.jpg) |
| O71 Class locomotive in Enterprise livery at Belfast Grand Central Station. No author provided, CC BY-SA 4.0 , via Wikimedia Commons. |
.jpg){kind=link}
The locomotives that pull carriages, known as diesel-electric
have engines that run on diesel. However the engines don't drive the
wheels directly. Instead, they power a generator and the wheels are
driven by electric motors. This makes it easier to control speed using
electronics/electrics, rather than controlling injectors on a diesel
engine to vary power. Also electric motors have full torque at zero RPM,
unlike an engine which has to spin up to suck in fuel to produce power,
and has zero torque at zero RPM. (Interestingly, steam engines also
have full torque at zero RPM). Both the 071 and 201 class locomotives,
used for intercity passenger and freight transport use this system. The
DART is of course electric and is supplied with power from overhead
lines that operate at 1500 V DC. Electricity is "collected" using pantographs
attached to the roofs of carriages. Suburban commuter service trains
are diesel multiple units (DMUs). They don't have a locomotive, apart
from a driving cab, each carriage being individually powered by a diesel
engine. While DMUs can be diesel-mechanical (i.e. direct-drive),
diesel-electric or diesel-hydraulic, the 2200 class units, widely used
by Iarnród Éireann for suburban use are diesel-hydraulic, hydraulic
motors being used to drive the wheels (like the tracks on a digger).
The
new DART+Fleet will use battery-electric carriages in advance of an
extension of the electrification of lines beyond the Greater Dublin
area. 155 of the 185 carriages on order are battery electric and a
five-carriage train will have a range of up to 80 km, with an onboard
840 kWh battery. These batteries are charged by regenerative braking and
also "replenished via fast charging stations at chosen terminus
locations". According to Iarnród Éireann, charging infrastructure is
currently under construction.
More info on the DART+ Programme here.