Environmental assessment of road transport fueled by ammonia from a life cycle perspective

Renewable energy penetration into the electricity market has been increasing over the last decades; however, it is a different story in the transport sector. Fossil fuels are still predominant; therefore, several alternatives are being studied to attain a low-carbon, more sustainable transport and, consequently, a sustainable society. Ammonia has the potential to be a viable option, and it is critical to study its environmental profile in this early phase to appraise its sustainability as a fuel for passenger road transportation. This work aimed to develop a life cycle assessment of an ammonia-fueled internal combustion engine passenger car from the cradle to the grave, considering 1 km traveled as the basis for comparison. The product system under study included four stages: (i) vehicle, (ii) infrastructure, (iii) energy production, and (iv) operation. Life cycle inventory data related to vehicle operation, specifically ammonia combustion, resulted from various simulations of a model that considered the effect of different operation modes and vehicle emission control strategies, which resulted in nine configurations. The results show that rich mixtures (with an equivalence ratio of 1.1) help to reduce both nitrogen oxides (NOX) and nitrous oxide (N2O) emissions. As for unburnt ammonia (NH3), the after-treatment system drastically di-minishes these and NOX emissions. Data on infrastructure and other upstream processes was taken from the Ecoinvent 3.7.1 database, and the ammonia production was based on the life cycle inventory from previous research. The life cycle impact assessment was performed on OpenLCA software implementing the ReCiPe2016 Midpoint (H) v1.13 methodology. On average, per 1 km traveled in an ammonia-based ICEV represents 0.098 kg CO2-eq for global warming potential (GWP100), 30.755 g oil-eq for fossil depletion potential (FDP), 38.974 mg P-eq for freshwater eutrophication potential (FEP), 8.907 mu g CFC-11-eq for ozone depletion potential (ODP), 0.906 g NMVOC-eq for photochemical oxidant formation potential (POFP), and 1.029 g SO2-eq for terrestrial acidification potential (TAP). These results show a significant reduction, above-70%, for GWP100, FDP, and ODP compared with the same vehicle fueled on gasoline.

Automated summary

Renewable energy has increased in the electricity market, but not in transport. Alternatives to fossil fuels are being studied, and ammonia is a potential viable option for sustainable transport. This study conducted a life cycle assessment of an ammonia-fueled passenger car to evaluate its sustainability.