drivetrain The power source (an engine or motor) and the components of the vehicle used to transmit this power to the wheels (transmission, drive shaft, etc.). Also called powertrain.
drop-in fuel A non-petroleum fuel that is compatible with existing infrastructure for petroleum-based fuels with little to no modification required of current ICE vehicles.
engine heat recovery About one-third of fuel energy is rejected as heat in the exhaust. Some of this energy can be recovered through mechanical or electric turbines (turbocompounding) or thermoelectric conversion and used to improve the efficiency of the vehicle.
ethanol Best known as the type of alcohol found in alcoholic beverages, ethanol can be used both as a fuel additive (in mixtures with gasoline, as in the E10 standard) and as a liquid fuel itself.
exhaust gas recirculation (EGR) EGR recirculates cooled exhaust gas back through the engine to reduce throttling losses and allow operation over a wider range of load and speed.
gasoline direct injection (GDI) Gasoline is directly injected into the combustion chamber of the engine, providing better fuel vaporization and more stable combustion. GDI reduces fuel consumption across the range of engine operations.
greenhouse gas (GHG) An atmospheric gas that absorbs and emits radiation in the infrared range. Common GHGs are CO2, NOx, CH4, and ozone (O3).
hemicellulose A matrix of polysaccharides present in almost all plant cell walls with cellulose.
Highway Fuel Economy Test
A component of the federal test procedure that simulates free-flowing highway driving.
hybrid electric vehicle (HEV) A vehicle combining a fuel-driven engine, electric motor(s), and a battery or ultracapacitor. It is designed to reduce fuel consumption primarily by turning off the engine during idle, braking, and coasting as well as by capturing braking energy using regenerative brakes. Types of hybrid vehicles include micro-or stop/start hybrids, P2 hybrids, and power-split hybrids.
hydrocarbon fuels Fuels that are organic compounds containing primarily carbon and hydrogen and only minor amounts of other atoms such as sulfur, nitrogen, and oxygen. Most hydrocarbon fuels are derived from petroleum.
hypoxia Low dissolved oxygen concentrations, generally less than 2 milligrams per liter.
internal combustion engine
An engine in which the combustion of a fuel (most often gasoline or diesel) drives a piston, producing useful mechanical energy.
land cover Plants or physical cover over the surface of land.
land use Anthropogenic activities, such as agriculture, forestry, and urban development, that alter land-surface processes, including biogeochemistry, hydrology, and biodiversity.

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