Cairo University Faculty of Engineering Mechanical Power Engineering Department Fourth Year Mechanical Assignment # 1 Internal Combustion Engines Name: Wael Kamal Mohamed Mahmoud Sec: 6

Internal Combustion Engines

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Page 1: Internal Combustion Engines

Cairo UniversityFaculty of EngineeringMechanical Power Engineering DepartmentFourth Year Mechanical

Assignment # 1

Internal Combustion Engines

Name: Wael Kamal Mohamed Mahmoud

Sec: 6

Page 2: Internal Combustion Engines



Engine:An engine in the broadest sense is

something that produces an output effect from agiven input. The origin of engineering however,came from the design, building and working of(military "engines") because before such devicescame to be employed in battles there were veryfew mechanical devices used. Military enginesincluded siege engines, large catapults,trebuchets, battering rams etc. So the firstengineers were military engineers, then later asengineering developed, there came Civilengineers. These were engineers who dealt withdesigning, building and commissioning roads,bridges, docks and wharves, large public andprivate buildings etc. There also exists an overlapin English between two meanings of the word "engineer": "those who operateengines" and "those who design and construct new items." An engine whose purposeis to produce kinetic energy output from a fuel source is called a prime mover;alternatively, a motor is a device which produces kinetic energy from a preprocessed"fuel" (such as electricity, a flow of hydraulic fluid or compressed air).Unfortunately some everyday English language confusion exists about thisterminology demarcation that sometimes leads to expensive errors. For example, aservice specialist (an electrical engineer) might be called upon to travel some way toexamine a faulty "motor" - to find on arrival at the site that the so-called "motor", isin fact, a rather large diesel engine that he has no knowledge of, as its operatingprinciples lie outside his area of specialization.An ordinary car has a starter motor, a windscreen wiper motor, windscreen washermotor, a fuel pump motor and motors to adjust the wing mirrors from within the carand a motorized radio antenna - but the power plant that propels the car is an engine.Again an aircraft will have many motors installed for operation of its many auxiliaryoperations and services, but aircraft are propelled by engines, in this case, jetengines.

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Modern: English inventor Sir Samuel Morland allegedly used gunpowder todrive water pumps in the 17th century. For more conventional, reciprocating internalcombustion engines the fundamental theory for two-stroke engines was establishedby Sadi Carnot, France, 1824, whilst the American Samuel Morey received a patenton April 1, 1826. (Dugald Clark) Sir Dugald Clark (1854 – 1932) designed the firsttwo-stroke engine in 1878 and patented it in England in 1881. Automotiveproduction has used a range of energy-conversion systems. These include electric,steam, solar, turbine, rotary, and piston-type internal combustion engines. The petrolinternal combustion engine, operating on a four-stroke Otto cycle, has been the mostsuccessful for automobiles, while diesel engines are used for trucks and buses. KarlBenz was one of the leaders in the development of new engines. In 1878 he began towork on new designs. He concentrated his efforts on creating a reliable gas two-stroke engine that was more powerful, based on Nikolaus Otto's design of the four-stroke engine. Karl Benz showed his real genius, however, through his successiveinventions registered while designing what would become the production standardfor his two-stroke engine. Benz finished his engine on New Year's Eve and wasgranted a patent for it in 1879. In 1896, Karl Benz was granted a patent for hisdesign of the first engine with horizontally-opposed pistons. Many BMWmotorcycles use this engine type. His design created an engine in which thecorresponding pistons move in horizontal cylinders and reach top dead centresimultaneously, thus automatically balancing each other with respect to theirindividual momentums. Engines of this design are often referred to as flat enginesbecause of their shape and lower profile. They must have an even number ofcylinders and six, four or two cylinder flat engines have all been common. The mostwell-known engine of this type is probably the Volkswagen beetle engine. Enginesof this type continue to be a common design principle for high performance aeroengines (for propeller driven aircraft) and, engines used by automobile producerssuch as Porsche and Subaru.Continuance of the use of the internal combustion engine for automobiles is partlydue to the improvement of engine control systems (onboard computers providingengine management processes, and electronically controlled fuel injection). Forcedair induction by turbo charging and supercharging have increased power outputs andefficiencies available. Similar changes have been applied to smaller diesel enginesgiving them almost the same power characteristics as petrol engines. This isespecially evident with the popularity of smaller diesel engine propelled cars inEurope. Larger diesel engines are still often used in trucks and heavy machinery.They don't burn as clean as gasoline engines; however they have far more torque.The internal combustion engine was originally selected for the automobile due to itsflexibility over a wide range of speeds. Also, the power developed for a givenweight engine was reasonable; it could be produced by economical mass-productionmethods; and it used a readily available, moderately priced fuel - petrol.

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In today’s world, there has been a growing emphasis on the pollution producingfeatures of automotive power systems. This has created new interest in alternatepower sources and internal-combustion engine refinements that were noteconomically feasible in prior years. Although a few limited-production battery-powered electric vehicles have appeared, they have not proved to be competitiveowing to costs and operating characteristics. In the twenty-first century the dieselengine has been increasing in popularity with automobile owners. However, thegasoline engine, with its new emission-control devices to improve emissionperformance, has not yet been challenged significantly.The first half of the twentieth century saw a trend to increase engine power,particularly in the American models. Design changes incorporated all knownmethods of raising engine capacity, including increasing the pressure in the cylindersto improve efficiency, increasing the size of the engine, and increasing the speed atwhich power is generated. The higher forces and pressures created by these changescreated engine vibration and size problems that led to stiffer, more compact engineswith V and opposed cylinder layouts replacing longer straight-line arrangements. Inpassenger cars, V-8 layouts were adopted for all piston displacements greater than250 cubic inches (4 litres).The design principles favored in Europe, because of economic and other restraints,leant toward smaller cars and corresponding design principles that concentrated onincreasing the combustion efficiency of smaller engines. This produced moreeconomical engines with earlier four-cylinder designs rated at 40 horsepower (30kW) and six-cylinder designs rated as low as 80 horsepower (60 kW), comparedwith the large volume V-8 American engines with power ratings in the range from250 to 350 hp (190 to 260 kW).Earlier automobile engine development produced a much larger range of enginesthan is in common use today. Engines have ranged from 1 to 12 cylinder designswith corresponding differences in overall size, weight, piston displacement, andcylinder bores. 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-cyclemodels were built while most engines had straight or in-line cylinders. There wereseveral V-type models and horizontally opposed two- and four-cylinder makes too.Overhead camshafts were frequently employed. The smaller engines werecommonly air-cooled and located at the rear of the vehicle; compression ratios wererelatively low. The 1970s and '80s saw an increased interest in improved fueleconomy which brought in a return to smaller V-6 and four-cylinder layouts, with asmany as five valves per cylinder to improve efficiency. The largest internalcombustion engine ever built is the Wärtsilä-Sulzer RTA96-C - a 14 cylinder, 2stroke, turbocharged diesel engine that was designed to power the Emma Maersk,the largest container ship in the world. This engine weighs 2300 tones, and whenrunning at 102 r/min produces 109000bhp (80080 kW) consuming some 13.7 tonesof fuel each hour.

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Internal Combustion Engine:The internal combustion engine is an engine in which the combustion of fuel and anoxidizer (typically air) occurs in a confined space called a combustion chamber. Thisexothermic reaction creates gases at high temperature and pressure, which arepermitted to expand. The defining feature of an internal combustion engine is thatuseful work is performed by the expanding hot gases acting directly to causemovement of solid parts of the engine, by acting on pistons, rotors, or even bypressing on and moving the entire engine itself.This contrasts with external combustion engines, such as steam engines and Stirlingengines, which use an external combustion chamber to heat a separate working fluid,which then in turn does work, for example by moving a piston or a turbine.The term Internal Combustion Engine (ICE) is almost always used to referspecifically to reciprocating piston engines, Wankel engines and similar designs inwhich combustion is intermittent. However, continuous combustion engines, such asjet engines, most rockets and many gas turbines are also internal combustionengines.Early internal-combustion engines were used to power farm equipment similar tothese models.The first internal combustion engines did not have compression, but ran on air/fuelmixture sucked or blown in during the first part of the intake stroke. The mostsignificant distinction between modern internal combustion engines and the earlydesigns is the use of compression and in particular of in-cylinder compression.1206: Al-Jazari demonstrates an early rotary to reciprocating motion, which is awaterwheel-powered pump1509: Leonardo da Vinci described a compression-less engine.1673: Christiaan Huygens described a compression-less engine.17th century: English inventor Sir Samuel Morland used gunpowder to drive waterpumps, essentially creating the first rudimentary internal combustion engine.1780's: Alessandro Volta built a toy electric pistol in which an electric sparkexploded a mixture of air and hydrogen, firing a cork from the end of the gun.1794: Robert Street built a compression-less engine whose principle of operationwould dominate for nearly a century.1806: Swiss engineer François Isaac de Rivaz built an internal combustion enginepowered by a mixture of hydrogen and oxygen.1823: Samuel Brown patented the first internal combustion engine to be appliedindustrially. It was compression-less and based on what Harden berg calls the"Leonardo cycle," which, as this name implies, was already out of date at that time.1824: French physicist Sadi Carnot established the thermodynamic theory ofidealized heat engines. This scientifically established the need for compression toincrease the difference between the upper and lower working temperatures.1826 April 1: The American Samuel Morey received a patent for a compression-less"Gas or Vapor Engine".

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1838: a patent was granted to William Barnet (English). This was the first recordedsuggestion of in-cylinder compression.1854: The Italians Eugenio Barsanti and Felice Matteucci patented the first workingefficient internal combustion engine in London (pt. Num. 1072) but did not go intoproduction with it. It was similar in concept to the successful Otto Langen indirectengine, but not so well worked out in detail.1856: in Florence at Fonderia del Pignone (now Nuovo Pignone, a subsidiary ofGeneral Electric) Pietro Benini realized a working prototype of the Barsanti-Matteucci engine, supplying 5 HP. In subsequent years he developed more powerfulengines - with one or two pistons - which served as steady power sources, replacingsteam engines.1860: Belgian Jean Joseph Etienne Lenoir (1822 - 1900) produced a gas-firedinternal combustion engine closely similar in appearance to a horizontal double-acting steam beam engine, with cylinders, pistons, connecting rods, and flywheel inwhich the gas essentially took the place of the steam. This was the first internalcombustion engine to be produced in numbers.1862: German inventor Nikolaus Otto designed an indirect-acting free-pistoncompression-less engine whose greater efficiency won the support of Langen andthen most of the market, which at that time, was mostly for small stationary enginesfueled by lighting gas.1870: In Vienna Siegfried Marcus put the first mobile gasoline engine on a handcart.1876: Nikolaus Otto working with Gottlieb Daimler and Wilhelm Maybachdeveloped a practical four-stroke cycle (Otto cycle) engine. The German courts,however, did not hold his patent to cover all in-cylinder compression engines oreven the four stroke cycle, and after this decision in-cylinder compression becameuniversal.

Karl Benz1879: Karl Benz, working independently, was granted apatent for his internal combustion engine, a reliable two-stroke gas engine, based on Nikolaus Otto's design of thefour-stroke engine. Later Benz designed and built his ownfour-stroke engine that was used in his automobiles, whichbecame the first automobiles in production.1882: James Atkinson invented the Atkinson cycle engine.Atkinson’s engine had one power phase per revolutiontogether with different intake and expansion volumesmaking it more efficient than the Otto cycle.1891 - Herbert Akroyd Stuart built his oil engine, leasingrights to Hornsby of England to build them. They build the first cold start,compression ignition engines. In 1892, they installed the first ones in a waterpumping station. An experimental higher-pressure version produced self-sustainingignition through compression alone in the same year.

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1892: Rudolf Diesel developed his Carnot heat engine type motor burning powderedcoal dust.1893 February 23: Rudolf Diesel received a patent for the diesel engine.1896: Karl Benz invented the boxer engine, also known as the horizontally opposedengine, in which the corresponding pistons reach top dead centre at the same time,thus balancing each other in momentum.1900: Rudolf Diesel demonstrated the diesel engine in the 1900 ExpositionUniversally using peanut oil.1900: Wilhelm Maybach designed an engine built at Daimler MotorenGesellschaft—following the specifications of Emil Jellinek—who required theengine to be named Daimler-Mercedes after his daughter. In 1902 automobiles withthat engine were put into production by DMG.ApplicationsInternal combustion engines are most commonly used for mobile propulsion inautomobiles, equipment, and other portable machinery. In mobile equipment internalcombustion is advantageous, since it can provide high power to weight ratiostogether with excellent fuel energy-density. These engines have appeared intransport in almost all automobiles, trucks, motorcycles, boats, and in a wide varietyof aircraft and locomotives, generally using petroleum (called All-Petroleum InternalCombustion Engine Vehicles or APICEVs). Where very high power is required,such as jet aircraft, helicopters and large ships, they appear mostly in the form ofturbines.


All internal combustion engines depend on the exothermic chemical process ofcombustion: the reaction of a fuel, typically with the oxygen from the air, althoughother oxidizers such as nitrous oxide may be employed. Also see stoichiometry.

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The most common modern fuels are made up of hydrocarbons and are derived frommostly petroleum. These include the fuels known as diesel fuel, gasoline andpetroleum gas, and the rarer use of propane gas. Most internal combustion enginesdesigned for gasoline can run on natural gas or liquefied petroleum gases withoutmajor modifications except for the fuel delivery components. Liquid and gaseousbiofuels, such as Ethanol and biodiesel, a form of diesel fuel that is produced fromcrops that yield triglycerides such as soy bean oil, can also be used. Some can alsorun on Hydrogen gas.All internal combustion engines must achieve ignition in their cylinders to createcombustion. Typically engines use either a spark ignition (SI) method or acompression ignition (CI) system. In the past other methods using hot tubes orflames have been used.

Petroleum internal combustion engines:o Gasoline Ignition Process:

Electrical/Gasoline-type ignition systemsgenerally rely on a combination of a lead-acid battery and an induction coil toprovide a high voltage electrical spark to ignite the air-fuel mix in the engine'scylinders. This battery can be recharged during operation using an electricity-generating device, such as an alternator or generator driven by the engine. Gasolineengines take in a mixture of air and gasoline and compress to less than 185 psi anduse a spark plug to ignite the mixture when it is compressed by the piston head ineach cylinder.

o Diesel Engine Ignition Process: Compression ignition systems, suchas the diesel engine and HCCI engines, rely solely on heat and pressure created bythe engine in its compression process for ignition. Compression that occurs isusually more than three times higher than a gasoline engine. Diesel engines will takein air only, and shortly before peak compression, a small quantity of diesel fuel issprayed into the cylinder via a fuel injector that allows the fuel to instantly ignite.HCCI type engines will take in both air and fuel but will continue to rely on anunaided auto-combustion process due to higher pressures and heat. This is also whydiesel and HCCI engines are also more susceptible to cold starting issues thoughthey will run just as well in cold weather once started. Most diesels also have batteryand charging systems, however this system is secondary and is added bymanufacturers as luxury for ease of starting, turning fuel on and off (which can alsobe done via a switch or mechanical apparatus), and for running auxiliary electricalcomponents and accessories. Most old engines, however, rely on electrical systemsthat also control the combustion process to increase efficiency and reduce emissions.Engine Efficiency:The efficiency of various types of internal combustion engines varies, but it is lowerthan electric motor energy efficiency. Most gasoline fueled internal combustionengines, even when aided with turbochargers and stock efficiency aids, have amechanical efficiency of about 20%. The efficiency may be as high as 37% at the

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optimum operating point in engines where this is a high priority such as that of thePrius. Most internal combustion engines waste about 36% of the energy in gasolineas heat lost to the cooling system and another 38% through the exhaust. The rest,about 6%, is lost to friction.Hydrogen Fuel Injection, or HFI, is an engine adds on system that improves the fueleconomy of internal combustion engines by injecting hydrogen as a combustionenhancement into the intake manifold. Fuel economy gains of 15% to 50% can beseen [citation needed]. A small amount of hydrogen added to the intake air-fuelcharge increases the octane rating of the combined fuel charge and enhances theflame velocity, thus permitting the engine to operate with more advanced ignitiontiming, a higher compression ratio, and a leaner air-to-fuel mixture than otherwisepossible. The result is lower pollution with more power and increased efficiency.Some HFI systems use an on board electrolyzer to generate the small amount ofhydrogen needed in the system, around 5% of total Btu. A small tank of pressurizedhydrogen can also be used, but this method necessitates refilling. Hydrogen in liquidform is seldom used because it is difficult to store.There has also been discussion of new types of internal combustion engines, such asthe Scuderi Split Cycle Engine, that utilize high compression pressures in excess of2000 psi and combust after top-dead-center (the highest & most compressed point inan internal combustion piston stroke). The claimed efficiency of this engine, bycalculation, is 42%.Parts: For a four-stroke engine, key parts of the engineinclude the crankshaft (purple), one or more camshafts (redand blue) and valves. For a two-stroke engine, there maysimply be an exhaust outlet and fuel inlet instead of a valvesystem. In both types of engines, there are one or morecylinders (grey and green) and for each cylinder there is aspark plug (darker-grey), a piston (yellow) and a crank(purple). A single sweep of the cylinder by the piston in anupward or downward motion is known as a stroke. Thedownward stroke that occurs directly after the air/fuel mixpasses from the carburetor to the cylinder where it isignited is known as a power stroke.A Wankel engine has a triangular rotor that orbits in an epitrochoidal (figure 8shape) chamber around an eccentric shaft. The four phases of operation (intake,compression, power, and exhaust) take place in separate locations, instead of onesingle location as in a reciprocating engine.A Bourke Engine uses a pair of pistons integrated to a Scotch Yoke that transmitsreciprocating force through a specially designed bearing assembly to turn a crankmechanism. Intake, compression, power, and exhaust occur in each stroke.

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Classification: The fundamental difference between an engine and a motor is that a

motor converts electricity into mechanical energy whereas an engine convertsthermal energy into mechanical energy. At one time, the word "engine" (from Latin,via Old French, ingenium, "ability") meant any piece of machinery — a sense thepersists in expressions such as siege engine. A "motor" (from Latin motor, "mover")is any machine that produces mechanical power. Traditionally, electric motors arenot referred to as "engines," but combustion engines are often referred to as"motors." (An electric engine refers to locomotive operated by electricity).However, many people consider engines as those things which generate their powerfrom within, and motors as requiring an outside source of energy to perform theirwork.Principles of operation:

Two-stroke cycle: Engines based on the two-stroke cycle use two strokes (one

up, one down) for every power stroke. Since there are no dedicated intake or exhauststrokes, alternative methods must be used to scavenge the cylinders. The mostcommon method in spark-ignition two-strokes is to use the downward motion of thepiston to pressurize fresh charge in the crankcase, which is then blown through thecylinder through ports in the cylinder walls.Spark-ignition two-strokes are small and light (for their power output), andmechanically very simple; they are also generally less efficient and more pollutingthan their four-stroke counterparts. However in single cylinder small motorapplications cc for cc, a two-stroke engine produces much more power thanequivalent 4 strokes due to the enormous advantage of having 1 power stroke forevery 360 degrees of crankshaft rotation (compared to 720 degrees in a 4 strokemotor).Small displacement, crankcase scavenged two-stroke engines have been less fuel-efficient than other types of engines when the fuel is mixed with the air prior toscavenging allowing some of it to escape out of the exhaust port. Modern designs(Sarich and Paggio) use air assisted fuel injection, which avoid this loss and aremore efficient than comparably sized four stroke engines. Fuel injection is essentialfor a modern two-stroke engine in order to meet ever stringent emission standards.Research continues into improving many aspects of two-stroke motors, includingdirect fuel injection amongst other things. Initial results have produced motors thatare much cleaner burning than their traditional counterparts.Two-stroke engines are widely used in snowmobiles, lawnmowers, weed-whackers,chain saws, jet skis, mopeds, outboard motors and many motorcycles.The largest compression-ignition engines are two-strokes, and are used in somelocomotives and large ships. These engines use forced induction to scavenge thecylinders. An example of this type of motor is the Wartsila-Sulzer turbocharged 2stroke diesel as used in large container ships. It is the most efficient and powerfulengine in the world, with over 50% thermal efficiency for comparison the most

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efficient small 4 stroke motors are around 43.0% thermal efficiency (SAE 900648),and size is an advantage for efficiency due to the increase in the ratio of volume toarea.

Four-stroke: Engines based on the four-stroke cycle or Otto cycle have one

power stroke for every four strokes (up-down-up-down) and are used in cars, largerboats and many light aircraft. They are generally quieter, more efficient and largerthan their two-stroke counterparts. There are a number of variations of these cycles,most notably the Atkinson and Miller cycles. Most truck and automotive dieselengines use a four-stroke cycle, but with a compression heating ignition system. Thisvariation is called the diesel cycle. The steps involved here are: 1. Suction stroke - Air and vaporized fuel are drawn in. 2. Compression stroke - Fuel vapor and air are compressed and ignited. 3. Power stroke - Fuel combusts and piston is pushed downwards. 4. Exhaust stroke - Exhaust is driven out.

Five-stroke: Engines based on the five-stroke cycle are a variant of the four

stroke cycle. Normally the four cycles are intake, compression, combustion andexhaust. The fifth cycle added by Delautour is refrigeration. Engines running on afive-stroke cycle are up to 30 percent more efficient than an equivalent four strokeengine.

Six-stroke: The six stroke engine captures the wasted heat from the 4 stroke

Otto cycle and creates steam which simultaneously cools the engine while providinga free power stroke. This removes the need for a cooling system making the enginelighter plus giving 40% increased efficiency over the Otto Cycle.

Beare Head Technology combines a four stroke engine bottom end with a portedcylinder which closely resembles that of a two stroke, thus 4+2= Six Stroke. It hasan opposing piston which acts in unison with auxiliary low pressure reed and rotaryvalves, allowing variable compression and a range of tuning options.

Bourke engine: In this engine, two diametrically opposed cylinders are linked

to the crank by the crank pin that floats on a "triple slipper bearing" (a type ofhydrodynamic tilting-pad fluid bearing) that goes through the common scotch yoke.Unlike the common two stroke engine, the burnt gases and the incoming fresh air donot mix in the cylinders, contributing to a cleaner, more efficient operation. Thescotch yoke mechanism also prevents side thrust, preventing any piston slap,allowing operation as a detonation or "explosion" engine. This also greatly reducesfriction between pistons and cylinder walls. The Bourke engine's combustion phasemore closely approximates constant volume combustion than either four stroke ortwo stroke cycles do. It also uses less moving parts and it has to overcome lessfriction than conventional crank and slider engines, with poppet valves. In addition,

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its greater expansion ratio also means more of the heat from its combustion phase isutilized than conventional spark ignition engines.

Controlled Combustion Engine: These are also cylinder based engines and

may be either single- or two-stroke but use, instead of a crankshaft and piston rods,two gear connected, counter rotating concentric cams to convert reciprocatingmotion into rotary movement. These cams practically cancel out sideward forces thatwould otherwise be exerted on the cylinders by the pistons, greatly improvingmechanical efficiency. The number of lobes of the cams (always an odd number notless than 3) determines the piston travel versus the torque delivered. In this engine,there are two cylinders that are 180 degrees apart for each pair of counter-rotatingcams. For single-stroke versions there are as many cycles per cylinder pair as thereare lobes on each cam, and twice as many for two-stroke engines.

Wankel: The Wankel engine (Rotary engine) does not have piston strokes so is

more properly called a four-phase than a four-stroke engine. It operates with thesame separation of phases as the four-stroke engine, with the phases taking place inseparate locations in the engine. This engine provides three power 'strokes' perrevolution per rotor (while it is true that 3 power strokes occur per ROTORrevolution, due to the 3/1 revolution ratio of the rotor to the eccentric shaft, only 1power stroke per shaft revolution actually occur), typically giving it a greater power-to-weight ratio than piston engines. This type of engine is most notably used in thecurrent Mazda RX-8, the earlier RX-7, and other models.

Gas turbine: Gas turbines cycles (notably jet engines), do not use the same

system to both compress and then expand the gases; instead separate compressionand expansion turbines are employed; giving continuous power. Essentially, theintake gas (normally air) is compressed, and then combusted with a fuel, whichgreatly raises the temperature and volume. The larger volume of hot gas from thecombustion chamber is then fed through the gas turbine which is then able to powerthe compressor. The exhaust gas may be used to provide thrust, supplying onlysufficient power to the turbine to compress incoming air (jet engine); or as muchenergy as possible can be supplied to the shaft (gas turbine proper).

Disused methods:In some old non-compressing internal combustion engines: In the first part of thepiston down stroke a fuel/air mixture was sucked or blown in. In the rest of thepiston down stroke the inlet valve closed and the fuel/air mixture fired. In the pistonupstroke the exhaust valve was open. This was an attempt at imitating the way apiston steam engine works. Since the explosive mixture was not compressed the heatand pressure generated by combustion was much less, causing lower overallefficiency.

Fuels and oxidizers: Nowadays, fuels used include:

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o Petroleum:Petroleum spirit (North American term: gasoline, British term:petrol)Petroleum diesel.Auto gas (liquefied petroleum gas).Compressed natural gas.Jet fuel (aviation fuel)

o Coal:Most methanols are made from coal.Gasoline-like fuels can be made from coal.

o Biofuels and vegoils:Peanut oil and other vegoils.Biofuels:

Biobutanol (replaces gasoline).Biodiesel (replaces petrodiesel).Bioethanol and Biomethanol (wood alcohol) and otherbiofuels (see Flexible-fuel vehicle).Biogas

o HydrogenEven fluidized metal powders and explosives have seen some use. Engines that usegases for fuel are called gas engines and those that use liquid hydrocarbons arecalled oil engines. However, gasoline engines are also often colloquially referred toas 'gas engines'.The main limitations on fuels are that it must be easily transportable through the fuelsystem to the combustion chamber, and that the fuel release sufficient energy in theform of heat upon combustion to make use of the engine practical.Diesel engines are generally heavier, noisier and more powerful at lower speeds thangasoline engines. They are also more fuel-efficient in most circumstances and areused in heavy road vehicles, some automobiles (increasingly so for their increasedfuel efficiency over gasoline engines), ships, railway locomotives, and light aircraft.Gasoline engines are used in most other road vehicles including most cars,motorcycles and mopeds. Note that in Europe, sophisticated diesel-engines cars havetaken over about 40% of the market since the 1990s. There are also engines that runon hydrogen, methanol, ethanol, liquefied petroleum gas (LPG) and biodiesel.Paraffin and tractor vaporizing oil (TVO) engines are no longer seen.Oxidizers:Since air is plentiful at the surface of the earth, the oxidizer is typically atmosphericoxygen, which has the advantage of not being stored within the vehicle, increasingthe power-to-weight and power to volume ratios. There are other materials that areused for special purposes, often to increase power output or to allow operation underwater or in space.

Compressed air has been commonly used in torpedoes.

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Compressed oxygen, as well as some compressed air, was used in the JapaneseType 93 torpedo. Some submarines are designed to carry pure oxygen.Nitro methane is added to some racing and model fuels to increase power andcontrol combustion.Nitrous oxide has been used, with extra gasoline, in tactical aircraft and inspecially equipped cars, to allow short bursts of added power from engines thatotherwise run on gasoline and air. (It is also used in the Burt Rutan rocketspacecraft).Hydrogen peroxide power was under development for German World War IIsubmarines and may have been used in some non-nuclear submarines.Black or smokeless gunpowder has been used in diesel engine starters, to deployor jettison equipment remotely, and by Alphonse Pénaud in pioneering modelaircraft.Other chemicals such as chlorine or fluorine have been used experimentally, buthave not been found to be practical.

Hydrogen engine:Some have theorized that in the future hydrogen might replace such fuels.Furthermore, with the introduction of hydrogen fuel cell technology, the use ofinternal combustion engines may be phased out. The advantage of hydrogen is thatits combustion produces only water. This is unlike the combustion of fossil fuels,which produce carbon dioxide, a known green house gas GHG, carbon monoxideresulting from incomplete combustion, and other local and atmospheric pollutantssuch as sulphur dioxide and nitrogen oxides that lead to urban respiratory problems,acid rain, and ozone gas problems. However, free hydrogen for fuel does not occurnaturally, oxidizing it liberates less energy than it takes to produce hydrogen in thefirst place due to the second law of thermodynamics.Although there are multiple ways of producing free hydrogen, those requireconverting combustible molecules into hydrogen or consuming electric energy, sohydrogen does not solve any energy crisis, moreover, it only addresses the issue ofportability and some pollution issues. The disadvantage of hydrogen in manysituations is its storage. Liquid hydrogen has extremely low density- 14 times lowerthan water and requires extensive insulation, whilst gaseous hydrogen requiresheavy tankage. Although hydrogen has a higher specific energy, the volumetricenergetic storage is still roughly five times lower than petrol, even when liquefied.(The 'Hydrogen on Demand' process, designed by Steven Amendola, createshydrogen as it is needed, but has other issues, such as the high price of the sodiumborohydride, the raw material. Sodium borohydride is renewable and could becomecheaper if more widely produced.)Cylinders:Internal combustion engines can contain any number of cylinders, with numbersbetween one and twelve being common, though as many as 36 (Lycoming R-7755)have been used. Having more cylinders in an engine yields two potential benefits:

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First, the engine can have a larger displacement with smaller individualreciprocating masses (that is, the mass of each piston can be less) thus making asmoother running engine (since the engine tends to vibrate as a result of the pistonsmoving up and down). Second, with a greater displacement and more pistons, morefuel can be combusted and there can be more combustion events (that is, morepower strokes) in a given period of time, meaning that such an engine can generatemore torque than a similar engine with fewer cylinders.The down side to having more pistons is that the engine will tend to weigh more andtend to generate more internal friction as the greater number of pistons rub againstthe inside of their cylinders. This tends to decrease fuel efficiency and rob the engineof some of its power. For high performance gasoline engines using current materialsand technology (such as the engines found in modern automobiles), there seems tobe a break point around 10 or 12 cylinders, after which addition of cylindersbecomes an overall detriment to performance and efficiency, although exceptionssuch as the W16 engine from Volkswagen exist.

Most car engines have four to eight cylinders, with some high performance carshaving ten, twelve, or even sixteen, and some very small cars and trucks havingtwo or three. In previous years some quite large cars, such as the DKW and Saab92, had two cylinders, two stroke engines.Radial aircraft engines, now obsolete, had from three to 28 cylinders. Anexample is the Pratt & Whitney R-4360. A row contains an odd number ofcylinders, so an even number indicates a two- or four-row engine. The largest ofthese was the Lycoming R-7755 with 36 cylinders (four rows of nine cylinders),but it did not enter production.Motorcycles commonly have from one to four cylinders, with a few highperformance models having six (though some 'novelties' exist with 8, 10 and 12).Snowmobiles usually have two cylinders. Some larger (not necessarily high-performance, but also touring machines) have four.Small portable appliances such as chainsaws, generators and domestic lawnmowers most commonly have one cylinder, although two-cylinder chainsawsexist.

Ignition system:An internal combustion engine can be classified by its ignition system.Today most engines use an electrical or compression heating system for ignition.However outside flame and hot-tube systems have been used historically. NikolaTesla gained one of the first patents on the mechanical ignition system with U.S.Patent 609,250 , "Electrical Igniter for Gas Engines", on 16 August 1898.SparkMain article: ignition systemThe mixture is ignited by an electrical spark from a spark plug, the timing of whichis very precisely controlled. Most gasoline engines are of this type, but not dieselengines.

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CompressionIgnition, after the engine is started, comes from oxidation heat and mechanicalcompression of the air or mixture. The vast majority of compression ignition enginesare diesels, in which the fuel is mixed with the air after the air has reached ignitiontemperature. In this case the timing comes from the fuel injection system. Verysmall model engines, for which simplicity is more important than fuel cost, usespecial fuels to control ignition timing.TimingThe point in the cycle at which the fuel/oxidizer mixture is ignited has a direct effecton the efficiency and output of the ICE. The thermodynamics of the idealized Carnotheat engine tells us that an ICE is most efficient if most of the burning takes place ata high temperature, resulting from compression, that is, near top "dead" center. Thespeed of the flame front is directly affected by compression ratio, fuel mixturetemperature and octane or cetane rating of the fuel. Leaner mixtures and lowermixture pressures burn more slowly requiring more advanced ignition timing. It isimportant to have combustion spread by a thermal flame front (deflagration), not bya shock wave. Combustion propagation by a shock wave is called detonation and, inengines, is also known as pinging or knocking.So, at least in gasoline burning engines, ignition timing is largely a compromisebetween an earlier "advanced" spark, which gives greater efficiency with highoctane fuel and a later "retarded" spark which avoids detonation, with the fuel used.For this reason, high-performance diesel automobile proponents such as Gale Banksbelieve thatThere’s only so far you can go with an air-throttled engine on 91-octane gasoline. Inother words, it is the fuel, gasoline that has become the limiting factor. While turbocharging has been applied to both gasoline and diesel engines, only limited boost canbe added to a gasoline engine before the fuel octane level again becomes a problem.With a diesel, boost pressure is essentially unlimited. It is literally possible to run asmuch boost as the engine will physically stand before breaking apart. Consequently,engine designers have come to realize that diesels are capable of substantially morepower and torque than any comparably sized gasoline engine.Fuel systems:Animated cut through diagram of a typical fuelinjector, a device used to deliver fuel to theinternal combustion engine.Fuels burn faster, and more completely whenthey have lots of surface area in contact withoxygen. In order for an engine to workefficiently the fuel must be vaporized into theincoming air in what is commonly referred to asa fuel air mixture. There are two commonly used methods of vaporizing fuel into theair, one is the carburetor and the other is fuel injection.

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Often for simpler reciprocating engines a carburetor is used to supply fuel into thecylinder. However, exact control of the correct amount of fuel supplied to the engineis impossible. Carburetors are the current most widespread fuel mixing device usedin lawnmowers and other small engine applications. Prior to the mid-1980scarburetors were also common in automobiles.Larger gasoline engines such as used in automobiles have mostly move do fuelinjection systems (see Gasoline Direct Injection). Diesel engines always use fuelinjection, because it is the fuel system that controls the ignition timing.Auto gas (LPG) engines use either fuel injection systems or open or closed loopcarburetors.Other internal combustion engines like jet engines use burners, and rocket enginesuse various different ideas including impinging jets, gas/liquid shear, preburners andmany other ideas.Engine configuration:Internal combustion engines can be classified by their configuration which affectstheir physical size and smoothness (with smoother engines producing less vibration).Common configurations include the straight or inline configuration, the morecompact V configuration and the wider but smoother flat or boxer configuration.Aircraft engines can also adopt a radial configuration which allows more effectivecooling. More unusual configurations, such as "H", "U", "X", or "W" have also beenused.Multiple-crankshaft configurations do not necessarily need a cylinder head at all, butcan instead have a piston at each end of the cylinder, called an opposed pistondesign. This design was used in the Junkers Jumo 205 diesel aircraft engine, usingtwo crankshafts, one at either end of a single bank of cylinders, and most remarkablyin the Napier Deltic diesel engines, which used three crankshafts to serve threebanks of double-ended cylinders arranged in an equilateral triangle with thecrankshafts at the corners. It was also used in single-bank locomotive engines, andcontinues to be used for marine engines, both for propulsion and for auxiliarygenerators. The Gnome Rotary engine, used in several early aircraft, had a stationarycrankshaft and a bank of radially arranged cylinders rotating around it.Engine capacity:An engine's capacity is the displacement or swept volume by the pistons of theengine. It is generally measured in litres (L) or cubic inches (c.i.d. or cu in or in³) forlarger engines and cubic centimeters (abbreviated to cc) for smaller engines. Engineswith greater capacities are usually more powerful and provide greater torque atlower rpm but also consume more fuel.Apart from designing an engine with more cylinders, there are two ways to increasean engine's capacity. The first is to lengthen the stroke and the second is to increasethe piston's diameter (See also: Stroke ratio). In either case, it may be necessary tomake further adjustments to the fuel intake of the engine to ensure optimalperformance.

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An engine's quoted capacity can be more a matter of marketing than of engineering.The Morris Minor 1000, the Morris 1100, and the Austin-Healey Sprite Mark IIwere all fitted with a BMC A-Series engine of the same stroke and bore according totheir specifications, and were from the same maker. However the engine capacitieswere quoted as 1000 cc, 1100 cc and 1098 cc respectively in the sales literature andon the vehicle badges.Lubrication Systems:Internal combustions engines require lubrication in operation to allow moving partsto slide smoothly over each other. Insufficient lubrication will cause the engine toseize up.Several different types of lubrication systems are used. Simple two-stroke enginesare lubricated by oil mixed into the fuel or injected into the induction stream as aspray. Early slow speed stationary and marine engines were lubricated by gravityfrom small chambers, similar to those used on steam engines at the time, with anengine tender refilling these as needed. As engines were adapted for automotive andaircraft use, the need for a high power to weight ratio lead to increased speeds,higher temperatures, and greater pressure on bearings, which in turn requiredpressure lubrication for crank bearing and connecting-rod journals, provided eitherby a direct lubrication from a pump, or indirectly by a jet of oil directed at pickupcups on the connecting rod ends, which had the advantage of providing higherpressures as engine speed increased.