Glossary

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

Adsorption:: The adhesion of the molecules of gases, dissolved substances, or liquids in more or less concentrated form to the surface of solids or liquids with which they are in contact. Commercial adsorbent materials have enormous internal surfaces.
AEMD (Automotive Electric Drive Motor):: A U.S. Department of Energy program to develop low-cost traction drive motors for automotive applications.
Aerosol:: A cloud consisting of particles dispersed in a gas or gases.
AIPM (Automotive Integrated Power Module): A U.S. Department of Energy program to integrate the power devices, control electronics, and thermal management of a vehicle into a single low-cost package that will meet all requirements for automotive motor control applications.
Aliphatic compounds: A class of organic compounds that consists of open chains of carbon atoms, the molecules of which do not have carbon atoms in a ring structure.
Alloy: Mixture containing mostly metals. For example, brass is an alloy of copper and zinc. Steel contains iron and other metals, but also carbon.
Ambient temperature: The temperature of the medium surrounding an object.
Anion: Negative ion. Alkali, molten carbonate, and solid oxide fuel cells are "anion-mobile" cells — anions migrate through the electrolyte toward the anode.
Anode: One of two electrodes in a fuel cell or battery. The anode, the negative post of the fuel cell, conducts the electrons that are freed from the hydrogen molecules so that they can be used in an external circuit. It has channels etched into it that disperse the hydrogen gas equally over the surface of the catalyst.
Autoclave: A closed vessel that can withstand high temperatures and pressures.
Auxiliary climate control devices: Specialized add-on heating units, or combination heating/cooling units, that operate with the truck engine turned off. They eliminate the need to leave engines idling solely to heat or cool the cab and sleeper compartment.

B

Base drag: Component of aerodynamic drag caused by a low-pressure region behind the vehicle.
Base pressure: Pressure exerted on the base, or extreme rear portion, of a body in a fluid flow.
Battery: Batteries are the principal energy storage devices for hybrid electric vehicles (HEVs). Desirable attributes of high-power batteries for HEV applications are high-peak and pulse-specific power, high specific energy at pulse power, a high charge acceptance to maximize regenerative braking utilization, and long calendar and cycle life. Developing methods/designs to balance the packs electrically and thermally, developing accurate techniques to determine a battery's state of charge, and developing abuse-tolerant batteries, and recyclability are additional technical challenges.
Bench-scale testing: Testing at conditions and in quantities encountered in a laboratory, rather than under real-world conditions.
Biaxial: Structures that are normally loaded (or stressed) in more than one direction at once are said to be biaxially loaded. Due to the uncertainty and limitations in understanding how these materials, while under multiple stresses, behave during impact, their adoption by industry has been slowed. Limiting material testing to uniaxial tests can misrepresent the behavior of a material in an engineering structure. Using more realistic, biaxial loadings during these tests leads to more accurate modeling of the expected behavior of the structure as would occur in specific applications, which could lead to greater use of composites.
Biodiesel: Biodiesel is a renewable diesel fuel substitute that can be made by chemically combining a natural oil or fat with an alcohol. Many vegetable oils, animal fats, and recycled cooking greases can be transformed into biodiesel fuel.
Bluff body: Nonstreamlined shape, especially one with a blunt tail that generates a recirculation zone at the rear.
Boattail: Transition section at the tail of a vehicle that narrows the body diameter, used to reduce base drag by directing air into the low-pressure zone.
Boundary conditions: The physical conditions that constrain the flow at its boundaries.
Brake horsepower: Power developed by an engine as measured at the flywheel or crankshaft.
Brake-specific fuel consumption: The ratio of engine fuel consumption to power output. It is a measure of engine efficiency.

C

CAFE Standard: Enacted by Congress in 1975, the Corporate Average Fuel Economy (CAFE) program mandates that all manufacturers marketing vehicles in the United States meet average fuel economy requirements for each class of vehicles they sell. Each manufacturer's fleet must average 27.5 mpg for cars and 20.7 mpg for light trucks. Manufacturers are subject to a fine of $55 per truck when the average fuel economy of their fleet falls short of the CAFE light-truck standard by one mile per gallon.
Catalyst: A substance that accelerates a chemical change without actually entering into the chemical reaction. A catalyst usually consists of platinum powder very thinly coated onto carbon paper or cloth. The catalyst is rough and porous so that the maximum surface area of the platinum can be exposed to the hydrogen or oxygen. The platinum-coated side of the catalyst faces the membrane in a fuel cell.
Catalytic oxidation: Process of oxidizing unburned hydrocarbons and carbon monoxide by means of a catalytic reaction to reduce pollution.
Cathode: One of two electrodes in a fuel cell or battery. The cathode, the positive post of the fuel cell, has channels etched into it that distribute the oxygen to the surface of the catalyst. It also conducts the electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water.
Cation: Positive ion. Phosphoric acid and proton exchange membrane (PEM) fuel cells are "cation-mobile" cells — the cation migrates through the electrolyte toward the cathode.
Cetane number (CN): The diesel fuel equivalent to a gasoline octane rating, this number expresses the fuel's ignition quality and its suitability for spontaneous self-ignition in an engine. The fuel must ignite spontaneously and quickly after being injected into the hot, compressed air inside the combustion chamber. A higher cetane number means a shorter ignition delay and a smaller amount of fuel in the combustion chamber when the fuel ignites.
Central Business District (CBD) Driving Cycle: The CBD cycle is a speed-versus-time cycle used to test for bus emissions. This pattern was developed as a general representation of transit vehicle operation in a downtown business district and consists of 14 identical segments. Each segment includes 10 seconds of acceleration, 18.5 seconds of cruising at 20 mph, 4.5 seconds of deceleration, and 7 seconds of idling. Total driving distance is two miles.
Class 8 trucks: Trucks or tractor-trailers with a manufacturer's listed gross vehicle weight (GVW) of 33,000 pounds or more.
Cold start: Difficulty of starting an internal combustion engine in cold weather because of gasoline, which evaporates more slowly when it is cold; oil, which gets thicker in cold weather; and the chemical reactions inside the battery, which progress more slowly in cold weather.
Common rail direct injection (CDI): A fuel-injection system that uses a single "rail" (fuel line) that maintains constant fuel pressure regardless of injection sequence (also called common rail injection). The engine's electronic timing regulates fuel-injection timing and quantity according to data from sensors on the camshafts and crankshafts so that compression and injection occur independently. Fuel is injected only as needed, which reduces fuel consumption and emissions.
Composite: Material brought about by combining materials differing in composition or form on a macroscale to obtain specific characteristics and properties. The constituents retain their identity; they can be physically identified, and they exhibit an interface between one another.
Compression ignition: The type of ignition that typically initiates combustion in a diesel engine. Rapidly compressing the air within the cylinders generates enough heat to ignite the fuel as it is injected. This is why diesel engines do not need spark plugs for ignition.
Compression-ignition direct-injection (CIDI) engine: Commonly called the diesel engine, has the highest thermal efficiency of any internal combustion engine. Challenges to improvements include a lower specific power than the gasoline engine; significant particulate matter and nitrogen oxides in the exhaust; and the noise, vibration, and smell of the engine.
Computer modeling: Use of a computer to develop a mathematical model of a complex system or process and to provide conditions for testing it.
Conductivity: Transmission of electricity by metallic substances. Metals have high electrical conductivity, and with few exceptions, their conductivity decreases with increasing temperature.
Cooperative fuel research engine: A standardized single-cylinder, overhead valve, variable-compression ratio engine used throughout the world for basic research into exhaust emissions and the suitability of alternate fuels.
Corrosion: Deteriorative loss of a metal as a result of environmental reactions.
Cost competitive: A new technology, when manufactured in automotive production volumes, should be perceived by the consumer as economically attractive when compared with conventional automotive technologies.

D

Diesel engine: Any internal-combustion engine in which air is compressed to a sufficiently high temperature to ignite fuel injected into a cylinder. A diesel engine differs from other internal-combustion engines, such as gasoline engines, in that it employs no ignition devices, such as an electric spark. For this reason, it is often called a compression-ignition engine.
Diesel equivalent gallon (DEG): The volume of natural gas it takes to equal the energy content of one gallon of diesel fuel. Since natural gas is not a liquid, its volume is measured in cubic feet, rather than gallons. Therefore, the DEG is a way of comparing equivalent volumes of fuel based on their energy content in British Thermal Units (Btu).
Diesel fuel: Petroleum products normally used as fuel for diesel engines are components of crude oil having heavy hydrocarbons containing at least 12 to 16 carbon atoms per molecule. These heavier fractions are taken from crude oil after the more volatile portions used in gasoline are removed.
Dimethyl ether (DME): A synthetic diesel fuel derived from natural gas, an excellent candidate for direct-injection engines. DME contains no sulfur and burns more cleanly than conventional diesel fuel, so it produces fewer particulates. It behaves much like propane, and its cetane number is 55–60, up to 20% better than modern diesel fuel. However, the viscosity of DME is 10 times less than that of diesel fuel, which makes it difficult to find pumps and valves that will not overheat or leak. Also, the entire fuel system must be kept under a pressure of at least 5 bars at room temperature to keep the DME liquid until it is injected.
Direct injection (DI): In DI, fuel is injected directly into the cylinder, as is typical in a diesel engine (also called direct fuel injection). Most other internal combustion engines use either carburetion (in which the air and fuel are mixed long before the air enters the cylinder) or port fuel injection (in which the fuel is injected just in front of the cylinder intake valve).
Downforce: Negative aerodynamic lift.
Drag: Horizontal aerodynamic retarding force on a vehicle parallel to the relative wind direction.
Drag coefficient: Factor representing the drag acting on a body (as an automobile or airfoil).
Drag coefficient: Drag divided by the product of dynamic pressure and projected area.
Dynamometer: A device used to simulate road conditions and loads in stationary settings and to gather data about vehicle performance under those conditions.

E

E85: A mixture of 85% denatured ethanol and 15% gasoline, by volume; an alternative engine fuel.
Electrochemistry: Science that deals with the relation of electricity to chemical changes and with the interconversion of chemical and electrical energy.
Electrode: Electrical terminal that conducts an electric current into or out of a fuel cell.
Electrolyte: Chemical compound that conducts electricity from one electrode to the other inside a fuel cell.
Emissions standards: Regulatory standards that govern the amount of a given substance that can be discharged into the air.
Endothermic: Chemical reaction that absorbs heat.
Energy loss: Typical internal combustion engine vehicles convert fuel energy to shaft work, which is used to overcome the tractive energy needed to drive forward. The same energy is used to operate a vehicle's accessories. A vehicle with only an internal combustion engine uses only about 16% of its energy to accelerate the vehicle. Thto decrease fuel consumption during partial load conditions and to improve acceleration.
Equivalence ratio: Actual air/fuel ratio divided by the stoichiometric air/fuel ratio. An air/fuel mixture is said to be stoichiometric when fuel combustion consumes all of the initial reacting species in going to completion.
Ethanol: A liquid alcohol made by fermenting sugars derived from starches in plants, such as corn or sugar cane (CH₃CH₂OH, ethyl or grain alcohol). When denatured (made unfit for human consumption), it can be used as an engine fuel.
Exhaust aftertreatment: A method of controlling emissions from internal combustion engines — primarily NO_x — by applying air pollution control technologies to engine exhaust (as opposed to treatments applied to the engine's intake air or during in-cylinder combustion stages).
Exhaust gas recirculation (EGR): An emissions control technique that reuses engine exhaust gases as part of the intake air supply to help reduce harmful emissions (especially NO_x).
Expander: Transducer that, for a given input amplitude range, produces a larger output range.

F

Feedstock: Raw material supplied for production of electricity, gases, or chemicals.
Finite-element method: Computational method that relies upon dividing regions into subregions, subject to boundary conditions, and generating a set of linear equations to be solved.
Fischer-Tropsch (FT) fuel: Diesel fuel made from natural gas using a method known as the Fischer-Tropsch process. FT fuels are liquid at ambient conditions, have a high cetane number, and effectively no sulfur content. They can be used in existing diesel engines.
Flow field: Velocity and the density of a fluid as functions of position and time. Also known as flow distribution.
Flywheel: A mechanical battery that stores kinetic energy. A flywheel is essentially a spinning wheel with a motor. Flywheels can be more responsive than chemical batteries, and they are less susceptible to the effects of weather.
Friction coefficient: A measure of how much force is needed to overcome friction just enough that one material will slide across another.
Fuel cell: An electromechanical "engine" (no moving parts) that converts the chemical energy of hydrogen and oxygen into electricity without combustion; the only by-product is water. The principal components of a fuel cell are catalytically activated electrodes for the fuel (anode) and the oxidant (cathode) and an electrolyte to conduct ions between the two electrodes.
Fuel flexible: Ability of a vehicle to operate on either (a) a wide range of fuels blends (e.g., blends of gasoline and alcohol) or (b) two different fuels carried aboard the vehicle (e.g., gasoline and compressed natural gas).
Fuel processor: Device used to remove the hydrogen from common fuels (like natural gas, propane, and gasoline) and less-common ones (like methanol and ethanol) and convert it to hydrogen for use in fuel-cell-powered vehicles.
Fuel reformer: An alternative to storing hydrogen fuel in fuel-cell-powered vehicles. No infrastructure currently exists for delivering hydrogen fuel to consumers, and hydrogen-storage technologies are so large they would limit the driving range of any car. Researchers have created onboard fuel-reforming devices that release the hydrogen bound up in readily available hydrocarbon fuels.

G

Gas chromatography: Method for separating mixtures based on differences in the speed at which they migrate over or through a stationary phase (a substance that shows different affinities for different compounds).
Gas diffusion: Mixing of two gases caused by random molecular motions. Gases diffuse very quickly; liquids diffuse much more slowly, and solids diffuse at very slow (but often measurable) rates. Molecular collisions make diffusion slower in liquids and solids.
Gas turbine: A rotary engine that draws energy from a fuel-air mixture. A compressor raises the pressure and temperature of the inlet air. The air is then moved into a burner, where fuel is injected and combusted to raise the temperature of the air. Power is produced when the heated, high-pressure mixture is expanded and cooled through the turbine.
Gasoline equivalent gallon (GEG): The volume of natural gas it takes to equal the energy content of one gallon of gasoline. Since natural gas is not a liquid, its volume is measured in cubic feet, rather than gallons. Therefore, the GEG is a way of comparing equivalent volumes of fuel based on their energy content in British Thermal Units (Btu).
Glow plug: An electrically heated wire that helps ignite diesel fuel when a compression ignition engine is cold and the compression process may not raise the air to a high enough temperature for ignition.
Graphite: Mineral consisting of a form of carbon; it is soft, black, and lustrous and has a greasy feeling; used in pencils, crucibles, lubricants, paints, and polishes.
Greenhouse gases: Gases, such as carbon dioxide, NO_x, methane, and water vapor, that help capture heat from the sun in the lower atmosphere of the earth. As the amount of greenhouse gases in the atmosphere increases, more heat is captured, which can lead to global warming (the greenhouse effect).

H

Hardware-in-the-loop

Testing and evaluation method that replicates a complete vehicle by employing a combination of (a) actual test hardware and (b) computer models.

Heat exchanger

Device (e.g., a radiator) that is designed to transfer heat from the hot coolant that flows through it to the air blown through it by the fan.

Heavy-duty federal test procedure

A transient engine dynamometer cycle for heavy-duty truck and bus engines. Includes segments designed to simulate both urban and highway driving. Used for emission certification testing of heavy-duty diesel engines in the United States.

Hybrid power unit

The engine (i.e., heat engine or fuel cell) in a hybrid propulsion subsystem.

Hybrid propulsion subsystem

A propulsion subsystem that joins two types of propulsion mechanisms so that the advantages of each can be exploited. Such a system generally consists of two energy storage elements (such as a liquid fuel and an electric battery) and two energy conversion elements (such as an engine and an electric motor).

Parallel configuration: In a parallel hybrid, the electric motor and the engine can apply torque to the wheels either simultaneously or individually.
Series configuration: In a series hybrid, only the electric motor can apply torque to the wheels. Propulsion power flows through a single path from engine to the generator, to the battery, to the traction motor, and to the drive wheels.

Hydrocarbons

Chemical compounds that contain only the elements carbon and hydrogen.

Hydrogen-rich fuel

Gas containing more than 40% hydrogen that is produced from reforming a hydrocarbon fuel.

Hydrogen sulfide (H₂S)

Flammable, toxic, colorless gas with offensive odor, boiling at -60°C; soluble in water and alcohol; used as an analytical reagent.

I

Indicated mean effective pressure: An average pressure value that theoretically must be present in a cylinder of an engine during the power stroke to generate the maximum horsepower possible, given the pressures recorded within the cylinder during a dynamometer test.
Indicated thermal efficiency: The work done by fuel combustion inside a cylinder over a given time interval divided by the total heat content of the fuel supplied to the cylinder during that time.
Internal combustion engine (ICE): Engine that converts the energy contained in the fuel inside the engine into motion. Combustion engines use the pressure created by the expansion of the gases to do mechanical work.
Ion: Atom that carries a positive or negative charge because of the loss or gain of an electron.
Ion chromatography: A form of liquid chromatography that uses ion-exchange resins to separate atomic or molecular ions based on their interaction with the resin.

K

KIVA: A transient, three-dimensional, multiphase, multicomponent computer modeling code for internal combustion engine calculations. The modular nature of KIVA allows for easy modifications in solving a variety of hydrodynamics problems involving chemical reactions. KIVA has found widespread application in the automotive industry.

L

Laser: A device that emits very pure and very intense light of a single wavelength. When operated in a suitable power, lasers can generate intense heat within materials.
Lean combustion limit: The point at which combustion may not occur because the fuel-air mixture contains too little fuel, resulting in misfires and increased hydrocarbon emissions. Engine operation with a "lean" fuel-air mixture (using as little fuel as possible) reduces NO_x and hydrocarbon emissions and improves fuel efficiency.
Lift: Vertical aerodynamic force on a vehicle perpendicular to the relative wind direction.

M

M85: A mixture of 85% methanol and 15% unleaded gasoline, by volume.
Mass balance: Structural counterpoise that brings about a desired balance under static or dynamic conditions.
Medium: Means of conveying something; a surrounding or enveloping substance.
Membrane: Material that allows some, but not all, of the components in a mixture to pass through it.
Methanol: An odorless, clear liquid alcohol made from natural gas, coal, or biomass, such as wood fiber (CH₃OH, methyl or wood alcohol), that can be used to as a fuel for engines.
Miles per gallon equivalent (mpge): Energy (Btu) content equivalent to that of a gallon of gasoline (114,32 Btu).
Model: Computer package used to help visualize something or predict behavior that either (1) cannot be directly observed or (2) would be time-consuming and expensive to test.
Moire interferometry: An optical method of measuring surface strains in which a microscopic-sized grating (grid pattern) is deposited on the surface of the material by using photolithography. Laser beams are then used to illuminate the surface and detect changes in the grating pattern that indicate the location and degree of surface strains.
Motor: In an HEV, an electric traction motor converts electrical energy from the energy storage unit to mechanical energy that drives the wheels of the vehicle. Unlike a traditional vehicle, where the engine must "ramp up" before full torque can be provided, an electric motor provides full torque at low speeds. This characteristic gives the vehicle excellent "off the line" acceleration.

N

Nafion®: Sulfuric acid in a solid polymer form that is usually the electrolyte of proton exchange membrane (PEM) fuel cells.
Nanocomposite: Mixture of cellulose and cellulose ester (plastic) in which each component has a dimension of several nanometers.
Nanometer: One nanometer (1 nm) is equal to one-billionth of a meter (10^–9 m).
NH₃: Ammonia.
Nitride: Compound of nitrogen and a metal, such as Mg₃N₂.
Nitrogen oxides (NO_x): A by-product of the combustion process when using petroleum-based fuels; one of the primary causes of acid rain and a contributor to global warming.
Noble metal: Metal, or alloy, such as gold, silver, or platinum, that has high resistance to corrosion and oxidation; used in the construction of thin-film circuits, metal-film resistors, and other metal-film devices.
Nonattainment area: A geographic area in the United States designated by the U.S. Environmental Protection Agency as having air quality that fails to meet the National Ambient Air Quality Standards under the Clean Air Act.

O

OICA test cycle: The test cycle of the Organisation Internationale des Constructeurs d'Automobiles (OICA) is used in Europe for emissions certification of heavy-duty diesel engines. Engines are monitored with a dynamometer over a sequence of 13 steady-state modes. Emissions are measured during each mode and averaged over the cycle by using a set of weighting factors.
Oxygen reduction reaction: Oxidation involves a loss of electrons by one molecule, and reduction involves an absorption of electrons by another. Both oxidation and reduction occur simultaneously and in equivalent amounts during any reaction involving either process.
Oxidation: Loss of one or more electrons by an atom, molecule, or ion. Oxidation is accompanied by an increase in oxidation number on the atoms, molecules, or ions that lose electrons.
Ozone (O₃): A three-atom form of oxygen; ozone, a criteria air pollutant, is a primary constituent of smog.

P

Parallel configuration: A hybrid electric vehicle (HEV) with a parallel configuration has a direct mechanical connection between the power unit and the wheels, as in a conventional vehicle, but also has an electric motor that drives the wheels. For example, a parallel vehicle could use the power created from an internal combustion engine for highway driving and the power from the electric motor for accelerating.
Particulate: Composed of distinct particles. Smoke is particulate; pure gases are not.
Permeability: Ability of a membrane or other material to permit a substance to pass through it.
Photolithography: An optical means for transferring patterns onto a substrate.
Plasma: Sometimes referred to as the fourth state of matter, plasma is a gas consisting of free electrons and ionized molecules in roughly equal proportions. Much of the use of plasmas in NO_x reduction involves non-thermal plasmas, for which ion and gas molecule mean energies are much lower than the mean energy of electrons.
Plasma-assisted catalysis: A diesel exhaust treatment system that uses a small amount of electricity from the engine to generate a nonthermal plasma (NTP) on a ceramic surface. The resulting reaction can reduce NO_x and particulates by up to 90% without onboard chemicals or heating.
Plasmatron: A compact thermal plasma reformer that generates hydrogen-rich gas mixtures from hydrocarbon fuel; an onboard fuel-reforming device for spark ignition engines.
Pneumatic aerodynamics: Use of low-pressure compressed air to favorably influence aerodynamic forces and moments.
Poisoning: Retardation of the rate of one catalyzed reaction by a catalyst poison.
Polymer: A natural or synthetic compound composed of repeated links of simple molecules.
Preferential oxidation (PrOx): Preferential attack by oxygen on one of the components in a material.
Preform: Compact mass of premixed plastic material that has been prepared for convenient handling and control of uniformity during the mold loading process.
Pressure ratio: Ratio of the critical pressure of a nozzle to the admission pressure of the nozzle (equals 0.53 for gases).
Production prototype: Soft-tooled vehicle of a particular size, shape, material composition, and powertrain, capable of being competitively mass produced within a 3- to 5-year time horizon, by using commercially validated manufacturing technologies.
Propulsion subsystem: Energy storage, energy conversion, and energy transmission devices required to convert fuel energy to torque at the wheels.
Proton exchange membrane (PEM): Specially treated material that looks something like ordinary kitchen plastic wrap but conducts only positively charged ions. It blocks electrons.
Proton-induced x-ray emission (PIXE) analysis: A technique for nondestructive analysis of mineral inclusions and other small samples.
Prototype: Functionally representative rendition of a device or system that is fabricated late in the development cycle, before production; an original model on which later improved models are based; an original piece of hardware that serves as the basis for evaluation, demonstration, and further development.

R

Reactant: Substance that reacts with another one to produce a new set of substances (products).
Reactive organic gas (ROG): Organic compounds (e.g., hydrocarbons) that produce ozone in the presence of NO_x.
Reactor: Device or process vessel in which chemical reactions (e.g., catalysis in fuel cells) take place.
Reformate: Hydrocarbon fuel that has been processed into hydrogen and other products for use in fuel cells.
Reformer: Device that extracts pure hydrogen from hydrocarbon fuels.
Reformulated gasoline: Gasoline that is blended so that, on average, it significantly reduces volatile organic compounds and air toxics emissions relative to conventional gasolines.
Regeneration: Process of flushing or cleaning a filtration medium.
Regenerative braking: Process of recovering some of a hybrid or electric vehicle's kinetic energy by allowing the wheels to drive a traction motor as a generator, thereby producing electric power that is stored for later use. When the driver brakes, the motor becomes a generator, using the kinetic energy of the vehicle to generate electricity that can be stored in the battery for later use. Traditional friction brakes are also necessary, as well as a strategy for smoothly blending the two braking mechanisms. Regenerative and friction brakes need to be controlled electronically so that stopping ability is maximized to make the dual brake operation transparent to the driver.
Resistance welding: The fusion of metals by controlled heat (electricity) and, in some cases, pressure or force. A high-density current is applied for a given length of time to produce the heat required to join two metal components into a single assembly. Typically, the electrode at the tip of the welder conducts the electricity and furnishes the pressure or force to center the current flow at the desired welding point. A weld's characteristics depend on the size, shape, and other key properties of the electrode. The contour of the electrode changes as the usage increases and if not continually dressed (reshaped) to the original or desired size, the weld itself changes physically and can weaken.
Reynolds number: A dimensionless number that is the ratio of the inertia force to the friction force on a fluid (gas or liquid). A very high Reynolds number (Re) may indicate a turbulent flow, while a lower value of Re is more likely to indicate a laminar flow.

Rolling resistance: Retarding force, parallel to the direction of travel, caused by tire resistance along the ground.

S

Scaling relations: Mathematical relations applied to events associated with a system at one scale to predict equivalent behavior at a different (usually larger) scale.
Scuffing: A form of localized surface damage caused by inadequate lubrication between rubbing surfaces.
Selectivity: Ability of a type of method, material, or instrumentation to respond to a specified substance or constituent and not to others.
Series configuration: Some hybrid electric vehicles (HEVs) use a series configuration, in which the heat engine or fuel cell together with a generator produce electricity for the battery pack and electric motor. Series HEVs have no mechanical connection between the hybrid power unit and the wheels; this means that all motive power is transferred from chemical energy to mechanical energy, to electrical energy, and back to mechanical energy to drive the wheels.
Smog: Aerosol mixture of ground-level ozone and other air pollutants produced through chemical reactions.
Spark-ignition (SI) engine: An internal combustion engine in which the fuel mixture is ignited electrically. A spark-ignition engine runs on an Otto cycle — most gasoline engines run on a modified Otto cycle. This cycle uses a homogeneous air-fuel mixture that is combined before it enters the combustion chamber. Once in the combustion chamber, the mixture is compressed, then ignited by a spark plug (spark ignition). The engine is controlled by limiting the amount of air allowed inside through the use of a throttling valve placed on the air intake (carburetor or throttle body).
Specific power: Power produced per unit mass of fuel.
Stack: Individual fuel cells connected in series.
Steady state: Condition of a body or system in which the conditions at each point do not change with time, after initial fluctuations have disappeared.
Substrate: Basic surface on which a material adheres — for example, paint or laminate.
Supercharger: An air compressor designed to force air, under pressure, into an engine's cylinders.
Superplastic forming (SPF): A metal-forming process that uses the extreme extendability of certain metal alloys to form complex parts, in fewer stages and with minimum waste. The process uses precisely controlled rates of strain and temperature to elongate metal without tearing or breaking. The cost can be as little as one-tenth the cost of conventional machining.

T

Technology benchmarking: Assessing technology by testing and evaluating representative components, subsystems, and complete vehicle systems to (a) determine attributes and (b) compare them with program objectives and technical targets.
Technology validation: Confirming that technical targets for a given technology have been met.
Technology-validation test-bed vehicle: Rolling platform with which integrated experimental components and subsystems can be operated on either a chassis dynamometer or test track. This tool can help validate whether new technologies are suitable for automotive applications.
Torque: The turning force produced by an engine.
Thermal efficiency: The percentage of the heat developed in burning fuel that is actually used to develop power.
Traction: A situation in which the friction between two surfaces allows them to stick together enough to do useful work.
Transducer: Device that converts variations in one energy form into corresponding variations in another, usually electrical.
Transmission electron microscope (TEM): A TEM allows a beam of electrons to interact with atoms of a thin sample (<100 nm), producing information about the sample from transmitted and deflected electrons, backscattered and secondary electrons, and emitted photons (x-rays). Because the electron beam travels through the sample, TEM and x-ray spectroscopy can reveal the structure and composition of its interior regions.
Turbine: Machine for generating rotary mechanical power from the energy in a stream of fluid. The energy, originally in the form of head or pressure energy, is converted to velocity energy by passing through a system of stationary and moving blades in the turbine.
Turbocharger: A turbine driven by exhaust gases that increases engine power by forcing relatively large amounts of air into the cylinders of an engine.

U

Ultracapacitor: Ultracapacitors are higher specific energy and power versions of electrolytic capacitors—devices that store energy as an electrostatic charge. They are electrochemical systems that store energy in a polarized liquid layer at the interface between an ionically conducting electrolyte and a conducting electrode. Energy storage capacity increases by increasing the surface area of the interface. Ultracapacitors are being developed as primary energy devices for power assist during acceleration and hill climbing, as well as recovery of braking energy.

V

Vehicle systems: Full spectrum of components and subsystems, as well as their configuration, that determines the attributes of a vehicle.
Vortex shedding: Swirling flow generated by a stream of fluid flowing past a flow obstruction, such as a solid body.
Vorticity: Vector measure of local rotation in a fluid flow.

W

Wastegate: A valve used to limit the boost developed in a turbocharger. A wastegate allows some of an engine's exhaust flow to bypass the turbocharger's turbine under certain conditions.

X

X-ray photoelectron spectroscopy: Analytical technique in which information about the surface of a specimen is obtained by studying the spectrum of photoelectrons emitted from the surface when it is bombarded by x-ray photons.

Y

Yaw angle: The angle of rotation of a body about a vertical axis with respect to the flow stream direction.

Printable Version