Dry ice pellet solution blasts slippery leaves off railway lines

In a new Network Rail-funded project, the researchers plan to install their leaf-busting technology underneath passenger services run by train operator Northern.

Developed by researchers from the University’s Department of Mechanical Engineering, the cleaning system fires dry ice pellets in a stream of air at supersonic speed at the railhead, which freezes any leaves on the line. The frozen leaves are then blasted away as the dry ice pellets turn back into a gas. 

Expected to be installed and ready for testing on the live rail network in 2023, it will enable passenger services to clean the track when needed, particularly in autumn and winter months when falling leaves form slippery layers and make it more difficult for trains to stop and start.

In 2021, Sheffield University worked with Northern to test the technology onboard an empty passenger train on the live rail network. The trials ran throughout autumn and winter 2021/2022 at speeds of up to 60mph and found that the dry ice system is more effective at removing leaves from the line, cleaning the track and reducing stopping distances, than methods currently used by the rail industry.

Following the successful trials, the Sheffield researchers are now modifying their system to fit underneath the carriage of passenger trains and giving a second lease of life to retired rolling stock as demonstrator units. The researchers have bought two retired Pacer trains, based at Wensleydale Railway, to test the new design and develop a plan for the system to be fitted throughout Northern’s fleet.

In a statement, Professor Roger Lewis, Professor of Mechanical Engineering at Sheffield University and lead researcher on the project, said: “The dry ice cleaning system we’ve developed…has the potential to revolutionise how we clean the UK’s railways. Our trials over the last year have shown how it is a much better system for removing leaves from the line with train drivers reporting that it restores rails to almost new-like condition. 

“By installing the dry ice system on passenger trains, it enables drivers to clean the track whenever they need it to help avoid dangerous sliding events. It also means we can clean more of the UK’s rail network - reaching the branch lines served by local stopping services that so many people rely on to get to work and travel throughout the autumn and winter months. Wherever passenger trains go, the cleaning system could go - it could be used to clean every railway line in the country, if adopted widely.”

The success of the technology’s development has led to the creation of Cryo Technologies Limited. Through an agreement with Sheffield University, Cryo Technologies is transitioning the research into a commercial opportunity. Already available through Cryo Technologies is the Cryogrip modular road-to-rail system which has been used successfully for an autumn season on the West Highland line in Scotland.

AI enhancement

Aside from the collaboration with Northern, the Sheffield University researchers have been awarded additional funding from Network Rail to test a new AI tool, which is set to turn their technology into a smart cleaning system.

The AI tool uses a camera and sensor fitted to the front and underneath the train to predict friction levels on the track. This could act as an early-warning system for drivers, alerting them to upcoming sections of the track with low-adhesion and increased risk of sliding events, so they know when the dry ice cleaning system needs to be used. 

The Sheffield researchers developed the AI tool as part of a collaboration with the Rail Safety and Standards Board (RSSB) and are set to test the technology in Scotland in partnership with Network Rail and ScotRail.

The Sheffield team is planning a demo of their cleaning system with Northern at Wensleydale Railway in March 2023.