was seen as the best option. Clearly they're no more a general purpose locomotive than was the HST power car, but they could be changed fairly readily if neccessary at depots.

 

[ac6000cw]

One thought on all this wrt DMUs, maintenance. I would have thought a single large engine would be simpler to maintain than multiple smaller ones. The benefits may not be enough to get a return to loco haulage however.

Don’t smaller engines have the benefit of usually being more mass produced for automotive, marine, mobile plant, etc.? This tends to lead to easier spares availability, wider fitter skills, earlier de-bugging and so on.

IIRC, Roger Ford reported in Modern Railways many years ago about research that BR had done into the relative 'whole life' costs (build + maintenance + running costs) of diesel passenger trains using distributed power versus concentrating the power equipment in one vehicle. IIRC up to about 6-7 passenger vehicles per train distributed power was cheaper, above that a power car was cheaper. I don't know if a similar comparison was done/reported on for electric trains.

As to whether a large diesel engine is more reliable than a small one - both have had problems over the years, so I think it depends far more on exactly which engines and their cooling systems than anything else (and how they are maintained). For example, the problems at times with the Valenta's in HSTs, the Mirlees in the original Brush 2s and the Class 60s, the Crossley in the Co-Bo's, MAN-NBL in some WR diesel-hydraulics, Sulzer 12LDA28-C in class 47s etc. compered with the EMD 645 and 710 series engines in the 59s and 66s and the EE SVT & CSVT in the 20s, 31s, 37s, 40s and 50s. Some underfloor DMU engines have been troublesome at times too.

 

[Dr Hoo]

Apart from the general issue of the ‘costs’ seen by Roger Ford being out of date many things have moved on.

Other considerations such as emissions and noise now really have to be part of the equation. Then there are secondary costs such as training, need for ground/shunting staff, need for a separate depot ‘pilot’ to move unpowered sets around, etc.

Other issues can include ‘waste’ of platform length, possible additional time to ‘prepare’, brake tests and whatnot. Each local of service case really needs to be assessed on its own merits.

 

[HSTEd]

If any serious attempt was to be made on reviving locomotive hauled stock, we would first have to define a cast iron compatibility specification for all features we want a modern train to have. It would have to have room for growth in capability in a backwards compatible manner.

Ofcourse, if we were to do that, we might as well just make one standard for all rail vehicles and be done with it!

 

[Sun Chariot]

... the problems at times with the Valenta's in HSTs, the Mirlees in the original Brush 2s and the Class 60s, the Crossley in the Co-Bo's, MAN-NBL in some WR diesel-hydraulics, Sulzer 12LDA28-C in class 47s etc. compered with the EMD 645 and 710 series engines in the 59s and 66s and the EE SVT & CSVT in the 20s, 31s, 37s, 40s and 50s.

To be fair - by the time of the 59 and 66, EMD had several decades of learning and continuous improvement (the only real "reliability exceptions" being the overstressed variants in SD45 and SD50).

British examples quoted were, in the main, from companies far less mature in designing and building reliable engines. MAN engines, reliable in native Germany, suffered from NBL's lack of precision when scaling MAN design to fit UK's loading gauge.

 

[Energy]

IIRC, Roger Ford reported in Modern Railways many years ago about research that BR had done into the relative 'whole life' costs (build + maintenance + running costs) of diesel passenger trains using distributed power versus concentrating the power equipment in one vehicle. IIRC up to about 6-7 passenger vehicles per train distributed power was cheaper, above that a power car was cheaper. I don't know if a similar comparison was done/reported on for electric trains.

Difficulty is getting enough power in 1 locomotive, 2 class 43s are 4500hp or 3540hp at the wheel. A class 68 is 3800hp but is only Bo-Bo so it struggles to get enough power down. The class 99 is only 2150hp so a single bimode locomotive with enough power to get a HST equivalent rake to 125mph isn't currently feasible.

 

[Sun Chariot]

Difficulty is getting enough power in 1 locomotive, 2 class 43s are 4500hp or 3540hp at the wheel. A class 68 is 3800hp but is only Bo-Bo so it struggles to get enough power down. The class 99 is only 2150hp so a single bimode locomotive with enough power to get a HST equivalent rake to 125mph isn't currently feasible.

EMD GP60 - 4-axle and 3800bhp engine - has no problems. I wonder if the 68 lacks the "wheel creep" technology, used by many US locos?

 

[HSTEd]

EMD GP60 - 4-axle and 3800bhp engine - has no problems. I wonder if the 68 lacks the "wheel creep" technology, used by many US locos?

A GP60 weighs ~273,000lb, which is 124 tonnes.
It's the weight of a UK Co-Co locomotive!

 

[43096]

A GP60 weighs ~273,000lb, which is 124 tonnes.
It's the weight of a UK Co-Co locomotive!

In addition, the EMD wheel creep system is something of a red herring given the 68 has AC motors which have much better inherent wheelslip control.

 

[ac6000cw]

To be fair - by the time of the 59 and 66, EMD had several decades of learning and continuous improvement (the only real "reliability exceptions" being the overstressed variants in SD45 and SD50).

British examples quoted were, in the main, from companies far less mature in designing and building reliable engines. MAN engines, reliable in native Germany, suffered from NBL's lack of precision when scaling MAN design to fit UK's loading gauge.

That was largely my point - engines from suppliers with experience of the railway operating environment tend to be more reliable than those from ones that haven't. But even the experienced suppliers get it wrong sometimes e.g. EMD's early 567 engines had problems, as did Alco's 244 engines.

Difficulty is getting enough power in 1 locomotive, 2 class 43s are 4500hp or 3540hp at the wheel. A class 68 is 3800hp but is only Bo-Bo so it struggles to get enough power down. The class 99 is only 2150hp so a single bimode locomotive with enough power to get a HST equivalent rake to 125mph isn't currently feasible.

I think the power limit for a diesel loco is largely a function of finding space and weight allowance for the cooling system and the fuel storage (plus the exhaust after-treatment system on recent designs). The cl. 87, 88, 90, 91, 93 electric locos are/were all more powerful than the 68 (and there's many 4-axle electric locos hauling freight trains all over mainland Europe and beyond).

EMD GP60 - 4-axle and 3800bhp engine - has no problems. I wonder if the 68 lacks the "wheel creep" technology, used by many US locos?

The GP60 was 'the end of the line' for new 4-axle freight locos in the US - everything afterwards has been 6-axle, largely to go beyond the loco weight limits imposed by a four axle design. But it's interesting that the present-day spiritual successors to the GP60 are 6-axle locos with only four AC-motored axles, used on the same intermodal traffic that the GP60s were built for.

Apart from the general issue of the ‘costs’ seen by Roger Ford being out of date many things have moved on.

Other considerations such as emissions and noise now really have to be part of the equation. Then there are secondary costs such as training, need for ground/shunting staff, need for a separate depot ‘pilot’ to move unpowered sets around, etc.

Other issues can include ‘waste’ of platform length, possible additional time to ‘prepare’, brake tests and whatnot. Each local of service case really needs to be assessed on its own merits.

I know and agree. MU trains have been the sensible choice for the vast majority of passenger trains in the UK for many decades and I don't see that changing.

 

[FGWHST43009]

From what I've seen (primarily from Youtube videos), I'd like to see a UK loading gauge version of the new Railjet sets. Especially as they have coaches with level boarding. If more electrification was done, I'd order sets with either electric or bi-mode locos, the latter would hopefully only need diesel power for lines with speed below 100mph.

 

[mr_jrt]

I always quite liked the idea of the future of loco-hauled services as basically a mobile generator for running a coupled EMU with its own distributed traction. Basically, everything new gets built as a bog standard EMU. Bi-modes obviously are the same idea, just in a different form.

From what I recall in previous discussions, the main stumbling block being the lack of a practical way of providing high voltage power between the loco and the EMU, though I also recall reading that the internal power bus on all EMUs is DC (rectified after the transformer on AC units), so presumably that's a solvable problem?

 

[JamesT]

I always quite liked the idea of the future of loco-hauled services as basically a mobile generator for running a coupled EMU with its own distributed traction. Basically, everything new gets built as a bog standard EMU. Bi-modes obviously are the same idea, just in a different form.

From what I recall in previous discussions, the main stumbling block being the lack of a practical way of providing high voltage power between the loco and the EMU, though I also recall reading that the internal power bus on all EMUs is DC (rectified after the transformer on AC units), so presumably that's a solvable problem?

The connectors between carriages will be something that's only interacted with inside a depot during maintenance. Whereas I assume with a locomotive you're expecting to couple and uncouple in service?
The power involved in a modern EMU is in the several MW range. At 750V DC you're looking at needing several kA to go across a connector. You're effectively looking for a pluggable version of a third rail which is mostly made safe by having people kept as far away as possible.

 

[Energy]

though I also recall reading that the internal power bus on all EMUs is DC (rectified after the transformer on AC units), so presumably that's a solvable problem?

It depends on the EMU, most have multiple buses anyway. Electrostars do have a DC bus but were designed primarily for 3rd rail.

The 800s (and other AT300s) have a 25kv bus running along the roof, you can see the pigtails at the top between cars, and I believe a 3-phase 230v feed for auxiliaries.