|
||||||||||||||||||||||
|
||||||||||||||||||||||
HistoryImage:Colorized car engine.jpg A colorized automobile engine Image:Early-gasoline-engine-models.jpg Early internal-combustion engines were used to power farm equipment similar to these models. The first internal combustion engines did not have compression, but ran on air/fuel mixture sucked or blown in during the first part of the intake stroke. The most significant distinction between modern internal combustion engines and the early designs is the use of compression and in particular of in-cylinder compression.
Image:CarlBenz.jpg Karl Benz
ApplicationsInternal combustion engines are most commonly used for mobile propulsion in automobiles, equipment, and other portable machinery. In mobile equipment internal combustion is advantageous, since it can provide high power to weight ratios together with excellent fuel energy-density. These engines have appeared in transport in almost all automobiles, motorcycles, boats, and in a wide variety of aircraft and locomotives, generally using petroleum . Where very high power is required, such as jet aircraft, helicopters and large ships, they appear mostly in the form of turbines. They are also used for electric generators (i.e. 12 V generators) and by industry. Operation
The most common modern fuels are made up of hydrocarbons and are derived from mostly petroleum. These include the fuels known as dieselfuel, gasoline and petroleum gas, and the rarer use of propane gas. Most internal combustion engines designed for gasoline can run on natural gas or liquefied petroleum gases without major modifications except for the fuel delivery components. Liquid and gaseous biofuels, such as Ethanol and biodiesel, a form of diesel fuel that is produced from crops that yield triglycerides such as soy bean oil, can also be used. Some can also run on Hydrogen gas. All internal combustion engines must achieve ignition in their cylinders to create combustion. Typically engines use either an spark ignition (SI) method or a compression ignition (CI) system. In the past other methods using hot tubes or flames have been used. Gasoline Ignition ProcessElectrical/Gasoline-type ignition systems (that can also run on other fuels as previously mentioned) generally rely on a combination of a lead-acid battery and an induction coil to provide a high voltage electrical spark to ignite the air-fuel mix in the engine's cylinders. This battery can be recharged during operation using an electricity-generating device, such as an alternator or generator driven by the engine. Gasoline engines take in a mixture of air and gasoline and compress to less than 170 psi and use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder. Diesel Engine Ignition ProcessCompression ignition systems, such as the diesel engine and HCCI engines, rely solely on heat and pressure created by the engine in its compression process for ignition. Compression that occurs is usually more than three times higher than a gasoline engine. Diesel engines will take in air only, and shortly before peak compression, a small quantity of diesel fuel is sprayed 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 an unaided auto-combustion process due to higher pressures and heat. This is also why diesel and HCCI engines are also more susceptible to cold starting issues though they will run just as well in cold weather once started. Most diesels also have battery and charging systems however this system is secondary and is added by manufacturers as luxury for ease of starting, turning fuel on and off which can also be done via a switch or mechanical apparatus, and for running auxiliary electrical components and accessories. Most old engines, however, rely on electrical systems that also control the combustion process to increase efficiency and reduce emissions. EnergyOnce ignited and burnt, the combustion products, hot gases, have more available energy than the original compressed fuel/air mixture (which had higher chemical energy). The available energy is manifested as high temperature and pressure which can be translated into work by the engine. In a reciprocating engine, the high pressure product gases inside the cylinders drive the engine's pistons. Once the available energy has been removed, the remaining hot gases are vented (often by opening a valve or exposing the exhaust outlet) and this allows the piston to return to its previous position (Top Dead Center - TDC). The piston can then proceed to the next phase of its cycle, which varies between engines. Any heat not translated into work is normally considered a waste product, and is removed from the engine either by an air or liquid cooling system. PartsImage:Four stroke cycle compression.jpg An illustration of several key components in a typical four-stroke engine For a four-stroke engine, key parts of the engine include the crankshaft (purple), one or more camshafts (red and blue) and valves. For a two-stroke engine, there may simply be an exhaust outlet and fuel inlet instead of a valve system. In both types of engines, there are one or more cylinders (grey and green) and for each cylinder there is a spark plug (darker-grey), a piston (yellow) and a crank (purple). A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke and the downward stroke that occurs directly after the air-fuel mix passes from the carburetor to the the cylinder, where it is ignited; this is known as a power stroke. A Wankel engine has a triangular rotor that orbits in an epitrochoidal (figure 8 shape) chamber around an eccentric shaft. The four phases of operation (intake, compression, power, exhaust) take place in separate locations, instead of one single location as in a reciprocating engine. A Bourke Engine uses a pair of pistons integrated to a Scotch Yoke that transmits reciprocating force through a specially designed bearing assembly to turn a crank mechanism. Intake, compression, power, and exhaust all occur in each stroke of this yoke. ClassificationAlthough the terms sometimes cause confusion, there is no difference between an "engine" and a "motor." At one time, the word "engine" (from Latin, via Old French, ingenium, "ability") meant any piece of machinery — a sense the persists in expressions such as siege engine. A "motor" (from Latin motor, "mover") is any machine that produces mechanical power. Traditionally, electric motors are not 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 power from within, and motors as requiring an outside source of energy to perform their work. Principles of operationImage:Antique gasoline engine.jpg A 1906 gasoline engine
Continuous combustion: Engine cycle====Two-stroke====engine 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 exhaust strokes, alternative methods must be used to scavenge the cylinders. The most common method in spark-ignition two-strokes is to use the downward motion of the piston to pressurize fresh charge in the crankcase, which is then blown through the cylinder through ports in the cylinder walls. Spark-ignition two-strokes are small and light (for their power output), and mechanically very simple; they are also generally less efficient and more polluting than their four-stroke counterparts. However in single cylinder small motor applications cc for cc, a two-stroke engine produces much more power than equivalent 4 strokes due to the enormous advantage of having 1 power stroke for every 360 degrees of crankshaft rotation (compared to 720 degrees in a 4 stroke motor). Two-stroke engines have been less fuel-efficient than other types of engines because unspent fuel being sprayed into the combustion chamber can sometimes escape out of the exhaust duct with the previously spent fuel. Without special exhaust processing, this can produce high pollution levels. Whilst two-stroke motors remain popular in Europe and Asia, they are penalised in some American markets such as California for this reason. Research continues into improving many aspects of two-stroke motors, including direct fuel injection amongst other things. Initial results have produced motors that are 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 manymotorcycles. The largest compression-ignition engines are two-strokes, and are used in some locomotives and large ships. These engines use forced induction to scavenge the cylinders. An example of this type of motor is the Wartsila-Sulzer turbocharged 2 stroke diesel as used in large container ships. It is the most efficient and powerful engine in the world, with over 50% thermal efficiency for comparison the most 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 to area. Four-strokeEngines 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, larger boats and many light aircraft. They are generally quieter, more efficient and larger than their two-stroke counterparts. There are a number of variations of these cycles, most notably the Atkinson and Miller cycles. Most truck and automotive diesel engines use a four-stroke cycle, but with a compression heating ignition system. This variation is called the diesel cycle. Five-strokeEngines based on the five-stroke cycle are a variant of the four stroke cycle. Normally the four cycles are intake, compression, combustion and exhaust. The fifth cycle added by Delautour[2] is refrigeration. Engines running on a five-stroke cycle are up to 30 percent more efficient than an equivalent four stroke engine. Beare HeadThe Beare Head Six Stroke was named such after its inventor. The Beare Head Six Stroke combines both a four stroke engine bottom end, plus a two stroke slanted top end, thus 4+2= SIX Stroke. It is a piston valve with auxiliary low pressure valves. With the hybrid of two- and four-stroke technology, the device supposedly achieves increased torque and power output, better fuel economy and cleaner burning with reduced emissions, longer service intervals, and considerably reduced tooling costs when compared with a conventional OHC four-stroke design. http://www.sixstroke.com/ Bourke EngineIn this engine, two diametrically opposed cylinders are linked to the crank by the crank pin that goes through the common scotch yoke. The cylinders and pistons are so constructed that there are, as in the usual two stroke cycle, two power strokes per revolution. However, unlike the common two stroke engine, the burnt gases and the incoming fresh air do not mix in the cylinders, contributing to a cleaner, more efficient operation. The scotch yoke mechanism also has low side thrust and thus greatly reduces friction between pistons and cylinder walls. The Bourke engine's combustion phase more closely approximates constant volume combustion than either four stroke or two stroke cycles do. It also uses less moving parts, hence needs to overcome less friction than the other two reciprocating types have to. In addition, its greater expansion ratio also means more of the heat from its combustion phase is utilized than is used by either four stroke or two stroke cycles. Controlled Combustion EngineThese 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 reciprocating motion into rotary movement. These cams practically cancel out sideward forces that would otherwise be exerted on the cylinders by the pistons, greatly improving mechanical efficiency. The number of lobes of the cams (always an odd number not less 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-rotating cams. For single-stroke versions there are as many cycles per cylinder pair as there are lobes on each cam, and twice as many for two-stroke engines. WankelThe Wankel engine does not have piston strokes so is more properly called a four-phase than a four-stroke engine. It operates with the same separation of phases as the four-stroke engine, with the phases taking place in separate locations in the engine. This engine provides three power 'strokes' per revolution per rotor, typically giving it a greater power-to-weight ratio than piston engines. This type of engine is most notably used in the current Mazda RX-8, the earlier RX-7, and other models. Gas turbineGas turbines cycles (notably jet engines), do not use the same piston to compress and then expand the gases; instead separate compressors and gas turbines are employed; giving continuous power. Essentially, the intake gas (normally air) is compressed, and then combusted with a fuel, which greatly raises the temperature and volume. The larger volume of hot gas from the combustion chamber is then fed through the gas turbine which is then easily able to power the compressor. The exhaust gas may be used to provide thrust, supplying only sufficient power to the turbine to compress incoming air (jet engine); or as much energy as possible can be supplied to the turbine (gas turbine proper). Disused methodsIn some old non-compressing internal combustion engines: In the first part of the piston downstroke a fuel/air mixture was sucked or blown in. In the rest of the piston downstroke the inlet valve closed and the fuel/air mixture fired. In the piston upstroke the exhaust valve was open. This was an attempt at imitating the way a piston steam engine works. Fuels and oxidizersFuels used include petroleum spirit (North American term: gasoline, British term: petrol), autogas (liquified petroleum gas), compressed natural gas, hydrogen, diesel fuel, jet fuel, landfill gas, biodiesel, biobutanol, peanut oil and other vegoils, bioethanol, biomethanol (methyl or wood alcohol) and other biofuels. Even fluidised metal powders and explosives have seen some use. Engines that use gases for fuel are called gas engines and those that use liquid hydrocarbons are called oil engines. However, gasoline engines are also often colloquially referred to as 'gas engines'. The main limitations on fuels are that it must be easily transportable through the fuel system to the combustion chamber, and that the fuel release sufficient energy in the form of heat upon combustion to make use of the engine practical. The oxidiser is typically air, and has the advantage of not being stored within the vehicle, increasing the power-to-weight ratio. Air can, however, be compressed and carried aboard a vehicle. Some submarines are designed to carry pure oxygen or hydrogen peroxide so that they do not need air from the atmosphere. Some race cars carry nitrous oxide as oxidizer. Other chemicals such as chlorine or fluorine have been used experimentally, but have not been found to be practical. Diesel engines are generally heavier, noisier and more powerful at lower speeds than gasoline engines. They are also more fuel-efficient in most circumstances and are used in heavy road vehicles, some automobiles (increasingly so for their increased fuel 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-engined cars have taken over about 40% of the market since the 1990s. There are also engines that run on hydrogen, methanol, ethanol, liquefied petroleum gas (LPG) and biodiesel. Paraffin and tractor vaporising oil (TVO) engines are no longer seen. Hydrogen engineSome have theorized that in the future hydrogen might replace such fuels. Furthermore, with the introduction of hydrogen fuel cell technology, the use of internal combustion engines may be phased out. The advantage of hydrogen is that its combustion produces only water. This is unlike the combustion of fossil fuels, which produce carbon dioxide, a gas some scientists theorize is a principal cause of global warming, carbon monoxide resulting from incomplete combustion, and other local and atmospheric pollutants such as sulfur dioxide and nitrogen oxides that lead to urban respiratory problems, acid rain, and ozone gas problems. However, free hydrogen for fuel does not occur naturally, burning it liberates less energy than it takes to produce hydrogen in the first place due to the second law of thermodynamics. Although there are multiple ways of producing free hydrogen, those require converting combustible molecules into hydrogen, so hydrogen does not solve any energy crisis, moreover, it only addresses the issue of portability and some pollution issues. The disadvantage of hydrogen in many situations is its storage. Liquid hydrogen has extremely low density- 14 times lower than water and requires extensive insulation, whilst gaseous hydrogen requires heavy tankage. Although hydrogen has a higher specific energy, the volumetric energetic storage is still roughly five times lower than petrol, even when liquified. (The 'Hydrogen on Demand' process, designed by Steven Amendola, creates hydrogen as it is needed, but has other issues, such as the high price of the sodium borohydride, the raw material. Sodium borohydride is renewable and could become cheaper if more widely produced.) Biofuels are less harmful to the environment and can be carbon-neutral. Image:Moore-single-cylinder-gasoline-engine.jpg One-cylinder gasoline engine (ca. 1910). CylindersInternal combustion engines can contain any number of cylinders, with numbers between 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: First, the engine can have a larger displacement with smaller individual reciprocating masses (that is, the mass of each piston can be less) thus making a smoother running engine (since the engine tends to vibrate as a result of the pistons moving up and down). Second, with a greater displacement and more pistons, more fuel can be combusted and there can be more combustion events (that is, more power strokes) in a given period of time, meaning that such an engine can generate more torque than a similar engine with fewer cylinders. The down side to having more pistons is that the engine will tend to weigh more and tend to generate more internal friction as the greater number of pistons rub against the inside of their cylinders. This tends to decrease fuel efficiency and rob the engine of some of its power. For high performance gasoline engines using current materials and technology (such as the engines found in modern automobiles), there seems to be a break point around 10 or 12 cylinders, after which addition of cylinders becomes an overall detriment to performance and efficiency, although exceptions such as the W16 engine from Volkswagen exist.
Ignition systemInternal combustion engines can be classified by their ignition system. The point in the cycle at which the fuel/oxidiser mixture are ignited has a direct effect on the efficiency and output of the ICE. For a typical 4 stroke automobile engine, the burning mixture has to reach its maximum pressure when the crankshaft is 90 degrees after TDC. The speed of the flame front is directly affected by compression ratio, fuel mixture temperature and octane or cetane rating of the fuel. Modern ignition systems are designed to ignite the mixture at the right time to ensure the flame front doesn't contact the descending piston crown. If the flame front contacts the piston, pinking or knocking results. Leaner mixtures and lower mixture pressures burn more slowly requiring more advanced ignition timing. Today most engines use an electrical or compression heating system for ignition. However outside flame and hot-tube systems have been used historically. Nikola Tesla gained one of the first patents on the mechanical ignition system with U.S. Patent 609250 , "Electrical Igniter for Gas Engines", on 16 August 1898. Fuel systemsFuels burn faster, and more completely when they have lots of surface area in contact with oxygen. In order for an engine to work efficiently the fuel must be vaporized into the incoming air in what is commonly referred to as a fuel air mixture. There are two commonly used methods of vaporizing fuel into the air, one is the carburetor and the other is fuel injection. Often for simpler reciprocating engines a carburetor is used to supply fuel into the cylinder. However, exact control of the correct amount of fuel supplied to the engine is impossible. Carburetors are the current most widespread fuel mixing device used in lawnmowers and other small engine applications. Prior to the mid-1980s carburetors were also common in automobiles. Larger gasoline engines such as used in automobiles have mostly moved to fuel injection systems (see Gasoline Direct Injection). Diesel engines always use fuel injection. Autogas (LPG) engines use either fuel injection systems or open or closed loop carburetors. Other internal combustion engines like jet engines use burners, and rocket engines use various different ideas including impinging jets, gas/liquid shear, preburners and many other ideas. Engine configurationInternal combustion engines can be classified by their configuration which affects their physical size and smoothness (with smoother engines producing less vibration). Common configurations include the straight or inline configuration, the more compact V configuration and the wider but smoother flat or boxer configuration. Aircraft engines can also adopt a radial configuration which allows more effective cooling. More unusual configurations, such as "H", "U", "X", or "W" have also been used. Multiple-crankshaft configurations do not necessarily need a cylinder head at all, but can instead have a piston at each end of the cylinder, called an opposed piston design. This design was used in the Junkers Jumo 205 diesel aircraft engine, using two crankshafts, one at either end of a single bank of cylinders, and most remarkably in the Napier Deltic diesel engines, which used three crankshafts to serve three banks of double-ended cylinders arranged in an equilateral triangle with the crankshafts at the corners. It was also used in single-bank locomotive engines, and continues to be used for marine engines, both for propulsion and for auxiliary generators. The Gnome Rotary engine, used in several early aircraft, had a stationary crankshaft and a bank of radially arranged cylinders rotating around it. Engine capacityAn engine's capacity is the displacement or swept volume by the pistons of the engine. It is generally measured in litres (L) or cubic inches (c.i. or in³) for larger engines and cubic centimetres (abbreviated to cc) for smaller engines. Engines with greater capacities are usually more powerful and provide greater torque at lower rpm but also consume more fuel. Apart from designing an engine with more cylinders, there are two ways to increase an engine's capacity. The first is to lengthen the stroke and the second is to increase the piston's diameter (See also: Stroke ratio). In either case, it may be necessary to make further adjustments to the fuel intake of the engine to ensure optimal performance. 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 II were all fitted with a BMC A-Series engine of the same stroke and bore according to their specifications, and were from the same maker. However the engine capacities were quoted as 1000cc, 1100cc and 1098cc respectively in the sales literature and on the vehicle badges. Lubrication SystemsInternal combustions engines require lubrication in operation to allow moving parts to slide smoothly over each other. Insufficient lubrication will cause the engine to seize up. Several different types of lubrication systems are used. Simple two-stroke engines are lubricated by oil mixed into the fuel or injected into the induction stream as a spray. Early slow speed stationary and marine engines were lubricated by gravity from small chambers, similar to those used on steam engines at the time, with an engine tender refilling these as needed. As engines were adapted for automotive and aircraft use, the need for a high power to weight ratio lead to increased speeds, higher temperatures, and greater pressure on bearings, which in turn required pressure lubrication for crank bearing and connecting rod journals, provided either by a direct lubrication from a pump, or indirectly by a jet of oil directed at pickup cups on the connecting rod ends, which had the advantage of providing higher pressures as engine speed increased. DiagnosisEngine on-board diagnosis are included in some cars (e.g. BMW).
Engine pollutionGenerally internal combustion engines, particularly reciprocating internal combustion engines, produce moderately high pollution levels, due to incomplete combustion of carbonaceous fuel, leading to carbon monoxide and some soot along with oxides of nitrogen & sulfur and some unburnt hydrocarbons depending on the operating conditions and the fuel/air ratio. The primary causes of this are the need to operate near the stoichiometric ratio for petrol engines in order to achieve combustion (the fuel would burn more completely in excess air) and the "quench" of the flame by the relatively cool cylinder walls. Quenching is commonly observed in diesel (compression ignition) engines which run on natural gas, when running at lower speed. It dramatically reduces the efficiency and increases knocking and might cause the engine to stall. Diesel engines produce a wide range of pollutants including aerosols of many small particles (PM10) that are believed to penetrate deeply into human lungs. Engines running on liquified petroleum gas (LPG) are very low in emissions as LPG burns very cleanly and does not contain sulphur or lead.
Engine EfficiencyThe efficiency of various types of internal combustion engines vary. Most gasoline fueled internal combustion engines, even when aided with turbochargers and stock efficiency aids, have a mechanical efficiency of about 20%[citation needed]. The efficiency may be as high as 37% at the optimum operating point in engines where this is a high priority such as that of the Prius. Most internal combustion engines waste about 36% of the energy in gasoline as 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 add on system that improves the fuel economy of internal combustion engines by injecting hydrogen as a combustion enhancement into the intake manifold. Fuel economy gains of 15% to 50% can be seen[citation needed]. A small amount of hydrogen added to the intake air-fuel charge increases the octane rating of the combined fuel charge and enhances the flame velocity, thus permitting the engine to operate with more advanced ignition timing, a higher compression ratio, and a leaner air-to-fuel mixture than otherwise possible. The result is lower pollution with more power and increased efficiency. Some HFI systems use an on board electrolyzer to generate the hydrogen used. A small tank of pressurized hydrogen can also be used, but this method necessitates refilling. There has also been discussion of new types of internal combustion engines, such as the Scuderi Split Cycle Engine, that utilize high compression pressures in excess of 2000 psi and combust after top-dead-center (the highest & most compressed point in an internal combustion piston stroke). The claimed efficiency of this engine, by calculation, is 42%. This has yet to be demonstrated as of March 2007. See also
References
Bibliography
|
Sites |
Searched sites for "Internal combustion engine" |
|
No sites found. |
Sorry, no matching site records were found. |
Want your site listed here?
|
||||||||||||||||
