Internal Combustion Engine1

  • View

  • Download

Embed Size (px)

Text of Internal Combustion Engine1

Internal combustion engine.

A colorized automobile engine An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. A piston internal combustion engine works by burning hydrocarbon or hydrogen fuel that presses on a piston; and a jet engine works as the hot combustion products press on the interior parts of the nozzle and combustion chamber, directly accelerating the engine forwards. The rotary combustion engine uses a rotor instead of reciprocating pistons. By way of contrast, an external combustion engine such as a steam engine, does work when the combustion process heats a separate working fluid, such as water or steam, which then in turn does work. Jet engines, most rockets and many gas turbines are classed as internal combustion engines, but the term "internal combustion engine" is often loosely used to refer specifically to a piston internal combustion engine and rotary combustion engine in which combustion is intermittent and the products act on reciprocating machinery, the most common subtype of this kind of engine


Early internal-combustion engines were used to power farm equipment. In the broadest sense of the term, the internal combustion engine can be said to have been invented in China, with the invention of fireworks during the Song dynasty (some sources put the invention a thousand years earlier still). English inventor Sir Samuel Morland used gunpowder to drive water pumps in the 17th century. For more conventional, reciprocating

internal combustion engines the fundamental theory for two-stroke engines was established by Sadi Carnot in France in 1824, whilst the American Samuel Morey received a patent on April 1, 1826 for a "Gas Or Vapor Engine". The Italians Eugenio Barsanti and Felice Matteucci patented a first working efficient version of an internal combustion engine in 1854 in London (pt. Num. 1072). Jean Joseph Etienne Lenoir produced in 1860 a gas-fired internal combustion engine not dissimilar in appearance to a steam beam engine. Nikolaus Otto working with Gottlieb Daimler and Wilhelm Maybach in the 1870's developed the four-stroke cycle (Otto cycle) engine.

ApplicationsInternal combustion engines are most commonly used for mobile propulsion systems. In mobile scenarios internal combustion is advantageous, since it can provide high power to weight ratios together with excellent fuel energy-density. These engines have appeared in almost all cars, motorbikes, many boats, and in a wide variety of aircraft and locomotives. Where very high power is required, such as jet aircraft, helicopters and large ships, they appear mostly in the form of gas turbines. They are also used for electric generators and by industry. For low power mobile and many non-mobile applications an electric motor is a competitive alternative. In the future, electric motors may also become competitive for most mobile applications. However, the high cost and weight and poor energy density of batteries and lack of affordable onboard electric generators such as fuel cells has largely restricted their use to specialist applications.


An illustration of several key components in a typical four-stroke engine

The parts of an engine vary depending on the engine's type. 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 in the cylinder is ignited is known as a power stroke.

A Wankel engine has a triangular rotor that orbits in an epitroichoidal (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 Quasiturbine has a four face articulated rotor that rotates inside a quasi-oval shaped chamber, as with the wankel the four phases take place in separate locations but differs in that a complete revolution of the output shaft is a complete four stroke cycle.

OperationAll internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with air, although other oxidisers such as nitrous oxide may be employed. Also see stoichiometry. The most common fuels in use today are made up of hydrocarbons and are derived from petroleum. These include the fuels known as diesel, gasoline and liquified petroleum gas. Most internal combustion engines designed for gasoline can run on natural gas or liquified petroleum gases without modifications except for the fuel delivery components. Liquid and gaseous biofuels of adequate formulation can also be used. Some have theorized that in the future hydrogen might replace such fuels. The advantage of hydrogen is that its combustion produces only water. This is unlike the combustion of hydrocarbons which also produces carbon dioxide, a major cause of global warming, and, as a result of incomplete combustion, carbon monoxide and nitrous oxides (NOx). The big disadvantage of hydrogen in many situations is storage; liquid hydrogen has extremely low density- 14 times lower than water and requires extensive insulation, whilst gaseous hydrogen requires very heavy tankage. Whilst hydrogen is light and therefore has a higher specific energy, the volumetric efficiency is still roughly five times lower than petrol. All internal combustion engines must have a means of ignition to promote combustion. Most engines use either an electrical or a compression heating ignition system. Electrical ignition systems generally rely on 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 alternator driven by the engine. Compression heating ignition systems (Diesel engines and HCCI engines) rely on the heat created in the air by compression in the engine's cylinders to ignite the fuel. Once successfully 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 a waste product and is removed from the engine either by an air or liquid cooling system.

ClassificationThere is a wide range of internal combustion engines corresponding to their many varied applications. Likewise there is a wide range of ways to classify internal-combustion engines, some of which are listed below. Although the terms sometimes cause confusion, there is no real 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 "motor" (from Latin motor, "mover") is any machine that produces mechanical power. Traditionally, electric motors are not referred to as "engines," but combusion engines are often referred to as "motors."

Principles of operation

Reciprocating: Two-stroke engine Four-stroke engine


Wankel engine quasiturbine

Continuous combustion:

gas turbine jet engine rocket engine

Engine cycleEngines based on the two-stroke cycle use two strokes (one up, one down) for every power stroke, relying on the action of the bottom of the piston within the crankcase to help move the fuel-air mixture, and are used where small size and weight are important, such as snowmobiles, lawnmowers, mopeds, outboard motors and some motorcycles. Gasoline two-stroke engines are generally louder, less efficient, more polluting, and smaller than their four-stroke counterparts, although large two-stroke diesel engines are not subject to these complaints and are used in many applications, for instance some locomotives built by EMD. 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, 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 it is possible to talk separately about a diesel cycle. The Wankel

engine operates with the same separation of phases as the four-stroke engine (but with no piston strokes, would more properly be called a four-phase engine), since the phases occur in separate locations in the engine; however like a two-stroke piston engine, it provides one power 'stroke' per revolution per rotor, giving it similar space and weight efficiency.

Fuel typeDiesel engines are generally heavier, noisier and more powerful at lower speeds than gasoline engines. They are also more fuel-efficient in some circumstances and are used in heavy road-vehicles, some automobiles, ships and some 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 are far more prevalent, representing around 40% of the market. Both gasoline and diesel engines produce significant emissions. 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. .

CylindersInternal combustion engines can contain any number of cylinders with numbers between one and twelve being common, though as many as 28 have been used. Having more cylinders in a 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, over all, 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 W-16 engine from Volkswagon

Ignition systemInternal combustion engines can be classified by their 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 609250, "Electrical Igniter for Gas Engines", on 16 August 1898.

Fuel systemsOften 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 difficult. Car engines have mostly moved to Fuel injection systems, and Diesel engines essentially always use this technique. 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. Technically this is a "rotary piston engine", to distinguish it from Wankel "rotary combustion engines".

Engine capacityAn engine's capacity is the displacement or swept volume by the pistons of the engine. It is generally measured in litres or cubic inches for larger engines and cubic centimetres (abbreviated to cc's) for smaller engines. Engines with greater capacities are usually more powerful and provide greater torque at lower rpms 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. 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 all had engines 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.

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 & sulphur and some unburnt hydrocarbons depending on the operating conditions and the fuel air ratio Diesel engines produce a wide range of pollutants including aerosols of many small particles that are believed to penetrate deeply into human lungs

Two-stroke cycle The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by having only two strokes (linear movements of the piston) instead of four, although the same four operations (intake, compression, power, exhaust) still occur. Thus, there is a power stroke per piston for every engine revolution, instead of every second revolution. Two stroke engines can be arranged to start and run in either direction. Two-stroke engines are used most among the smallest and largest reciprocating powerplants, but less commonly among medium sized ones. The smallest gasoline engines are usually two-strokes. They are commonly used in outboard motors, high-performance, small-capacity motorcycles, mopeds, scooters, snowmobiles, karts, model airplane and motorized garden appliances like chainsaws and lawnmowers. In each application, they are popular because of their simple design (and consequent low cost) and very high power-to-weight ratios (because the engine has twice as many combustions per second as a four stroke engine revolving at the same speed). For handheld devices, they also have the advantage of working in any orientation, as there is no oil reservoir dependent upon gravity. Two-stroke cycles have also been used in diesel engines, notably opposed piston designs, low speed units such as large marine engines, and V8 engines for trucks and heavy machinery. Various two-stroke design types To understand the operation of the Two-stroke engine it is necessary to know which type of design is in question because different design types operate in different ways.

The design types of the two-stroke cycle engine vary according to the method of intake of fresh air/fuel mixture from the outside, the method of scavenging the cylinder (exchanging burnt exhaust for fresh mixture) and the method of exhausting the cylinder. These are the main variations. They can be found alone or in various combinations. Piston port Piston port is the simplest of the designs. All functions are controlled solely by the piston covering and uncovering the ports (which are holes in the side of the cylinder) as it moves up and down in the cylinder. Reed valve Similar to and almost as simple as the piston port but with a check valve in the intake tract. Reed valve engines deliver power over a wider RPM range than does the piston port making them more useful in most situations. Disk rotary valve The intake tract is opened and closed by a thin disk attached to the crankshaft and spins at crankshaft speed. The intake tract is arranged so that it passes through the disk. This disk has a section cut from it and when this cut passes the intake pipe it opens, otherwise it is closed. Valve in head Instead of the exhaust exiting from a hole in the side of the cylinder, valves are provided in the cylinder head. The valves function the same way as fourstroke exhaust valves do but at twice the speed. Diesel Spark ignition gasoline engines require a spark plug to ignite the fuel. Diesels rely on the heat of very high compression to ignite the fuel. Fuel is sprayed into the hot compressed air and ignites; therefore the scavenging is done with air only. Diesels are blower scavenged. Blower-scavenged Instead of using the crank case as a pump to pump fresh air/fuel mixture into the cylinder, an auxiliary air pump is used to blow air through the cylinder and clear out burnt exhaust (hence the term blower). Blowers are used in conjunction with diesels. Loop-scavenged This method of scavenging uses carefully aimed transfer ports to loop fresh mixture up one side of the cylinder and down the other pushing the burnt

exhaust ahead of it and out the exhaust port. It features a flat or slightly domed piston crown for efficient combustion. Loop scavenging is by far the most used system of scavenging. Cross flow-scavenged In a cross flow engine the transfer ports and exhaust ports are on opposite sides of the cylinder and a baffle shaped piston dome directs the fresh mixture up and over the dome pushing the exhaust down the other side of the baffle and out the exhaust port. Before loop scavenging was invented almost all two strokes were made this way. The heavy piston with its very high heat absorption along with its poor scavenging and combustion characteristics make it an antiquated design now except where there is no way to use loop scavenging. Power Valve Systems Many modern two stroke engines employ a Power valve system. The valves are normaly in or around the exhaust ports. They work in one of two ways, either they alter the exhaust port size (and therefore port time) such as Suzuki AETC system or alter the volume on the exhaust, such as Honda V-TACS system. The result is an engine with better low down power and much more high rpm power.

Basic operation The two-stroke engine is simple in construction, but complex dynamics are employed in its operation. A typical simple two-stroke contains a piston whose face is shaped, an exhaust port on one side of the cylinder, and an intake port on the other side. The downward movement of the piston first uncovers the exhaust port, allowing most of the exhaust to be expelled, and

then uncovers the intake port through which an air-fuel mixture (the fuel normally has some oil mixed in) is let into the cylinder. The piston then moves upwards, compressing the mixture which is ignited by a spark plug, driving the piston back down. In more detail: Intake and compression The rising piston creates a partial vacuum in the sealed crankcase. A connection (inlet port) between the crankcase and the carburetor is uncovered by the piston as it rises, and the air-fuel mixture is sucked into the crankcase. At the same time, the air-fuel mixture already in the cylinder is being compressed. Steps of two-stroke cycle: Expansion stroke: The piston is at Top Dead Center (TDC) Crank is at 0 or 360. In real engines the process is completed from 0 to 150 but in this model it is completed at 120. Intake/Compression stroke: The piston moves from Bottom Dead Center (BDC) to T.D.C. The intake port is opened and working substance flows in. Intake gases move inside due to partial vacuum and also blowers are used to push intake gases in. The vacuum opens the reed valve (thin flexible sheets made of steel, glass fiber or even carbon fiber) allowing the mixture to enter the crankcase. the air-fuel mixture already in the cylinder is being compressed. As the piston nears the top of the stroke, the ignition system ignites the charge in the combustion chamber. In diesel engines, at 11-13 fuel is injected in TDC Up till now only air is compressed. Fuel is injected till the last stage of compression. Exhaust and scavenging process: The piston moves from TDC to BDC At 120 exhaust port is opened and exhaust gases move out of the cylinder due to inertia of steam. After 8-12 fresh scavenging gases are then let into to the cylinder. the air/fuel/oil mixture that was let into the cylinder pushes the exhaust out the exhaust port the pistion, then, compresses the air/fuel/oil mixture and lets left over exhaust out

Operation of a piston port engine Power and exhaust When the piston reaches the top of its stroke, the mixture is ignited, and the piston is forced down by the rapidly expanding gases of combustion. As the piston descends, a hole in the side of the cylinder connected to the exhaust pipe (exhaust port) is opened, and the burned gases can escape. Furthermore, the descending piston closes the inlet port and pressurizes the crankcase. This pushes also some mixture from the crankcase back to the inlet tract, causing the reed valve to close and preventing the mixture from entering the air filter. The air fuel mixture is forced into passageways that connect the crankcase to the cylinder. Holes connecting these passages to the upper cylinder (transfer ports) are uncovered by the descending piston and air-fuel mixture is forced into the upper cylinder. The transfer ports are just a bit lower than the top of the exhaust port, so there is a period of time when fresh air-fuel mixture is coming in while exhaust is leaving. The incoming fresh charge assists in forcing the exhaust gas out. As the piston reaches the bottom and then starts to rise again, the transfer ports are closed by the piston and the air/fuel mixture is compressed. The next cycle starts. Design issues

A major problem with the two-stroke engine has been the short-circuiting of fresh charge from intake to exhaust which increases fuel consumption and emissions of unburned hydrocarbons. The cylinder ports and piston top are shaped to minimise this mixing of the intake and exhaust flows. Furthermore, a tuned pipe with an expansion chamber provides back pressure at just the right time to push fresh air-fuel mixture sneaking out the exhaust back in again. The major components of two-stroke engines are tuned so that optimum airflow results. Intake and exhaust pipes are tuned so that resonances in airflow give better flow. Two stroke engines mix lubricant with their fuel (either manually at refueling or by injecting oil into the fuel stream); this mixture lubricates the cylinder, crankshaft and connecting rod bearings. The lubricant is subsequently burned, resulting in undesirable emissions. An independent lubrication system from below, as is used in four-stroke designs, cannot be used in the above-described two stroke engine design, since the crank case is being used to hold the airfuel mixture. This problem has been addressed in newer engines which employ direct injection, similar to diesel two-strokes. [ Two-stroke diesel engines A two-stroke cycle has also been used for some diesel engines. As the fuel is injected directly into the cylinder, the lubrication of the crankshaft must be independent in these engines. There is no mixing of lubricating oil into the fuel. There are three patterns. Some modern designs differ from the gasoline twostroke cycle in that they have intake and exhaust valves in the cylinder head, exactly like a four-stroke engine. In these engines, the two-stroke cycle is used to improve power-to-weight ratio and/or reduce the engine speed to increase reliability. This pattern, the Clark cycle, is common in truck, railroad locomotive and machinery engines. Other engines have used the same ported arrangement as the gasoline twostroke, although the charge air is generally delivered under pressure from a blower through ducting rather than through the crankcase. Examples are the Junkers Jumo 205 and Napier Deltic high-speed opposed piston engines. A third pattern uses the induction method of the gasoline two-stroke, but with an exhaust valve in the cylinder head. Large marine diesels commonly use this arrangement. These engines commonly also use a crosshead bearing, which together with a sliding seal on the piston rod allows the air path to be separated from the crankshaft while still using the piston movement as an air pump. The simpler stroke in the fully valved diesel two-stroke cycle is the compression stroke; both valves are closed, and the rising piston compresses

the air, heating it. At the top of the stroke, diesel fuel is injected into the cylinder, where it ignites and burns. The hot, high pressure gases produced by the combustion push against the piston as it descends in the initial part of the second stroke, delivering power. At this point, both valves are still closed. When the piston nears the bottom of the stroke, the exhaust valve opens, and the exhaust gases, still under pressure, rush out. The intake valve then opens. Air under pressure rushes into the cylinder, blowing out the remainder of the exhaust gases. The exhaust valve closes at that point, and shortly after that, and at about bottom dead center, so does the intake valve. If the crankcase is not used as an air pump, some other means of forced induction is required, and is often used for efficiency in any case. The intake air must be under pressure, since the engine does not have an induction stroke and cannot suck the air in by itself. A low-pressure supercharger (blower) is needed at minimum, but many are turbocharged. The diesel two-stroke generally lacks the inefficiency and pollution problems of the gasoline two-stroke, since no unburned fuel, only air, can get blown out of the exhaust valve before it closes. Also, there is no mixing of lubricant with the fuel. Compared with four-stroke engines Two-stroke engines have several marked disadvantages that have largely precluded their use in automobiles (although there was some use, such as in historic Saabs and DKWs and until recently in several automobiles produced in the Eastern bloc, including Trabants and Wartburgs, among others) and are reducing their prevalence in the above applications. Firstly, they require much more fuel than a comparably powerful four-stroke engine due to less efficient combustion. The burning oil, and the less efficient combustion, makes their exhaust far smellier and more damaging than a four-stroke engine, thus struggling to meet current emission control laws. They are noisier, partly due to the more penetrating high-frequency buzzing and partly due to the fact that muffling them reduces engine power far more than on a four-stroke engine (high-performance two-stroke engine exhausts are tuned by determining the resonant frequency of the exhaust systems and exploiting it to top-up the fuel air charge just before the cylinder port closes). Finally, they are considered less reliable and durable than four stroke engines. A notable area of use today is in small displacement motorcycles, mostly in off-road "dirt-bikes", and scooters, where their higher power-to-weight ratio, and smaller size outweigh their aforementioned disadvantages. There are more elaborate possible two-stroke engine configurations, but these often have enough complications that they do not outperform comparable four-stroke engines. New two-stroke designs rely on electronically-controlled fuel injection, oil injection and other design tweaks to reduce pollution and increase fuel efficiency. However, such systems increase the cost of the

engines to the point that for small systems simple four-stroke engines are most cost-effective. Many large manufacturers, including Ford and Honda are still actively researching ways to build practical and clean two strokes for automotive use.

Four-stroke cycle From Wikipedia, the free encyclopedia. The four-stroke cycle (or Otto cycle) of an internal combustion engine is the cycle most commonly used for automotive and industrial purposes today (cars and trucks, generators, etc). It was invented by German engineer Nikolaus Otto in 1876. The four-stroke cycle is more fuel-efficient and clean burning than the two-stroke cycle, but requires considerably more moving parts and manufacturing expertise and the resulting engine is larger and heavier than a two-stroke engine of comparable power output. The later-invented Wankel engine has four similar phases but is a rotary combustion engine rather than the much more usual, reciprocating engine of the four-stroke cycle.

four-stroke cycle The Otto cycle is characterized by four strokes, or straight movements alternately, back and forth, of a piston inside a cylinder: 1. intake (induction) stroke 2. compression stroke 3. power (ignition) stroke 4. exhaust stroke The cycle begins at top dead center, when the piston is at its topmost point. On the first downward stroke (intake) of the piston, a mixture of fuel and air is drawn into the cylinder through the intake (inlet) port. The intake (inlet) valve (or valves) then close(s), and the following upward stroke (compression) compresses the fuel-air mixture.

Starting position, intake stroke, and compression stroke. . The air-fuel mixture is then ignited, usually by a spark plug for a gasoline or Otto cycle engine, or by the heat and pressure of compression for a Diesel cycle of compression ignition engine, at approximately the top of the compression stroke. The resulting expansion of burning gases then forces the piston downward for the third stroke (power), and the fourth and final upward stroke (exhaust) evacuates the spent exhaust gases from the cylinder past the then-open exhaust valve or valves, through the exhaust port.

Ignition of fuel, power stroke, and exhaust stroke. . Valve Timing In its original configuration, the four-stroke engine relies entirely on the piston's motion to draw in fuel and air, and to force out the exhaust gasses. As the piston descends on the intake (inlet) stroke, a partial vacuum is created within the cylinder which draws in the fuel/air mixture. The intake valve then closes, the piston ascends, and the mixture is compressed and ignited, causing the piston to descend again. As the exhaust valve opens, the piston ascends once more and forces the exhaust gases out. This was the technique used in early four-stroke engines. It was soon discovered, however, that at rotational speeds approaching 100 revolutions per minute (RPM) or greater, the exhaust gasses could not change direction quickly enough to exit past the exhaust valve by the piston's motion alone. At high rotational speeds, consistent flow through the intake and exhaust ports is maintained by allowing the intake and exhaust valves to be open simultaneously at top dead center. The momentum of the exhausting gas

maintains the outward flow and initiates the induction flow. The trick is to close the exhaust valve before much fresh mixture is drawn into the exhaust port. After ignition of the fuel/air charge, as the piston approaches bottom dead center, it becomes less useful to retain the hot, high-pressure gasses within the cylinder. To this end, the exhaust valve is typically opened at about twenty degrees of crankshaft rotation before bottom dead center. This allows the development of gas momentum in the exhaust port before the piston rises to push the gas out. The advantage of the extra time available for more complete exhaust of the cylinder outweighs the loss of the slight potential power in the still expanding gas. As the piston ascends through the exhaust stroke, the intake valve will be opened, also approximately twenty degrees before top dead center. Ideally, the momentum of the exhaust flow will cause a lower pressure within the cylinder, pulling the fuel/air mixture in more easily. Consequently, both valves may be open simultaneously for a total of more than forty-five degrees of rotation, a technique called valve overlap. Under ideal conditions, the fresh fuel/air charge will push remaining exhaust gasses out the cylinder before the exhaust valve closes, leaving only a clean fuel/air mixture. Aiding the exhaust flow in this way is called scavenging. The disadvantage is lower fuel efficiency owing to the loss of fresh mixture into the exhaust port which can, however, serve the useful purpose of cooling the exhaust valve, an important consideration at high engine speeds, such as are experienced during races. Exhaust noise and emissions equipment may impede smooth exhaust flow out of the cylinder. When exhaust ports are close together and feeding into a manifold, the pressure wave of another exhausting cylinder may interfere with the first, trapping exhaust gasses. The same effect occurs in an intake manifold, generally being too restrictive for optimum power production. Also, excessive pressure in the cylinder may cause an exhaust back-flow into the intake manifold when the intake valve opens. The internal pressure problems with an induction manifold can be overcome by using a carburetor or injector for each cylinder. Accomplishing maximum volumetric efficiency for a given engine is not a formulaic process. Different intake and exhaust equipment is tested at different speeds and loads. The end result is always a compromise, and automobile manufacturers will usually choose the most cost effective solution. Valve train The valves are typically operated by a camshaft, which is a rod with a series of projecting cams (lobes), each with a carefully calculated profile designed to push the valve open by the required degree at the right moment and to hold it open as required as the camshaft rotates. Between the valve stem and the cam is a tappet, a cam follower, which accommodates variations in the line of contact of the cam. In older engine designs, the cam shaft was in the crankcase

and its motion transmitted by a push rod and rocker, the entire chain of parts being known as the valve train). The valve is held closed by a strong spring against the force of which the cam pushes to open it. Each valve is needed to open only once during the four-stroke cycle. Therefore, the camshaft makes one rotation for every two rotations of the crankshaft. Assuming the engine is robust enough in design not to break, the speed and therefore power output of the engine is typically limited by the ability to maintain a large volume flow of each of air-fuel mixture and exhaust gas through the respective valve ports. Therefore a great deal of work goes into designing this part of an engine. Common strategies are to enlarge the valves to take up as much of the cylinder diameter as possible, to lighten the valve train by eliminating parts, to open the valves as far as possible into the cylinder, or to use multiple smaller valves with more total area. Each of these methods has its drawbacks, causing the recent development of engines with computer controlled valve operation to optimize the engine's operation at any speed and load. The illustrations show an engine with Double overhead cams, which has for many years, been a standard strategy for increasing the highspeed capability of an engine Desmodromic valve timing In the vast majority of four-stroke engines, the valves are closed simply by return springs. As the rotational speed of the engine increases, the time taken for the spring to pull the valve shut can become significant. The cam follower then fails to follow the closing profile of the cam, changing the timing and therefore the engine performance detrimentally. To reduce this, lighter valves and stronger springs are used, but there is a practical limit to how low the inertial mass of the valve can be reduced, and increasing the strength of the valve return spring greatly increases the already considerable wear on the camshaft. One solution to this problem is the desmodromic valve timing system. This eliminates the valve return spring and uses a mechanical arrangement to both directly open and directly close the valve positively. Much higher engine speeds can then be obtained. Some designs use an additional cam and rocker, others a cam which has a channel milled into its vertical face which the follower runs in (as opposed to following the outside profile only), others a crank arrangement similar to the crankshaft. The drawback of the system is its increased complexity and therefore cost. One manufacturer using this system is Ducati, for some of its motorcycle engines. Pneumatic Valve Springs Recent Formula 1 engines have resorted to use of pneumatic valve springs to overcome the high-RPM limitations of metallic springs while still using conventional camshafts. The valve "spring" is actually a piston filled with

high pressure nitrogen. When the valve is actuated by the cam, the nitrogen is compressed, and as the cam continues its rotation, the increased pressure in the piston returns the valve to a closed position. With this system, previously unimaginable engine speeds have become routine. Output limit The amount of power output generated by a 4-stroke engine is ultimately limited by piston speed. If piston speed exceeds a certain velocity, the rapid acceleration of the piston, and the inertia of the piston rings conspire to cause ring flutter, a condition that will instantly cause a decrease in output. The only way to decrease the piston speed of any given engine is to increase the bore (cylinder diamerter), while decreasing the stroke. An engine where the bore dimension is larger than the stroke is commonly known as an oversquare engine, and such engines have the ability to attain high RPM. Conversely, an engine with a bore that is smaller than its stroke is an undersquare engine. Respectively, it cannot attain high RPM, but is liable to make higher torque at low RPM. In addition, an engine with a bore and stroke that are the same is referred to as a square engine

Wankel engine From Wikipedia, the free encyclopedia.

Wankel Engine in Deutsches Museum Munich, Germany The Wankel rotary engine is a type of internal combustion engine, invented by German engineer Felix Wankel, which uses a rotor instead of reciprocating pistons. This design promises smooth high-rpm power from a compact, lightweight engine; however Wankel engines are criticized for poor fuel efficiency and exhaust emissions. Introduction Since its introduction in the NSU Motorenwerke AG (NSU) and Mazda cars of the 1960s, the engine has also been commonly referred to as the "rotary engine"; however, that name also applies to a wide variety of other engine designs, most notably the rotary piston engine once commonly used in aircraft, as well other rotary combustion engine designs such as a more recent concept called the Quasiturbine. Although many manufacturers licensed the design, only Mazda has produced Wankel engines in large numbers. Today, the engine is only available in a single Mazda car currently produced, the Mazda RX-8. [edit] How it works In the Wankel engine, the four strokes of a typical Otto cycle engine are arranged sequentially around an oval, unlike the reciprocating motion of a piston engine. In the basic single rotor Wankel engine, a single oval (technically an epitrochoid) housing surrounds a three-sided rotor (a Reuleaux triangle) which turns and moves within the housing. The sides of the rotor seal against the sides of the housing, and the corners of the rotor seal against the inner periphery of the housing, dividing it into three combustion chambers.

The Wankel cycle: Intake (cyan), Compression (green), Ignition (red), Exhaust (yellow) As the rotor turns, its motion and shape and the shape of the housing cause each side of the rotor to get closer and farther from the wall of the housing, compressing and expanding the combustion chamber similarly to the "strokes" in a reciprocating engine. However, whereas a normal four stroke cycle engine produces one combustion stroke per cylinder for every two revolutions (that is, one half power stroke per revolution per cylinder) each combustion chamber of each rotor in the Wankel generates one combustion 'stroke' per revolution (that is, three power strokes per rotor revolution). Since the Wankel output shaft is geared to spin at three times the rotor speed, this becomes one combustion 'stroke' per output shaft revolution per rotor, twice as many as the four-stroke piston engine, and similar to the output of a two stroke cycle engine. Thus, power output of a Wankel engine is generally higher than that of a four-stroke piston engine of similar engine displacement in a similar state of tune, and higher than that of a four-stroke piston engine of similar physical dimensions and weight. National agencies which tax automobiles according to displacement and regulatory bodies in automobile racing variously consider the Wankel engine to be equivalent to a four-stroke engine of 1.5 to 2 times the displacement; some racing regulatory agencies view it as offering so pronounced an advantage that they ban it altogether. [edit] Advantages Wankel engines have several major advantages over reciprocating piston designs, in addition to having higher output for similar displacement and physical size. Wankel engines are considerably simpler and contain far fewer moving parts. For instance, because valving is accomplished by simple ports

cut into the walls of the rotor housing, they have no valves or complex valve trains; in addition, since the rotor is geared directly to the output shaft, there is no need for connecting rods, a conventional crankshaft, crankshaft balance weights, etc. The elimination of these parts not only makes a Wankel engine much lighter (typically half that of a conventional engine with equivalent power), but it also completely eliminates the reciprocating mass of a piston engine with its internal strain and inherent vibration due to repetitious acceleration and deceleration, producing not only a smoother flow of power but also the ability to produce more power by running at higher rpm. In addition to the enhanced reliability due to the elimination of this reciprocating strain on internal parts, the construction of the engine, with an iron rotor within a housing made of aluminum which has greater thermal expansion, ensures that even when grossly overheated the Wankel engine will not seize, as an overheated piston engine is likely to do; this has substantial benefit for aircraft use. The simplicity of design and smaller size of the Wankel engine also allow for a savings in construction costs, compared to piston engines of comparable power output. As another advantage, the shape of the Wankel combustion chamber and the turbulence induced by the moving rotor prevent localized hot spots from forming, thereby allowing the use of fuel of very low octane number without preignition or detonation, a particular advantage for Hydrogen cars. This feature also led to a great deal of interest in the Soviet Union, where high octane gasoline was rare. [edit] Disadvantages The design of the Wankel engine requires numerous sliding seals and a housing that is typically built as a sandwich of cast iron and aluminum pieces that expand and contract by different degrees when exposed to heating and cooling cycles in use. These elements led to a very high incidence of loss of sealing, both between the rotor and the housing and also between the various pieces making up the housing. Further engineering work by Mazda brought these problems under control, but the company was then confronted with a sudden global concern over both hydrocarbon emission and a rise in the cost of gasoline, the two most serious drawbacks of the Wankel engine. Just as the shape of the Wankel combustion chamber prevents preignition, it also leads to incomplete combustion of the air-fuel charge, with the remaining unburned hydrocarbons released into the exhaust. At first, while manufacturers of piston-engine cars were turning to expensive catalytic converters to completely oxidize the unburned hydrocarbons, Mazda was able to avoid this cost by paradoxically enriching the air/fuel mixture enough to produce an exhaust stream which was rich enough in hydrocarbons to actually support complete combustion in a 'thermal reactor' (just an enlarged open

chamber in the exhaust manifold) without the need for a catalytic converter, thereby producing a clean exhaust at the cost of some extra fuel consumption. Unfortunately for Mazda, their switch to this solution was immediately followed by a sharp rise in the cost of gasoline worldwide, so that not only the added fuel cost of their 'thermal reactor' design, but even the basically lower fuel economy of the Wankel engine caused sales to drop alarmingly. Another disadvantage of the Wankel engine is the difficulty of expanding the engine to more than two rotors. The complex shapes of the rotor, housing, and output shaft and the way they fit together requires that engines with more than two rotors use an output shaft made of several sections assembled during the assembly of the rest of the engine. While this technique has been used successfully in Wankel powered racing cars, it negates a great deal of the relative simplicity and lower cost of the Wankel engine construction. The main problems with the engine, however, have been fixed in the engine of the RX-8. The ports, formerly on the sides, are now placed to the rear of the engine. Fuel consumption is within normal limits while passing California State emissions requirements. History Wankel first conceived his rotary engine in 1924 and finally received a patent for it in 1929. He worked through the 1940s to improve the design. Considerable effort went into designing rotary engines in the 1950s and 1960s. They were of particular interest because they were smooth and very quiet running, and the reliability resulting from their simplicity. In Britain, Norton Motorcycles developed a Wankel rotary engine for motorcycles, which was included in their Commander; Suzuki also produced a production motorcycle with a Wankel engine, the RE-5. John Deere Inc, in the US, had a major research effort in rotary engines and designed a version which was capable of using a variety of fuels without changing the engine. The design was proposed as the power source for several US Marine combat vehicles in the late 1980s. After occasional use in automobiles, for instance by NSU with their Ro 80 model, Citron with the M35 and GS Birotor using engines produced by Comotor, and abortive attempts by General Motors and Mercedes Benz to design Wankel-engine automobiles, the most extensive automotive use of the Wankel engine has been by the Japanese company Mazda.

3-Rotor Eunos Cosmo engine After years of development, Mazda's first Wankel engined car was the 1967 Mazda Cosmo. The company followed with a number of Wankel ("rotary" in the company's terminology) vehicles, including a bus and a pickup truck. Customers generally loved them, notably the smoothness. However they had the very bad luck of being released in the middle of efforts to decrease emissions and increase fuel economy. Mazda later abandoned the Wankel in most of their automotive designs, but continued using it in their RX-7 sports car until August of 2002 (although RX-7 importation for North America ceased with the 1995 model year). The company normally used two-rotor designs, but received considerable attention with their 1991 Eunos Cosmo, which used a twin-turbo three-rotor engine. In 2003, Mazda re-launched the rotary with the new RX-8. This new engine relocated the ports for exhaust and intake from the peripheral of the rotary housing to the sides, allowing for larger overall ports, better airflow, and further power gains. The renesis is capable of delivering 238 horsepower from its minute 1.3 liter displacement at better fuel economy, reliability, and environmental friendliness than any other Mazda rotary engine in history. The Malibu Grand Prix chain, similar in concept to commercial recreational kart racing tracks, operates several venues in the United States where a customer can purchase several laps around a track in a vehicle very similar to open wheel racing vehicles, but powered by a small Curtiss-Wright rotary engine. Although VAZ, the Soviet automobile manufacturer, is known to have produced Wankel-engine automobiles, and Aviadvigatel, the Soviet aircraft engine design bureau, is known to have produced Wankel engines for aircraft and helicopters, little specific information has surfaced in the outside world; what has been seen indicates a general similarity to Wankel designs by NSU, Comotor, and Mazda, therefore it is likely that many Western patents were infringed upon by these designs, the probable reason for their being hidden. The People's Republic of China is also known to have experimented with Wankel engines, but even less is known in the West about the work done there, other than one paper, #880628, delivered to the SAE in 1988 by Chen Teluan of the South China Institute of Technology at Guangzhou. Automobile racing In the racing world, Mazda has had substantial success with two-rotor, threerotor, and four-rotor cars, and private racers have also had considerable success with stock and modified Mazda Wankel-engine cars. The Sigma MC74 powered by a Mazda 12A engine was the first engine and team from outside Western Europe or the United States to finish the entire 24 hours of the 24 Hours of Le Mans race, in 1974. Mazda is the only team from outside Western Europe or the United States to have won Le Mans outright

and the only non-piston engine ever to win Le Mans, which the company accomplished in 1991 with their four-rotor 787B (2622 cc actual displacement, rated by FIA formula at 4708 cc). Mazda is also the most reliable finisher at LeMans (with the exception of Honda, who have entered only three cars in only one year), with 67% of entries finishing. The Mazda RX-7 has won more IMSA races in its class than any other model of automobile, with its one hundredth victory on September 2, 1990. Following that, the RX-7 won its class in the IMSA 24 hours of Daytona race ten years in a row, starting in 1982. The RX7 won the IMSA Grand Touring Under Two Liter (GTU) championship each year from 1980 through 1987, inclusive. Formula Mazda Racing features open-wheel race cars with Mazda Wankel engines, adaptable to both oval tracks and road courses, on several levels of competition. Since 1991, the professionally organized Star Mazda Series has been the most popular format for sponsors, spectators, and upward bound drivers. The engines are all built by one engine builder, certified to produce the prescribed power, and sealed to discourage tampering. They are in a relatively mild state of racing tune, so that they are extremely reliable and can go years between motor rebuilds. Aircraft engines The Wankel's superb power-to-weight ratio, reliability, and small frontal area make it particularly well suited to aircraft engine use. There was intense interest in them in this role in the 1950s when the design was first becoming well known, but it was at this same time that almost the entire industry was moving to the jet engine, which many believed would be the only engine in use within a decade. The Wankel suffered from a lack of interest, and when it later became clear that the jet engine was far too expensive for all roles, the general aviation world had already shrunk so much that there was little money for new engine designs. Nevertheless, interest in them for small aircraft has continued. The first rotary-engine aircraft was the experimental Lockheed Q-Star civilian version of the U.S. Army's reconnaissance QT-2, basically a powered Schweizer sailplane, in 1968 or 1969. It was powered by a 185 horsepower (138 kW) Curtiss-Wright RC2-60 Wankel rotary engine. Aircraft Wankels have made something of a comeback in recent years. None of their advantages have been lost in comparison to other engines, and the introduction of better materials has helped the tip-seal (Apex-seal) problem. They are being found increasingly in roles where their compact size and quiet running is important, notably in drones, or UAVs. Many companies and hobbyists adapt Mazda rotary engines to aircraft use; others, including Wankel GmbH itself, manufacture Wankel rotary engines dedicated for the purpose. [edit] Other uses

Small Wankel engines are being found increasingly in other roles, such as gokarts, personal water craft and auxiliary power units for aircraft. The Graupner/O.S. 49-PI is a 1.27 horsepower (947 W) 5 cc Wankel engine for model airplane use which has been in production essentially unchanged since 1970; even with a large muffler, the entire package weighs only 13.4 ounces (380 grams). The simplicity of the Wankel makes it ideal for mini, micro, and micro-mini engine designs. The MicroElectroMechanical Systems (MEMS) Rotary Engine Lab at the University of California, Berkeley has been developing Wankel engines of down to 1 mm in diameter with displacements less than 0.1 cm. Materials include silicon and motive power includes compressed air. The goal is to eventually develop an internal combustion engine that will deliver 100 milliwatts of electrical power; the engine itself will serve as the rotor of the generator, with magnets built into the engine rotor itself. The largest Wankel engine was built by Ingersoll-Rand; available in 550 horsepower (410 kW) one rotor and 1100 horsepower (820 kW) two rotor versions, displacing 41 liters per rotor with a rotor approximately one meter in diameter, it was available between 1975 and 1985. It was derived from a previous, unsuccessful, Curtiss-Wright design, which failed because of a wellknown problem with all internal combustion engines; the fixed speed at which the flame front travels limits the distance combustion can travel from the point of ignition in a given time, and thereby the maximum size of the cylinder or rotor chamber which can be used. This problem was solved by limiting the engine speed to only 1200 rpm and use of natural gas as fuel; this was particularly well chosen, as one of the major uses of the engine was to drive pumps on natural gas pipelines. Aside from being used for internal combustion engines, the basic Wankel design has also been utilized for air compressors, and superchargers for internal combustion engines, but in these cases, although the design still offers advantages in reliability, the basic advantages of the Wankel in size and weight over the four-stroke internal combustion engine are irrelevant. In a design using a Wankel supercharger on a Wankel engine, the supercharger is twice the size of the engine! Perhaps the most exotic use of the Wankel design is in the seat belt pretensioner system of the Volkswagen New Beetle. In this car, when deceleration sensors sense a potential crash, small explosive cartridges are triggered electrically and the resulting pressurized gas feeds into tiny Wankel engines which rotate to take up the slack in the seat belt systems, anchoring the driver and passengers firmly in the seat before any collision.


From Wikipedia, the free encyclopedia.

The Quasiturbine combustion cycle: Intake (aqua), Compression (fuchsia), Ignition (red), Exhaust (black). A spark plug is located at the top (green) The Quasiturbine engine is a type of rotary combustion engine, invented by the Saint-Hilaire family and first patented in 1996. The engine uses a foursided articulated rotor that turns within a curve of constant width, creating regions of increasing and decreasing volumes as the rotor turns. The Quasiturbine design can also be used as an air motor, steam engine, gas compressor, hot air engine, or pump. It is capable of burning fuel using photodetonation, an optimal combustion type.

Definition : The Quasiturbine (Qurbine) is a no crankshaft rotary engine having a 4-faced articulated rotor with a free and accessible centre, rotating without vibration or dead time, and producing a strong torque at low RPM under a variety of modes and fuels. The Quasiturbine is also an optimization theory for extremely compact and efficient engine concepts. Contents [show] [edit] How it works In the Quasiturbine engine, the four strokes of a typical cycle de Beau de Rochas (Otto cycle) are arranged sequentially around a near oval, unlike the reciprocating motion of a piston engine. In the basic single rotor Quasiturbine engine, an oval housing surrounds a four-sided articulated rotor which turns and moves within the housing. The sides of the rotor seal against the sides of the housing, and the corners of the rotor seal against the inner periphery,

dividing it into four chambers. In contrast to the Wankel engine where the crankshaft moves the rotary piston face inward and outward, the Quasiturbine rotor face rocks back and forth with reference to the engine radius, but stays at a constant distance from the engine center at all time, producing only pure tangential rotational forces. Because the Quasiturbine has no crankshaft, the internal volume variations do not follow the usual sinusoidal engine movement, which provides very different characteristics from the piston or the Wankel engine. As the rotor turns, its motion and the shape of the housing cause each side of the housing to get closer and farther from the rotor, compressing and expanding the chambers similarly to the "strokes" in a reciprocating engine. However, whereas a four stroke cycle engine produces one combustion stroke per cylinder for every two revolutions, i.e. one half power stroke per revolution per cylinder, the four chambers of the Quasiturbine rotor generate four combustion "strokes" per rotor revolution; this is eight times more than a four-stroke piston engine. [edit] Advantages Quasiturbine engines are simpler, and contain no gears and far fewer moving parts. For instance, because intake and exhaust are openings cut into the walls of the rotor housing, there are no valves or valve trains. This simplicity and small size allows for a savings in construction costs. Because its center of mass is immobile during rotation, the Quasiturbine tends to have very little or no vibrations. Due to the absence of dead time between strokes, the Quasiturbine can be driven by compressed air or steam without synchronized valve, and also with liquid as hydraulic motor or pump. Other claimed advantages include high torque at low rpm, combustion of hydrogen and compatibility with photo-detonation mode in Quasiturbine with carriages, where high surface-to-volume ratio is an attenuating factor of the violence of the detonation.

Quasiturbine configured as a steam engine [edit] Disadvantages The design of the Quasiturbine engine is typically built of aluminum and cast iron which expand and contract by different degrees when exposed to heat leading to some incidence of leakage. A similar problem was encountered in early Wankel engines but engineering development has brought these problems under control for both engines. [edit] History The Quasiturbine was conceived by a group of 4 researchers lead by Dr. Gilles Saint-Hilaire, a thermonuclear physicist. The original objective was to make a turbo-shaft turbine engine where the compressor portion and the power portion would be in the same plane. In order to achieve this, they had to disconnect the blades from the main shaft, and chain them around in such a way that a single rotor acts as a compressor for a quarter turn, and as an engine the following quarter of a turn. The general concept of the Quasiturbine was first patented in 1996. Small pneumatic and steam units are available for research, academic training and industrial demonstration. Similar combustion prototypes are also intended for demonstration. In November 2004, a Quasiturbine engine was demonstrated on a go-kart. [edit] Potential applications The Quasiturbine's high power-to-weight ratio makes it exceptionally suitable for aircraft engine and its no-vibration attributes make it suitable for use in, for example: chainsaws, powered parachutes, snowmobiles, jet skis and other watercraft, aircraft,etc. Variations on the basic Quasiturbine design also have applications as air compressors and as turbochargers/superchargers. [edit] Wankel comparison The Quasiturbine is superficially similar to the Wankel engine, but is quite distinct from it. The Wankel engine has a single rigid triangular rotor synchronized by gears with the housing, and driven by a crankshaft rotating at three times the rotor speed, which moves the rotor faces radially inward and outward. The Wankel attempt to realize the four strokes with a three-sided rotor, limits overlapping port optimization, and because of the crankshaft, the Wankel has near sinusoidal volume pulse characteristics like the piston. The Quasiturbine has a four-sided articulated rotor, rotating on a circular supporting track with a shaft rotating at the same speed as the rotor. It has no synchronization gears and no crankshaft, which allows carriage types to shape

"almost at will" the pressure pulse characteristics for specific needs, including achieving photo-detonation. The Wankel engine divides the perimeter into three sections while the Quasiturbine divides it into four, for a 30% less elongated combustion chamber. The Wankel geometry further imposes a top dead center residual volume which limits its compression ratio and prevents compliance with the Pressure-Volume diagram. The Wankel has three 30 degree dead times per rotor rotation, while the Quasiturbine has none which allows continuous combustion by flame transfer, and allows it to be driven by compressed air or steam without synchronized valves (also by liquid as a hydraulic motor or pump). During rotation, the Wankel apex seals intercept the housing contour at variable angles from -60 to +60 degrees, while the Quasiturbine contour seals are almost perpendicular to the housing at all time. While the Wankel engine requires dual (or more) out-of-phase rotors for vibration compensation, the Quasiturbine is suitable as a single rotor engine, because its center of mass is immobile during rotation. While the Wankel shaft rotates continuously, the rotor does not, as it stops its rotation (even reverses) near top dead center, an important rotor angular velocity modulation generating strong internal stresses not present in the Quasiturbine. [edit] Photo-detonation Photo-detonation is the optimum combustion mode, like a laser volumetric combustion, a mode the sinusoidal piston or Wankel pressure pulse shape cannot withstand. Diesel combustion is driven by thermal ignition; gasoline piston engine is driven by thermal combustion wave; knocking detonation is driven by a supersonic shock wave; while photo-detonation is a volumetric combustion driven by intense radiation in the combustion chamber. Because the Quasiturbine has no crankshaft and can have carriages, the pressure pulse can be shaped like the minuscule cursive letter " i ", with a high pressure tip 15 to 30 times shorter that the piston or Wankel volume pulse, and with rapid linear rising and falling ramps. This kind of volume pulse is photo-detonation self-synchronizing and reduces the immense stresses by shortening the high pressure duration. [edit] Efficiency at low power The modern high-power piston engine in automobiles is generally used with only a 15% average load factor. The efficiency of a 200 kW gas piston engine falls dramatically when used at 20 kW because of high vacuum depressurization needed in the intake manifold, which vacuum become less as the power produced by the engine increases. Photo-detonation engines do not need intake vacuum as they intake all the air available, and mainly for this reason, efficiency stays high even at low engine power.

The development of a photo-detonation engine may provide a means to avoid that low-power-efficiency-penalty; may be more environment friendly as it will require low octane additive-free gasoline or diesel fuel; may be multi-fuel compatible, including direct hydrogen combustion; and may offer reduction in the overall propulsion system weight, size, maintenance and cost. For these reasons it could be better or competitive with hybrid car technology. [edit] Hybrid alternative It is the purpose of the hybrid car concept to avoid the low efficiency of the Otto cycle engine at reduced power. There is a 50% fuel saving potential, of which about half could be harvested the hybrid way. But getting extra efficiency this way requires additional power components and energy storage, with associated counter-productive increases in weight, space, maintenance, cost and environmental recycling process. The development of a photodetonation engine like the Quasiturbine would provide more direct means to achieve the same or better. However, it has not been proven that the Quasiturbine engine would be able to use the hoped for photo-detonation. And although a working prototype has now been constructed, there are no results indicating fuel consumption per unit power. Furthermore, a vehicle powered by a Quasiturbine, photodetonating engine will not provide one of the most important benefits of hybrid technology, regenerative braking, without additional equipment. Because the engine is still in the prototype phase, it may be decades before it is ready to be a competitive technology for vehicles

Gas turbine

This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings. A gas turbine is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber inbetween. (Gas turbine may also refer to just the turbine element.) Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a diffuser (nozzle) over the turbine's blades, spinning the turbine and powering the compressor. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships,generators, and even tanks

Theory of operationGas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.

As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the

turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (co-generation) uses waste heat for hot water production. Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft/compressor/turbine/alternator-rotor assembly (see image above), not counting the fuel system. More sophisticated turbines may have multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast system of complex piping, combustors and heat exchangers. The largest gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid. They require a dedicated building. Smaller turbines, with fewer compressor/turbine stages, spin faster. Jet engines operate around 10,000 rpm and micro turbines around 100,000 rpm. Thrust bearings and journal bearings are a critical part of design. Traditionally, they have been hydrodynamic oil bearings, or oil-cooled ball bearings. This is giving way to hydrodynamic foil bearings, which have become common place in micro turbines and APUs (auxiliary power units.)edit

Jet enginesSee jet engine page.]

Gas turbines for electrical power production

GE H series power generation gas turbine. This 400-megawatt unit has a rated thermal efficiency of 60% in combined cycle configurations. Powerplant gas turbines range in size from truck-mounted mobile plants to enormous, complex systems.

They can be particularly efficientup to 60 percentwhen waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration. Simple cycle gas turbines in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or large amounts of power. Also, the actual construction process can take a little as several weeks to a few months, compared to years for baseload plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40 percent thermal efficiency. [edit]

Micro turbines

A micro turbine designed for DARPA by M-Dot Also known as: Turbo alternators Gensets MicroTurbine (registered trademark of Capstone Turbine Corporation) Turbogenerator (registered tradenameHoneywell Power Systems)

Micro turbines are becoming wide spread for distributed power and combined heat and power applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts. Part of their success is due to advances in electronics, which allow unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows, for example, the generator to be integrated with the turbine shaft, and to double as the starter motor.

Micro turbine systems have many advantages over piston engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. However, piston engine generators are quicker to respond to changes in output power requirement. They accept most commercial fuels, such as natural gas, propane, diesel and kerosene. The are also able to produce renewable energy when fueled with biogas from landfills and sewage treatment plants. Micro turbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy. Typical micro turbine efficiencies are 25 to 35 percent. When in a combined heat and power cogeneration system, efficiencies of greater than 80 percent are commonly achieved. Nye Thermodynamics Corporation [1] is developing a wood fueled microturbine for cogeneration applications. [edit]

Auxiliary power unitsAPUs are small gas turbines designed for auxiliary power of larger machines, usually aircraft. They are well suited for supplying compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power. (These are not to be confused with the auxiliary propulsion units, also abbreviated APUs, aboard the gas-turbine-powered Oliver Hazard Perry-class guidedmissile frigates. The Perrys' APUs are large electric motors that provide maneuvering help in close waters, or emergency backup if the gas turbines are not working.) [edit]

Gas turbines in vehiclesGas turbines are used on ships, locomotives, helicopters, and in the M1 Abrams and T-80 tanks. A number of experiments have been conducted with gas turbine powered automobiles. In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The twoseater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined

forces to produce a gas turbine powered coupe, which entered the 1963 24 hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km) and had a top speed of 142 mph (229 km/h). American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. A history of Chrysler turbine cars. In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicleas a limited production run of the EV-1. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator. Gas turbines do offer a high-powered engine in a very small and light package, but there remain unchanged three main reasons why small turbines have not succeeded in an automotive application. Firstly, small turbines are fundamentally less fuel-efficient than small piston engines. Secondly, this problem is exacerbated by the requirement for automotive engines to run efficiently at idle and low throttle openings; turbines are notably inefficient at this. Finally, turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small turbines are rarities. It is also worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the second problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles. Their use in military tanks has been more successful. As well as their production use in the T-80 and Abrams, in the 1950's an FV214 Conqueror tank Heavy Tank was experimentally fitted with a Parsons 650 hp gas-turbine. Production gas turbine motorcycle first appeared in MTT Turbine SUPERBIKE in 2000. This high-priced machine is produced in miniscule numbers. [edit]

Amateur gas turbinesKurt Schreckling pioneered home constructed turbojet engines for model aircraft. There are several small businesses producing plans, kits and assembled turbines. A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. See external links for resources. [edit]

Advances in technologyGas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher

compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system. On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power. An excellent example is the Capstone line of micro turbines, which do not require an oil system and can run unattended for months on end. [edit]

Naval useGas turbines are used in many naval vessels, where they are valued for their high power-toweight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961. The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines.

Combustion. Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer), usually O2, to release heat. In a complete combustion reaction, a compound reacts with an oxidizing element, and the products are compounds of each element in the fuel with the oxidizing element. For example: CH2S + 6 F2 CF4 + 2 HF + SF6 + heat

Rapid combustion

Rapid combustion is a form of combustion in which large amounts of heat and light energy are released. This often occurs as a fire. This is used in forms of machinery, such as internal combustion engines, and in fuel-air explosives. [edit]

Slow combustionSlow combustion is a form of combustion which takes place at low temperatures. Respiration is an example of slow combustion. [edit]

Complete combustionIn complete combustion, the reactant will burn in oxygen, producing a limited amount of products. When a hydrocarbon burns in oxygen, the reaction will only yield carbon dioxide and water. When elements such as carbon, nitrogen, sulfur, and iron are burned, they will yield the most common oxides. Carbon will yield carbon dioxide. Nitrogen will yield nitrogen dioxide. Sulfur will yield sulfur dioxide. Iron will yield iron(III) oxide. Complete combustion is generally impossible to achieve unless the reaction occurs in a lab environment where all the conditions are being controlled. [edit]

Incomplete combustionIn incomplete combustion, where sufficient oxygen for complete combustion is lacking, the reactant will burn in oxygen, but will produce numerous products. When a hydrocarbon burns in oxygen, the reaction will yield carbon dioxide, water, carbon monoxide, and various other compounds such as nitrogen oxides. Incomplete combustion is much more common and will produce large amounts of byproducts, and in the case of burning fuel in automobiles, these byproducts can be quite lethal and damaging to the environment. [edit]

Chemical equationGenerally, the chemical equation for burning a hydrocarbon (such as octane) in oxygen is as follows: CxHy + (x + y/4)O2 xCO2 + (y/2)H2O For example, the burning of propane is: C3H8 + 5O2 3CO2 + 4H2O

The simple word equation for the combustion of a hydrocarbon is: Fuel + Oxygen Heat + Water + Carbon dioxide.


Combustion temperaturesAssuming perfect combustion conditions, such as an adiabatic (i.e. no heat loss) and complete combustion, the adiabatic combustion temperature can be determined. This formula for this temperature is based on the first law of thermodynamics and takes note of the fact that the heat of combustion generated during combustion (calculated from the fuel's heating value) is used entirely for warming up fuel and gas (e.g. oxygen or air). In the case of fossil fuels burnt in air, the combustion temperature depends on the heating value the stoichiometric air ratio the heat capacity of fuel and air air and fuel inlet temperatures

The adiabatic combustion temperature increases for higher heating values and inlet temperatures and stoiciometric ratios towards one. Typically, the adiabatic combustion temperatures for coals are around 1500 deg C (for inlet temperatures of room temperatures and = 1.0), around 2000 deg C for oil and 2200 deg C for natural gas. Spacecraft propulsion From Wikipedia, the free encyclopedia. (Redirected from Rocket engine)

A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Spacecraft propulsion is used to change the velocity of spacecraft and artificial satellites, or in short, to provide delta-v. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. Most

spacecraft today are propelled by heating the reaction mass and allowing it to flow out the back of the vehicle. This sort of engine is called a rocket engine. All current spacecraft use chemical rocket engines (bipropellant or solid-fuel) for launch, though some (such as the Pegasus rocket and SpaceShipOne) have used air-breathing engines on their first stage. Most satellites have simple reliable chemical rockets (often monopropellant rockets) or resistojet rockets to keep their station, although some use momentum wheels for attitude control. Newer geo-orbiting spacecraft are starting to use electric propulsion for north-south stationkeeping. Interplanetary vehicles mostly use chemical rockets as well, although a few have experimentally used ion thrusters with some success (a form of electric propulsion). Contents [show] [edit] The necessity for propulsion systems Artificial satellites must be launched into orbit, and once there they must accelerate to circularize their orbit. Once in the desired orbit, they often need some form of attitude control so that they are correctly pointed with respect to the Earth, the Sun, and possibly some astronomical object of interest. They are also subject to drag from the thin atmosphere, so that to stay in orbit for a long period of time some form of propulsion is occasionally necessary to make small corrections (orbital stationkeeping). Many satellites need to be moved from one orbit to another from time to time, and this also requires propulsion. When a satellite has exhausted its ability to adjust its orbit, its useful life is over. Spacecraft designed to travel further also need propulsion methods. They need to be launched out of the Earth's atmosphere just as do satellites. Once there, they need to leave orbit and move around. For interplanetary travel, a spacecraft must use its engines to leave Earth orbit. Once it has done so, it must somehow make its way to its destination. Current interplanetary spacecraft do this with a series of short-term orbital adjustments. In between these adjustments, the spacecraft simply falls freely along its orbit. The simplest fuel-efficient means to move from one circular orbit to another is with a Hohmann transfer orbit: the spacecraft begins in a roughly circular orbit around the Sun. A short period of thrust in the direction of motion accelerates or decelerates the spacecraft into an elliptical orbit around the Sun which is tangential to its previous orbit and also to the orbit of its destination. The spacecraft falls freely along this elliptical orbit until it reaches its destination, where another short period of thrust accelerates or decelerates it to match the orbit of its destination. Special methods such as aerobraking are sometimes used for this final orbital adjustment.

Artist's conception of a solar sail

Some spacecraft propulsion methods such as solar sails provide very low but inexhaustible thrust; an interplanetary vehicle using one of these methods would follow a rather different trajectory, either constantly thrusting against its direction of motion in order to decrease its distance from the Sun or constantly thrusting along its direction of motion to increase its distance from the Sun. Spacecraft for interstellar travel also need propulsion methods. No such spacecraft has yet been built, but many designs have been discussed. Since interstellar distances are very great, a tremendous velocity is needed to get a spacecraft to its destination in a reasonable amount of time. Acquiring such a velocity on launch and getting rid of it on arrival will be a formidable challenge for spacecraft designers. [edit] Effectiveness of propulsion systems When in space, the purpose of a propulsion system is to change the velocity v of a spacecraft. Since this is more difficult for more massive spacecraft, designers generally discuss momentum, mv. The amount of change in momentum is called impulse. So the goal of a propulsion method in space is to create an impulse. When launching a spacecraft from the Earth, a propulsion method must overcome the Earth's gravitational pull in addition to providing acceleration. The rate of change of velocity is called acceleration, and the rate of change of momentum is called force. To reach a given velocity, one can apply a small acceleration over a long period of time, or one can apply a large acceleration over a short time. Similarly, one can achieve a given impulse with a large force over a short time or a small force over a long time. This means that for maneuvering in space, a propulsion method that produces tiny accelerations but runs for a long time can produce the same impulse as a propulsion method that produces large accelerations for a short time. When launching from a planet, tiny accelerations cannot overcome the planet's gravitational pull and so cannot be used. The law of conservation of momentum means that in order for a propulsion method to change the momentum of a space craft it must change the momentum of something else as well. A few designs take advantage of things like magnetic fields or light pressure in order to change the spacecraft's momentum, but in free space the rocket must bring along some mass to accelerate away in order to push itself forward. Such mass is called reaction mass.

An ion engine test In order for a rocket to work, it needs two things: reaction mass and energy. The impulse provided by launching a particle of reaction mass having mass m at velocity v is mv. But this particle has kinetic energy mv2/2, which must come from somewhere. In a conventional solid fuel rocket, the fuel is burned, providing the energy, and the reaction products are allowed to flow out the back, providing the reaction mass. In an ion thruster, electricity is

used to accelerate ions out the back. Here some other source must provide the electrical energy (perhaps a solar panel or a nuclear reactor) while the ions provide the reaction mass. When discussing the efficiency of a propulsion system, designers often