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82-438: The three-stream adaptive cycle design can direct air to the bypass third stream for increased fuel efficiency and cooling or to the core and fan streams for additional thrust and performance. The engine thrust has not been disclosed, although it is speculated by aviation reporters to be in the 35,000–40,000 lbf (156–178 kN) thrust class. The U.S. Air Force and U.S. Navy began pursuing adaptive cycle engines in 2007 with

164-403: A helicopter . The fuel economy of an automobile relates to the distance traveled by a vehicle and the amount of fuel consumed . Consumption can be expressed in terms of the volume of fuel to travel a distance, or the distance traveled per unit volume of fuel consumed. Since fuel consumption of vehicles is a significant factor in air pollution, and since the importation of motor fuel can be

246-617: A car and the production, transmission and storage of electricity and hydrogen, the label "zero pollution" applies only to the car's conversion of stored energy into movement. In 2004, a consortium of major auto-makers — BMW , General Motors , Honda , Toyota and Volkswagen / Audi — came up with "Top Tier Detergent Gasoline Standard" to gasoline brands in the US and Canada that meet their minimum standards for detergent content and do not contain metallic additives. Top Tier gasoline contains higher levels of detergent additives in order to prevent

328-399: A change in buying habits with a propensity to heavier vehicles that are less fuel-efficient. Energy efficiency is similar to fuel efficiency but the input is usually in units of energy such as megajoules (MJ), kilowatt-hours (kW·h), kilocalories (kcal) or British thermal units (BTU). The inverse of "energy efficiency" is " energy intensity ", or the amount of input energy required for

410-459: A constant speed. In AC electrical generation maintaining an extremely constant turbine speed is necessary to maintain the correct frequency. The Stirling engine has the highest theoretical efficiency of any thermal engine but it has a low output power to weight ratio, therefore Stirling engines of practical output tend to be large. The size effect of the Stirling engine is due to its reliance on

492-486: A diesel engine. See Brake-specific fuel consumption for more information. The energy efficiency in transport is the useful travelled distance , of passengers, goods or any type of load; divided by the total energy put into the transport propulsion means. The energy input might be rendered in several different types depending on the type of propulsion, and normally such energy is presented in liquid fuels , electrical energy or food energy . The energy efficiency

574-469: 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: 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

656-513: A high pressure compressor derived from CFM LEAP's ten-stage compressor; the tests in 2015 yielded the highest combined compressor and turbine temperatures in the history of jet propulsion. The follow-on Adaptive Engine Transition Program (AETP) was launched in 2016 to develop and test adaptive engines for sixth generation fighter propulsion as well as potential re-engining of the F-35 from the existing F135 turbofan engine. The demonstrators were assigned

738-467: A large part of a nation's foreign trade , many countries impose requirements for fuel economy. Different methods are used to approximate the actual performance of the vehicle. The energy in fuel is required to overcome various losses ( wind resistance , tire drag , and others) encountered while propelling the vehicle, and in providing power to vehicle systems such as ignition or air conditioning. Various strategies can be employed to reduce losses at each of

820-501: A much slower rate and more efficiently than even a candle on Earth, and last much longer. Engine efficiency Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel , and the amount of energy used to perform useful work. There are two classifications of thermal engines- Each of these engines has thermal efficiency characteristics that are unique to it. Engine efficiency, transmission design, and tire design all contribute to

902-426: A multi-cylinder engine from some of the cylinders (by deactivating them) to the remaining cylinders so that they may operate under higher individual loads and with correspondingly higher effective compression ratios. This technique is known as variable displacement . Most petrol (gasoline, Otto cycle ) and diesel ( Diesel cycle ) engines have an expansion ratio equal to the compression ratio . Some engines, which use

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984-502: A number of countries still using other systems, fuel economy is expressed in miles per gallon (mpg), for example in the US 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. Traditionally, litres per mil were used in Norway and Sweden , but both have aligned to

1066-572: A prechamber to make possible the high RPM operation required in automobiles/cars and light trucks. The thermal and gas dynamic losses from the prechamber result in direct injection diesels (despite their lower compression / expansion ratio) being more efficient. An engine has many moving parts that produce friction . Some of these friction forces remain constant (as long as the applied load is constant); some of these friction losses increase as engine speed increases, such as piston side forces and connecting bearing forces (due to increased inertia forces from

1148-494: A process that converts chemical potential energy contained in a carrier ( fuel ) into kinetic 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 a continuous energy profile . Non-transportation applications, such as industry , benefit from increased fuel efficiency, especially fossil fuel power plants or industries dealing with combustion , such as ammonia production during

1230-403: A series of hydrogen fueling stations has been established. 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

1312-433: A short prototype series of them for real-world evaluation. Driving comfort was good, but overall economy lacked due to reasons mentioned above. This is also why gas turbines can be used for permanent and peak power electric plants. In this application they are only run at or close to full power, where they are efficient, or shut down when not needed. Gas turbines do have an advantage in power density – gas turbines are used as

1394-459: 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. The larger batteries in these vehicles power the car's electronics , allowing the engine to shut off and avoid prolonged idling . Fleet efficiency describes the average efficiency of a population of vehicles. Technological advances in efficiency may be offset by

1476-497: A traction storage battery. The hybrid drivetrain can achieve effective efficiencies of close to 40%. Engines using the Diesel cycle are usually more efficient, although the Diesel cycle itself is less efficient at equal compression ratios. Since diesel engines use much higher compression ratios (the heat of compression is used to ignite the slow-burning diesel fuel ), that higher ratio more than compensates for air pumping losses within

1558-466: A typical gasoline (petrol) is 10:1 ( premium fuel ) or 9:1 (regular fuel), with some engines reaching a ratio of 12:1 or more. The greater the expansion ratio, the more efficient the engine, in principle, and higher compression / expansion -ratio conventional engines in principle need gasoline with higher octane value, though this simplistic analysis is complicated by the difference between actual and geometric compression ratios. High octane value inhibits

1640-472: A unit of output such as MJ/passenger-km (of passenger transport), BTU/ton-mile or kJ/t-km (of freight transport), GJ/t (for production of steel and other materials), 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 travelled. For example: Fuel economy in automobiles . Given

1722-420: A vehicle's fuel efficiency . The efficiency of an engine is defined as ratio of the useful work done to the heat provided. where, Q 1 {\displaystyle Q_{1}} is the heat absorbed and Q 1 − Q 2 {\displaystyle Q_{1}-Q_{2}} is the work done. Please note that the term work done relates to the power delivered at

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1804-517: Is a popular topic in the field of artificial intelligence (AI) and machine learning (ML). The main factors representing and influencing driving behavior include velocity, acceleration, gear, road parameters, weather, etc. Simple things such as keeping tires properly inflated, having a vehicle well-maintained and avoiding idling can dramatically improve fuel efficiency. Careful use of acceleration and deceleration and especially limiting use of high speeds helps efficiency. The use of multiple such techniques

1886-401: Is also occasionally known as energy intensity . The inverse of the energy efficiency in transport is the energy consumption in transport. Energy efficiency in transport is often described in terms of fuel consumption , fuel consumption being the reciprocal of fuel economy. Nonetheless, fuel consumption is linked with a means of propulsion which uses liquid fuels , whilst energy efficiency

1968-548: Is applicable to any sort of propulsion. To avoid said confusion, and to be able to compare the energy efficiency in any type of vehicle, experts tend to measure the energy in the International System of Units , i.e., joules . Therefore, in the International System of Units, the energy efficiency in transport is measured in terms of metre per joule, or m/J, while the energy consumption in transport

2050-485: Is called " hypermiling ". 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. Railway trains can be powered using electricity, delivered through an additional running rail, overhead catenary system or by on-board generators used in diesel-electric locomotives as common on

2132-400: Is dependent on many parameters of a vehicle, including its engine parameters, aerodynamic drag , weight, AC usage, fuel and rolling resistance . There have been advances in all areas of vehicle design in recent decades. Fuel efficiency of vehicles can also be improved by careful maintenance and driving habits. Hybrid vehicles use two or more power sources for propulsion. In many designs,

2214-444: Is drawn into an engine because the downward motion of the pistons induces a partial vacuum. A compressor can additionally be used to force a larger charge (forced induction) into the cylinder to produce more power. The compressor is either mechanically driven supercharging or exhaust driven turbocharging . Either way, forced induction increases the air pressure exterior to the cylinder inlet port. There are other methods to increase

2296-443: Is measured in terms of joules per metre, or J/m. The more efficient the vehicle, the more metres it covers with one joule (more efficiency), or the fewer joules it uses to travel over one metre (less consumption). The energy efficiency in transport largely varies by means of transport. Different types of transport range from some hundred kilojoules per kilometre (kJ/km) for a bicycle to tens of megajoules per kilometre (MJ/km) for

2378-441: Is minimal at low speed, but increases approximately as the square of the speed, until at rated power an engine is using about 20% of total power production to overcome friction and pumping losses. Air is approximately 21% oxygen . If there is not enough oxygen for proper combustion, the fuel will not burn completely and will produce less energy. An excessively rich fuel to air ratio will increase unburnt hydrocarbon pollutants from

2460-533: Is not formed and complete combustion occurs., National Aeronautics and Space Administration, April 2005. 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. LSP-1 experiment results , National Aeronautics and Space Administration, April 2005. Premixed flames in microgravity burn at

2542-412: Is proportional to the difference between the starting pressure and the ending pressure during the expansion phase. Hence, increasing the starting pressure is an effective way to increase the work extracted (decreasing the ending pressure, as is done with steam turbines by exhausting into a vacuum, is likewise effective). The compression ratio (calculated purely from the geometry of the mechanical parts) of

General Electric XA102 - Misplaced Pages Continue

2624-400: Is the highest conversion of fuel into power by any single-cycle internal or external combustion engine. Engines in large diesel trucks, buses, and newer diesel cars can achieve peak efficiencies around 45%. The gas turbine is most efficient at maximum power output in the same way reciprocating engines are most efficient at maximum load. The difference is that at lower rotational speed

2706-434: 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 2 , per passenger, than planes, helped in part by French nuclear generation. In the future, hydrogen cars may be commercially available. Toyota is test-marketing vehicles powered by hydrogen fuel cells in southern California, where

2788-616: The Adaptive Versatile Engine Technology (ADVENT) program, a part of the larger Versatile Affordable Advanced Turbine Engines (VAATE) program. This technology research program was then followed by the Adaptive Engine Technology Demonstrator (AETD) program in 2012, which continued to mature the technology, with tests performed using demonstrator engines. GE's ground demonstrator consists of a three-stage adaptive fan and

2870-534: The Atkinson cycle or the Miller cycle achieve increased efficiency by having an expansion ratio larger than the compression ratio. Diesel engines have a compression/expansion ratio between 14:1 and 25:1. In this case the general rule of higher efficiency from higher compression does not apply because diesels with compression ratios over 20:1 are indirect injection diesels (as opposed to direct injection). These use

2952-531: The Haber process . In the context of transport , fuel economy is the energy efficiency of a particular vehicle, given as a ratio of distance traveled per unit of fuel consumed. It is dependent on several factors including engine efficiency , transmission design, and tire design. In most countries, using the metric system , fuel economy is stated as "fuel consumption" in liters per 100 kilometers (L/100 km) or kilometers per liter (km/L or kmpl). In

3034-458: The Newcomen engine , the most significant of which was the external condenser, which prevented the cooling water from cooling the cylinder. Watt's engine operated with steam at slightly above atmospheric pressure. Watt's improvements increased efficiency by a factor of over 2.5. The lack of general mechanical ability, including skilled mechanics, machine tools , and manufacturing methods, limited

3116-470: The Rankine cycle which has a maximum Carnot efficiency of 63% for practical engines, with steam turbine power plants able to achieve efficiency in the mid 40% range. The efficiency of steam engines is primarily related to the steam temperature and pressure and the number of stages or expansions . Steam engine efficiency improved as the operating principles were discovered, which led to the development of

3198-486: The critical point have efficiencies in the low 40% range. Turbines produce direct rotary motion and are far more compact and weigh far less than reciprocating engines and can be controlled to within a very constant speed. As is the case with the gas turbine, the steam turbine works most efficiently at full power, and poorly at slower speeds. For this reason, despite their high power to weight ratio, steam turbines have been primarily used in applications where they can be run at

3280-399: 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) 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

3362-419: The oxygen content of the air to combine with the fuel, which is a mixture of several hydrocarbons , resulting in water vapor , carbon dioxide , and sometimes carbon monoxide and partially burned hydrocarbons. In addition, at high temperatures the oxygen tends to combine with nitrogen , forming oxides of nitrogen (usually referred to as NOx , since the number of oxygen atoms in the compound can vary, thus

General Electric XA102 - Misplaced Pages Continue

3444-621: The "X" subscript). This mixture, along with the unused nitrogen and other trace atmospheric elements , is what is found in the exhaust . The most efficient cycle is the Atkinson Cycle, but most gasoline engine makers use the Otto Cycle for higher power and torque. Some engine design, such as Mazda's Skyactiv-G and some hybrid engines designed by Toyota utilize the Atkinson and Otto cycles together with an electric motor/generator and

3526-457: The EU standard of L/100 km. Fuel consumption is a more accurate measure of a vehicle's performance because it is a linear relationship while 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) for passenger vehicles. Fuel efficiency

3608-523: The FT units that they were just putting into service in significant numbers. They determined that the cost of a ton of oil fuel used in steam engines was $ 5.04 and yielded 20.37 train miles system wide on average. Diesel fuel cost $ 11.61 but produced 133.13 train miles per ton. In effect, diesels ran six times as far as steamers utilizing fuel that cost only twice as much. This was due to the much better thermal efficiency of diesel engines compared to steam. Presumably

3690-686: The Next Generation Adaptive Propulsion (NGAP) and the entrants were the General Electric XA102 and Pratt & Whitney XA103 . Critical design review of the XA102 was completed in December 2023, and flight testing is expected to begin in the late 2020s. The XA102 is a three-stream adaptive cycle engine that can adjust the bypass ratio and fan pressure to increase fuel efficiency or thrust, depending on

3772-525: The US and UK rail networks. Pollution produced from centralised generation of electricity is emitted at a distant power station, rather than "on site". Pollution can be reduced by using more railway electrification and low carbon power for electricity. 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

3854-552: The amount of condensation in the cylinder, resulting in increased efficiency. Compound engines gave further improvements in efficiency. By the 1870s triple-expansion engines were being used on ships. Compound engines allowed ships to carry less coal than freight. Compound engines were used on some locomotives but were not widely adopted because of their mechanical complexity. A very well-designed and built steam locomotive used to get around 7-8% efficiency in its heyday. The most efficient reciprocating steam engine design (per stage)

3936-441: The amount of oxygen available inside the engine; one of them, is to inject nitrous oxide , (N 2 O) to the mixture, and some engines use nitromethane , a fuel that provides the oxygen itself it needs to burn. Because of that, the mixture could be 1 part of fuel and 3 parts of air; thus, it is possible to burn more fuel inside the engine, and get higher power outputs. Reciprocating engines at idle have low thermal efficiency because

4018-458: The atmosphere to drive the piston down. Using the cylinder as the vessel in which to condense the steam also cooled the cylinder, so that some of the heat in the incoming steam on the next cycle was lost in warming the cylinder, reducing the thermal efficiency. Improvements made by John Smeaton to the Newcomen engine increased the efficiency to over 1%. James Watt made several improvements to

4100-422: The build-up of deposits (typically, on fuel injector and intake valve ) known to reduce fuel economy and engine performance. 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

4182-417: The clutch or at the driveshaft . This means the friction and other losses are subtracted from the work done by thermodynamic expansion. Thus an engine not delivering any work to the outside environment has zero efficiency. The efficiency of internal combustion engines depends on several factors, the most important of which is the expansion ratio. For any heat engine the work which can be extracted from it

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4264-541: The combustion chamber to cool down the incoming air through evaporative cooling. This can increase the total charge entering the cylinder (as cooler air will be more dense), resulting in more power but also higher levels of hydrocarbon pollutants and lower levels of nitrogen oxide pollutants. With direct injection this effect is not as dramatic but it can cool down the combustion chamber enough to reduce certain pollutants such as nitrogen oxides (NOx), while raising others such as partially decomposed hydrocarbons. The air-fuel mix

4346-495: The conversions between the chemical energy in the fuel and the kinetic energy of the vehicle. Driver behavior can affect fuel economy; maneuvers such as sudden acceleration and heavy braking waste energy. Energy-efficient driving techniques are used by drivers who wish to reduce their fuel consumption, and thus maximize fuel efficiency. Many drivers have the potential to improve their fuel efficiency significantly. The relationship between fuel consumption and driving behavior

4428-414: The cost of higher wear and emissions. In other words, even when the engine is operating at its point of maximum thermal efficiency, of the total heat energy released by the gasoline consumed, about 60-80% of total power is emitted as heat without being turned into useful work, i.e. turning the crankshaft. Approximately half of this rejected heat is carried away by the exhaust gases, and half passes through

4510-413: The cylinder walls or cylinder head into the engine cooling system, and is passed to the atmosphere via the cooling system radiator. Some of the work generated is also lost as friction, noise, air turbulence, and work used to turn engine equipment and appliances such as water and oil pumps and the electrical generator , leaving only about 20-40% of the energy released by the fuel consumed available to move

4592-526: The designation XA100 for General Electric's design and XA101 for Pratt & Whitney's. While the XA100 and XA101 became focused on the potential re-engine of the F-35, a separate engine program was initiated for the Air Force's Next Generation Air Dominance fighter, which is expected to be optimized differently with a greater emphasis on supersonic cruise (or supercruise) performance; this program became

4674-501: The efficiency increase of the Corliss engine. Others before Corliss had at least part of this idea, including Zachariah Allen , who patented variable cut-off, but lack of demand, increased cost and complexity and poorly developed machining technology delayed introduction until Corliss. The Porter-Allen high-speed engine (ca. 1862) operated at from three to five times the speed of other similar-sized engines. The higher speed minimized

4756-430: The efficiency of actual engines and their design until about 1840. Higher-pressured engines were developed by Oliver Evans and Richard Trevithick , working independently. These engines were not very efficient but had high power-to-weight ratio , allowing them to be used for powering locomotives and boats. The centrifugal governor , which had first been used by Watt to maintain a constant speed, worked by throttling

4838-406: The engine also uses new heat-resistant materials such as ceramic matrix composites (CMC) to enable higher turbine temperatures and improved performance. Data from Royal Aeronautics Society Related development Comparable engines Related lists Fuel efficiency Fuel efficiency (or fuel economy ) is a form of thermal efficiency , meaning the ratio of effort to result of

4920-476: The engine. Modern turbo-diesel engines use electronically controlled common-rail fuel injection to increase efficiency. With the help of geometrically variable turbo-charging system (albeit more maintenance) this also increases the engines' torque at low engine speeds (1,200–1,800 rpm). Low speed diesel engines like the MAN S80ME-C7 have achieved an overall energy conversion efficiency of 54.4%, which

5002-416: The engine. If all of the oxygen is consumed because there is too much fuel, the engine's power is reduced. As combustion temperature tends to increase with leaner fuel air mixtures, unburnt hydrocarbon pollutants must be balanced against higher levels of pollutants such as nitrogen oxides ( NOx ), which are created at higher combustion temperatures. This is sometimes mitigated by introducing fuel upstream of

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5084-538: The engines in heavy armored vehicles and armored tanks and in power generators in jet fighters. One other factor negatively affecting the gas turbine efficiency is the ambient air temperature. With increasing temperature, intake air becomes less dense and therefore the gas turbine experiences power loss proportional to the increase in ambient air temperature. Latest generation gas turbine engines have achieved an efficiency of 46% in simple cycle and 61% when used in combined cycle . Steam engines and turbines operate on

5166-417: The expansion of a gas with an increase in temperature and practical limits on the working temperature of engine components. For an ideal gas, increasing its absolute temperature for a given volume, only increases its pressure proportionally, therefore, where the low pressure of the Stirling engine is atmospheric, its practical pressure difference is constrained by temperature limits and is typically not more than

5248-539: The fuel's tendency to burn nearly instantaneously (known as detonation or knock ) at high compression/high heat conditions. However, in engines that utilize compression rather than spark ignition, by means of very high compression ratios (14–25:1), such as the diesel engine or Bourke engine , high octane fuel is not necessary. In fact, lower-octane fuels, typically rated by cetane number , are preferable in these applications because they are more easily ignited under compression. Under part throttle conditions (i.e. when

5330-402: The inlet and exhaust steam so the hot feed steam never contacted the cooler exhaust ports and valving. The valves were quick acting, which reduced the amount of throttling of the steam and resulted in faster response. Instead of operating a throttling valve, the governor was used to adjust the valve timing to give a variable steam cut-off. The variable cut-off was responsible for a major portion of

5412-471: The inlet steam, which lowered the pressure, resulting in a loss of efficiency on the high (above atmospheric) pressure engines. Later control methods reduced or eliminated this pressure loss. The improved valving mechanism of the Corliss steam engine (Patented. 1849) was better able to adjust speed with varying load and increased efficiency by about 30%. The Corliss engine had separate valves and headers for

5494-400: The mechanical pumping efficiency is not known. The first piston steam engine, developed by Thomas Newcomen around 1710, was slightly over one half percent (0.5%) efficient. It operated with steam at near atmospheric pressure drawn into the cylinder by the load, then condensed by a spray of cold water into the steam filled cylinder, causing a partial vacuum in the cylinder and the pressure of

5576-488: 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

5658-422: The only usable work being drawn off the engine is from the generator. At low speeds, gasoline engines suffer efficiency losses at small throttle openings from the high turbulence and frictional (head) loss when the incoming air must fight its way around the nearly closed throttle (pump loss); diesel engines do not suffer this loss because the incoming air is not throttled, but suffer "compression loss" due to use of

5740-417: The oscillating piston). A few friction forces decrease at higher speed, such as the friction force on the cam 's lobes used to operate the inlet and outlet valves (the valves' inertia at high speed tends to pull the cam follower away from the cam lobe). Along with friction forces, an operating engine has pumping losses , which is the work required to move air into and out of the cylinders. This pumping loss

5822-444: The pressure of the compressed air drops and thus thermal and fuel efficiency drop dramatically. Efficiency declines steadily with reduced power output and is very poor in the low power range. General Motors at one time manufactured a bus powered by a gas turbine, but due to rise of crude oil prices in the 1970s this concept was abandoned. Rover , Chrysler , and Toyota also built prototypes of turbine-powered cars. Chrysler built

5904-426: 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

5986-464: The scenario. It does this by employing an adaptive fan that can direct air into a third bypass stream in order to increase fuel economy and act as a heat sink for cooling. The increased cooling and power generation also enables the potential employment of directed energy weapons in the future. When additional thrust is needed, the air from the third stream can be directed to the core and fan streams. In addition to three-stream adaptive cycle configuration,

6068-401: The science of thermodynamics . See graph: Steam Engine Efficiency In earliest steam engines the boiler was considered part of the engine. Today they are considered separate, so it is necessary to know whether stated efficiency is overall, which includes the boiler, or just of the engine. Comparisons of efficiency and power of the early steam engines is difficult for several reasons: 1) there

6150-408: 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 nuclear. Commercial hydrogen production uses fossil fuels and produces more carbon dioxide than hydrogen. Because there are pollutants involved in the manufacture and destruction of

6232-401: The throttle is less than fully open), the effective compression ratio is less than when the engine is operating at full throttle, due to the simple fact that the incoming fuel-air mixture is being restricted and cannot fill the chamber to full atmospheric pressure. The engine efficiency is less than when the engine is operating at full throttle. One solution to this issue is to shift the load in

6314-435: 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

6396-406: The trains used as a milage standard were 4,000 ton freight consists which was the normal tannage l (sic) at that time. The steam turbine is the most efficient steam engine and for this reason is universally used for electrical generation. Steam expansion in a turbine is nearly continuous, which makes a turbine comparable to a very large number of expansion stages. Steam power stations operating at

6478-420: The vehicle. A gasoline engine burns a mix of gasoline and air, consisting of a range of about twelve to eighteen parts (by weight) of air to one part of fuel (by weight). A mixture with a 14.7:1 air/fuel ratio is stoichiometric , that is when burned, 100% of the fuel and the oxygen are consumed. Mixtures with slightly less fuel, called lean burn are more efficient. The combustion is a reaction which uses

6560-512: The whole charge to compress the air to small amount of power output. At high speeds, efficiency in both types of engine is reduced by pumping and mechanical frictional losses, and the shorter period within which combustion has to take place. High speeds also results in more drag. Modern gasoline engines have a maximum thermal efficiency of more than 50%, but most road legal cars only achieve about 20% to 40% efficiency. Many engines would be capable of running at higher thermal efficiency but at

6642-464: Was no standard weight for a bushel of coal, which could be anywhere from 82 to 96 pounds (37 to 44 kg). 2) There was no standard heating value for coal, and probably no way to measure heating value. The coals had much higher heating value than today's steam coals, with 13,500 BTU/pound (31 megajoules/kg) sometimes mentioned. 3) Efficiency was reported as "duty", meaning how many foot pounds (or newton-metres) of work lifting water were produced, but

6724-482: Was the uniflow engine , but by the time it appeared steam was being displaced by diesel engines, which were even more efficient and had the advantages of requiring less labor (for coal handling and oiling), being a more dense fuel, and displaced less cargo. Using statistics collected during the early 1940s, the Santa Fe Railroad measured the efficiency of their fleet of steam locomotives in comparison with

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