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A colored automobile engine
The internal combustion engine is an engine in which the combustion of fuel and an oxidizer (typically air) occurs in a confined space called a combustion chamber. This exothermic reaction creates gases at high temperature and pressure, which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement of solid parts of the engine, by acting on pistons, rotors, or even by pressing on and moving the entire engine itself.
This contrasts with external combustion engines, such as steam engines and Stirling engines, 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 refer specifically to reciprocating piston engines, Wankel engines and similar designs in which combustion is intermittent. However, continuous combustion engines, such as jet engines, most rockets and many gas turbines are also internal combustion engines.
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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 an 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, in-cylinder compression.
Karl Benz
Internal 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, trucks, motorcycles, boats, and in a wide variety of aircraft and locomotives, generally using petroleum (called All-Petroleum Internal Combustion Engine Vehicles or APICEVs). 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., 12V generators) and by industry.
Four-stroke cycle (or Otto cycle)
1. Induction
2. compression
3. power
4. exhaust
All internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with the oxygen from the air, although other oxidizers such as nitrous oxide may be employed. Also see stoichiometry.
The most common modern fuels are made up of hydrocarbons and are derived mostly from 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 soybean 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 a spark ignition (SI) method or a compression ignition (CI) system. In the past, other methods using hot tubes or flames have been used.
Electrical/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 185 psi and use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.
Diesel Engine 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. The 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 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.
Once 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 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, or 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.
The efficiency of various types of internal combustion engines varies, but it is nearly always lower than electric motor energy efficiency. Most gasoline-fueled internal combustion engines, even when aided with turbochargers and stock efficiency aids, have a mechanical efficiency of about 20% Physics In an Automotive EngineImproving IC Engine Efficiency. The efficiency may be as high as 37% at the optimum operating point. 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. Rocket engines can approach 70% efficiency at some parts of a flight; made possible by the very high combustion temperature and lower exhaust temperatures, but while the average efficiency depends on the mission, for a launch vehicle to reach Low Earth Orbit the overall efficiency is only around 10%.
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% have been claimed[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 small amount of hydrogen needed in the system, around 5% of total BTU. A small tank of pressurized hydrogen can also be used, but this method necessitates refilling. Hydrogen in liquid form is seldom used because it is difficult to store.
There has also been discussion of other types of internal combustion engines, such as the 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.
Internal combustion engines—particularly reciprocating internal combustion engines—produce air pollution emissions, due to incomplete combustion of carbonaceous fuel, leading to carbon monoxide and some soot along with oxides of nitrogen and sulfur and some uncombusted 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 gasoline 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 that run on natural gas, when running at lower speed. It reduces the efficiency and increases knocking and sometimes causes the engine to stall.
Diesel engines produce a range of pollutants, including aerosols of particulate matter that are known to penetrate deeply into human lungs. Engines running on liquified petroleum gas (LPG) are low in emissions as LPG burns with low emissions and does not contain sulfur or lead.
In addition, significant contributions to noise pollution are made by internal combustion engines. Most of this noise produced is due to automobile and truck traffic operating on highways and street systems.
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. The downward stroke that occurs directly after the air/fuel mix passes from the carburetor or fuel injector to the cylinder where it is ignited 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 what is effectively a moving, variable-volume chamber.
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 occur in each stroke.
At one time, the word "engine" (from Latin, via Old French, ingenium, "ability") meant any piece of machinery — a sense that 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.
Continuous combustion:
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; however, they are also generally less efficient and more polluting than their four-stroke counterparts. However, in single-cylinder small motor applications, cc for cc,(cc meaning cubic centimeter), 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).
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 to scavenging, allowing some of it to escape out of the exhaust port. Modern designs (Sarich and Paggio) use air-assisted fuel injection, which avoids this loss, and are more efficient than comparably sized four-stroke engines. Fuel injection is essential for a modern two-stroke engine in order to meet ever more stringent emission standards.
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 many motorcycles.
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% thermal efficiency (SAE 900648), and size is an advantage for efficiency due to the increase in the ratio of volume to area.
Engines based on the four-stroke or Otto cycle have one power stroke for every four strokes (up-down-up-down) and are used in cars, larger boats, some motorcycles, 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. The steps involved here are:
Engines 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 DelautourWilliams, Tony (2006). 101 Ingenious Kiwis. Reed Publishing (NZ) Ltd, pp.83. is refrigeration. Engines running on a five-stroke cycle are claimed to be up to 30 percent more efficient than equivalent four-stroke engines.
The six stroke engine captures the wasted heat from the 4-stroke Otto cycle and creates steam, which simultaneously cools the engine while providing a free power stroke. This removes the need for a cooling system, making the engine lighter while giving 40% increased efficiency over the Otto Cycle.
Beare Head Technology combines a four-stroke engine bottom end with a ported cylinder, which closely resembles that of a two-stroke: thus, 4+2 = six-stroke. It has an opposing piston that acts in unison with auxiliary low pressure reed and rotary valves, allowing variable compression and a range of tuning options.
In this engine, two opposed cylinders are linked to the crank by a Scotch yoke. The Scotch yoke mechanism prevents side thrust, preventing any piston slap, allowing operation as a detonation or "explosion" engine. This also greatly reduces friction between pistons and cylinder walls. The Bourke engine uses fewer moving parts and has to overcome less friction than conventional crank and slider engines with poppet valves. However no independent testing of this engine has ever borne out any of these claims.
These are also cylinder-based engines, which may be one or two-stroke but use, instead of a crankshaft and piston rods, two gear-connected, counterrotating 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 counterrotating 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.
The Wankel engine (rotary engine) does not have piston strokes, so is more properly called a four-phase, rather 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 (while it is true that 3 power strokes occur per ROTOR revolution, due to the 3/1 revolution ratio of the rotor to the eccentric shaft, only 1 power stroke per shaft revolution actually occurs), 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 turbines cycles (notably jet engines) do not use the same system to both compress and then expand the gases; instead, separate compression and expansion 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 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 shaft (gas turbine proper).
In some old noncompressing 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. Since the explosive mixture was not compressed, the heat and pressure generated by combustion was much less, causing lower overall efficiency.
Nowadays, fuels used include:
Even fluidized 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 releases sufficient energy in the form of heat upon combustion to make use of the engine 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 vaporizing oil (TVO) engines are no longer seen.
Since air is plentiful at the surface of the earth, the oxidizer is typically atmospheric oxygen, which has the advantage of not being stored within the vehicle, increasing the power-to-weight and power to volume ratios. There are other materials that are used for special purposes, often to increase power output or to allow operation under water or in space.
Some 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, carbon monoxide resulting from incomplete combustion; and other local and atmospheric pollutants such as sulphur dioxide and nitrogen oxides that lead to urban air pollution, acid rain, and ozone layer problems. However, free hydrogen for fuel does not occur naturally, and oxidizing it liberates less energy than it takes to produce hydrogen in the first place, due to the second law of thermodynamics. Note also, that if the atmosphere is used as the oxidizer in high temperature combustion, the resultant nitrogen oxide byproducts must be reduced by an appropriate catalytic converter.
Another problem with hydrogen as a fuel in a conventional four-stroke poppet valve engine is a tendency to preignite, due to the presence of a hot exhaust valve. Certain engine types such as the Wankel rotary engine and various uniflow reciprocating types do not have this inherent problem. A recently developed nutating disc engine also appears to offer an alternative solution to this problem[citation needed].
Being a thermodynamic process, the overall efficiency will likely be substantially less than if the hydrogen were converted to electricity in a fuel cell and stored in batteries or supercapacitors for high-demand portions of a vehicle\'s operating cycle.
Although there are multiple ways of producing free hydrogen, those require converting combustible molecules into hydrogen or consuming electric energy, 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 liquefied. The \'Hydrogen on Demand\' process (see direct borohydride fuel cell), 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.
One-cylinder gasoline engine (ca. 1910).
Internal 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 downside to having more pistons is that the engine will tend to weigh more and generate more internal friction as the greater number of pistons rub against the inside of their cylinders. This tends to decrease fuel efficiency and robs 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 the addition of cylinders becomes an overall detriment to performance and efficiency, although exceptions such as the W16 engine from Volkswagen exist.
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. Nikola Tesla 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. ignition systems are classifed as follows.
The mixture is ignited by an electrical spark from a spark plug, the timing of which is very precisely controlled. Almost all gasoline engines are of this type, but not diesel engines.
Ignition, after the engine is started, comes from oxidation heat and mechanical compression of the air or mixture. The vast majority of compression ignition engines are diesels, in which the fuel is mixed with the air after the air has reached ignition temperature. In this case, the timing comes from the fuel injection system. Very small model engines, for which simplicity is more important than fuel cost, use special fuels to control ignition timing.
The point in the cycle at which the fuel/oxidizer mixture is ignited has a direct effect on the efficiency and output of the ICE. The thermodynamics of the idealized Carnot heat engine tells us that an ICE is most efficient if most of the burning takes place at a high temperature, resulting from compression—that is, near top dead center. The speed of the flame front is directly affected by compression ratio, fuel mixture temperature, and octane or cetane rating of the fuel. Leaner mixtures and lower mixture pressures burn more slowly, requiring more advanced ignition timing. It is important to have combustion spread by a thermal flame front (deflagration), not by a shock wave. Combustion propagation by a shock wave is called detonation and, in engines, is also known as pinging or knocking.
So, at least in gasoline-burning engines, ignition timing is largely a compromise between an earlier "advanced" spark—which gives greater efficiency with high octane fuel—and a later "retarded" spark, which avoids detonation with the fuel used. For this reason, high-performance diesel automobile proponents such as Gale Banks believe that
Fuels 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 lawn mowers 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, because it is the fuel system that controls the ignition timing.
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. [Fuel system movie flash][3]
Internal 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.
An engine\'s capacity is the displacement or swept volume by the pistons of the engine. It is generally measured in liters (L) or cubic inches (c.i.d. or cu in or in³) for larger engines and cubic centimeters (abbreviated 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.
Internal 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 led to increased speeds, higher temperatures, and greater pressure on bearings, which in turn required pressure lubrication for crank bearings 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.
Engine On Board Diagnostics (also known as OBD) is a computerized system that allows for electronic diagnosis of a vehicle\'s powerplant. The first generation, known as OBD1, was introduced 10 years after the U.S. Congress passed the Clean Air Act in 1970 as a way to monitor a vehicle\'s fuel injection system. OBD2, the second generation of computerized on-board diagnostics, was codified and recommended by the California Air Resource Board in 1994 and became mandatory equipment aboard all vehicles sold in the United States as of 1996.
| | Energy Portal |
| Thermodynamic cycles | |||||
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| Cycles normally with external combustion |
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| Cycles normally with internal combustion | Atkinson cycle · Brayton/Joule cycle · Diesel cycle · Otto cycle · Lenoir cycle · Miller cycle | ||||
| Cycle mixing | Combined cycle · HEHC cycle[9][10] · Mixed/Dual Cycle | ||||
| Not categorized | Claude cycle [11] · Fickett-Jacobs cycle · Gifford-McMahon cycle [12] · Hirn cycle · Homogeneous Charge Compression Ignition · Humphrey cycle · Linde-Hampson cycle | ||||
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