there are several ways to limit vehicle
acceleration:
1) engine rev
cut-off (i.e. engines cannot rev above a given rpm, i.e.
1500rpm) in certain
gears
2) torque
limitation through manipulation of fuel injection and
turbocharger boost pressures in certain gears
3) across-the-board engine detuning (i.e. overall torque limitation
irregardless of gear)
i suspect the issue lies more with (3) rather than (1) or (2)
because across-the-board detuning serves to reduce fuel consumption
more effectively than temporary limiting torque.
for operators with a fuel bill burden, the best strategy would
be to reduce overall fuel consumption of the engine irregardless of
accceeration/cruising, and that can only be done by detuning the
maximum output permissible by the engine.
such across-the-board detuning creates several
issues,
1) you lack the torque much needed for quick acceleration, and the
Citaro doesnt have that much (1120Nm) to start with.
2) driver safety is compromised when judgement is impaired by
sub-par vehicle acceleration and manuverability from
bus-stops.
3) if SCR after-treatment is also disabled, expect emission
standards to fall below E5.
4) fuel economy is hampered because turbocharger boost pressures
are reduced to reduce combustion (and thereby power generated),
therefore you are not getting the most out every drop of fuel
rev-limiting doesnt limit the acceleration, but the maximum speed possible in the given
gear. that will create another danger when power/torque
only possibly attained at a given speed is required but not
delivered. again, it compromises the BC's ability to maneuver out
of bus stops under tricky conditions when the BC may require a
higher than usual-speed along with power/torque.
that said, the OM906hLA cut off at about 2200rpm or slightly
higher, because 2200rpm is the red-line for the engine. 2000rpm and
above is, supposedly, more than sufficient for any BC to move off
from a bus stop!
also, turbochargers cannot be over-spooled as a waste-gate
diverts exhaust gases away from the turbine once maximum boost
pressure is achieved! like it or not, over-acceleration is very
unlikely to be an issue on the Citaro given its engine output,
transmission design and potential across-board engine
detuning.
Wow, that's a very comprehensive set of info there, many thanks
for clarifying. 
So, I suppose that since you pointed out that it's likely
across-the-board engine detuning for the Ctiaros, so you're
guessing too that the Citaros are using too much fuel than what is
needed?
I had always thought that they wanted to limit the damage the
extra revs in the first 2-3 gears would cause to the turbochargers
in the long-run if the gears were allowed to "slip" still from the
initial days till now. Do you think this is possible to happen
too?
