Through reading various sources I'm led to believe that the Class 800 engines are always unmuzzled (or unfettered
) in passenger service. What hasn't changed from the original
DfT» mandated spec is the acceleration curve. This is limited by engine management software to 0.7m/s
2. Increasing this is possible, but then the component maintenance cycles would need changing. This would be another contract variation to be hammered out between the DfT and Hitachi. They've done one with the engine uprating and have seemingly determined that's all that's needed until the leccyfication catches up. Of course, overall, the traction components (excepting the diesel engines) are designed to run at up to 140mph.
That acceleration was based on not needing to get beyond 110mph on diesel, as all areas of up to 125mph operation were supposed to be electrified prior to introduction.
Distributed traction, a generally lighter consist, and the engine uprating mean the acceleration on diesel is initially better from a stand than the
HST▸ , but, after hitting the 0.7m/s
2 limit, the HST edges ahead again on acceleration.
Of course once the wires reach Chippenham/Bristol/Cardiff the Class 800s will leave the HSTs trailing in their wake. That's when we should see the timetable recast and the promised modest journey time improvements.
It'll also be interesting to see whether the Class 802s have the same acceleration curve. As these have been ordered in the traditional way - by an operator and funded by a RoSCo - they could potentially be even more 'unmuzzled' by not having a DfT mandated acceleration limit.
Finally, it's worth remembering that 'speed' was not a primary reason for ordering these trains. An ageing fleet had to be replaced, and an increase in capacity was needed.
That doesn't sound right to me.
The acceleration limit in the
IEP▸ final spec. isn't just a fixed limit (of 0.75 m/s
2), but above 45 km/hr it's a power limit. So if the limit implemented is 0.7 m/s
2 (to be below the required maximum) that applies from starting up to the threshold (or "knee") velocity, then does not above.
Lifting that fixed limit would mean a threshold at a lower velocity, so it would only have a limited effect. It would also call for greater adhesion; 0.7 m/s
2 already implies about 12%.
That high-speed curve on the graph is above the line for a muzzled diesel, or even one on full power, but just below that for the full motor rated power. It's probably about right or electric mode once you allow for mechanical losses. And this limit does apply in all modes.
The words above that curve talk about "compatible with the infrastructure", and come under section 3.23 Signalling Compatibility. Now, what's that about? A clever signalling system night measure the train's speed and need to assume it won't change too quickly. However, as far as I know we don't have one that clever. But I can't believe signalling imposes any limit versus speed with quite that shape.
If it is a signalling constraint, it looks unlikely it will be any different for other variants, or indeed for other trains. While that acceleration limit isn't mentioned in connection with track wear, I can imagine it might affect that. If so raising it should, by rights, lead to an increase in track access charges (but probably only a small one).
Higher traction or torque might have wear implications for the train too, mostly in electric mode. You'd need to be a designer to know, but I can imagine that the motors, gears, and wheelsets would all take more of a hammering. To some extent that depends how the train applies WSP - that's not mentioned in the spec. nor in Hitachi's suppliers list; presumably it's "only software" (plus a wheel-speed sensor).
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