The 2020 version of the suite of GREET (Greenhouse Gases, Regulated Emissions, and Energy use in Transportation) models and associated documentation has been issued by U.S. Argonne National Laboratory. The modeling tools provide a common, transparent platform for lifecycle analysis (LCA) of the energy and environmental effects of different transportation fuels and vehicle technologies in major transportation sectors.

Vehicle technologies covered by GREET include conventional internal combustion engines, hybrid-electric systems, battery-electric vehicles and fuel-cell-electric vehicles. Fuel/energy options include petroleum fuels, natural gas-based fuels, biofuels, hydrogen and electricity. LCAs conducted with the GREET platform permit consideration of a host of different fuel production, and vehicle material and production pathways, as well as alternative vehicle utilization assumptions.

Changes to the expanded and updated model include:

• Carbon dioxide utilization and carbon capture and sequestration (CCS). A new “E-fuel” tab covers several e-fuel production pathways. Users can evaluate the impacts on energy use, water consumption and emissions of e-fuel production pathways using different hydrogen and electricity sources. A CCS Energy and environmental impacts of vehicle and fuel technologies are analyzed by considering the full life cycle from well to wheels for fuels and from raw material mining to vehicle disposal for automobiles. Source: U.S. Argonne National Laboratory option was added for capturing and sequestering fermentation CO₂ in corn ethanol plants.
• CO₂-derived ethanol. The life-cycle greenhouse gas (GHG) emissions of ethanol produced via gas fermentation and electrochemical reduction processes from the CO₂ emitted from corn ethanol plants have been evaluated.
• CO₂-derived Fischer-Tropsch (FT) fuels and methanol. GREET now includes two e-fuel pathways with Fischer-Tropsch (FT) synthesis process and two e-fuel pathways for methanol production using CO₂ (from corn ethanol plants) and renewable hydrogen.
• Supply chain sustainability analysis (SCSA) of six biofuel production pathways. The SCSA takes the LCA approach to identify energy consumption and environmental sustainability hotspots that could be mitigated through improved process materials and energy conversion efficiencies.
• Delivery of high-purity CO₂ for algae growth. Energy consumption for the compression and delivery of high-purity (>95%) CO₂ from natural gas steam methane reforming, ammonia manufacturing facilities, and corn ethanol plants is now included.
• PFAD to Renewable Diesel. A pathway of palm fatty acid distillate (PFAD) to renewable diesel is now added.
• New pathways for co-optimized fuels and engines. Developers added four pathways for fuels for use in engines co-optimized with drop-in biofuel blends to improve engine performance. Two of the pathways produce isobutanol and aromatic rich hydrocarbons as two bio-blendstocks. Blended with a petroleum gasoline blendstock, these bio-blendstocks are designed to improve engine efficiency for light-duty, boosted-spark ignition engines. The other two pathways produce bio-blendstocks capable of reducing engine-out emissions for mixing-controlled compression ignition engines in heavy-duty vehicles. These fuels are both diesel-like bio-blendstocks blended with conventional diesel.
• Renewable natural gas and lactic acid production from wet waste feedstocks. Researchers evaluated the life-cycle GHG emissions of renewable natural gas (RNG) and lactic acid (LA) production from four waste feedstocks (wastewater sludge, food waste, swine manure, and fats, oil, and grease) via anaerobic digestion (AD) and arrested AD, respectively, in collaboration with U.S. National Renewable Energy Laboratory. The results show that both waste-derived RNG and LA production pathways bring significant GHG emission reduction benefits.
• Green ammonia. The following low-carbon alternative ammonia production pathways have been implemented in GREET 2020 release. The stoichiometric nitrogen and hydrogen is compressed and enters the electricity-driven Haber-Bosch synthesis loop to produce ammonia, with high purity nitrogen obtained from air separation technologies, namely, cryogenic distillation and pressure swing adsorption; and high purity hydrogen produced from various technologies: 1) low-temperature electrolysis; 2) high-temperature electrolysis; 3) as a by-product from chlor-alkali processes; and 4) as a by-product in steam cracker plants. Users can choose between different nitrogen and hydrogen production technologies. In addition, users can specify the shares between conventional and low- carbon ammonia production pathways to determine the impacts of ammonia production on the downstream activities.
• Hydrogen and fuel cell vehicles: by-product hydrogen from steam cracker. To estimate the energy use and air emissions of by-product hydrogen from steam crackers, the steam cracking process has been updated using reported operational data from U.S. steam cracking facilities.
• Electricity generation efficiency and criteria air pollutant emission factors. New updates characterize emission factors, generation efficiencies and generation technology mixes of the U.S. electricity generation sector.
• Methanol as marine fuels. Six discrete methanol pathways for maritime applications are added to the GREET Marine Fuels Module and include methanol derived from natural gas, flare gas, biomass, renewable natural gas, coal and black liquor.