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{{ref improve|date=May 2013}}
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'''Fuel efficiency''' is a form of [[thermal efficiency]], meaning the efficiency of a process that converts chemical potential energy contained in a carrier [[fuel]] into [[kinetic energy]] or [[Mechanical work|work]]. Overall fuel efficiency may vary per device, which in turn may vary per application fuel efficiency, especially [[fossil fuel power plant]]s or industries dealing with combustion, such as [[ammonia]] production during the [[Haber process]].
 
In the context of [[transport]], fuel economy is the energy efficiency of a particular vehicle,  is given as a [[ratio]] of distance travelled per unit of [[Motor fuel|fuel]] consumed.  Fuel economy is expressed in [[mile]]s per [[gallon]] (mpg) in the USA and usually also in the UK ([[imperial]] gallon);there is sometimes confusion as the imperial gallon is 20% larger than the US gallon so that mpg values are not directly comparable. In countries using the [[metric system]] fuel economy is stated in kilometres per litre (km/L) in the [[Netherland]]s, [[Denmark]] and in several [[Latin America]]n or Asian countries such as [[India]], [[Japan]], [[South Korea]], or as the reciprocal ratio, "fuel consumption" in [[liter]]s per 100 [[kilometers]] (L/100&nbsp;km) in much of Europe, Canada, New Zealand and Australia. Litres per [[Scandinavian mile|mil]] are used in [[Norway]] and [[Sweden]].
 
Fuel consumption is a more accurate measure of a vehicle’s performance because it is a linear relationship while [http://www.fueleconomy.gov/feg/label/learn-more-gasoline-label.shtml#fuel-consumption-rate fuel economy leads to distortions] in efficiency improvements.
 
Weight-specific efficiency (efficiency per unit weight) may be stated for [[freight]], and passenger-specific efficiency (vehicle efficiency per passenger).
 
==Vehicle design==
Fuel efficiency is dependent on many parameters of a vehicle, including its [[engine]] parameters, [[Drag (physics)|aerodynamic drag]], weight, and [[rolling resistance]]. There have been advances in all areas of vehicle design in recent decades.
 
[[Hybrid vehicles]] use two or more power sources for propulsion. In many designs, a small combustion engine is combined with electric motors.  Kinetic energy which would otherwise be lost to heat during braking is recaptured as electrical power to improve fuel efficiency. Engines automatically shut off when vehicles come to a stop and start again when the accelerator is pressed preventing wasted energy from idling. <ref>{{cite web|title=How Hybrid Work|url=http://www.fueleconomy.gov|publisher=U.S. Department of Energy|accessdate=01/16/2014}}</ref>
 
==Fleet efficiency==
Fleet efficiency describes the average efficiency of a population of vehicles.  Technological advances in efficiency may be offset by a change in buying habits with a propensity to heavier vehicles, which are less efficient, all else being equal.
 
==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&nbsp;km (of vehicle travel). Litres per 100&nbsp;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]] travelled.  For example: [[Fuel economy in automobiles]].
 
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]] 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 liquid water 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.
 
<!--This table originally contained MJ/L values that were too low compared to the BTU/gal figures, with a reference to an ''Automotive Handbook''.<ref>''Automotive Handbook, 4th Edition'', Robert Bosch GmbH, 1996. ISBN 0-8376-0333-1</ref> These have now been replaced with values from the ''Transportation Energy Data Book'',<ref name=TEDB>[http://www-cta.ornl.gov/data/Appendix_B.html Appendix B, Transportation Energy Data Book] from the [[Center for Transportation Analysis]] of the [[Oak Ridge National Laboratory]]</ref>
but which does not give the MJ/kg or the densities.)
 
Note: I modified this table because the values in SI units did not agree with the values in British or U.S. units. So I used another source, but it did not have MJ/kg, and I did not have the time to try to find accurate densities in order to convert to MJ/kg. If someone can fill in the blanks using good data, it would be useful.-->
{| class="wikitable sortable"
! align = "left"|Fuel type
! align ="right"|MJ/L
! align ="right"|MJ/kg
! align ="right"|[[British thermal unit|BTU]]/[[gallon|imp gal]]
! align ="right"|BTU/[[US gallon|US gal]]
! align ="right"|[[octane rating|Research octane<br /> number (RON)]]
|-
| Regular [[gasoline]]/petrol
| align ="right"|34.8
| align ="right"|~47
| align ="right"|150,100
| align ="right"|125,000
| align ="right"|Min. 91
|-
| Premium [[gasoline]]/petrol
| align ="right"|
| align ="right"|~46
| align ="right"|
| align ="right"|
| align ="right"|Min. 95
|-
| [[Autogas]] ([[Liquefied petroleum gas|LPG]]) (60% [[propane]] and 40% [[butane]])
| align ="right"|25.5–28.7
| align ="right"|~51
| align ="right"|
| align ="right"|
| align ="right"|108–110
|-
|[[ethanol fuel|Ethanol]]
| align ="right"|23.5
| align ="right"|31.1<ref>Calculated from heats of formation. Does not correspond exactly to the figure for MJ/L divided by density.</ref>
| align ="right"|101,600
| align ="right"|84,600
| align ="right"|129
|-
| [[Methanol]]
| align ="right"|17.9
| align ="right"|19.9
| align ="right"|77,600
| align ="right"|64,600
| align ="right"|123
|-
| [[Alcohol fuel|Gasohol]] (10% ethanol and 90% gasoline)
| align ="right"|33.7
| align ="right"|~45
| align ="right"|145,200
| align ="right"|121,000
| align ="right"|93/94
|-
| [[E85]] (85% ethanol and 15% gasoline)
| align ="right"|33.1
| align ="right"|44
| align ="right"|108,878
| align ="right"|90,660
| align ="right"|100–105
|-
| [[Diesel fuel|Diesel]]
| align ="right"|38.6
| align ="right"|~48
| align ="right"|166,600
| align ="right"|138,700
| align ="right"|[[cetane number|N/A (see cetane)]]
|-
| [[Biodiesel]]
| align ="right"|35.1
| align ="right"|39.9
| align ="right"|151,600
| align ="right"|126,200
| align ="right"|[[cetane number|N/A (see cetane)]]
|-
| [[WVO|Vegetable oil]] (using 9.00&nbsp;kcal/g)
| align ="right"|34.3
| align ="right"|37.7
| align ="right"|147,894
| align ="right"|123,143
| align ="right"|
|-
| [[Aviation gasoline]]
| align ="right"|33.5
| align ="right"|46.8
| align ="right"|144,400
| align ="right"|120,200
| align ="right"|80-145
|-
| [[Jet fuel]], naphtha
| align ="right"|35.5
| align ="right"|46.6
| align ="right"|153,100
| align ="right"|127,500
| align ="right"|N/A to turbine engines
|-
| [[Jet fuel]], kerosene
| align ="right"|37.6
| align ="right"|~47
| align ="right"|162,100
| align ="right"|135,000
| align ="right"|N/A to turbine engines
|-
| [[Liquefied natural gas]]
| align ="right"|25.3
| align ="right"|~55
| align ="right"|109,000
| align ="right"|90,800
| align ="right"|
|-
| [[Liquid hydrogen]]
| align ="right"|9.3
| align ="right"|~130
| align ="right"|40,467
| align ="right"|33,696
| align ="right"|
|}
 
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&nbsp;MJ/kg for gasoline.) The actual amount of mechanical work obtained from fuel (the inverse of the [[Brake specific fuel consumption|specific fuel consumption]]) depends on the engine. A figure of 17.6&nbsp;MJ/kg is possible with a gasoline engine, and 19.1&nbsp;MJ/kg for a diesel engine. See [[Brake specific fuel consumption]] for more information.
 
== Fuel efficiency of vehicles ==
{{See also|Fuel economy in automobiles}}
The fuel efficiency of vehicles can be expressed in more ways:
 
*'''Fuel consumption''' is the amount of fuel used per unit distance; for example, '''[[litre]]s per 100 [[kilometre]]s (L/100&nbsp;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 (except the UK, Denmark and The Netherlands - see below), New Zealand, Australia and Canada. Also in Uruguay, Paraguay, Guatemala, Colombia, China, and Madagascar.{{Citation needed|date=November 2010}}, as also in post-Soviet space.
 
*'''Fuel economy''' is the distance travelled per unit volume of fuel used; for example, '''kilometres per litre (km/L)''' or '''[[mile]]s per [[gallon]] (MPG)''', where 1 MPG (imperial) ≈ 0.354006&nbsp;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), but in Europe, India, Japan, South Korea and Latin America the metric unit ''km/L'' is used instead.
 
Converting from mpg or to L/100&nbsp;km (or vice versa) involves the use of the [[multiplicative inverse|reciprocal]] function, which is not [[distributive]]. Therefore, the average of two fuel economy numbers gives different values if those units are used, because one of the functions is reciprocal, thus not linear. 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. However, from the point of energy used as a shared method of measure, the result shall be the same in both the cases.
 
The formula for converting to miles per US gallon (exactly 3.785411784 L) from L/100&nbsp;km is <math>\textstyle \frac{235.215}{x}</math>, where <math>x</math> is value of L/100&nbsp;km. For miles per Imperial gallon (exactly 4.54609 L) the formula is <math>\textstyle \frac{282.481}{x}</math>.
 
In parts of Europe, the two standard measuring cycles for "litre/100 km" value are "urban" traffic with speeds up to 50&nbsp;km/h from a cold start, and then "extra urban" travel at various speeds up to 120&nbsp;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 car|supermini]] and many mid-size cars, including station wagons, may manage [[motorway]] travel at 5 L/100&nbsp;km (47 mpg US/56 mpg imp) or 6.5 L/100&nbsp;km in city traffic (36 mpg US/43 mpg imp), with [[carbon dioxide]] emissions of around 140 g/km.
 
An average [[North America]]n [[mid-size car]] travels 21 mpg (US) (11 L/100&nbsp;km) city, 27 mpg (US) (9 L/100&nbsp;km) highway; a [[full-size car|full-size]] [[SUV]] usually travels 13 mpg (US) (18 L/100&nbsp;km) city and 16 mpg (US) (15 L/100&nbsp;km) highway.  [[Pickup truck]]s vary considerably; whereas a 4 cylinder-engined light pickup can achieve 28 mpg (8 L/100&nbsp;km), a [[V8 engine|V8]] full-size pickup with extended cabin only travels 13 mpg (US) (18 L/100&nbsp;km) city and 15 mpg (US) (15 L/100&nbsp;km) highway.
 
The average fuel economy is higher in Europe due to the higher cost of fuel. In the UK, a gallon of gas without tax would cost US$1.97, but with taxes cost US$6.06 in 2005. The average cost in the United States was US$2.61. Consumers prefer "muscle cars" but choose more fuel efficient ones when gas prices increase.<ref>[http://www.csmonitor.com/2005/0826/p01s03-woeu.html Gas prices too high? Try Europe.]</ref>
 
European-built cars are generally more fuel-efficient than US vehicles. While Europe has many higher efficiency diesel cars, European gasoline vehicles are on average also more efficient than gasoline-powered vehicles in the USA. 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 in 2007. Another reason why many European models are not marketed in the United States is that labor unions object to having the big 3 import any new foreign built models regardless of fuel economy while laying off workers at home.<ref>[http://www.msnbc.msn.com/id/17344368/ EuropeVsUS Efficiency<!-- Bot generated title -->]</ref>
 
An example of European cars' capabilities of fuel economy is the [[microcar]] ''[[Smart Fortwo]]'' cdi, which can achieve up to 3.4 l/100&nbsp;km (69.2 mpg US) using a [[turbocharger|turbocharged]] three-cylinder 41&nbsp;bhp (30&nbsp;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#Lupo 3L|Volkswagen Lupo]] and the [[Audi A2#1.2 TDI|Audi A2]], consuming as little as {{convert|3|L/100 km|abbr=on}}.<ref>[http://usatoday30.usatoday.com/money/consumer/autos/mareview/mauto497.htm VW Lupo: Rough road to fuel economy]</ref>
 
[[Diesel engine]]s generally achieve greater fuel efficiency than petrol (gasoline) engines. Passenger car diesel engines have [[Energy conversion efficiency|energy efficiency]] of up to 41% but more typically 30%, and petrol engines of up to 37.3%, but more typically 20%. That is one of the reasons why diesels have better fuel efficiency than equivalent petrol cars. A common margin is 25% 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 41.3 mpg for the {{convert|105|bhp|abbr=on}} petrol engine and 52.3 mpg for the {{convert|105|bhp|abbr=on}} — and heavier — diesel engine. The higher compression ratio is helpful in raising the energy efficiency, but diesel fuel also contains approximately 10% more energy per unit volume than gasoline which contributes to the reduced fuel consumption for a given power output.
 
In 2002, the United States had 85,174,776 trucks, and averaged {{convert|13.5|mpgus}}. Large trucks, over {{convert|33,000|lb}}, averaged {{convert|5.7|mpgus}}.<ref>[http://cta.ornl.gov/data/chapter5.shtml Heavy Vehicles and Characteristics] Table 5.4</ref>
 
{| class=wikitable
|+Truck fuel economy
|-
![[Gross vehicle weight rating|GVWR]] lbs!!Number!!Percentage!!Average miles per truck!!fuel economy!!Percentage of fuel use
|-
|6,000&nbsp;lbs and less||51,941,389||61.00%||11,882||17.6||42.70%
|-
|6,001 – 10,000&nbsp;lbs||28,041,234||32.90%||12,684||14.3||30.50%
|-
!Light truck subtotal!!79,982,623!!93.90%!!12,163!!16.2!!73.20%
|-
|10,001 – 14,000&nbsp;lbs||691,342||0.80%||14,094||10.5||1.10%
|-
|14,001 – 16,000&nbsp;lbs||290,980||0.30%||15,441||8.5||0.50%
|-
|16,001 – 19,500&nbsp;lbs||166,472||0.20%||11,645||7.9||0.30%
|-
|19,501 – 26,000&nbsp;lbs||1,709,574||2.00%||12,671||7||3.20%
|-
!Medium truck subtotal!!2,858,368!!3.40%!!13,237!!8!!5.20%
|-
|26,001 – 33,000&nbsp;lbs||179,790||0.20%||30,708||6.4||0.90%
|-
|33,001&nbsp;lbs and up||2,153,996||2.50%||45,739||5.7||20.70%
|-
!Heavy truck subtotal!!2,333,786!!2.70%!!44,581!!5.8!!21.60%
|-
!Total!!85,174,776!!100.00%!!13,088!!13.5!!100.00%
|}
 
The average economy of automobiles in the United States in 2002 was {{convert|22.0|mpgus}}. By 2010 this had increased to {{convert|23.0|mpgus}}. Average fuel economy in the United States gradually declined until 1973, when it reached a low of {{convert|13.4|mpgus}} and gradually has increased since, as a result of higher fuel cost.<ref>[http://cta.ornl.gov/data/chapter4.shtml Light Vehicles and Characteristics] Table 4.1</ref> A study indicates that a 10% increase in gas prices will eventually produce a 2.04% increase in fuel economy.<ref>[http://www.aeaweb.org/articles.php?doi=10.1257/pol.1.2.113  How Do Gasoline Prices Affect Fleet Fuel Economy?]</ref>
 
==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 [[sphere|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., National Aeronautics and Space Administration, April 2005. Experiments by NASA in microgravity reveal that [[diffusion flame]]s 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.[http://microgravity.grc.nasa.gov/combustion/lsp/lsp1_results.htm LSP-1 experiment results], National Aeronautics and Space Administration, April 2005. [[Premixed flame]]s in microgravity burn at a much slower rate and more efficiently than even a candle on Earth, and last much longer.<ref>[http://microgravity.grc.nasa.gov/combustion/lsp/lsp1_results.htm SOFBAL-2 experiment results], National Aeronautics and Space Administration, April 2005.</ref>
 
== Transportation ==
 
===Fuel efficiency in transportation===
{{Main|Energy efficiency in transportation}}
 
=== Vehicle efficiency and transportation pollution ===
{{Main|Gas-guzzler|Vehicle Efficiency Initiative}}
 
Fuel efficiency directly affects emissions causing pollution by affecting the amount of fuel used. However, it also depends on the fuel source used to drive the vehicle concerned. Cars for example, can run on a number of fuel types other than gasoline, such as [[Natural gas vehicle|natural gas]], [[Liquefied petroleum 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 3.6&nbsp;kg of [[CO2|CO<sub>2</sub>]] emissions.<ref name="EPA CO2 est">{{cite web| title=Emission Facts: Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel | url = http://www.epa.gov/OMS/climate/420f05001.htm | publisher=United States Environmental Protection Agency |date=February 2005 | work = Office of Transportation and Air Quality | accessdate = 2009-07-28 }}</ref>  Due to the carbon content of gasoline, its combustion emits 2.3&nbsp;kg/l (19.4&nbsp;lb/US gal) of [[CO2|CO<sub>2</sub>]]; since diesel fuel is more energy dense per unit volume, diesel emits 2.6&nbsp;kg/l (22.2&nbsp;lb/US gal).<ref name="EPA CO2 est" />  This figure is only the CO<sub>2</sub> emissions of the final fuel product and does not include additional CO<sub>2</sub> 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 conditioner]]s, lights and tires.
 
==Driving technique==
There is a growing community of enthusiasts known as [[hypermiler]]s who develop and practice driving techniques to increase fuel efficiency and reduce consumption. Hypermilers have broken records of fuel efficiency, for example, achieving 109 miles per gallon in 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]].<ref name="This Guy Can Get 59 MPG in a Plain Old Accord. Beat That, Punk.">{{cite news|last=Gaffney|first=Dennis|title=This Guy Can Get 59 MPG in a Plain Old Accord. Beat That, Punk.|publisher=Mother Jones|date=2007-01-01|url=http://www.motherjones.com/news/feature/2007/01/king_of_the_hypermilers.html|accessdate=2007-04-20}}</ref>
 
All drivers have the potential to improve their fuel efficiency.<ref name="Beusen">{{cite journal |author=Beusen et al.|title=Using on-board logging devices to study the long-term impact of an eco-driving course |journal=Transportation Research D |volume=14 |issue= |pages=514-520 |year=2009 |month= |pmid= |doi= |url=https://www.researchgate.net/publication/231614817_Using_on-board_logging_devices_to_study_the_long-term_impact_of_an_eco-driving_course?ev=prf_pub}}</ref> Applying these [http://oee.nrcan.gc.ca/cars-light-trucks/driving/fuel-efficient-driving-techniques/17823 five basic fuel-efficient driving techniques] can potentially reduce your fuel consumption by up to 25% and save you hundreds of dollars a year in fuel. [http://oee.nrcan.gc.ca/cars-light-trucks/driving/trip-planning-tips/17866 Plan your routes], calculate your fuel consumption and adopt [http://oee.nrcan.gc.ca/cars-light-trucks/driving/more-fuel-saving-tips/17868 other fuel-efficient driving habits] to save even more.  Fuel-efficient driving is easy. In fact, it’s one of the simplest and most effective ways any driver can cut their fuel costs, shrink their environmental footprints and ward off climate change.
 
==Advanced Technology improvements to improve fuel efficiency==
 
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 [[overhead lines|catenary]] system or by on-board generators used in [[Diesel-electric transmission|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 CO<sub>2</sub>, per passenger, than planes, helped in part by French nuclear generation.<ref>[http://www.transportenvironment.org/Article267.html European Federation for Transport and Environment]</ref> This can be changed using more [[renewable energy|renewable sources]] for [[electric generation]].
 
In the future, [[hydrogen vehicle|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]] or thermochemically by the use of the [[Thorium fuel cycle]] in a [[molten salt reactor]].
 
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.
 
In 2004, a consortium of major automakers — [[BMW]], [[General Motors]], [[Honda]], [[Toyota]] and [[Volkswagen]]/[[Audi]] — came up with ''"Top Tier Detergent Gasoline Standard"'' to [[gasoline]] brands in the U.S. and Canada that meet their minimum standards for [[detergent]] content<ref name="Top Tier Gasoline">[http://www.toptiergas.com/retailers.html Top Tier Gasoline]</ref> and do not contain metallic additives. Top Tier gasoline contains higher levels of detergent additives in order to prevent the build-up of deposits (typically, on [[fuel injector]] and [[intake valve]]) known to reduce fuel economy and engine performance.<ref>{{Cite web
| url = http://www.toptiergas.com/deposit_control.html
| title = Deposit Control Standards
| accessdate = 2012-10-19
| author =
| last =
| first =
| authorlink =
| coauthors =
| date =
| year =
| month =
| work =
| publisher =
| pages =
| language =
| quote =
| archiveurl =
| archivedate =
}}</ref>
 
==See also==
{{Portal|Energy}}
{{columns|width=auto
| col1 =
*[[Annual fuel utilization efficiency]] (AFUE)
*[[ACEA agreement]]
*[[Alternative propulsion]]
*[[Association for the Study of Peak Oil and Gas]] (ASPO)
*[[Carbon dioxide equivalent]]
*[[Corporate Average Fuel Economy]] (CAFE)
 
*[[EcoAuto]] (in Canada)
*[[Emission standard]]
*[[Energy content of Biofuel]]
*[[Energy conservation]]
*[[Energy conversion efficiency]]
*[[Energy density]]
 
| col2 =
*[[Fuel economy in automobiles]]
*[[Fuel economy-maximizing behaviors|Fuel economy maximising behaviors]]
*[[Fuel efficiency in transportation]]
*[[Gas-guzzler]]
*[[Heating value]]
 
*[[Life cycle assessment]]
*[[Low-energy vehicle]]
*[[Low-rolling resistance tires]]
*[[Marine fuel management]]
*[[Twinjet]]
*[[Automobile costs]]
}}
 
==References==
{{Reflist}}
 
==External links==
*[http://www.fueleconomy.gov/ US Government website on fuel economy]
*[http://www.dft.gov.uk/stellent/groups/dft_railways/documents/page/dft_railways_611287.pdf UK DfT comparisons on road and rail]
*[http://apps1.eere.energy.gov/news/news_detail.cfm/news_id=12694 NASA Offers a $1.5 Million Prize for a Fast and Fuel-Efficient Aircraft]
*[http://www.carfuelconsumption.com Car Fuel Consumption Official Figures]
*[http://www.spritmonitor.de/de/die_sparsamsten_autos.html Spritmonitor.de "the most fuel efficient cars" - Database of thousands of (mostly German) car owners' actual fuel consumption figures]
*[http://fueleconomy.carconsumption.com/ Searchable fuel economy data from the EPA - United States Environmental Protection Agency]
 
 
{{DEFAULTSORT:Fuel Efficiency}}
[[Category:Energy economics]]
[[Category:Physical quantities]]
[[Category:Energy conservation]]
[[Category:Transport economics]]

Latest revision as of 18:18, 12 November 2014

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