UK: The researchers from the School of Engineering, University of Birmingham, and Birmingham Centre for Railway Research and Education have analysed the technical and economic feasibility of using ammonia fuel cells in mainline freight locomotives and compared those to diesel and hydrogen fuel cells. A paper on the findings will be published in Transportation Research Part D: Transport and Environment this June. The researchers have concluded that ammonia is more sustainable and requires much less storage space and milder safety precautions during transport than diesel.
For the simulation, the researchers have selected a 318 km freight line from Felixstowe to Hams Hall and a freight train of 20 cars carrying a load of 1,235 t with a single run daily.
Three types of ammonia systems have been analysed:
- ammonia cracker-PEM drive-system (cracker-PEM),
- ammonia cracker-SOFC drive-system (cracker-SOFC),
- direct ammonia-fuelled SOFC drive-system (NH3-SOFC).
Two others are a system used in a Class 66 diesel locomotive with a Caterpillar EMD-710 engine and a system of a theoretical hydrogen locomotive (H2-PEM). No battery, hybrid, or fully- or semi-electric traction systems are included in the study. The researchers highlight that although electric locomotives are the best choice for minimising environmental impact, their use entails high capital cost, while battery locomotives are not suitable now for freight transportation as their range and capacity are relatively low and limited by battery parameters.
The researchers have studied such performance indicators as fuel consumption, required storage volume, and CO2 emissions of all five types of traction systems. Economic metrics to assess the potential for adoption in the UK include capital cost, fuel cost, operating and maintenance cost, replacement cost for end-of-life fuel cells and batteries, levelised cost of electricity, and discounted payback period.
The study has shown that diesel locomotives are the most cost-effective with the levelised cost of electricity (£0.144/kWh). They also feature the shortest payback period and the highest profit. The advantages are explained by low capital costs, high technology readiness level, and a lifespan of a traction system comparable to its life cycle while fuel cells require replacement after 10 years. The obvious disadvantage of diesel locomotives is high carbon emissions.
According to the researchers, today hydrogen is considered the main alternative fuel with many times lower carbon emissions. In part, PEM fuel cells are similar to diesel: levelised cost of electricity in the case of H2-PEM is £0.164/kWh, and of cracker-PEM is £0.157/kWh, and the payback period is 4–5 years. However, they need new approaches to storage, transportation, and safe operation. Even under 35 MPa, hydrogen requires 30 times bigger tanks than diesel, and blue hydrogen is 16 times more expensive than diesel.
The researchers state that by switching from hydrogen to ammonia, fuel tanks can decrease in size. Ammonia is stored under 0.8–20 MPa, and tanks for cracker-PEM and cracker-SOFC are 62% and 75% smaller than those used for hydrogen. Still, diesel can be stored in 4–5.5 times smaller tanks. So, accommodating an ammonia tank entails either a different layout in a locomotive or a separate platform. Alstom and Wabtec, for example, offer locomotives with tenders for hydrogen tanks.
Cracker-SOFC, as the researchers say, can overcome these limitations due to higher efficiency (+52%) and compactness. However, the challenge with SOFCs is their low commercial readiness level because both cracker-SOFC and NH3-SOFC are only available as laboratory prototypes. The cost-effectiveness analysis has shown that SOFCs can be regarded as a commercially viable traction system when their total cost reduces by 70%.
The researchers conclude that ammonia has the potential of using as a fuel in freight rail transport. It generates far fewer carbon emissions than diesel and requires much less storage space and milder safety precautions during transport than hydrogen. The combination of properties makes cracker-PEM the best powertrain option for freight locomotives. In the future, however, the situation can change as cracker-SOFC and NH3-SOFC are more promising if their prices lower and the technology readiness level grows. According to the researchers, new studies of ammonia fuel cells and the development of the technology are needed to offer cost-effective SOFCs capable of moving locomotives.
It is worth noting that several projects to explore the use of ammonia as a fuel and cleaning agent have recently been announced. For example, in 2022, Deutsche Bahn made public the development of a diesel engine powered by partially cracked ammonia in cooperation with FFI, Australia. The latter also works with Siemens and GeoPura in a UK project on ammonia cracking for the hydrogen power sector. The Russian business incubator of the Kuybyshev Railway of the Russian Railways and the Samara State Transport University has developed a denitrification technology for harmful emissions from diesel locomotives by upgrading engines and adding ammonia to fuel.