The Glossary lists and defines all of the terms used to tag documents on FATHOMS. Click on a term to view its full definition and a searchable table of all the documents with that tag.
- Ammonia: A nitrogen-based fuel (NH₃) produced from hydrogen and nitrogen.
- Battery Electric: Propulsion powered by onboard electrochemical energy storage systems, using electricity stored in batteries to drive electric motors with zero onboard emissions.
- Biodiesel (FAME): A liquid fuel composed of fatty acid methyl esters produced via transesterification of fats, oils, or greases and used in compression-ignition engines, typically in blends.
- Bio-Crude: A heavy, energy-dense liquid produced via hydrothermal liquefaction of wet biomass, resembling petroleum crude oil and requiring refining to produce usable fuels.
- Bio-Oil: A liquid product of biomass pyrolysis consisting of oxygenated organic compounds, typically requiring upgrading before use as a transportation fuel.
- Ethanol: A two-carbon alcohol (C₂H₅OH) produced primarily via fermentation of sugars or starches and used as a fuel or fuel blend component.
- Gasoline: A light distillate fuel commonly used in internal combustion engines found on recreational boats and some commercial harbor craft.
- Heavy Fuel Oil (HFO): A residual petroleum fuel derived from crude oil refining, commonly used in large marine engines due to its low cost and high energy density.
- Hydrogen: A gaseous energy carrier (H₂) used as a fuel in combustion engines or fuel cells, producible from fossil, biogenic, or electrolytic pathways.
- Marine Diesel Oil (MDO): A low-viscosity distillate marine fuel with minimal residual content, suitable for medium- and high-speed diesel engines.
- Marine Gas Oil (MGO): A blended marine fuel consisting primarily of distillate fuels with some residual components, widely used to meet emissions regulations.
- Methane (Natural Gas): A gaseous hydrocarbon fuel composed primarily of methane (CH₄), used in marine engines as liquefied natural gas (LNG) or compressed gas and sourced from fossil or biogenic pathways. Biogenic variants are sometimes referred to as biomethane, renewable natural gas, or bio-LNG.
- Methanol: A simple alcohol (CH₃OH) used as a liquid marine fuel or fuel intermediate, producible from fossil feedstocks, biomass, or carbon dioxide combined with hydrogen.
- Nuclear: Energy derived from nuclear fission used to generate propulsion power directly or via onboard electricity generation, primarily applied in naval and specialized vessels.
- Other Alcohols: Alcohol-based fuels or intermediates consisting of carbon chains with three or more carbon atoms (C₃–Cₙ), such as isobutanol, excluding alcohols with dedicated categories (e.g., methanol, ethanol). Includes both straight-chain and branched alcohols.
- Renewable Diesel (HVO / FT): A hydrocarbon diesel fuel produced from biomass or waste feedstocks via hydrotreating (HVO) or Fischer–Tropsch synthesis, chemically similar to petroleum diesel.
- Straight Vegetable Oil (SVO): Unmodified vegetable oil used directly as a fuel in adapted diesel engines, typically requiring fuel heating and engine modifications.
- Agriculture: Energy Crops: Non-food crops cultivated specifically for energy or fuel production, such as perennial grasses and short-rotation woody crops. Examples include miscanthus, switchgrass, energy sorghum, willow, and poplar. Food crops grown for biofuels are still classified as agricultural biomass.
- Agriculture: Food and Oil Crops: Primary agricultural crops grown for food, sugar, starch, or vegetable oil. Used when the feedstock is the harvested crop itself, such as corn, soybeans, sugarcane, or rapeseed, not the leftover residues.
- Agriculture: Residues: Non-food agricultural materials left over after harvesting or processing of crops, including stalks, straw, husks, and agricultural processing byproducts that are not primary food or oil commodities.
- Biogenic Gases: Gaseous fuels produced from biological decomposition or digestion of organic matter, including biogas, biomethane, landfill gas, and digester gas.
- CO2: A carbon-dioxide-dominant stream captured from industrial point sources or from ambient air via direct air capture and used as a carbon feedstock (e.g., methanol or e-fuel production).
- Forest Biomass: Biomass originating from forests and forest product industries, including wood, forest residues, and wood-processing byproducts such as roundwood, pulpwood, sawdust, wood chips, bark, forest thinnings, and black liquor. Short-rotation woody crops belong under energy crops.
- Fossil-derived Hydrocarbons: Carbon-based feedstocks originating from fossil resources, including crude oil, natural gas, coal, and refined fossil products. Industrial off-gases are categorized separately.
- Hydrogen: Molecular hydrogen used as a material input rather than a carbon source. Apply this category when a pathway explicitly relies on an external hydrogen supply, regardless of production method.
- Industrial Process Gases (Non-biogenic): Mixed industrial byproduct gas streams, typically containing carbon monoxide and/or hydrogen, often with carbon dioxide, nitrogen, or methane, used as syngas-like feeds or fuels. Examples include blast furnace gas, coke oven gas, refinery fuel gas, and fossil-derived gasifier syngas.
- Macroalgae: Large, multicellular seaweeds grown or harvested in marine or coastal environments, such as kelp and sea lettuce. Excludes microscopic algae.
- Microalgae: Microscopic, photosynthetic aquatic organisms cultivated in ponds, tanks, or photobioreactors, often discussed in the context of high-lipid or rapid-growth systems.
- Wastes and Byproducts: Discarded or secondary materials from municipal, industrial, or commercial activities that are not purpose-grown crops or forest materials. Includes mixed waste streams, organic wastes, sludge, and fats, oils, and greases. Excludes agricultural wastes and residues.
- Unspecified Feedstock: Used when a document discusses fuels or fuel production pathways but does not identify the feedstock used.
- Biochemical: Conversion processes driven primarily by microorganisms or biological catalysts under moderate temperatures and pressures. Used when the pathway relies on biological metabolism to break down organic material or produce fuel intermediates, such as fermentation or anaerobic digestion.
- Catalysis: Fuel production pathways in which small molecules such as carbon monoxide, carbon dioxide, hydrogen, or nitrogen are chemically combined over a catalyst to form larger fuel molecules. Used when the defining step is catalytic fuel formation from gases or simple intermediates, as in Haber–Bosch, Fischer–Tropsch, methanol synthesis, or SME synthesis.
- Chemical Upgrading: Catalytic or chemical processes that modify existing organic molecules into fuel-compatible products without fully breaking them down into syngas. Applies to upgrading of oils, fats, bio-oils, or intermediates via reactions such as hydrogenation, hydrotreating, or transesterification.
- Co-processing: Production routes where biomass-derived oils, gases, or intermediates are processed alongside fossil feedstocks in existing petroleum refineries or industrial plants. Used when the defining feature is integration into conventional infrastructure rather than a standalone conversion pathway.
- Electrochemical: Fuel production pathways where electricity is the primary energy input driving chemical conversion, typically through electrolysis or electrically powered synthesis steps. Apply when hydrogen production and subsequent fuel synthesis are fundamentally electricity-driven.
- Thermochemical: High-temperature conversion processes that use heat, pressure, and sometimes controlled oxygen or water to transform solid or wet carbonaceous materials into oils, gases, or syngas. Used when thermal decomposition or high-temperature chemical breakdown is the core step, such as pyrolysis, gasification, or hydrothermal liquefaction.
- Unspecified Pathway: Used when a document discusses fuel production but does not provide enough detail to determine the primary conversion pathway.