Switching diesel locomotives to electric

Locomotives that run on diesel can be electrified. This would both cut CO₂ emissions and significantly reduce overall energy consumption, according to a new study.

Researchers at SINTEF have now studied the effect of electrifying a shunter locomotive at Norway's Fagernes terminal in Narvik municipality. This is the main terminal on the Ofoten-Lofoten-Vesterålen train line for incoming consumables and outgoing fish products.

The trains running on the Ofotbanen line use electric locomotives. However, there are no overhead electrical lines in the terminal area, as they would get in the way of the equipment that lifts goods and containers onto and off the train wagons.

That is why the diesel-powered shunting locomotive is used at the terminal. These locomotives move the train wagons from one track to another.

Running the locomotives on batteries would—in addition to the environmental benefits—eliminate the need to change locomotives at the terminal and avoid the problems that overhead lines cause.

Theoretical electrification

In the report, the researchers carried out a theoretical electrification of a diesel-hydraulic shunting locomotive.

"The changeover to electric involves removing the diesel engine, fuel tank and hydraulic switch. This will be replaced with a battery, or possibly a fuel cell and battery, as well as one or two electric motors with associated control equipment," says Roar Andreassen, a senior research scientist at SINTEF.

The study was conducted in two parts. First, the researchers made a theoretical calculation in which a 300-ton train (including locomotive) accelerates before braking over a distance of a few hundred meters. This simulates a typical switching operation where wagons are moved from one track to another.

The calculations show that the train would use 1.6 kWh of energy to the point of initial deceleration. In an electric drive locomotive, part of the kinetic energy can be harvested by regeneration. With 80% energy regeneration, the train would only use 0.4 kWh until it comes to a stop.

"An electrified locomotive with regeneration would therefore only use 25% as much energy as a diesel locomotive for this kind of operation," says Andreassen.

GPS logger followed the locomotive

The second study was carried out by having a GPS logger follow the locomotive through an entire work shift, which takes place at night. Wagons are emptied and reloaded. New trains are also set up for departure the following morning.

The GPS data was analyzed from the locomotive movements to document speeds and distances. For each individual movement, the weight of the train was calculated based on the acceleration achieved.

The diesel locomotive must have its engine running throughout the shift for braking and control system reasons. In the experiment, it was in operation for about six hours. The work of moving, alone or with wagons, lasted about an hour. The total energy consumption was calculated to be about 28 kWh.

Of this amount, 11 kWh could have been harvested if the locomotive had been electrified with energy regeneration. The total diesel consumption was 21 liters of diesel fuel with a CO₂ emission of 56.3 kilograms.

"Electrification would both eliminate this CO₂ emission and provide significantly lower energy consumption," says the SINTEF researcher.

On cold days, however, the waste heat from the diesel engine that heats the driver's cab must be obtained from a heat pump, like in electric cars. The energy consumption would still be low compared to diesel operation.

Existing locomotives can be reused

If everyone in the world used as many resources as Europe does, we would need 2.8 planet Earths to meet consumer demand, according to the UN. Facilitating the reuse of materials will both save nature and reduce waste and emissions in the production and transport of materials.

Shunter locomotives are robust machines that have already had engine replacements and new control systems rebuilt several times.

"The study findings give reason to assume that they can also be electrified, and thus made more climate-friendly—not least because we can reuse the existing locomotives," says Andreassen.

Provided by Norwegian University of Science and Technology