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Fuel efficiency, in its basic sense, is the same as Thermal Efficiency , meaning the efficiency of a process that converts energy contained in a carrier Fuel into Energy or Work . Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is often illustrated as an 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 Energy Efficiency Of A ''particular Vehicle Model ,'' where its total output (range, or "mileage" {Link without Title} ) 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 " Litre s per 100 Kilometre " (L/100 km) or " Mile s per Gallon " ( Mpg ). 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 Engines has improved in recent decades, this does not necessarily translate into ''fuel economy'' of Cars , as people in Developed Countries tend to buy bigger and heavier cars (i.e. SUV s will get less range per unit fuel than an Economy Car ). Modern Hybrid Vehicle designs use smaller combustion engines in Synergetic combination with high- Torque electric motors (also increased Aerodynamics and reduced rolling resistance), to produce greater range per unit fuel, and (proportionally) less Fuel Emissions ( CO2 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 . 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:
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''.''Automotive Handbook, 4th Edition'', Robert Bosch GmbH, 1996. ISBN 0-8376-0333-1 These have now been replaced with values from the ''Transportation Energy Data Book'' Appendix B, Transportation Energy Data Book from the Center For Transportation Analysis of the Oak Ridge National Laboratory , but which does not give the MJ/kg or the densities.) 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 See Also: Fuel economy in automobiles Fuel economy is usually expressed in one of two ways:
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 between miles per US gallon (3.785 L) and L/100 km is , where is value of miles per gallon or L/100km. For miles per Imperial gallon (4.546 L) the formula is . 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 may manage Motorway travel at 5 L/100 km (47 mpg US) or 6.5 L/100 km in city traffic (36 mpg US), 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 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. An interesting example of fuel economy is the popular , 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 US Gallon or 94 miles per 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% http://www.volvo.com/group/global/en-gb/Volvo+Group/ourvalues/environmentalcare/products/dieselengines.htm. 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.http://www.fusel.com/diesel_engines.html FUEL EFFICIENCY IN MICROGRAVITY The energy produced from fuels occurs during combustion. However, how well the fuel burns will affect how much energy is produced. Recent research by the National Aeronautics And Space Administration (NASA) has gained possible insights to increasing fuel efficiency if fuel consumption takes place in Microgravity . The common distribution of a flame under normal gravity conditions depends on s in microgravity burn at a much slower rate and more efficiently than even a candle on Earth, and last much longer. SOFBAL-2 experiment results , National Aeronautics and Space Administration, April 2005. TRANSPORTATION Fuel efficiency in transportation See Also: Fuel efficiency in transportation Vehicle efficiency and transportation pollution See Also: Gas-guzzler 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 petrol, diesel, kerosene and the like in a vehicle leads to approximately 3.15 kg of CO2 emissions, or 2.3 kg/L (19 lb/gal). 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 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 .1 Hybrid Vehicle s can conserve petroleum fuel and therefore be more efficient than conventional vehicles. The most efficient propulsion system is electricity, as used in ). This can be changed using more Renewable Sources for Electric Generation . In the future Hydrogen Cars may be commercially available. Powered by chemical reactions in a Fuel Cell , that creates electricity to drive very efficient electrical motors; these vehicles promise to have zero pollution from the tailpipe (exhaust pipe). Potentially the atmospheric pollution could be near zero, provided the hydrogen is made by Electrolysis using electricity from sustainable sources such as solar, wind, or Hydroelectricity , or from Nuclear Power . Controversially, it is thought by scientists that where emissions take place in the Earth's atmosphere has an overall effect on climate change. Atmospheric changes from aircraft result from three types of processes: direct emission of radiatively active substances (e.g., CO2 or water vapor); emission of chemical species that produce or destroy radiatively active substances (e.g., NOx, which modifies O3 concentration); and emission of substances that trigger the generation of aerosol particles or lead to changes in natural clouds (e.g., contrails). What this means is that the total warming effect of aircraft emissions is 2.7 times as great as the effect of that carbon dioxide released by an automobile. Aviation and the Global Atmosphere, IPCC : SEE ALSO
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