The Clean Fuel That Warms the Sea

Ammonia is a leading candidate zero-carbon fuel for shipping, but its combustion in marine engines produces nitrous oxide (N2O) — a greenhouse gas with ~273× the warming potential of CO2 over 100 years. At partial engine loads (which dominate actual ship operations during maneuvering and slow steaming), N2O emissions are worst and poorly characterized. No after-treatment catalyst simultaneously addresses NOx, N2O, and unburned ammonia slip across the full operating range.

International shipping accounts for ~3% of global CO2 emissions. Ammonia is the most viable zero-carbon fuel for deep-sea vessels because of its energy density and existing global handling infrastructure. But if N2O slip is not controlled, ammonia-fueled ships could have a *worse* climate impact than the fossil fuels they replace — each milligram of N2O per gram of ammonia consumed reduces the climate benefit by ~25%.

Engine manufacturers (MAN, WinGD) are developing two-stroke ammonia engines, with WinGD reporting <3 ppm N2O at full load. Selective catalytic reduction (SCR) can reduce NOx by 95% in diesel engines. Dual-fuel engine designs co-fire ammonia with pilot fuels. However, the <3 ppm results are at full load only; partial-load N2O data is sparse and significantly worse. SCR catalysts designed for NOx do not reliably decompose N2O. Engine-out emissions vary dramatically with ammonia/pilot fuel ratio, injection timing, and charge temperature, making single-catalyst solutions inadequate. No standardized emissions testing protocol exists for ammonia engines across real operating profiles.

After-treatment catalysts effective against N2O across partial to full load conditions. Combustion chamber geometries that minimize N2O formation at low loads. Standardized emissions testing protocols for ammonia marine engines across real operating profiles including maneuvering and slow steaming.

A team could characterize N2O formation mechanisms in ammonia combustion at varying equivalence ratios and temperatures using a bench-scale combustor, mapping the conditions that maximize N2O production. A catalysis-focused team could screen candidate materials for simultaneous N2O decomposition and unburned ammonia oxidation. Combustion science, catalysis, and marine engineering skills apply.