I was doing some research on "bi-mode" or "dual-mode" locomotives, which can use both electric power from an overhead catenary, as well as diesel power. Diesel-electric locos already use electric engines to turn the wheels: the diesel engine drives an electric generator which in turn drives the wheels. Why this apparently inefficient arrangement? Because an electric engine can provide full torque at zero RPM, unlike plain diesel engines, allowing for faster acceleration from stops.
Locos which can use both diesel and electricity as energy sources are called electro-diesel locos, whereas, locos using a diesel motor to drive an electric generator are called diesel-electric. Some diesel-electric locos also have a battery to allow for a larger power draw during acceleration.
Obviously, if the loco is on a stretch of track where there is electric power, then it would make sense to use the electricity available to run the loco's electric engine. That is exactly what Siemens Vectron Dual-Mode locomotives does.
From Siemens website:
Vectron Dual Mode – keeps going where the wire ends
The Vectron Dual Mode is the up-to-date answer to changing route requirements. The dual power locomotives unite the advantages of full-featured diesel locomotives with those of electric locomotives. This combination empowers you to respond flexibly at all times to your traction requirements – so you'll always keep moving, with or without an overhead wire.
Whenever an overhead wire is available, it should be used. Electrical operation is much more cost-effective and environmentally friendly than diesel operation. But because Germany [and the UK, Australia, the USA .....] will continue to have many non-electrified sections of track for a long time to come, many diesel locomotives still run under an overhead wire – without actually using it. This makes very little economic or ecological sense. The Vectron Dual Mode excels in both operating modes, offering a real alternative to diesel-only operation.
Whether you want to react flexibly to unplanned diversions or boost environmental performance in conurbations: the Vectron Dual Mode offers you a wealth of advantages in your day-to-day operations.
With the Vectron Dual Mode, you'll handle a wide range of traction tasks much more economically than with a standard diesel locomotive. Every kilometre saves fuel, and thereby reduces energy costs. You'll also reduce the number of hours your diesel alternator set is operating. Altogether, you'll benefit from a reduction in energy and maintenance costs of up to 53%. [The savings obviously depend on what percentage of the total network is electrified. On the other hand, diesel locos have to keep running even when they are stationary. Given that hybrid cars use up to 40% less fuel than petrol cars because the engines don't run when the car is stationary, and also because they recharge their battery as they slow down or go down a hill, significant energy savings appear quite possible, provided the loco also has a battery.]
The issue of environmental pollution is becoming increasingly important in cities and metropolitan areas. With the Vectron Dual Mode, you'll make an important contribution to sustainable freight transport. By taking advantage of electricity wherever possible, you reduce carbon dioxide, nitrogen oxides and particulate matter emissions. This lets you reduce your annual local emissions by 950t of CO2, 6t of nitrogen oxides and 37kg of particulate matter compared with a standard diesel locomotive – and significantly improve your fleet's environmental performance. [Again, the percentage of electrified track will alter these numbers. For example, only 10% of Australia's railway track is electrified. However, a much larger percentage of track in urban areas and conurbations is electrified, and a larger percentage of total traffic takes place on these networks. For example, in Victoria, V-Line trains which serve regional and country destinations travel for part of their journey on electrified tracks. On my journeys from a provincial town 200 kms from the city into the big smoke, half the distance is electrified.]
There is another advantage. To extend existing electrified sections, installing overhead electric wires has to be done from the edge of the existing electrification to the next station or to a depot, which makes for substantial lump-sum outlays. In other words, it has to be done in expensive chunks. With a bi-mode loco, electrification can proceed at, say, 5 kilometres at a time, so that the electrified network can be gradually extended over time. The loco just keeps going under diesel power when it reaches the end of the wire. Also, the electrified sectors don't need to be contiguous, as the diesel engine could be used across the gaps.
A good idea.
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