Fuel efficiency 342520 225950871 2008-07-16T04:26:33Z 24.207.126.100 {{portal|Energy}} '''Fuel efficiency''', in its basic sense, is the same as [[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, and this spectrum of variance is often illustrated as a continuous [[energy profile]]. Non-transportation applications, such as [[industry]], benefit from increased 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 [[transportation]], "fuel efficiency" more commonly refers to the [[fuel economy in automobiles|energy efficiency of a ''particular vehicle model]],'' where its total output (range, or "mileage" [U.S.]) is given as a [[ratio]] of ''range units'' per a unit amount of input fuel ([[gasoline]], diesel, etc.). This ratio is given in common measures such as "[[liter]]s per 100 [[kilometers]]" (L/100 km) (common in Europe and Canada or "[[mile]]s per [[gallon]]" ([[mileage|mpg]]) (prevalent in USA, UK, and often in Canada , using their respective gallon measurements) or "kilometers per liter"(kmpl) (prevalent in Asian countries such as India and Japan). Though the typical output measure is vehicle ''range'', for certain applications output can also be measured in terms of weight per range units ([[freight]]) or individual passenger-range (vehicle range / passenger capacity). This ratio is based on a car's total properties, including its [[engine]] properties, its [[body drag]], weight, and rolling resistance (friction), and as such may vary substantially from the profile of the engine alone. While the ''thermal efficiency'' of [[petroleum]] [[internal combustion engine|engines]] has improved in recent decades, this does not necessarily translate into ''fuel economy'' of [[automobile|cars]], as people in [[developed countries]] tend to buy bigger and heavier cars (i.e. [[sport utility|SUV]]s will get less range per unit fuel than an [[economy car]]). [[Hybrid vehicle]] 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]] ([[Carbon dioxide equivalent|CO<sub>2</sub> grams]]) than a conventional (combustion engine) vehicle of similar size and capacity. ==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). This last term "litres per 100 km" is also a measure of "fuel economy" where the input is measured by the amount of fuel and the output is measured by the [[distance]] traveled. 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). Which one do we use for converting fuel to energy? * 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, etc.). 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. <!--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"|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MJ/L ! align ="right"|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MJ/kg ! align ="right"|&nbsp;&nbsp;&nbsp;&nbsp;[[British thermal unit|BTU]]/[[gallon|Imp gal]] ! align ="right"|&nbsp;&nbsp;&nbsp;&nbsp;BTU/[[US gallon|US gal]] ! align ="right"|&nbsp;&nbsp;&nbsp;&nbsp;[[octane rating|Research octane<br> number (RON)]] |- | Regular [[Gasoline]] / Petrol | align ="right"|34.83 | 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]] + 40% [[Butane]]) | align ="right"| | align ="right"|~51 | align ="right"| | align ="right"| | align ="right"| |- |[[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 + 90% gasoline) | align ="right"|33.7 | align ="right"|~45 | align ="right"|145,200 | align ="right"|120,900 | align ="right"|93/94 |- | [[Diesel]] | align ="right"|38.60 | align ="right"|~48 | align ="right"|166,600 | align ="right"|138,700 | align ="right"|[[cetane number|N/A (see cetane)]] |- | [[Biodiesel]] | align ="right"|35.10 | align ="right"|39.89 | align ="right"|151,600 | align ="right"|126,200 | align ="right"| |- | [[WVO|Vegetable oil]] (using 9.00 kcal/g) | align ="right"|34.32 | align ="right"|37.66 | 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"| |- | [[Jet fuel]], naphtha | align ="right"|35.5 | align ="right"|46.6 | align ="right"|153,100 | align ="right"|127,500 | align ="right"| |- | [[Jet fuel]], kerosene | align ="right"|37.60 | align ="right"| | align ="right"|162,100 | align ="right"|135,000 | align ="right"| |- | [[Liquefied natural gas]] | align ="right"|25.3 | align ="right"|~55 | align ="right"|109,000 | align ="right"|90,800 | align ="right"| |- | [[Liquid hydrogen]] | align ="right"|9.36 | align ="right"|140.4 | 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 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 [[specific fuel consumption]] for more information. ==Fuel economy== {{Main|Fuel economy in automobiles}} Fuel economy is usually expressed in one of two ways: *The amount of fuel used per unit distance; for example, '''[[litre]]s per 100 [[kilometre]]s (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 notation generally used across Europe. *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 = 0.42514371 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 notation in popular in the USA (mpg), India and Latin America (km/L). Converting from mpg or to L/100 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. 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 <math>\frac{235.2}{x}</math>, where <math>x</math> is value of L/100km. For miles per Imperial gallon (4.546 L) the formula is <math>\frac{282.5}{x}</math>. In Europe, the two standard measuring cycles for "L/100 km" value are [[motorway]] travel at 90 km/h and rush hour city traffic. A reasonably modern European [[supermini car|supermini]] 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 America]]n [[mid-size car]] travels 27 mpg (US) (9 L/100 km) highway, 21 mpg (US) (11 L/100 km) city; a [[full-size car|full-size]] [[SUV]] usually travels 13 mpg (US) (18 L/100 km) city and 16 mpg (US) (15 L/100 km) highway. [[Pickup truck]]s 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. So, in general, cars are far more fuel-efficient in Europe. Part is because there are lots of diesel vehicles (more efficient) nevertheless, gasoline vehicles are also more efficient. The problem in the US is that American car buyers have downplayed the importancy of energy usage and pollution, relative to flexibility and cost of ownership.<ref>[http://www.msnbc.msn.com/id/17344368/ EuropeVsUS Efficiency<!-- Bot generated title -->]</ref> An interesting example 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 [[turbocharger|turbocharged]] three-cylinder 41 hp (30 kW) Diesel engine. The Fortwo is produced by [[Daimler_AG]] and is currently only sold by one company in the United States (see external link [http://www.zapworld.com/ ZAP]). The current record in fuel economy of production cars is held by [[Volkswagen]], with a special production model of the [[Volkswagen Lupo]] (the '''Lupo 3L''') that can consume as little as 3 [[litre]]s per 100 [[kilometre]]s (78 miles per [[U.S. customary units|US]] [[gallon]] or 94 miles per [[Imperial unit|Imperial]] gallon). The last Lupo was built in July 2005. [[Diesel engine]]s often achieve greater fuel efficiency than petrol (gasoline) engines. Diesel engines have [[energy efficiency]] of 45% and petrol engines of 30%.<ref>[http://www.volvo.com/group/global/en-gb/Volvo+Group/ourvalues/environment/products/dieselengines.htm Diesel engines - Products : Volvo Group - Global<!-- Bot generated title -->]</ref> That is one of the reasons why diesels have better fuel efficiency that 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 petrol engine and 53.3 mpg for the 105 bhp — and heavier — diesel engine. The higher compression ratio is helpful in raising efficiency, but diesel fuel also contains approximately 10-20% more energy per unit volume than gasoline.<ref>[http://www.fusel.com/diesel_engines.html Diesel Engines<!-- Bot generated title -->]</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 that the cause is the hypothesis that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs.<ref> [http://microgravity.grc.nasa.gov/combustion/cfm/usml-1_results.htm CFM-1 experiment results], National Aeronautics and Space Administration, April 2005.</ref> 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.<ref>[http://microgravity.grc.nasa.gov/combustion/lsp/lsp1_results.htm LSP-1 experiment results], National Aeronautics and Space Administration, April 2005.</ref> [[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|Fuel efficiency in transportation}} === Vehicle efficiency and transportation pollution === {{Main|Gas-guzzler|Vehicle Efficiency Initiative}} 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 vehicle|natural gas]], [[LPG]] or [[biofuel]] or electricity which creates various quantities of atmospheric pollution. A kilogram of petrol, diesel, kerosene and the like in a vehicle leads to approximately 3.15 kg of [[CO2|CO<sub>2</sub>]] emissions, or 2.3 kg/L (19 lb/gal). 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. 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 [[hypermiler|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]].<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> [[Hybrid vehicle]]s 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 current, 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 which, however, creates its own [[radioactive waste|radioactive waste]] which air flight does not. So only comparing CO2 is misleading. <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 nonpolluting sources such as solar, wind, or [[hydroelectricity]]. One advantage of fuel cell vehicles is that they can electrolyze 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, i.e., cradle-to-grave. 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]] *[[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]] *[[Post carbon]] ==References== <references /> ==External links== *[http://www.fuel-economy.co.uk/indepth1.shtml In-depth advice to help increase fuel efficiency] *[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] [[Category:Energy economics]] [[Category:Physical quantity]] [[Category:Energy conservation]] [[ja:燃費]] [[ru:Часовой расход топлива самолётов]]