East Coast HSTs only go 115?? Nope, thats not true. They still manage 125.
Yes slower acceleration, but as you say, that doesnt matter on long distance services. The HSTs should not be used on local stoppers at all. They arent designed for it. FGW should have ordered new stock, and not ruined the HSTs. Well again, thats my opinion that they are ruined.
I agree that the HSTs are not at all suited to the frequent stop, outer suburban duties that FGW are using on them. However, new trains are not forthcoming, so they did the best that they could with what they had available. Better than sitting on their laurels and sticking with rammed Turbos, which would have had them slated much more vociferously.
The problem with HST acceleration is power falloff over the medium-speed range. Off the mark, HSTs can hit 15mph before the rear power car clears the platform, and roughly equal 317s between King's Cross and Finsbury Park. The problem comes at anything over 50 mph, where tractive effort tends to fall away with a diesel-electric before the relatively-constant horsepower delivery comes back at over 100. That just so happens to be the point where electrics can deliver both maximum tractive effort and horsepower, although a high-geared electric can be mighty slow off the mark (especially an Electra). Above that, the risk of flashovers and overheating means that field-weakening has to come in, therefore reducing the power and allowing diesels to make a comeback. An added bonus with electrics is the ability to climb hills at regular speed, where a diesel would simply run out of power or overheat.
What that means is that a Class 90, with lower gearing and lower top speed, is faster than both an HST and an Electra on a semi-fast (say London-Newark as planned) while an Electra and an HST are roughly equal on a flat route, but Electras are slightly better at pulling away from signal checks and climbing hills. Their additional 15 mph of top speed would be helpful if they could use it, but that is one reason for the high gear ratio. Swings and roundabouts.
Exactly. What's a power station? A VERY big engine (perhaps not exactly literally of course). Electric trains are more efficient than diesel, and why is that? Either a power station (VERY big engine) is more efficient than loads of small engines or it's all to do with the weight saving on the train, or most likely a combination of both. Either way, bi-mode looks pretty emmisions intensive compared to all-electric. I have heard mentioned somewhere that the bi-modes might be able to keep to the electric timetable on diesel power in the event of OHLE failure. If this is the case they will need a heck of a lot more power than a (reletivly) sluggishly accelerating IC125 so the emmisions of the bi-modes would be VERY MUCH GREATER for any given stretch of diesel running than an IC125. The extra weight will mean their emmisions on OHLE power (especially if one diesel engine per coach is still running) will not be much better, if at all, than an IC125 running under the wires.
One thing with diesel-electrics in particular is that the power is fed through two sets of electrical equipment, alternator and motors. Unlike power station alternators, these both have to run at variable speeds, which adds weight and reduces efficiency. Diesel-hydraulics are a lot lighter, but thermal efficiency is about the same, because there the power train includes torque-converter and final drive. However, the weight saving is no real benefit, because hydraulic systems are not as reliable on a large (locomotive) scale. DMUs seem to manage fine.
That sounds like a logical reason why multiple engines could be needed, but as I said I agree that a single larger engine is likely to be more efficient than several smaller ones.
The best way to compare there would be to look at aircraft. Comparing say an A-330 with an A-340 would give some interesting results, since they both use the same fuselage and basically the same engine. The 330 needs more power, in case an engine fails on takeoff, but in the cruise, two big engines are slightly less efficient than four smaller ones. However, the 340 needs twice the number of parts, needs to service twice the number of engines and uses about 1.5 times the ammount of lubricant. That pushes costs up. The 340 is quieter and slightly safer, since losing one engine is less of a penalty, but twice as many engines means twice as many things to go wrong. The biggest difference is range, but that is simply because the 340 is not covered by ETOPS. Once again, swings and roundabouts.
I'd like to see the figures of just how much less greenhouse footprint dragging an EMU with a locomotive would produce over the bi-mode option. It obviously would be less, even if you assume none of the engines on the bi-mode are running under the wires. This is because not having to haul the weight of all that diesel fuel and the engines would reduce the electric power consumpsion, it is common sence. The logistics are more of a problem, which is why bi-mode might be unavoidable for the Worcester/Great Malvern/Hereford route (hourly service and, I am told, an inapropriate station layout at Oxford). However, if 34 years ago a 4TC could be uncoupled from another 4TC and a 4REP and coupled to class 33 at Bournemouth for the train to go on to Weymouth every hour then I'm sure today's railwaymen can manage to swap a class 91 for a class 57 at Swansea 2 or 3 times per day for the Carmarthen/Pembroke Dock services. Attaching a locomotive to an EMU to go to Aberdeen/Inverness etc. would be even easier, due to not having to get the electric loco off first. No pulling diesels about through electrified sections, simples.
That's roughly what I've been saying. Electric on the south end, diesel on the north end and a rake with two driving cabs. Diagrams should be easy to work out, assuming that the diesel comes off a southbound train at Waverley, then heads up into the Mound Tunnel and backs down directly onto a northbound train. If 80 years ago with screw couplings, we could manage the high-intensity Jazz service, then with modern couplers it should be easy. Only issue is whether the train could run straight in and couple to the new loco or whether the loco would have to back down.
Oh, but there is a way round that. If Hitachi won't do electric locos, you can't get an IC225 type electric train with loco swaps at the end of wires (which would be the most energy efficient method, thanks to not having the (admittedly small) extra weight of the pantograph, transformers etc. while off-wire). However, you can still have Hitachi EMUs, dragged by diesel locos sourced from elsewhere (you don't even have to build new, we have plenty spare, even if most are a little old.) Whether you build new diesel locos or repair our existing ones (whichever is cheaper) you still get the advantages of avoiding bi-mode.
I'd go for 67 conversions. Possibly regear them for 100 mph to increase low-speed adhesion (their biggest problem AIUI). 57s would probably do OK as well, and even 66s at a pinch (but only in the summer).
True, but a multiple unit can never offer all the advantages of LHCS either. LHCS is very wastefull if you have fewer than 3 coaches, and short (1-3 car), slow (no faster than 100mph) MUs with corridor connections at the unit ends are highly flexible. However, trains that can exceed 100mph cannot have a corridor connection at the leading end, so multiple unit flexibility falls down here. Long multiple units also suffer from being a fixed length, you can't easily decide to shorten some sets for less popular services and lengthen others at peak times. Here LHCS flexibility comes in, as you can change the formation to your hearts content, no messing around with complicated software necessary. Also, if Hitachi would build LHCS, cheap follow on orders of additional coaches to lengthen trains or replace the Mrk3 stock behind the class 90s in East Anglia would be possible. You could also order 4-car or 5-car rakes with a DBSO to run with TDM equiped 57s, like those needed for the Pembroke services, on routes which are currently doubled-up 158s, allowing those 158s to increase service frequencies elsewhere.
You can't make the MkIII rakes any longer, because of Liverpool Street, but it must be possible to build new DBSOs to replace the DVTs. However, the MkIV rakes could do with an extra coach. Since some have been written off, I would go for concentrating them into DVT+10 rakes and move the W&SR MkIIIs over here plus any other spares, form them into two or three rakes and set them to work. New stock (possibly Irish-style from CAF) could replace them in time.
