Life cycle assessment of ammonia as carbon-free fuel in internal combustion engine-driven orchard vehicle

The study regards comparative LCA of ammonia- and diesel-fueled mini tractor destined for orchard activities. The LCA, compliant with ISO 14040 standards, encompasses production, operation, and utilization stages, considering both the vehicle and fuel life cycle. The analysis was conducted using the LCA for Experts software and utilizes hectare-year of tractor operation as a functional unit. Ammonia is synthesized via the Haber-Bosch process using the following sources of hydrogen: steam methane reforming (SMR), SMR with carbon capture and storage, and electrolysis using energy from PV, wind, and nuclear sources. The ammonia-fueled engine employs dual-fuel combustion with rapeseed oil-based biodiesel, utilizing a port injection strategy for ammonia. The operation phase is based on primary data sourced from experimental measurements, with fuel and vehicle production based on literature and Sphera's Managed LCA Content database. Environmental impacts are assessed using ReCiPe method, accounting for climate change (CC), fossil depletion, freshwater consumption, human health (HH), and ecosystem quality (EQ) environmental categories. Results show that electrolysis-based ammonia from wind and nuclear power achieves the highest climate change reductions, around 42 % and 44 %, respectively; however, nuclear scenario causes the highest impacts on fossil depletion and freshwater consumption. Nevertheless, high NO_x and NH₃ emissions from the operation phase, even including the residual ammonia-based SCR after-treatment method, render a stronger impact in terms of HH and EQ categories for the ammonia-fueled vehicle compared to the diesel scenario. Further improvements should target stronger reductions of NO_x, N₂O and NH₃ emissions, e.g. through combustion or after-treatment improvements.