A spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine. A spark plug has a metal threaded shell, electrically isolated from a central electrode by a porcelain insulator; the central electrode, which may contain a resistor, is connected by a insulated wire to the output terminal of an ignition coil or magneto. The spark plug's metal shell is screwed into the engine's cylinder head and thus electrically grounded; the central electrode protrudes through the porcelain insulator into the combustion chamber, forming one or more spark gaps between the inner end of the central electrode and one or more protuberances or structures attached to the inner end of the threaded shell and designated the side, earth, or ground electrode. Spark plugs may be used for other purposes. Spark plugs may be used in other applications such as furnaces wherein a combustible fuel/air mixture must be ignited.
In this case, they are sometimes referred to as flame igniters. In 1860 Étienne Lenoir used an electric spark plug in his gas engine, the first internal combustion piston engine. Lenoir is credited with the invention of the spark plug; some sources credit Edmond Berger, an African American believed to have immigrated from Togo, with creating a spark plug in early 1839, though records show he did not receive a patent for his device. Early patents for spark plugs included those by Nikola Tesla, Frederick Richard Simms and Robert Bosch. Only the invention of the first commercially viable high-voltage spark plug as part of a magneto-based ignition system by Robert Bosch's engineer Gottlob Honold in 1902 made possible the development of the spark-ignition engine. Subsequent manufacturing improvements can be credited to Albert Champion, to the Lodge brothers, sons of Sir Oliver Lodge, who developed and manufactured their father's idea and to Kenelm Lee Guinness, of the Guinness brewing family, who developed the KLG brand.
Helen Blair Bartlett played a vital role in making the insulator in 1930. The plug is connected to the high voltage generated by magneto; as current flows from the coil, a voltage develops between the central and side electrodes. No current can flow because the fuel and air in the gap is an insulator, but as the voltage rises further it begins to change the structure of the gases between the electrodes. Once the voltage exceeds the dielectric strength of the gases, the gases become ionized; the ionized gas allows current to flow across the gap. Spark plugs require voltage of 12,000–25,000 volts or more to "fire" properly, although it can go up to 45,000 volts, they supply higher current during the discharge process, resulting in a hotter and longer-duration spark. As the current of electrons surges across the gap, it raises the temperature of the spark channel to 60,000 K; the intense heat in the spark channel causes the ionized gas to expand quickly, like a small explosion. This is the "click" heard when observing a spark, similar to thunder.
The heat and pressure force the gases to react with each other, at the end of the spark event there should be a small ball of fire in the spark gap as the gases burn on their own. The size of this fireball, or kernel, depends on the exact composition of the mixture between the electrodes and the level of combustion chamber turbulence at the time of the spark. A small kernel will make the engine run as though the ignition timing was retarded, a large one as though the timing was advanced. A spark plug is composed of a shell and the central conductor, it passes through the wall of the combustion chamber and therefore must seal the combustion chamber against high pressures and temperatures without deteriorating over long periods of time and extended use. Spark plugs are specified by size, either thread or nut, sealing type, spark gap. Common thread sizes in Europe are 10 mm, 14 mm, 18 mm. In the United States, common thread sizes are 12 mm, 14 mm and 18 mm; the top of the spark plug contains a terminal to connect to the ignition system.
Over of the years variations in the terminal configuration have been introduced by manufacturers. The exact terminal construction varies depending on the use of the spark plug. Most passenger car spark plug wires snap onto the terminal of the plug, but some wires have eyelet connectors which are fastened onto the plug under a nut; the standard solid non-removable nut SAE configuration is common for many trucks. Plugs which are used for these applications have the end of the terminal serve a double purpose as the nut on a thin threaded shaft so that they can be used for either type of connection; this type of spark plug has a removable nut or knurl, which enables its users to attach them to two different kinds of spark plug boots. Some spark plugs have a bare thread, a common type for motorcycles and ATVs. In recent years, a cup-style terminal has been introduced, which allows for a longer ceramic insulator in the same confined space; the main part of t
Multifuel, sometimes spelled multi-fuel, is any type of engine, boiler, or heater or other fuel-burning device, designed to burn multiple types of fuels in its operation. One common application of multifuel technology is in military settings, where the normally-used diesel or gas turbine fuel might not be available during combat operations for vehicles or heating units. Multifuel engines and boilers have a long history, but the growing need to establish fuel sources other than petroleum for transportation and other uses has led to increased development of multifuel technology for non-military use as well, leading to many flexible-fuel vehicle designs in recent decades. A multifuel engine is constructed so that its compression ratio permits firing the lowest octane fuel of the various accepted alternative fuels. A strengthening of the engine is necessary. Multifuel engines sometimes have switch settings that are set manually to take different octanes, or types, of fuel. One common use of this technology is in military vehicles, so that they may run a wide range of alternative fuels such as gasoline or jet fuel.
This is seen as desirable in a military setting as enemy action or unit isolation may limit the available fuel supply, conversely enemy fuel sources, or civilian sources, may become available for usage. One large use of a military multi-fuel engine was the LD series used in the US M35 2 1⁄2-ton and M54 5-ton trucks built between 1963 and 1970. A military standard design using M. A. N. Technology, it was able to use different fuels without preparation, its primary fuel was Diesel #1, #2, or AP, but 70% to 90% of other fuels could be mixed with diesel, depending on how smooth the engine would run. Low octane commercial and aviation gasoline could be used if motor oil was added, jet fuel Jet A, B, JP-4, 5, 7, 8 could be used, in an emergency fuel oil #1 and #2 could be used. In practice, they only used diesel fuel, their tactical advantage was never needed, in time they were replaced with commercial diesel engines. A wide range of Russian military vehicles employ multifuel engines, such as the T-72 tank and the T-80.
Many other types of engines and other heat-generating machinery are designed to burn more than one type of fuel. For instance, some heaters and boilers designed for home use can burn wood and other fuel sources; these offer fuel flexibility and security, but are more expensive than are standard single fuel engines. Portable stoves are sometimes designed with multifuel functionality, in order to burn whatever fuel is found during an outing; the movement to establish alternatives to automobiles running on gasoline has increased the number of automobiles available which use multifuel engines, such vehicles being termed a bi-fuel vehicle or flexible-fuel vehicle. Multifuel engines are not underpowered, but in practice some engines have had issues with power due to design compromises necessary to burn multiple types of fuel in the same engine; the most notorious example from a military perspective is the L60 engine used by the British Chieftain Main Battle Tank, which resulted in a sluggish performance -- in fact, the Mark I Chieftain was so underpowered that some were incapable of mounting a tank transporter.
An serious issue was that changing from one fuel to another required hours of preparation. The US LD series had a power output comparible to commercial diesels of the time, it was underpowered for the 5-ton trucks, but, the engine size itself, the replacement diesel was much larger and more powerful. The LD engines did burn diesel fuel poorly and were smokey, the final LDT-465 model had a turbocharger to clean up the exhaust, there was little power increase. Flexible-fuel vehicle Crismon, Fred W.. Modern U. S. Military Vehicles. MBI Publishing. ISBN 978-0-7603-0526-3. Doyle, David. Standard catalog of U. S. Military Vehicles. Krause Publications. ISBN 978-0-87349-508-0. Dunstan, Simon. Chieftain Main Battle Tank 1965-2003. Osprey Publishing, 2003. ISBN 1-84176-719-0 Jacobson, Cliff. Expedition Canoeing: A Guide To Canoeing Wild Rivers In North America. Globe Pequot, 2005. ISBN 0-7627-3809-X Pahl, Greg. Natural Home Heating: The Complete Guide to Renewable Energy. Chelsea Green Publishing, 2003. ISBN 1-931498-22-9 Taylor, Charles Fayette.
The Internal-combustion Engine in Theory and Practice. MIT Press, 1985. ISBN 0-262-70027-1 "TM 9-2320-209-10-1 Operation and Reference Data Operator's Level 2 1⁄2-ton, 6x6, M44A1 and M44A2 Series". US Dept. of the Army. 1980. Retrieved 27 Aug 2016
A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. This broad definition includes airbreathing jet engines. In general, jet engines are combustion engines. Common parlance applies the term jet engine only to various airbreathing jet engines; these feature a rotating air compressor powered by a turbine, with the leftover power providing thrust via a propelling nozzle – this process is known as the Brayton thermodynamic cycle. Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines which were inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines, they give higher speed and greater fuel efficiency than piston and propeller aeroengines over long distances. A few air-breathing engines made for high speed applications use the ram effect of the vehicle's speed instead of a mechanical compressor; the thrust of a typical jetliner engine went from 5,000 lbf in the 1950s to 115,000 lbf in the 1990s, their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000 in the late 1990s.
This, combined with decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where before a similar journey would have required multiple fuel stops. Jet engines date back to the invention of the aeolipile before the first century AD; this device directed steam power through two nozzles to cause a sphere to spin on its axis. It was seen as a curiosity. Jet propulsion only gained practical applications with the invention of the gunpowder-powered rocket by the Chinese in the 13th century as a type of firework, progressed to propel formidable weaponry. Jet propulsion technology stalled for hundreds of years; the earliest attempts at airbreathing jet engines were hybrid designs in which an external power source first compressed air, mixed with fuel and burned for jet thrust. The Caproni Campini N.1, the Japanese Tsu-11 engine intended to power Ohka kamikaze planes towards the end of World War II were unsuccessful. Before the start of World War II, engineers were beginning to realize that engines driving propellers were approaching limits due to issues related to propeller efficiency, which declined as blade tips approached the speed of sound.
If aircraft performance were to increase beyond such a barrier, a different propulsion mechanism was necessary. This was the motivation behind the development of the gas turbine engine, the commonest form of jet engine; the key to a practical jet engine was the gas turbine, extracting power from the engine itself to drive the compressor. The gas turbine was not a new idea: the patent for a stationary turbine was granted to John Barber in England in 1791; the first gas turbine to run self-sustaining was built in 1903 by Norwegian engineer Ægidius Elling. Such engines did not reach manufacture due to issues of safety, reliability and sustained operation; the first patent for using a gas turbine to power an aircraft was filed in 1921 by Frenchman Maxime Guillaume. His engine was an axial-flow turbojet, but was never constructed, as it would have required considerable advances over the state of the art in compressors. Alan Arnold Griffith published An Aerodynamic Theory of Turbine Design in 1926 leading to experimental work at the RAE.
In 1928, RAF College Cranwell cadet Frank Whittle formally submitted his ideas for a turbojet to his superiors. In October 1929 he developed his ideas further. On 16 January 1930 in England, Whittle submitted his first patent; the patent showed a two-stage axial compressor feeding a single-sided centrifugal compressor. Practical axial compressors were made possible by ideas from A. A. Griffith in a seminal paper in 1926. Whittle would concentrate on the simpler centrifugal compressor only. Whittle was unable to interest the government in his invention, development continued at a slow pace. In 1935 Hans von Ohain started work on a similar design in Germany, both compressor and turbine being radial, on opposite sides of same disc unaware of Whittle's work. Von Ohain's first device was experimental and could run only under external power, but he was able to demonstrate the basic concept. Ohain was introduced to Ernst Heinkel, one of the larger aircraft industrialists of the day, who saw the promise of the design.
Heinkel had purchased the Hirth engine company, Ohain and his master machinist Max Hahn were set up there as a new division of the Hirth company. They had their first HeS 1 centrifugal engine running by September 1937. Unlike Whittle's design, Ohain used hydrogen as fuel, supplied under external pressure, their subsequent designs culminated in the gasoline-fuelled HeS 3 of 5 kN, fitted to Heinkel's simple and compact He 178 airframe and flown by Erich Warsitz in the early morning of August 27, 1939, from Rostock-Marienehe aerodrome, an impressively short time for development. The He 178 was the world's first jet plane. Heinkel applied for a US patent covering the Aircraft Power Plant by Hans Joachim Pabst von Ohain in May 31, 1939. Austrian Anselm Franz of Junkers' engine division introduced the axial-flow compressor in their jet engine. Jumo was assigned the next engine number in the RLM 109-0xx numbering sequence for gas turbine aircraft powerplants, "004", the result was t
The Diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel, injected into the combustion chamber, is caused by the elevated temperature of the air in the cylinder due to the mechanical compression. Diesel engines work by compressing only the air; this increases the air temperature inside the cylinder to such a high degree that atomised Diesel fuel injected into the combustion chamber ignites spontaneously. With the fuel being injected into the air just before combustion, the dispersion of the fuel is uneven; the process of mixing air and fuel happens entirely during combustion, the oxygen diffuses into the flame, which means that the Diesel engine operates with a diffusion flame. The torque a Diesel engine produces is controlled by manipulating the air ratio; the Diesel engine has the highest thermal efficiency of any practical internal or external combustion engine due to its high expansion ratio and inherent lean burn which enables heat dissipation by the excess air.
A small efficiency loss is avoided compared with two-stroke non-direct-injection gasoline engines since unburned fuel is not present at valve overlap and therefore no fuel goes directly from the intake/injection to the exhaust. Low-speed Diesel engines can reach effective efficiencies of up to 55%. Diesel engines may be designed as either four-stroke cycles, they were used as a more efficient replacement for stationary steam engines. Since the 1910s they have been used in ships. Use in locomotives, heavy equipment and electricity generation plants followed later. In the 1930s, they began to be used in a few automobiles. Since the 1970s, the use of Diesel engines in larger on-road and off-road vehicles in the US has increased. According to Konrad Reif, the EU average for Diesel cars accounts for 50% of the total newly registered; the world's largest Diesel engines put in service are 14-cylinder, two-stroke watercraft Diesel engines. In 1878, Rudolf Diesel, a student at the "Polytechnikum" in Munich, attended the lectures of Carl von Linde.
Linde explained that steam engines are capable of converting just 6-10 % of the heat energy into work, but that the Carnot cycle allows conversion of all the heat energy into work by means of isothermal change in condition. According to Diesel, this ignited the idea of creating a machine that could work on the Carnot cycle. After several years of working on his ideas, Diesel published them in 1893 in the essay Theory and Construction of a Rational Heat Motor. Diesel was criticised for his essay, but only few found the mistake that he made. Diesel's idea was to compress the air so that the temperature of the air would exceed that of combustion. However, such an engine could never perform any usable work. In his 1892 US patent #542846 Diesel describes the compression required for his cycle: "pure atmospheric air is compressed, according to curve 1 2, to such a degree that, before ignition or combustion takes place, the highest pressure of the diagram and the highest temperature are obtained-that is to say, the temperature at which the subsequent combustion has to take place, not the burning or igniting point.
To make this more clear, let it be assumed that the subsequent combustion shall take place at a temperature of 700°. In that case the initial pressure must be sixty-four atmospheres, or for 800° centigrade the pressure must be ninety atmospheres, so on. Into the air thus compressed is gradually introduced from the exterior finely divided fuel, which ignites on introduction, since the air is at a temperature far above the igniting-point of the fuel; the characteristic features of the cycle according to my present invention are therefore, increase of pressure and temperature up to the maximum, not by combustion, but prior to combustion by mechanical compression of air, there upon the subsequent performance of work without increase of pressure and temperature by gradual combustion during a prescribed part of the stroke determined by the cut-oil". By June 1893, Diesel had realised his original cycle would not work and he adopted the constant pressure cycle. Diesel describes the cycle in his 1895 patent application.
Notice that there is no longer a mention of compression temperatures exceeding the temperature of combustion. Now it is stated that the compression must be sufficient to trigger ignition. "1. In an internal-combustion engine, the combination of a cylinder and piston constructed and arranged to compress air to a degree producing a temperature above the igniting-point of the fuel, a supply for compressed air or gas. See US patent # 608845 filed 1895 / granted 1898In 1892, Diesel received patents in Germany, the United Kingdom and the United States for "Method of and Apparatus for Converting Heat into Work". In 1894 and 1895, he filed patents and addenda in various
A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Sir Charles Parsons in 1884; because the turbine generates rotary motion, it is suited to be used to drive an electrical generator—about 85% of all electricity generation in the United States in the year 2014 was by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency from the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible expansion process; the first device that may be classified as a reaction steam turbine was little more than a toy, the classic Aeolipile, described in the 1st century by Hero of Alexandria in Roman Egypt. In 1551, Taqi al-Din in Ottoman Egypt described a steam turbine with the practical application of rotating a spit. Steam turbines were described by the Italian Giovanni Branca and John Wilkins in England.
The devices described by Taqi al-Din and Wilkins are today known as steam jacks. In 1672 an impulse steam turbine driven car was designed by Ferdinand Verbiest. A more modern version of this car was produced some time in the late 18th century by an unknown German mechanic. In 1775 at Soho James Watt designed a reaction turbine, put to work there. In 1827 the Frenchmen Real and Pichon constructed a compound impulse turbine; the modern steam turbine was invented in 1884 by Sir Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kW of electricity. The invention of Parsons' steam turbine made cheap and plentiful electricity possible and revolutionized marine transport and naval warfare. Parsons' design was a reaction type, his patent was the turbine scaled-up shortly after by an American, George Westinghouse. The Parsons turbine turned out to be easy to scale up. Parsons had the satisfaction of seeing his invention adopted for all major world power stations, the size of generators had increased from his first 7.5 kW set up to units of 50,000 kW capacity.
Within Parson's lifetime, the generating capacity of a unit was scaled up by about 10,000 times, the total output from turbo-generators constructed by his firm C. A. Parsons and Company and by their licensees, for land purposes alone, had exceeded thirty million horse-power. A number of other variations of turbines have been developed that work with steam; the de Laval turbine accelerated the steam to full speed before running it against a turbine blade. De Laval's impulse turbine does not need to be pressure-proof, it can operate with any pressure of steam, but is less efficient. Auguste Rateau developed a pressure compounded impulse turbine using the de Laval principle as early as 1896, obtained a US patent in 1903, applied the turbine to a French torpedo boat in 1904, he taught at the École des mines de Saint-Étienne for a decade until 1897, founded a successful company, incorporated into the Alstom firm after his death. One of the founders of the modern theory of steam and gas turbines was Aurel Stodola, a Slovak physicist and engineer and professor at the Swiss Polytechnical Institute in Zurich.
His work Die Dampfturbinen und ihre Aussichten als Wärmekraftmaschinen was published in Berlin in 1903. A further book Dampf und Gas-Turbinen was published in 1922; the Brown-Curtis turbine, an impulse type, developed and patented by the U. S. company International Curtis Marine Turbine Company, was developed in the 1900s in conjunction with John Brown & Company. It was used in John Brown-engined merchant ships and warships, including liners and Royal Navy warships; the present-day manufacturing industry for steam turbines is dominated by Chinese power equipment makers. Harbin Electric, Shanghai Electric, Dongfang Electric, the top three power equipment makers in China, collectively hold a majority stake in the worldwide market share for steam turbines in 2009-10 according to Platts. Other manufacturers with minor market share include Bharat Heavy Electricals Limited, Alstom, General Electric, Doosan Škoda Power, Mitsubishi Heavy Industries, Toshiba; the consulting firm Frost & Sullivan projects that manufacturing of steam turbines will become more consolidated by 2020 as Chinese power manufacturers win increasing business outside of China.
Steam turbines are made in a variety of sizes ranging from small <0.75 kW units used as mechanical drives for pumps and other shaft driven equipment, to 1.5 GW turbines used to generate electricity. There are several classifications for modern steam turbines. Turbine blades are of two basic types and nozzles. Blades move due to the impact of steam on them and their profiles do not converge; this results in a steam velocity drop and no pressure drop as steam moves through the blades. A turbine composed of blades alternating with fixed nozzles is called an impulse turbine, Curtis turbine, Rateau turbine, or Brown-Curtis turbine. Nozzles appear similar to blades; this results in a steam pressure velocity increase as steam moves through the nozzles. Nozzles move due to both the impact of steam on them and the reaction due to the high-velocity steam at the exit. A turbine composed of moving nozzles alternating with fixed nozzles is called a reaction turbine or Parsons turbine. Except for low-power applications, turbine blades are arranged in multiple stages in series, called c
Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the Universe, constituting 75% of all baryonic mass. Non-remnant stars are composed of hydrogen in the plasma state; the most common isotope of hydrogen, termed protium, has no neutrons. The universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, tasteless, non-toxic, nonmetallic combustible diatomic gas with the molecular formula H2. Since hydrogen forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays a important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge when it is known as a hydride, or as a positively charged species denoted by the symbol H+.
The hydrogen cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds are always more complex. As the only neutral atom for which the Schrödinger equation can be solved analytically, study of the energetics and bonding of the hydrogen atom has played a key role in the development of quantum mechanics. Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. In 1766–81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance, that it produces water when burned, the property for which it was named: in Greek, hydrogen means "water-former". Industrial production is from steam reforming natural gas, less from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production for the fertilizer market. Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks.
Hydrogen gas is flammable and will burn in air at a wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol: 2 H2 + O2 → 2 H2O + 572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74% and with chlorine at 5–95%; the explosive reactions may be triggered by heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C. Pure hydrogen-oxygen flames emit ultraviolet light and with high oxygen mix are nearly invisible to the naked eye, as illustrated by the faint plume of the Space Shuttle Main Engine, compared to the visible plume of a Space Shuttle Solid Rocket Booster, which uses an ammonium perchlorate composite; the detection of a burning hydrogen leak may require a flame detector. Hydrogen flames in other conditions are blue; the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a rich mixture of hydrogen to oxygen combined with carbon compounds from the airship skin.
H2 reacts with every oxidizing element. Hydrogen can react spontaneously and violently at room temperature with chlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, which are potentially dangerous acids; the ground state energy level of the electron in a hydrogen atom is −13.6 eV, equivalent to an ultraviolet photon of 91 nm wavelength. The energy levels of hydrogen can be calculated accurately using the Bohr model of the atom, which conceptualizes the electron as "orbiting" the proton in analogy to the Earth's orbit of the Sun. However, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity; because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, therefore only certain allowed energies. A more accurate description of the hydrogen atom comes from a purely quantum mechanical treatment that uses the Schrödinger equation, Dirac equation or the Feynman path integral formulation to calculate the probability density of the electron around the proton.
The most complicated treatments allow for the small effects of special relativity and vacuum polarization. In the quantum mechanical treatment, the electron in a ground state hydrogen atom has no angular momentum at all—illustrating how the "planetary orbit" differs from electron motion. There exist two different spin isomers of hydrogen diatomic molecules that differ by the relative spin of their nuclei. In the orthohydrogen form, the spins of the two protons are parallel and form a triplet state with a molecular spin quantum number of 1. At standard temperature and pressure, hydrogen gas contains about 25% of the para form and 75% of the ortho form known as the "normal form"; the equilibrium ratio of orthohydrogen to parahydrogen depends on temperature, but because the ortho form is an excited state and has a higher energy
A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels. In most petrol engines, the fuel and air are mixed after compression; the pre-mixing was done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed, the fuel is injected into hot air at the end of the compression stroke, self-ignites; the first practical petrol engine was built in 1876 in Germany by Nikolaus August Otto, although there had been earlier attempts by Étienne Lenoir, Siegfried Marcus, Julius Hock and George Brayton. With both air and fuel in a closed cylinder, compressing the mixture too much poses the danger of auto-ignition — or behaving like a diesel engine.
Because of the difference in burn rates between the two different fuels, petrol engines are mechanically designed with different timing than diesels, so to auto-ignite a petrol engine causes the expansion of gas inside the cylinder to reach its greatest point before the cylinder has reached the "top dead center" position. Spark plugs are set statically or at idle at a minimum of 10 degrees or so of crankshaft rotation before the piston reaches T. D. C, but at much higher values at higher engine speeds to allow time for the fuel-air charge to complete combustion before too much expansion has occurred - gas expansion occurring with the piston moving down in the power stroke. Higher octane petrol burns slower, therefore it has a lower propensity to auto-ignite and its rate of expansion is lower. Thus, engines designed to run high-octane fuel can achieve higher compression ratios. Most modern automobile petrol engines have a compression ratio of 10.0:1 to 13.5:1. Engines with a knock sensor can and have C.
R higher than 11.1:1 and approaches 14.0:1 and engines without a knock sensor have C. R of 8.0:1 to 10.5:1. Petrol engines run at higher rotation speeds than diesels due to their lighter pistons, connecting rods and crankshaft and due to petrol burning more than diesel; because pistons in petrol engines tend to have much shorter strokes than pistons in diesel engines it takes less time for a piston in a petrol engine to complete its stroke than a piston in a diesel engine. However, the lower compression ratios of petrol engines give petrol engines lower efficiency than diesel engines. Most petrol engines have 20% thermal efficiency, nearly half of diesel engines; however some newer engines are reported to be much more efficient than previous spark-ignition engines. Petrol engines have many applications, including: Automobiles Motorcycles Aircraft Motorboats Small engines, such as lawn mowers and portable engine-generators Before the use of diesel engines became widespread, petrol engines were used in buses, lorries and a few railway locomotives.
Examples: Bedford OB bus Bedford M series lorry GE 57-ton gas-electric boxcab locomotive Petrol engines may run on the four-stroke cycle or the two-stroke cycle. For details of working cycles see: Four-stroke cycle Two-stroke cycle Wankel engine Common cylinder arrangements are from 1 to 6 cylinders in-line or from 2 to 16 cylinders in V-formation. Flat engines – like a V design flattened out – are common in small airplanes and motorcycles and were a hallmark of Volkswagen automobiles into the 1990s. Flat 6s are still used in many modern Porsches, as well as Subarus. Many flat engines are air-cooled. Less common, but notable in vehicles designed for high speeds is the W formation, similar to having 2 V engines side by side. Alternatives include rotary and radial engines the latter have 7 or 9 cylinders in a single ring, or 10 or 14 cylinders in two rings. Petrol engines may be air-cooled, with fins; the coolant was water, but is now a mixture of water and either ethylene glycol or propylene glycol.
These mixtures have lower freezing points and higher boiling points than pure water and prevent corrosion, with modern antifreezes containing lubricants and other additives to protect water pump seals and bearings. The cooling system is slightly pressurized to further raise the boiling point of the coolant. Petrol engines use spark ignition and high voltage current for the spark may be provided by a magneto or an ignition coil. In modern car engines the ignition timing is managed by an electronic Engine Control Unit; the most common way of engine rating is what is known as the brake power, measured at the flywheel, given in kilowatts or horsepower. This is the actual mechanical power output of the engine in a complete form; the term "brake" comes from the use of a brake in a dynamometer test to load the engine. For accuracy, it is important to understand what is meant by complete. For example, for a car engine, apart from friction and thermodynamic losses inside the engine, power is absorbed by the water pump and radiator fan, thus reducing the power available at the flywheel to move the car along.
Power is abso