Fuel efficiency, is a form of thermal efficiency In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example. The input, , to the device is heat, or the heat-content of a fuel that is consumed. The desired output is mechanical work, , or heat, , or, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel Fuel is any material that is burned or altered to obtain energy and to heat or to move objects. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion. An important property of a useful fuel is that its energy can be stored to be released only when needed, into kinetic energy The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. Negative work of the same magnitude or work In physics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI units of joules. The term work was first coined in 1826 by the French mathematician Gaspard-Gustave Coriolis. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is often illustrated as a continuous energy profile In standardization, a profile consists of an agreed-upon subset and interpretation of a specification. Many complex technical specifications have many optional features, such that two conforming implementations may not inter-operate due to choosing different sets of optional features to support. Even when no formal optional features exist within a. Non-transportation applications, such as industry An industry is the manufacturing of a good or service within a category. Although industry is a broad term for any kind of economic production, in economics and urban planning industry is a synonym for the secondary sector, which is a type of economic activity involved in the manufacturing of raw materials into goods and products, benefit from increased fuel efficiency, especially fossil fuel power plants A fossil-fuel power plant is a power plant that burns fossil fuels such as coal, natural gas or petroleum to produce electricity or industries dealing with combustion, such as ammonia Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is normally encountered as a gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block production during the Haber process The Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron catalyst, to produce ammonia. The Haber process is important because ammonia is difficult to produce on an industrial scale, and the fertilizer generated from the ammonia is responsible for sustaining.

In the context of transport Transport or transportation is the movement of people and goods from one location to another. Transport is performed by modes, such as air, rail, road, water, cable, pipeline and space. The field can be divided into infrastructure, vehicles, and operations, "fuel efficiency" more commonly refers to the energy efficiency of a particular vehicle model Fuel usage in automobiles refers to the relationship between distance traveled by an automobile and the amount of fuel consumed. There are no quantities or units for fuel usage defined in the International Standard ISO 80000 Quantities and Units, so the nationally-defined reciprocal quantities fuel economy and fuel consumption are used in this, where its total output (range, or mileage [U.S.]) is given as a ratio In mathematics, a ratio expresses the magnitude of quantities relative to each other. Specifically, the ratio of two quantities indicates how many times the first quantity is contained in the second and may be expressed algebraically as their quotient of range units per a unit amount of input fuel (gasoline Gasoline or petrol (Commonwealth) is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines. It is also used as a solvent, mainly known for its ability to dilute paints, diesel, etc.). This ratio is given in common measures such as liters The litre is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case (l and L). The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau. Although the litre is not an SI unit, it is accepted for use with the SI, and has appeared in several per 100 kilometers The kilometre , symbol km is a unit of length in the metric system, equal to one thousand metres and is therefore exactly equal to the distance travelled by light in free space in 1⁄ 299,792.458 of a second. It is the conventionally used measurement unit for expressing distances between geographical places in most of the world; notable (L/100 km) (common in Europe, Canada and Australia) or litres per mil A mil is a unit of length, usually used to measure geographic distance, fairly common in Norway and Sweden. Today, it measures by definition 10 kilometres, (≈6.2 miles) but earlier in history it had different values (Norway Norway (pronounced /ˈnɔrweɪ/ ; Norwegian: Norge (Bokmål), Noreg (Nynorsk) or Norga (North Sami)), officially the Kingdom of Norway, is a country in Northern Europe occupying the western portion of the Scandinavian Peninsula, as well as Jan Mayen and the Arctic archipelago of Svalbard under the Spitsbergen Treaty. The majority of the country/Sweden c. ^ Since July 1, 2009 Five other languages are officially recognized as minority languages. They are: ) or miles A mile is a unit of length in a number of different systems. In contemporary English, a mile most commonly refers to the statute mile of 5,280 feet or the nautical mile of 1,852 meters (6,076.12 ft). There are many other historical miles and similar units in other systems translated as miles in English, varying between one and fifteen kilometers per gallon A gallon is a measure of volume of approximately four litres. Historically it has had many different definitions, but there are three definitions in current use. These are the U.S. liquid gallon and the lesser used U.S. dry gallon (≈ 4.4 L) which are in use in the United States, and the Imperial (UK) gallon (≈ 4.5 L) which is in unofficial use (mpg Fuel usage in automobiles refers to the relationship between distance traveled by an automobile and the amount of fuel consumed. There are no quantities or units for fuel usage defined in the International Standard ISO 31 Quantities and Units, so the nationally-defined reciprocal quantities fuel economy and fuel consumption are used in this) (prevalent in the USA, UK, and often in Canada, using their respective gallon measurements) or kilometres per litre (km/L) (prevalent in Asian countries such as India India, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal on the east, India has a coastline of 7,517 and Japan Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The characters which make up Japan's name mean "sun-origin", which is why Japan is). Though the typical output measure is vehicle range, for certain applications output can also be measured in terms of weight per range units (freight Cargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport) or individual passenger-range (vehicle range / passenger capacity).

This ratio is based on a car's total properties, including its engine An engine is a machine that produces mechanical force and motion from another form of energy . It is also referred to as a prime mover. An automobile makes use of several motors to start the car and drive the car's various pumps – but the power plant that propels the car is called an engine. The term motor was originally used to distinguish the properties, its body drag In fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas). Drag forces act in a direction opposite to the oncoming flow velocity. Unlike other resistive forces such as dry friction, which is nearly independent of velocity, drag forces depend on velocity, weight, and rolling resistance Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface. It is caused mainly by the deformation of the object, the deformation of the surface, or both. Additional contributing factors include wheel radius, forward speed, surface adhesion,, and as such may vary substantially from the profile of the engine alone. While the thermal efficiency of petroleum Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights, and other organic compounds, that is found in geologic formations beneath the earth's surface engines The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the has improved in recent decades, this does not necessarily translate into fuel economy of cars An automobile, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally for the, as people in developed countries The term developed country is used to describe countries that have a high level of development according to some criteria. Which criteria, and which countries are classified as being developed, is a contentious issue and is surrounded by fierce debate. Economic criteria have tended to dominate discussions. One such criterion is income per capita; tend to buy bigger and heavier cars (i.e. SUVs A sport utility vehicle is a generic marketing term for a vehicle similar to a station wagon, but built on a light-truck chassis. Usually equipped with four-wheel drive for on- or off-road ability, and with some pretension or ability to be used as an off-road vehicle, some SUVs include the towing capacity of a pickup truck with the passenger- will get less range per unit fuel than an economy car An economy car is an automobile that is designed for low cost operation. Typical economy cars are small, light weight, and inexpensive to buy).

Hybrid vehicle A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles , which combine an internal combustion engine and one or more electric motors designs use smaller combustion engines as electric generators to produce greater range per unit fuel than directly powering the wheels with an engine would, and (proportionally) less fuel emissions The atmosphere is a complex, dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth's ecosystems (CO₂ grams Carbon dioxide equivalent and Equivalent carbon dioxide (or CO2e) are two related but distinct measures for describing how much global warming a given type and amount of greenhouse gas may cause, using the functionally equivalent amount or concentration of carbon dioxide (CO2) as the reference) than a conventional (combustion engine) vehicle of similar size and capacity. Energy otherwise wasted in stopping is converted to electricity and stored in batteries which are then used to drive the small electric motors. Torque from these motors is very quickly supplied complementing power from the combustion engine. Fixed cylinder sizes can thus be designed more efficiently.

Energy-efficiency terminology

Energy efficiency is similar to fuel efficiency but the input is usually in units of energy such as British thermal units (BTU), megajoules (MJ), gigajoules (GJ), kilocalories (kcal), or kilowatt-hours (kW·h). The inverse of "energy efficiency" is "energy intensity", or the amount of input energy required for a unit of output such as MJ/passenger-km (of passenger transport), BTU/ton-mile (of freight transport, for long/short/metric tons), GJ/t (for steel production), BTU/(kW·h) (for electricity generation), or litres/100 km (of vehicle travel). Litres per 100 km is also a measure of "energy intensity" where the input is measured by the amount of fuel and the output is measured by the distance Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance. A metric is a function that behaves according to a specific travelled. For example: Fuel economy in automobiles Fuel usage in automobiles refers to the relationship between distance traveled by an automobile and the amount of fuel consumed. There are no quantities or units for fuel usage defined in the International Standard ISO 80000 Quantities and Units, so the nationally-defined reciprocal quantities fuel economy and fuel consumption are used in this.

Given a heat value of a fuel, it would be trivial to convert from fuel units (such as litres of gasoline) to energy units (such as MJ) and conversely. But there are two problems with comparisons made using energy units:

• There are two different heat values for any hydrogen-containing fuel which can differ by several percent (see below).
• When comparing transportation energy costs, it must be remembered that a kilowatt hour The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules of electric energy may require an amount of fuel with heating value of 2 or 3 kilowatt hours to produce it.

Energy content of fuel

The specific energy content of a fuel is the heat energy obtained when a certain quantity is burned (such as a gallon, litre, kilogram). It is sometimes called the heat of combustion. There exists two different values of specific heat energy for the same batch of fuel. One is the high (or gross) heat of combustion and the other is the low (or net) heat of combustion. The high value is obtained when, after the combustion, the water in the exhaust is in liquid form. For the low value, the exhaust has all the water in vapor form (steam). Since water vapor gives up heat energy when it changes from vapor to liquid, the high value is larger since it includes the latent heat of vaporization of water. The difference between the high and low values is significant, about 8 or 9%. This accounts for most of the apparent discrepancy in the heat value of gasoline. In the U.S. (and the table below) the high heat values have traditionally been used, but in many other countries, the low heat values are commonly used.

Neither the gross heat of combustion nor the net heat of combustion gives the theoretical amount of mechanical energy (work) that can be obtained from the reaction. (This is given by the change in Gibbs free energy, and is around 45.7 MJ/kg for gasoline.) The actual amount of mechanical work obtained from fuel (the inverse of the specific fuel consumption) depends on the engine. A figure of 17.6 MJ/kg is possible with a gasoline engine, and 19.1 MJ/kg for a diesel engine. See Brake specific fuel consumption for more information.

Fuel efficiency of vehicles

The fuel efficiency of vehicles is usually expressed in one of two ways:

• Fuel consumption is the amount of fuel used per unit distance; for example, litres per 100 kilometres (L/100 km). In this case, the lower the value, the more economic a vehicle is (the less fuel it needs to travel a certain distance); this is the measure generally used across Europe.

• Fuel economy is the distance travelled per unit volume of fuel used; for example, kilometres per litre (km/L) or miles per gallon (MPG), where 1 MPG (imperial) = 0.354013 km/l. In this case, the higher the value, the more economic a vehicle is (the more distance it can travel with a certain volume of fuel). This measure is popular in the USA and the UK (mpg), India, Japan and Latin America (km/L).

Converting from mpg or to L/100 km (or vice versa) involves the use of the reciprocal function, which is not distributive. Therefore, the average of two fuel economy numbers gives different values if those units are used. If two people calculate the fuel economy average of two groups of cars with different units, the group with better fuel economy may be one or the other.

The formula for converting to miles per US gallon (3.785 L) from L/100 km is , where x is value of L/100 km. For miles per Imperial gallon (4.546 L) the formula is .

In Europe, the two standard measuring cycles for "litre/100 km" value are "urban" traffic with speeds up to 50 km/h from a cold start, and then "extra urban" travel at various speeds up to 120 km/h which follows the urban test. A combined figure is also quoted showing the total fuel consumed in divided by the total distance traveled in both tests. A reasonably modern European supermini and many mid-size cars, including station wagons, may manage motorway travel at 5 L/100 km (47 mpg US/56 mpg imp) or 6.5 L/100 km in city traffic (36 mpg US/43 mpg imp), with carbon dioxide emissions of around 140 g/km.

An average North American mid-size car travels 27 mpg (US) (9 L/100 km) highway, 21 mpg (US) (11 L/100 km) city; a full-size SUV usually travels 13 mpg (US) (18 L/100 km) city and 16 mpg (US) (15 L/100 km) highway. Pickup trucks vary considerably; whereas a 4 cylinder-engined light pickup can achieve 28 mpg (8 L/100 km), a V8 full-size pickup with extended cabin only travels 13 mpg (US) (18 L/100 km) city and 15 mpg (US) (15 L/100 km) highway.

European-built cars are generally more fuel-efficient than American vehicles. While Europe has lots of higher efficiency diesel cars, gasoline vehicles are also more efficient. Most European vehicles cited in the CSI study run on diesel engines, which tend to achieve greater fuel efficiency than gas engines. Selling those cars in the United States is difficult because of emission standards, notes Walter McManus, a fuel economy expert at the University of Michigan Transportation Research Institute. “For the most part, European diesels don’t meet U.S. emission standards,” McManus said. Another reason why many European models are not marketed in the United States is that labor unions object.^[2]

An interesting example of European cars' capabilities of fuel economy is the microcar Smart Fortwo cdi, which can achieve up to 3.4 l/100 km (69.2 mpg US) using a turbocharged three-cylinder 41 bhp (30 kW) Diesel engine. The Fortwo is produced by Daimler AG and is currently only sold by one company in the United States. Furthermore, the current (and to date already 10 year old) world record in fuel economy of production cars is held by the Volkswagen Group, with special production models (labeled "3L") of the Volkswagen Lupo and the Audi A2, consuming (NEDC ratified) as little as 2.99 litres of diesel fuel per 100 kilometres (78 miles per US gallon or 94 miles per Imperial gallon).

Diesel engines generally achieve greater fuel efficiency than petrol (gasoline) engines. Diesel engines have energy efficiency of 45% and petrol engines of 30%.^[3] That is one of the reasons why diesels have better fuel efficiency than equivalent petrol cars. A common margin is 40% more miles per gallon for an efficient turbodiesel. For example, the current model Skoda Octavia, using Volkswagen engines, has a combined European fuel efficiency of 38.2 mpg for the 102 bhp (76 kW) petrol engine and 53.3 mpg for the 105 bhp (78 kW) — and heavier — diesel engine. The higher compression ratio is helpful in raising the energy efficiency, but diesel fuel also contains approximately 10-20% more energy per unit volume than gasoline which contributes to the reduced fuel consumption for a given power output.^[4]

Fuel efficiency in microgravity

How fuel combusts affects how much energy is produced. The National Aeronautics and Space Administration (NASA) has investigated fuel consumption in microgravity.

The common distribution of a flame under normal gravity conditions depends on convection, because soot tends to rise to the top of a flame, such as in a candle, making the flame yellow. In microgravity or zero gravity, such as an environment in outer space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient. There are several possible explanations for this difference, of which the most likely one given is the hypothesis that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs.^[5] Experiments by NASA in microgravity reveal that diffusion flames in microgravity allow more soot to be completely oxidised after they are produced than diffusion flames on Earth, because of a series of mechanisms that behaved differently in microgravity when compared to normal gravity conditions.^[6] Premixed flames in microgravity burn at a much slower rate and more efficiently than even a candle on Earth, and last much longer.^[7]

Transportation

Fuel efficiency in transportation

Vehicle efficiency and transportation pollution

Fuel efficiency directly affects emissions causing pollution and potentially leading to climate change by affecting the amount of fuel used. However, it also depends on the fuel source used to drive the vehicle concerned. Cars can, for example, run on a number of fuel types other than gasoline, such as natural gas, LPG or biofuel or electricity which creates various quantities of atmospheric pollution.

A kilogram of carbon, whether contained in petrol, diesel, kerosene, or any other hydrocarbon fuel in a vehicle, leads to approximately 3.63 kg of CO₂ emissions.^[8] Due to the carbon content of gasoline, its combustion emits 2.32 kg/L (19.4 lb/US gal); since diesel fuel is more energy dense per unit volume, diesel emits 2.66 kg/L (22.2 lb/US gal).^[8] This figure is only the CO₂ emissions of the final fuel product and does not include additional CO₂ emissions created during the drilling, pumping, transportation and refining steps required to produce the fuel. Additional measures to reduce overall emission includes improvements to the efficiency of air conditioners, lights and tires.

There is also a growing movement of drivers who practice ways to increase their MPG and save fuel through driving techniques. They are often referred to as hypermilers. Hypermilers have broken records of fuel efficiency, averaging 109 miles per gallon driving a Prius. In non-hybrid vehicles these techniques are also beneficial. Hypermiler Wayne Gerdes can get 59 MPG in a Honda Accord and 30 MPG in an Acura MDX.^[9]

Hybrid vehicles can conserve petroleum fuel and therefore be more efficient than conventional vehicles.

The most efficient machines for converting energy to rotary motion are electric motors, as used in electric vehicles. However, electricity is not a primary energy source so the efficiency of the electricity production has also to be taken into account. Currently railway trains can be powered using electricity, delivered through an additional running rail, overhead catenary system or by onboard generators used in diesel-electric locomotives as common on the UK rail network. Pollution produced from centralised generation of electricity is emitted at a distant power station, rather than "on site". Some railways, such as the French SNCF and Swiss federal railways derive most, if not 100% of their power, from hydroelectric or nuclear power stations, therefore atmospheric pollution from their rail networks is very low. This was reflected in a study by AEA Technology between a Eurostar train and airline journeys between London and Paris, which showed the trains on average emitting 10 times less CO₂, per passenger, than planes, helped in part by French nuclear generation which, however, creates its own radioactive waste which air flight does not.^[10]. This can be changed using more renewable sources for electric generation.

In the future hydrogen cars may be commercially available. Powered either through chemical reactions in a fuel cell that create electricity to drive very efficient electrical motors or by directly burning hydrogen in a combustion engine (near identically to a natural gas vehicle, and similarly compatible with both natural gas and gasoline); these vehicles promise to have near zero pollution from the tailpipe (exhaust pipe). Potentially the atmospheric pollution could be minimal, provided the hydrogen is made by electrolysis using electricity from non-polluting sources such as solar, wind, or hydroelectricity. One advantage of fuel cell vehicles is that they can electrolyse water using their own fuel cells, operating in exactly the same closed-loop fashion as any other rechargeable electric battery.

In any process, it is vitally important to account for all of the energy used throughout the process. Thus, in addition to the energy cost of the electricity or hydrogen production, we must also account for transmission and/or storage losses to support large-scale use of such vehicles. For this reason the use of the idea "zero pollution" should be avoided.

See also

• Annual fuel utilization efficiency (AFUE)
• ACEA agreement
• Alternative propulsion
• Association for the Study of Peak Oil and Gas (ASPO)
• Corporate Average Fuel Economy (CAFE)
• Carbon dioxide equivalent
• EcoAuto (in Canada)
• Emission standard
• Energy conservation
• Energy content of Biofuel
• Energy density
• Energy efficiency
• Fuel economy in automobiles
• Fuel efficiency in transportation
• Gas-guzzler
• Heating value
• IRIS engine
• Life cycle assessment
• Low-energy vehicle
• Low-rolling resistance tires
• Marine fuel management

References

1. ^ Calculated from heats of formation. Does not correspond exactly to the figure for MJ/L divided by density.
2. ^ EuropeVsUS Efficiency
3. ^ Diesel engines - Products : Volvo Group - Global
4. ^ Diesel Engines
5. ^ CFM-1 experiment results, National Aeronautics and Space Administration, April 2005.
6. ^ LSP-1 experiment results, National Aeronautics and Space Administration, April 2005.
7. ^ SOFBAL-2 experiment results, National Aeronautics and Space Administration, April 2005.
8. ^ ^{a b} "Emission Facts: Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel". Office of Transportation and Air Quality. United States Environmental Protection Agency. February 2005. http://www.epa.gov/OMS/climate/420f05001.htm. Retrieved 2009-07-28.
9. ^ Gaffney, Dennis (2007-01-01). "This Guy Can Get 59 MPG in a Plain Old Accord. Beat That, Punk.". Mother Jones. http://www.motherjones.com/news/feature/2007/01/king_of_the_hypermilers.html. Retrieved 2007-04-20.
10. ^ European Federation for Transport and Environment

The United States Department of Energy and the Environmental Protection Agency maintain a Web site with fuel economy information, including testing results and frequently asked questions.

External links

• US Government website on fuel economy
• UK DfT comparisons on road and rail
• NASA Offers a $1.5 Million Prize for a Fast and Fuel-Efficient Aircraft
• Spritmonitor.de "the most fuel efficient cars" - Database of thousands of (mostly German) car owners' actual fuel consumption figures

Categories: Energy economics | Physical quantities | Energy conservation | Transport economics

See Also:

• Fuel Efficiency
• Fuel Economy In Automobiles
• Corporate Average Fuel Economy

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