Section Contents:- Nitromethane is added to some racing and model fuels to increase power and control combustion.(More...)
- You might want to know what's going on simply out of curiosity.(More...)
- As the piston moves upward, the air/fuel mixture is compressed.(More...)
Nitromethane is added to some racing and model fuels to increase power and control combustion. Nitrous oxide has been used, with extra gasoline, in tactical aircraft and in specially equipped cars, to allow short bursts of added power from engines that otherwise run on gasoline and air. (It is also used in the Burt Rutan rocket spacecraft).
[1] Combustion propagation by a shock wave is called detonation and, in engines, is also known as pinging or knocking. 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.
[1] 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.
[1] 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%.
[1] Most old engines, however, rely on electrical systems that also control the combustion process to increase efficiency and reduce emissions.
[1] 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.
[1] 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.
[1] 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.
[1] 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).
[1] 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. Increasing the amount of air in the engine reduces the amount of the first two pollutants but tends to encourage the oxygen and nitrogen in the air to combine to produce Nitrogen Oxides (NOx), demonstrated to be hazardous to both plant and animal health.
[1] 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.
[1] Ignition, after the engine is started, comes from oxidation heat and mechanical compression of the air or mixture.
[1] 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.
[1] Very small model engines, for which simplicity is more important than fuel cost, use special fuels to control ignition timing.
[1] 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.
[1] 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.
[1] Atkinson"s engine had one power phase per revolution together with different intake and expansion volumes, making it more efficient than the Otto cycle. They built the first cold-start compression-ignition engines. In 1892, they installed the first ones in a water pumping station.
[1] There are a lot of inventions about increasing the efficiency of IC-Engines (some examples are shown below). In general, practical engines are always compromises, or trade-off"s, between different properties, such as efficiency, weight, power, response, exhaust emissions, noise etc. etc. Sometimes economy also plays a role, not only as the cost of manufacturing the engine itself, but also manufacuring and distibution of the fuel.
[1] Increasing the engine efficiency brings a better fuel economy, but only if the fuel cost per energy content is the same.
[1] Often, for simpler reciprocating engines, a carburetor is used to supply fuel into the cylinder.
[1] Carburetors are the current most widespread fuel mixing device used in lawn mowers and other small engine applications.
[1] 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.
[1] The Gnome Rotary engine, used in several early aircraft, had a stationary crankshaft and a bank of radially arranged cylinders rotating around it.
[1] 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.
[1] 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.
[1] 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.
[1] 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.
[1] A row contains an odd number of cylinders, so an even number indicates a two- or four-row engine. The largest of these was the Lycoming R-7755 with 36 cylinders (four rows of nine cylinders), but it did not enter production.
[1] In that case a four cylinder engine would be less powerful than a six or eight cylinder engine.
[1] 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.
[1] In either case, it may be necessary to make further adjustments to the fuel intake of the engine to ensure optimal performance.
[1] Engines with greater capacities are usually more powerful and provide greater torque at lower rpm but also consume more fuel.
[1] Exact control of the correct amount of fuel supplied to the engine is impossible.
[1] The German courts, however, did not hold his patent to cover all in-cylinder compression engines or even the four-stroke cycle, and after this decision, in-cylinder compression became universal.
[1] Engines based on the five-stroke cycle are a variant of the four-stroke cycle.
[1] 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.
[1] 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.
[1] Typically engines use either a spark ignition (SI) method or a compression ignition (CI) system.
[1] Today most engines use an electrical or compression heating system for ignition.
[1] Apart from designing an engine with more cylinders, there are two ways to increase an engine's capacity.
[1] The available energy is manifested as high temperature and pressure which can be translated into work by the engine.
[1] With a diesel, boost pressure is essentially unlimited. It is literally possible to run as much boost as the engine will physically stand before breaking apart.
[1] 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.
[1] 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.
[1] There are also engines that run on hydrogen, methanol, ethanol, liquefied petroleum gas (LPG) and biodiesel.
[1] In 1902 automobiles with that engine were put into production by DMG. His economisers worked as well in cars as they did in motorcycles.
[1] A Wankel engine has a triangular rotor that orbits in an epitrochoidal (figure 8 shape) chamber around an eccentric shaft.
[1] 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 cuin or in") for larger engines and cubic centimeters (abbreviated cc) for smaller engines.
[1] 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).
[1] 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.
[1] The fuel does not get completely burned in the engine and passes through the exhaust unchanged. 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.
[1] 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.
[1] 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.
[1] There"s only so far you can go with an air-throttled engine on 91-octane gasoline. 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 can be added to a gasoline engine before the fuel octane level again becomes a problem.
[1] 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.
[1] 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.
[1] 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.
[1] Most car engines have four to eight cylinders, with some high performance cars having ten, twelve, or even sixteen, and some very small cars and trucks having two or three. In previous years, some quite large cars, such as the DKW and Saab 92, had two-cylinder, two-stroke engines.
[1] 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.
[1] 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.
[1] Later, Benz designed and built his own four-stroke engine that was used in his automobiles, which became the first automobiles in production.
[1] 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 ).
[1] Gasoline engines are used in most other road vehicles, including most cars, motorcycles and mopeds.
[1] Engine designers have come to realize that diesels are capable of substantially more power and torque than any comparably sized gasoline engine.
[1] The compression that occurs is usually more than three times higher than a gasoline engine.
[1] 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.
[1] 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.
[1] Diesel engines always use fuel injection, because it is the fuel system that controls the ignition timing.
[1] 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.
[1] For a four-stroke engine, key parts of the engine include the crankshaft (purple), one or more camshafts (red and blue), and valves.
[1] 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).
[1] Two-stroke engines are widely used in snowmobiles, lawnmowers, weed-whackers, chain saws, jet skis, mopeds, outboard motors, and many motorcycles.
[1] Black or smokeless gunpowder has been used in diesel engine starters, to deploy or jettison equipment remotely, and by Alphonse P"naud in pioneering model aircraft. Other chemicals such as chlorine or fluorine have been used experimentally, but have not been found to be practical.
[1] In the piston upstroke, the exhaust valve was open. This was an attempt at imitating the way a piston steam engine works.
[1] In this engine, two opposed cylinders are linked to the crank by a Scotch yoke.
[1] Engines running on a five-stroke cycle are claimed to be up to 30 percent more efficient than equivalent four-stroke engines.
[1] Fuel injection is essential for a modern two-stroke engine in order to meet ever more stringent emission standards.
[1] Since the explosive mixture was not compressed, the heat and pressure generated by combustion was much less, causing lower overall efficiency.
[1] 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.
[1] 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.
[1] 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 ).
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You might want to know what's going on simply out of curiosity. Or perhaps you are buying a new car, and you hear things like "3.0 liter V-6" and "dual overhead cams" and "tuned port fuel injection." In this article, we'll discuss the basic idea behind an engine and then go into detail about how all the pieces fit together, what can go wrong and how to increase performance.
[2] The purpose of a gasoline car engine is to convert gasoline
gasoline into motion so that your car can move.
[2] Have you ever opened the hood of your car
car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated.
[2] The types of engines you'll learn about in this section include diesel, rotary, HEMI, stirling and quasiturbine, to name a few.
[2] The fuel (coal, wood, oil, whatever) in a steam engine burns outside the engine to create steam, and the steam creates motion inside the engine.
[2] In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft.
[3] As the crankshaft revolves, it has the effect of "resetting the cannon." Here's what happens as the engine goes through its cycle: Your browser does not support JavaScript or it is disabled.
[3] Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion.
[3] Inside the cylinder is a moving piston piston which compresses compresses a mixture of fuel and air before combustion and is then forced back down the cylinder following combustion.
[5] The basic mechanical design of the Wright engine is remarkably similar to modern, four-stroke four-stroke, four cylinder four cylinder automobile engines.
[5] Individual web pages for all of the major systems and parts parts are provided so that you can study each item in some detail. This page shows an interactive Java applet which allows you to change the view of the 1903 aircraft engine by pushing buttons to stop, step or rotate the image.
[5] While there are some important differences between modern aircraft engines and the Wright 1903 engine, the simplicity of the Wright engine design makes it a good starting point for students.
[5] The engine consisted of four cylinders cylinders like the one shown above, with each piston connected to a common crankshaft crankshaft.
[4] The engine cycle cycle begins with the intake stroke intake stroke as the piston is pulled towards the crankshaft (to the left in the figure).
[4] Because the exhaust valve is open, the exhaust gas is pushed past the valve and exits the engine. The intake valve is closed and the electrical contact is open during this movement of the piston.
[4] Notice how the cam moves the exhaust valve at just the right time and how quickly the intake valve opens after the exhaust valve is closed. In real engine operation, the exhaust stroke can not push all of the exhaust out of the cylinder, so a real engine doesn't perform as well as the ideal engine described on this page.
[4] In the animation and in all the figures, we have colored the fuel/air intake system fuel/air intake system red, the electrical system electrical system green, and the exhaust system exhaust system blue. We also represent the fuel/air mixture and the exhaust gases by small colored balls to show how these gases move through the engine.
[4] Modern automobile engines adjust the fuel/air ratio with computer controlled fuel injectors to maintain high performance. The brothers just had to watch the horsepower of their engine drop from about 16 horsepower when the engine was first started to about 12 horsepower when it was running hot.
[4] At the end of the exhaust stroke, the exhaust valve is closed and the engine begins another intake stroke.
[4] Historical note - The exhaust system used by the Wright brothers caused the hot exhaust to exit each cylinder independently. right next to the pilot. This engine was very loud as well.
[4] This is an animated computer drawing of one cylinder of the Wright brothers' 1903 aircraft engine. This engine powered the first, heavier than air, self-propelled, maneuverable, piloted aircraft; the Wright 1903 Flyer.
[4] The intake valve is open, and fuel and air are drawn past the valve and into the combustion chamber and cylinder from the intake manifold located on top of the combustion chamber.
[4] The cylinder and combustion chamber are full of the low pressure fuel/air mixture and, as the piston begins to move to the right, the intake valve closes.
[4] As the exhaust stroke begins, the cylinder and combustion chamber are full of exhaust products at low pressure (colored blue on the figure above.)
[4] Rapid combustion combustion of the fuel releases heat, and produces exhaust gases in the combustion chamber.
[4] The combustion increases the temperature temperature of the exhaust gases, any residual air in the combustion chamber, and the combustion chamber itself.
[4] From the ideal gas law ideal gas law, the increased temperature of the gases also produces an increased pressure in the combustion chamber.
[4] Cams and rocker arms provide better control and timing of the opening and closing of the valves. With both valves closed, the combination of the cylinder and combustion chamber form a completely closed vessel containing the fuel/air mixture.
[4] The sudden opening of the contact produces a spark in the combustion chamber which ignites the fuel/air mixture.
[4] Because the intake and exhaust valves are closed, the combustion of the fuel takes place in a totally enclosed (and nearly constant volume) vessel.
[4] As the piston moves upward, the air/fuel mixture is compressed. On some small high compression engines, by the time the piston reaches the top of its travel, the mixture is compressed to as little as one-tenth its original volume.
[6] The process continuously repeats itself during the operation of the engine. If a four-cylinder engine requires two complete revolutions of the crankshaft to ignite all of its cylinders, how many revolutions does an eight-cylinder engine require.
[6] The four strokes are continuously repeated during the operation of the engine.
[6] The Diesel engine differs from the gasoline engine in that the intake stroke only pulls in air, not air and fuel.
[6] The Diesel engine is designed heavier and more powerful than gasoline engines and utilizes oil as fuel.
[6] In Diesel engines, compression ratios are as high as (22.5 to 1) and provide pressures of (500psi) at the end of the compression stroke.
[6] Hopefully you answered two. It only takes two revolutions of the crankshaft to fire all of the cylinders of any four-stroke engine.
[6] Before explaining the operation of the four-stroke engine, some of the internal parts must be identified.
[6] The high pressure of the explosion forces the piston down as in the gasoline engine.
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