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FREIGHT
New technology currently under development in Derby could cut emissions, increase efficiency and reduce cost for freight operations in the future
Powered axles are the way to go
T
he UK Government has made its decarbonisation strategy for the railway industry clear, although there are many who doubt that the intended timescale can be achieved. To reach net zero by 2050, all diesel-only trains will be banned from 2040, and all diesel-hybrids by 2050. As a result, the passenger train market has already started looking at solutions. The simplest one would be to electrify the whole network by 2040. That is unlikely to happen, so trials are taking place with hydrogen and battery-powered trains that can run on non-electrified lines. Hydrogen will be used to generate electricity using fuel cells and this will charge batteries that will power the train. Battery-powered trains will charge similar batteries, either from the conventional electrification on the main line parts of the route, or at charging points located at stations so the train charges up while it is at the platform.
The weight factor Neither of these solutions will work with freight. The Class 66 diesel locomotive, workhorse of the UK rail freight industry, has a power output of 2,400kW (3,200hp) and 1,850kW (2,480hp) at the rails. The more powerful Class 70 produces 2,750kW (3,670hp) and has hauled a train weighing 4,624 tonnes. In contrast, the hydrogen fuel cells that power Alstom’s iLint two-car
passenger train are rated at 314kW each and are supplied by hydrogen fuel tanks that each have a maximum capacity of 94kg. A two-car iLint, without passengers, weighs just 107 tonnes, although even that is nine tonnes more than the diesel version due to the extra weight of the batteries and hydrogen tanks. By simple mathematics, a hydrogen-powered freight train would need nine such fuel cells, complete with their associated batteries and control gear, and storage for 846kg of hydrogen. Hydrogen fuel tanks are heavy due to the pressures involved, though lighter versions that use composite materials are being developed. Currently, a tank to contain around 5kg of hydrogen at 350-700 bar pressure weighs around 100kg. The correlation is not linear, but tanks to store 840kg of hydrogen would certainly be very heavy! So are the batteries. An iLint carries around five tonnes of batteries, meaning that a freight locomotive using similar technology would need 45 tonnes of batteries. So, it’s not impossible – a locomotive with nine fuel cells, 45 tonnes of batteries and another 18 tonnes of hydrogen storage could certainly be built, particularly if it was configured as a two-car unit. This, though, would reduce the train’s overall capacity, as the length of a freight train in the UK is limited to an absolute maximum of 775 metres and on many routes can be as low as 520 metres.
October 2023
Different solution Some alternative thinking is needed, and that is precisely what engineers at Wabtec have been doing. Working at the company’s Derby offices, they are developing solutions that will certainly see the rail freight industry through until 2050 while markedly reducing emissions. Their plan is not to add heavy batteries to the locomotive, but to add them to each wagon in the consist (or pair of wagons in an intermodal train, where two flat-bed wagons are permanently coupled into two-wagon units). The technology employs the concept of regenerative braking, widely used on passenger trains. Under braking, the functionality of the traction motors is reversed, utilising the motors as generators. The resistance of the generator applies braking forces to the wheels while generating electricity that is then routed back to the train’s pantograph and returned to the network, to be used to power other trains or to go back to the grid and reduce the train’s net power consumption. Under Wabtec’s plans, one bogie on each wagon would be fitted with a small electric motor that can both drive the axle and also regenerate power that will be used to charge a battery. The electricity generated would therefore be free, replacing the energy normally lost in heating up brake pads and discs.