Mechanical heat engines convertheat into work via various thermodynamic processes. Theinternal combustion engine is perhaps the most common example of a mechanical heat engine in which heat from thecombustion of afuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive apiston, which turns acrankshaft. Unlike internal combustion engines, areaction engine (such as ajet engine) producesthrust by expellingreaction mass, in accordance withNewton's third law of motion.
Chemical heat engines which employ air (ambient atmospheric gas) as a part of the fuel reaction are regarded as airbreathing engines. Chemical heat engines designed to operate outside of Earth's atmosphere (e.g.rockets, deeply submergedsubmarines) need to carry an additional fuel component called theoxidizer (although there existsuper-oxidizers suitable for use in rockets, such asfluorine, a more powerful oxidant than oxygen itself); or the application needs to obtain heat by non-chemical means, such as by means ofnuclear reactions.
All chemically fueled heat engines emit exhaust gases. The cleanest engines emit water only. Strictzero-emissions generally means zero emissions other than water and water vapour. Only heat engines which combust pure hydrogen (fuel) and pure oxygen (oxidizer) achieve zero-emission by a strict definition (in practice, one type of rocket engine). If hydrogen is burnt in combination with air (all airbreathing engines), a side reaction occurs between atmospheric oxygen and atmosphericnitrogen resulting in small emissions ofNOx. If ahydrocarbon (such asalcohol or gasoline) is burnt as fuel,CO2, agreenhouse gas, is emitted. Hydrogen and oxygen from air can be reacted into water by afuel cell without side production ofNOx, but this is anelectrochemical engine not a heat engine.
The wordengine derives fromOld Frenchengin, from theLatiningenium–the root of the wordingenious. Pre-industrial weapons of war, such ascatapults,trebuchets andbattering rams, were calledsiege engines, and knowledge of how to construct them was often treated as a military secret. The wordgin, as incotton gin, is short forengine. Most mechanical devices invented during theIndustrial Revolution were described as engines—the steam engine being a notable example. However, the original steam engines, such as those byThomas Savery, were not mechanical engines but pumps. In this manner, afire engine in its original form was merely a water pump, with the engine being transported to the fire by horses.[3]
In modern usage, the termengine typically describes devices, like steam engines and internal combustion engines, that burn or otherwise consume fuel to performmechanical work by exerting atorque or linearforce (usually in the form ofthrust). Devices converting heat energy into motion are commonly referred to simply asengines.[4] Examples of engines which exert a torque include the familiar automobile gasoline and diesel engines, as well asturboshafts. Examples of engines which produce thrust includeturbofans androckets.
When the internal combustion engine was invented, the termmotor was initially used to distinguish it from the steam engine—which was in wide use at the time, powering locomotives and other vehicles such assteam rollers. The termmotor derives from the Latin verbmoto which means 'to set in motion', or 'maintain motion'. Thus a motor is a device that imparts motion.
Motor andengine are interchangeable in standard English.[5] In some engineering jargons, the two words have different meanings, in whichengine is a device thatburns or otherwise consumes fuel, changing its chemical composition, and a motor is a device driven byelectricity,air, orhydraulic pressure, which does not change the chemical composition of its energy source.[6][7] However,rocketry uses the termrocket motor, even though they consume fuel.
A heat engine may also serve as aprime mover—a component that transforms the flow or changes in pressure of afluid intomechanical energy.[8] Anautomobile powered by an internal combustion engine may make use of various motors and pumps, but ultimately all such devices derive their power from the engine. Another way of looking at it is that a motor receives power from an external source, and then converts it into mechanical energy, while an engine creates power from pressure (derived directly from the explosive force of combustion or otherchemical reaction, or secondarily from the action of some such force on other substances such as air, water, or steam).[9][better source needed]
According toStrabo, a water-powered mill was built in Kaberia of thekingdom of Mithridates during the 1st century BC. Use ofwater wheels in mills spread throughout theRoman Empire over the next few centuries. Some were quite complex, withaqueducts,dams, andsluices to maintain and channel the water, along with systems ofgears, or toothed-wheels made of wood and metal to regulate the speed of rotation. More sophisticated small devices, such as theAntikythera Mechanism used complex trains of gears and dials to act as calendars or predict astronomical events. In a poem byAusonius in the 4th century AD, he mentions a stone-cutting saw powered by water.Hero of Alexandria is credited with many suchwind andsteam powered machines in the 1st century AD, including theAeolipile and thevending machine, often these machines were associated with worship, such as animated altars and automated temple doors.
Medieval Muslim engineers employedgears in mills and water-raising machines, and useddams as a source of water power to provide additional power to watermills and water-raising machines.[10] In themedieval Islamic world, such advances made it possible tomechanize many industrial tasks previously carried out bymanual labour.
In the 13th century, the solidrocket motor was invented in China. Driven by gunpowder, this simplest form of internal combustion engine was unable to deliver sustained power, but was useful for propelling weaponry at high speeds towards enemies in battle and forfireworks. After invention, this innovation spread throughout Europe.
TheWatt steam engine was the first type of steam engine to make use of steam at a pressure just aboveatmospheric to drive the piston helped by a partial vacuum. Improving on the design of the 1712Newcomen steam engine, the Watt steam engine, developed sporadically from 1763 to 1775, was a great step in the development of the steam engine. Offering a dramatic increase infuel efficiency,James Watt's design became synonymous with steam engines, due in no small part to his business partner,Matthew Boulton. It enabled rapid development of efficient semi-automated factories on a previously unimaginable scale in places where waterpower was not available. Later development led tosteam locomotives and great expansion ofrailway transportation.
In 1877, theOtto cycle was capable of giving a far higherpower-to-weight ratio than steam engines and worked much better for many transportation applications such as cars and aircraft.
The first commercially successful automobile, created byKarl Benz, added to the interest in light and powerful engines. The lightweight gasoline internal combustion engine, operating on a four-stroke Otto cycle, has been the most successful for light automobiles, while the thermally more-efficientDiesel engine is used for trucks and buses. However, in recent years,turbocharged Diesel engines have become increasingly popular in automobiles, especially outside of the United States, even for quite small cars.
In 1896, Karl Benz was granted a patent for his design of the first engine with horizontally opposed pistons. His design created an engine in which the corresponding pistons move in horizontal cylinders and reach top dead center simultaneously, thus automatically balancing each other with respect to their individual momentum. Engines of this design are often referred to as “flat” or “boxer” engines due to their shape and low profile. They were used in theVolkswagen Beetle, theCitroën 2CV, some Porsche and Subaru cars, manyBMW andHondamotorcycles. Opposed four- and six-cylinder engines continue to be used asa power source in small,propeller-drivenaircraft.
The continued use of internal combustion engines in automobiles is partly due to the improvement of engine control systems, such as on-board computers providing engine management processes, and electronically controlled fuel injection. Forced air induction by turbocharging and supercharging have increased the power output of smaller displacement engines that are lighter in weight and more fuel-efficient at normal cruise power. Similar changes have been applied to smaller Diesel engines, giving them almost the same performance characteristics as gasoline engines. This is especially evident with the popularity of smaller diesel engine-propelled cars in Europe. Diesel engines produce lowerhydrocarbon and CO2 emissions, but greaterparticulate andNOx pollution, than gasoline engines.[16] Diesel engines are also 40% more fuel efficient than comparable gasoline engines.[16]
In the first half of the 20th century, a trend of increasing engine power occurred, particularly in the U.S. models.[clarification needed] Design changes incorporated all known methods of increasing engine capacity, including increasing the pressure in the cylinders to improve efficiency, increasing the size of the engine, and increasing the rate at which the engine produces work. The higher forces and pressures created by these changes created engine vibration and size problems that led to stiffer, more compact engines with V and opposed cylinder layouts replacing longer straight-line arrangements.
Earlier automobile engine development produced a much larger range of engines than is in common use today. Engines have ranged from 1- to 16-cylinder designs with corresponding differences in overall size, weight,engine displacement, and cylinderbores. Four cylinders and power ratings from 19 to 120 hp (14 to 90 kW) were followed in a majority of the models. Several three-cylinder, two-stroke-cycle models were built while most engines had straight or in-line cylinders. There were several V-type models and horizontally opposed two- and four-cylinder makes too. Overheadcamshafts were frequently employed. The smaller engines were commonly air-cooled and located at the rear of the vehicle; compression ratios were relatively low. The 1970s and 1980s saw an increased interest in improvedfuel economy, which caused a return to smaller V-6 and four-cylinder layouts, with as many as five valves per cylinder to improve efficiency. TheBugatti Veyron 16.4 operates with aW16 engine, meaning that twoV8 cylinder layouts are positioned next to each other to create the W shape sharing the same crankshaft.
The largest internal combustion engine ever built is theWärtsilä-Sulzer RTA96-C, a 14-cylinder, 2-stroke turbocharged diesel engine that was designed to power theEmma Mærsk, the largest container ship in the world when launched in 2006. This engine has a mass of 2,300 tonnes, and when running at 102 rpm (1.7 Hz) produces over 80 MW, and can use up to 250 tonnes of fuel per day.
An engine can be put into a category according to two criteria: the form of energy it accepts in order to create motion, and the type of motion it outputs.
Theinternal combustion engine is an engine in which thecombustion of a fuel (generally,fossil fuel) occurs with an oxidizer (usually air) in acombustion chamber. In an internal combustion engine the expansion of the hightemperature and highpressure gases, which are produced by the combustion, directly appliesforce to components of the engine, such as thepistons orturbine blades or anozzle, and by moving it over a distance, generates mechanicalwork.[18][19][20][21]
Anexternal combustion engine (EC engine) is aheat engine where an internal workingfluid is heated by combustion of an external source, through the engine wall or aheat exchanger. Thefluid then, by expanding and acting on themechanism of the engine produces motion and usablework.[22] The fluid is then cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine).
"Combustion" refers toburning fuel with anoxidizer, to supply the heat. Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; but are not then strictly classed as external combustion engines, but as external thermal engines.
The working fluid can be a gas as in aStirling engine, orsteam as in a steam engine or an organic liquid such as n-pentane in anOrganic Rankine cycle. The fluid can be of any composition; gas is by far the most common, although even single-phaseliquid is sometimes used. In the case of the steam engine, the fluid changesphases between liquid and gas.
Air-breathing combustion engines are combustion engines that use theoxygen in atmospheric air tooxidise ('burn') the fuel, rather than carrying anoxidiser, as in arocket. Theoretically, this should result in a betterspecific impulse than for rocket engines.
A continuous stream of air flows through the air-breathing engine. This air is compressed, mixed with fuel, ignited and expelled as theexhaust gas. Inreaction engines, the majority of the combustion energy (heat) exits the engine as exhaust gas, which provides thrust directly.
The operation of engines typically has a negative impact uponair quality and ambientsound levels. There has been a growing emphasis on the pollution producing features of automotive power systems. This has created new interest in alternate power sources and internal-combustion engine refinements. Though a few limited-production battery-powered electric vehicles have appeared, they have not proved competitive owing to costs and operating characteristics.[citation needed] In the 21st century the diesel engine has been increasing in popularity with automobile owners. However, the gasoline engine and the Diesel engine, with their new emission-control devices to improve emission performance, have not yet been significantly challenged.[citation needed] A number of manufacturers have introduced hybrid engines, mainly involving a small gasoline engine coupled with an electric motor and with a large battery bank, these are starting to become a popular option because of their environment awareness.
Some engines convert heat from noncombustive processes into mechanical work, for example a nuclear power plant uses the heat from the nuclear reaction to produce steam and drive a steam engine, or a gas turbine in a rocket engine may be driven by decomposinghydrogen peroxide. Apart from the different energy source, the engine is often engineered much the same as an internal or external combustion engine.
Another group of noncombustive engines includesthermoacoustic heat engines (sometimes called "TA engines") which are thermoacoustic devices that use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices.[24]
Stirling engines can be another form of non-combustive heat engine. They use the Stirling thermodynamic cycle to convert heat into work. An example is the alpha type Stirling engine, whereby gas flows, via arecuperator, between a hot cylinder and a cold cylinder, which are attached to reciprocating pistons 90° out of phase. The gas receives heat at the hot cylinder and expands, driving the piston that turns thecrankshaft. After expanding and flowing through the recuperator, the gas rejects heat at the cold cylinder and the ensuing pressure drop leads to its compression by the other (displacement) piston, which forces it back to the hot cylinder.[25]
Anelectric motor useselectrical energy to producemechanical energy, usually through the interaction ofmagnetic fields andcurrent-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by agenerator ordynamo.Traction motors used on vehicles often perform both tasks. Electric motors can be run as generators and vice versa, although this is not always practical.Electric motors are ubiquitous, being found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances,power tools, anddisk drives. They may be powered by direct current (for example abattery powered portable device or motor vehicle), or byalternating current from a central electrical distribution grid. The smallest motors may be found in electric wristwatches. Medium-size motors of highly standardized dimensions and characteristics provide convenient mechanical power for industrial uses. The very largest electric motors are used for propulsion of large ships, and for such purposes as pipeline compressors, with ratings in the thousands ofkilowatts. Electric motors may be classified by the source of electric power, by their internal construction, and by their application.
Electric motor
The physical principle of production of mechanical force by the interactions of an electric current and a magnetic field was known as early as 1821. Electric motors of increasing efficiency were constructed throughout the 19th century, but commercial exploitation of electric motors on a large scale required efficient electrical generators and electrical distribution networks.
To reduce the electricenergy consumption from motors and their associatedcarbon footprints, various regulatory authorities in many countries have introduced and implemented legislation to encourage the manufacture and use of higher efficiency electric motors. A well-designed motor can convert over 90% of its input energy into useful power for decades.[26] When the efficiency of a motor is raised by even a few percentage points, the savings, inkilowatt hours (and therefore in cost), are enormous. The electricalenergy efficiency of a typical industrialinduction motor can be improved by: 1) reducing the electrical losses in thestator windings (e.g., by increasing the cross-sectional area of theconductor, improving thewinding technique, and using materials with higherelectrical conductivities, such ascopper), 2) reducing the electrical losses in therotor coil or casting (e.g., by using materials with higher electrical conductivities, such as copper), 3) reducing magnetic losses by using better quality magneticsteel, 4) improving theaerodynamics of motors to reduce mechanical windage losses, 5) improvingbearings to reducefriction losses, and 6) minimizing manufacturingtolerances.For further discussion on this subject, seePremium efficiency).
By convention,electric engine refers to a railroadelectric locomotive, rather than an electric motor.
Some motors are powered by potential or kinetic energy, for example somefuniculars,gravity plane andropeway conveyors have used the energy from moving water or rocks, and some clocks have a weight that falls under gravity. Other forms of potential energy include compressed gases (such aspneumatic motors), springs (clockwork motors) andelastic bands.
Apneumatic motor is a machine that converts potential energy in the form ofcompressed air intomechanical work. Pneumatic motors generally convert the compressed air to mechanical work through either linear or rotary motion. Linear motion can come from either a diaphragm or a piston actuator, while rotary motion is supplied by either a vane type air motor or piston air motor. Pneumatic motors have found widespread success in the hand-held tool industry and continual attempts are being made to expand their use to the transportation industry. However, pneumatic motors must overcome efficiency deficiencies before being seen as a viable option in the transportation industry.
Some motor units can have multiple sources of energy. For example, aplug-in hybrid electric vehicle's electric motor could source electricity from either a battery or fromfossil fuels inputs via an internal combustion engine and a generator.
Speed refers to crankshaft rotation in piston engines and the speed of compressor/turbine rotors and electric motor rotors. It is typically measured inrevolutions per minute (rpm).
Thrust is the force exerted on an airplane as a consequence of its propeller or jet engine accelerating the air passing through it. It is also the force exerted on a ship as a consequence of its propeller accelerating the water passing through it.
Vehicle noise is predominantly from the engine at low vehicle speeds and from tires and the air flowing past the vehicle at higher speeds.[28] Electric motors are quieter than internal combustion engines. Thrust-producing engines, such as turbofans, turbojets and rockets emit the greatest amount of noise due to the way their thrust-producing, high-velocity exhaust streams interact with the surrounding stationary air.Noise reduction technology includes intake and exhaust systemmufflers (silencers) on gasoline and diesel engines and noise attenuation liners in turbofan inlets.
^"Motor". Dictionary.reference.com.Archived from the original on 2008-04-07. Retrieved2011-05-09.a person or thing that imparts motion, esp. a contrivance, as a steam engine, that receives and modifies energy from some source in order to use it in driving machinery.
^"La documentazione essenziale per l'attribuzione della scoperta". Archived fromthe original on 25 February 2017. Retrieved24 February 2014.A later request was presented to the Patent Office of the Reign of Piedmont, under No. 700 of Volume VII of that Office. The text of this patent request is not available, only a photo of the table containing a drawing of the engine. This may have been either a new patent or an extension of a patent granted three days earlier, on 30 December 1857, at Turin.
