Marine Fuels Research

NREL's marine fuels research focuses on understanding fuel quality issues, such as stability and compatibility, particularly in net-zero-carbon fuels intended for marine applications.

Shipping containers on a cargo ship at sea.

Net-zero-carbon fuels are the most promising option for marine transportation decarbonization. The "omnivorous" nature of marine engines and the low quality of current fuel provides opportunities for more diverse solutions, including bio-distillate and methanol.

NREL measures critical properties of marine fuels. An important issue with marine fuels is precipitation of heavy hydrocarbons called asphaltenes. Bio-distillates may be insoluble in marine fuel or cause asphaltene precipitation. NREL measures precipitate formation as total sediment and also uses optical microscopy and other methods to assess fuel blend stability over extended times.

Ammonia-Based Marine Fuels

NREL has the expertise to understand and develop efficient, thermally integrated catalytic reforming reactors to generate requisite hydrogen (H2) fuel at a range of purity specifications onboard of maritime vessels or other ammonia-powered vehicles.

Beyond the grand challenges of its renewable synthesis, the prospect of ammonia (NH3) as a next-generation, "carbon-free" marine fuel and hydrogen carrier will require significant research and development to enable its adoption. Given strict nitrogen oxide emission regulations and concerns over unburned NH3 release, an attractive alternative to burning neat NH3 fuel is to convert it into H2 via onboard catalytic reforming (i.e., NH3 dissociation or decomposition), akin to hydrocarbon fuel reforming strategies. Internal combustion engines may be flexibly adapted for partial NH3 reformate fuel feeds that burn at higher performance, while proton-exchange membrane and alkaline fuel cell converters may be employed if ultra-high purity H2 can be generated from the NH3 carrier.

Low-Sulfur Marine Biofuels

NREL also researches biofuel options for marine applications. All biofuels have much lower sulfur than is required today for marine heavy fuel oil, and among these low-sulfur fuels, biodiesel has been used as a blend with marine fuel oil in several ship trials. Biomass pyrolysis products are also being considered for marine fuel blending. NREL is researching the stability of marine fuel-biofuel blends in terms of asphaltene precipitation, polymerization, and oxidation. Characterization of the storage projects using the fuel suite of test methods reveals potential issues or advantages of biofuels.