A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process.
61-683: The RD-193 is a high performance single- combustion chamber rocket engine , developed in Russia from 2011 to 2013. It is derived from the RD-170 originally used in the Energia launcher. The RD-193 is fueled by a kerosene / LOX mixture and uses an oxygen-rich staged combustion cycle . RD-193 was proposed as a replacement for the NK-33 , which is being used in the Soyuz-2-1v vehicle. The engine
122-406: A certain "swirl" pattern (rotational component to the gas flow) and turbulence , which improves the mixing and increases the flow rate of gasses. The shape of the piston top also affects the amount of swirl. Another design feature to promote turbulence for good fuel/air mixing is squish , where the fuel/air mix is "squished" at high pressure by the rising piston. The location of the spark plug
183-521: A crucial role in determining many of an engine's operating characteristics, such as fuel efficiency , levels of emissions, and transient response (the response to changing conditions such as fuel flow and air speed). The objective of the combustor in a gas turbine is to add energy to the system to power the turbines , and produce a high-velocity gas to exhaust through the nozzle in aircraft applications. As with any engineering challenge, accomplishing this requires balancing many design considerations, such as
244-401: A gas turbine engine, the combustor or combustion chamber is fed high-pressure air by the compression system. The combustor then heats this air at constant pressure as the fuel/air mix burns. As it burns the fuel/air mix heats and rapidly expands. The burned mix is exhausted from the combustor through the nozzle guide vanes to the turbine. In the case of ramjet or scramjet engines, the exhaust
305-689: A large change in area in the combustor (rather than swirlers in many gas turbine combustors). That said, many ramjet combustors are also similar to traditional gas turbine combustors, such as the combustor in the ramjet used by the RIM-8 Talos missile, which used a can-type combustor. Scramjet ( supersonic combustion ramjet ) engines present a much different situation for the combustor than conventional gas turbine engines (scramjets are not gas turbines, as they generally have few or no moving parts). While scramjet combustors may be physically quite different from conventional combustors, they face many of
366-444: A pressure vessel. The combustion zones can also "communicate" with each other via liner holes or connecting tubes that allow some air to flow circumferentially. The exit flow from the can-annular combustor generally has a more uniform temperature profile, which is better for the turbine section. It also eliminates the need for each chamber to have its own igniter. Once the fire is lit in one or two cans, it can easily spread to and ignite
427-424: A relatively compact combustion chamber without any protrusions to the side (i.e. all of the chamber is located directly above the piston). Common shapes for the combustion chamber are typically similar to one or more half-spheres (such as the hemi , pent-roof , wedge or kidney-shaped chambers). The older flathead engine design uses a "bathtub"-shaped combustion chamber, with an elongated shape that sits above both
488-428: A renewed focus on reducing emissions, particularly nitrogen oxides . Combustor technology is still being actively researched and advanced, and much modern research focuses on improving the same aspects. The case is the outer shell of the combustor, and is a fairly simple structure. The casing generally requires little maintenance. The case is protected from thermal loads by the air flowing in it, so thermal performance
549-449: A result of this close relation, a combustor that is well optimized for CO emissions is inherently well optimized for UHC emissions, so most design work focuses on CO emissions. Carbon monoxide is an intermediate product of combustion, and it is eliminated by oxidation . CO and OH react to form CO 2 and H . This process, which consumes the CO, requires a relatively long time ("relatively"
610-411: A sheet of fuel with a stream of air, atomizing the fuel into homogeneous droplets. This type of fuel injector led to the first smokeless combustors. The air used is just some of the primary air (see Air flow paths below) that is diverted through the injector, rather than the swirler. This type of injector also requires lower fuel pressures than the pressure atomizing type. The vaporizing fuel injector,
671-420: A single can, rather than have to test the whole system). Can-type combustors are easy to maintain, as only a single can needs to be removed, rather than the whole combustion section. Most modern gas turbine engines (particularly for aircraft applications) do not use can combustors, as they often weigh more than alternatives. Additionally, the pressure drop across the can is generally higher than other combustors (on
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#1732780547122732-408: Is a more modern approach that uses a porous material for the liner. The porous liner allows a small amount of cooling air to pass through it, providing cooling benefits similar to film cooling. The two primary differences are in the resulting temperature profile of the liner and the amount of cooling air required. Transpiration cooling results in a much more even temperature profile, as the cooling air
793-452: Is a simplified version of the RD-191 , omitting the swing assembly chamber and its related structural elements, thus reducing size and weight (300 kg) and lowering cost. Combustion chamber In an internal combustion engine , the pressure caused by the burning air/fuel mixture applies direct force to part of the engine (e.g. for a piston engine, the force is applied to the top of
854-405: Is air injected through holes in the liner at the end of the combustion chamber to cool the flue gas before it reaches the turbines. The air is carefully used to produce the uniform temperature profile desired in the combustor. However, as turbine blade technology improves, allowing them to withstand higher temperatures, dilution air is used less, allowing the use of more combustion air. Cooling air
915-425: Is air that is injected through small holes in the liner to generate a layer (film) of cool air to protect the liner from the combustion temperatures. The implementation of cooling air has to be carefully designed so it does not directly interact with the combustion air and process. In some cases, as much as 50% of the inlet air is used as cooling air. There are several different methods of injecting this cooling air, and
976-418: Is also an important factor, since this is the starting point of the flame front (the leading edge of the burning gasses) which then travels downwards towards the piston. Good design should avoid narrow crevices where stagnant "end gas" can become trapped, reducing the power output of the engine and potentially leading to engine knocking . Most engines use a single spark plug per cylinder, however some (such as
1037-549: Is directly fed out through the nozzle. A combustor must contain and maintain stable combustion despite very high air flow rates. To do so combustors are carefully designed to first mix and ignite the air and fuel, and then mix in more air to complete the combustion process. Early gas turbine engines used a single chamber known as a can-type combustor. Today three main configurations exist: can, annular, and cannular (also referred to as can-annular tubo-annular). Afterburners are often considered another type of combustor. Combustors play
1098-419: Is more and more important for high-performance, high-thrust engines. The snout is an extension of the dome (see below) that acts as an air splitter, separating the primary air from the secondary air flows (intermediate, dilution, and cooling air; see Air flow paths section below). The dome and swirler are the part of the combustor that the primary air (see Air flow paths below) flows through as it enters
1159-399: Is not damaged by the combustion itself. Once the combustion is initially started by the igniter, it is self-sustaining, and the igniter is no longer used. In can-annular and annular combustors (see Types of combustors below), the flame can propagate from one combustion zone to another, so igniters are not needed at each one. In some systems ignition-assist techniques are used. One such method
1220-421: Is of limited concern. However, the casing serves as a pressure vessel that must withstand the difference between the high pressures inside the combustor and the lower pressure outside. That mechanical (rather than thermal) load is a driving design factor in the case. The purpose of the diffuser is to slow the high-speed, highly compressed, air from the compressor to a velocity optimal for the combustor. Reducing
1281-414: Is oxygen injection, where oxygen is fed to the ignition area, helping the fuel easily combust. This is particularly useful in some aircraft applications where the engine may have to restart at high altitude. This is the main combustion air. It is highly compressed air from the high-pressure compressor (often decelerated via the diffuser) that is fed through the main channels in the dome of the combustor and
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#17327805471221342-500: Is reducing emissions, and the combustor is the primary contributor to a gas turbine's emissions. Generally speaking, there are five major types of emissions from gas turbine engines: smoke, carbon dioxide (CO 2 ), carbon monoxide (CO), unburned hydrocarbons (UHC), and nitrogen oxides (NO x ). Smoke is primarily mitigated by more evenly mixing the fuel with air. As discussed in the fuel injector section above, modern fuel injectors (such as airblast fuel injectors) evenly atomize
1403-454: Is still required. In general, there are two main types of liner cooling; film cooling and transpiration cooling. Film cooling works by injecting (by one of several methods) cool air from outside of the liner to just inside of the liner. This creates a thin film of cool air that protects the liner, reducing the temperature at the liner from around 1800 kelvins (K) to around 830 K, for example. The other type of liner cooling, transpiration cooling,
1464-414: Is that fuel may auto-ignite or otherwise combust before the fuel-air mixture reaches the combustion zone. If this happens the combustor can be seriously damaged. Most igniters in gas turbine applications are electrical spark igniters, similar to automotive spark plugs . The igniter needs to be in the combustion zone where the fuel and air are already mixed, but it needs to be far enough upstream so that it
1525-401: Is the fully annular combustor. Annular combustors do away with the separate combustion zones and simply have a continuous liner and casing in a ring (the annulus). There are many advantages to annular combustors, including more uniform combustion, shorter size (therefore lighter), and less surface area. Additionally, annular combustors tend to have very uniform exit temperatures. They also have
1586-413: Is uniformly introduced through pores. Film cooling air is generally introduced through slats or louvers, resulting in an uneven profile where it is cooler at the slat and warmer between the slats. More importantly, transpiration cooling uses much less cooling air (on the order of 10% of total airflow, rather than 20-50% for film cooling). Using less air for cooling allows more to be used for combustion, which
1647-681: Is used because the combustion process happens incredibly quickly), high temperatures, and high pressures. This fact means that a low-CO combustor has a long residence time (essentially the amount of time the gases are in the combustion chamber). Like CO, Nitrogen oxides (NO x ) are produced in the combustion zone. However, unlike CO, it is most produced during the conditions that CO is most consumed (high temperature, high pressure, long residence time). This means that, in general, reducing CO emissions results in an increase in NO x , and vice versa. This fact means that most successful emission reductions require
1708-405: Is usually used. Jet engines are referred to as operating wet when afterburning is being used and dry when the engine is used without afterburning. An engine producing maximum thrust wet is at maximum power or max reheat (this is the maximum power the engine can produce); an engine producing maximum thrust dry is at military power or max dry . As with the main combustor in a gas turbine,
1769-424: Is where the fuel is burned. However, in the context of a steam engine, the term "combustion chamber" has also been used for a specific area between the firebox and the boiler . This extension of the firebox is designed to allow a more complete combustion of the fuel, improving fuel efficiency and reducing build-up of soot and scale. The use of this type of combustion chamber is large steam locomotive engines, allows
1830-561: The Emissions section below). The 1970s also saw improvement in combustor durability, as new manufacturing methods improved liner (see Components below) lifetime by nearly 100 times that of early liners. In the 1980s combustors began to improve their efficiency across the whole operating range; combustors tended to be highly efficient (99%+) at full power, but that efficiency dropped off at lower settings. Development over that decade improved efficiencies at lower levels. The 1990s and 2000s saw
1891-463: The Ricardo Comet . In a continuous flow system, for example a jet engine combustor , the pressure is controlled and the combustion creates an increase in volume. The combustion chamber in gas turbines and jet engines (including ramjets and scramjets ) is called the combustor . The combustor is fed with high pressure air by the compression system, adds fuel and burns the mix and feeds
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1952-444: The cylinder head . The engines are often designed such that the bottom of combustion chamber is roughly in line with the top of the engine block . Modern engines with overhead valves or overhead camshaft(s) use the top of the piston (when it is near top dead centre ) as the bottom of the combustion chamber. Above this, the sides and roof of the combustion chamber include the intake valves, exhaust valves and spark plug. This forms
2013-454: The 1986-2009 Alfa Romeo Twin Spark engine ) use two spark plugs per cylinder. Compression-ignition engines, such as diesel engines , are typically classified as either: Direct injection engines usually give better fuel economy but indirect injection engines can use a lower grade of fuel. Harry Ricardo was prominent in developing combustion chambers for diesel engines, the best known being
2074-443: The afterburner has both a case and a liner, serving the same purpose as their main combustor counterparts. One major difference between a main combustor and an afterburner is that the temperature rise is not constrained by a turbine section, therefore afterburners tend to have a much higher temperature rise than main combustors. Another difference is that afterburners are not designed to mix fuel as well as primary combustors, so not all
2135-406: The combination of several methods. An afterburner (or reheat) is an additional component added to some jet engines , primarily those on military supersonic aircraft. Its purpose is to provide a temporary increase in thrust , both for supersonic flight and for takeoff (as the high wing loading typical of supersonic aircraft designs means that take-off speed is very high). On military aircraft
2196-495: The combustion process and introduces the various airflows (intermediate, dilution, and cooling, see Air flow paths below) into the combustion zone. The liner must be designed and built to withstand extended high-temperature cycles. For that reason liners tend to be made from superalloys like Hastelloy X . Furthermore, even though high-performance alloys are used, the liners must be cooled with air flow. Some combustors also make use of thermal barrier coatings . However, air cooling
2257-447: The combustion zone. Their role is to generate turbulence in the flow to rapidly mix the air with fuel. Early combustors tended to use bluff body domes (rather than swirlers), which used a simple plate to create wake turbulence to mix the fuel and air. Most modern designs, however, are swirl stabilized (use swirlers). The swirler establishes a local low pressure zone that forces some of the combustion products to recirculate, creating
2318-514: The compressor, where it is fed outside of the liner (inside of which is where the combustion is taking place). The secondary air is then fed, usually through slits in the liner, into the combustion zone to cool the liner via thin film cooling. In most applications, multiple cans are arranged around the central axis of the engine, and their shared exhaust is fed to the turbine(s). Can-type combustors were most widely used in early gas turbine engines, owing to their ease of design and testing (one can test
2379-402: The extra thrust is also useful for combat situations. This is achieved by injecting additional fuel into the jet pipe downstream of (i.e. after ) the turbine and combusting it. The advantage of afterburning is significantly increased thrust; the disadvantage is its very high fuel consumption and inefficiency, though this is often regarded as acceptable for the short periods during which it
2440-421: The first set of liner holes. This air is mixed with fuel, and then combusted. Intermediate air is the air injected into the combustion zone through the second set of liner holes (primary air goes through the first set). This air completes the reaction processes, diluting the high concentrations of carbon monoxide (CO) and hydrogen (H 2 ), and also helps cooling down the gases from combustion. Dilution air
2501-466: The following: Sources: Advancements in combustor technology focused on several distinct areas; emissions, operating range, and durability. Early jet engines produced large amounts of smoke, so early combustor advances, in the 1950s, were aimed at reducing the smoke produced by the engine. Once smoke was essentially eliminated, efforts turned in the 1970s to reducing other emissions, like unburned hydrocarbons and carbon monoxide (for more details, see
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2562-411: The fuel and eliminate local pockets of high fuel concentration. Most modern engines use these types of fuel injectors and are essentially smokeless. Carbon dioxide is a product of the combustion process, and it is primarily mitigated by reducing fuel usage. On average, 1 kg of jet fuel burned produces 3.2 kg of CO 2 . Carbon dioxide emissions will continue to drop as manufacturers improve
2623-452: The fuel is burned within the afterburner section. Afterburners also often require the use of flameholders to keep the velocity of the air in the afterburner from blowing the flame out. These are often bluff bodies or "vee-gutters" directly behind the fuel injectors that create localized low-speed flow in the same manner the dome does in the main combustor. Ramjet engines differ in many ways from traditional gas turbine engines, but most of
2684-404: The fuel. This type of fuel injector has the advantage of being very simple, but it has several disadvantages. The fuel system must be robust enough to withstand such high pressures, and the fuel tends to be heterogeneously atomized, resulting in incomplete or uneven combustion which has more pollutants and smoke. The second type of fuel injector is the air blast injector. This injector "blasts"
2745-663: The high turbulence. However, the higher the turbulence, the higher the pressure loss will be for the combustor, so the dome and swirler must be carefully designed so as not to generate more turbulence than is needed to sufficiently mix the fuel and air. The fuel injector is responsible for introducing fuel to the combustion zone and, along with the swirler (above), is responsible for mixing the fuel and air. There are four primary types of fuel injectors; pressure-atomizing, air blast, vaporizing, and premix/prevaporizing injectors. Pressure atomizing fuel injectors rely on high fuel pressures (as much as 3,400 kilopascals (500 psi)) to atomize
2806-412: The hot, high pressure exhaust into the turbine components of the engine or out the exhaust nozzle. Different types of combustors exist, mainly: If the gas velocity changes, thrust is produced, such as in the nozzle of a rocket engine . Considering the definition of combustion chamber used for internal combustion engines, the equivalent part of a steam engine would be the firebox , since this
2867-433: The liner. However, the vaporizer tube may have serious durability problems with low fuel flow within it (the fuel inside of the tube protects the tube from the combustion heat). The premixing/prevaporizing injectors work by mixing or vaporizing the fuel before it reaches the combustion zone. This method allows the fuel to be very uniformly mixed with the air, reducing emissions from the engine. One disadvantage of this method
2928-482: The lowest pressure drop of the three designs (on the order of 5%). The annular design is also simpler, although testing generally requires a full size test rig. An engine that uses an annular combustor is the CFM International CFM56 . Almost all of the modern gas turbine engines use annular combustors; likewise, most combustor research and development focuses on improving this type. One variation on
2989-447: The main zone is used as well, increasing air and mass flow through the combustor. GE's implementation of this type of combustor focuses on reducing NO x and CO 2 emissions. A good diagram of a DAC is available from Purdue . Extending the same principles as the double annular combustor, triple annular and "multiple annular" combustors have been proposed and even patented. One of the driving factors in modern gas turbine design
3050-402: The method can influence the temperature profile that the liner is exposed to (see Liner , above). Can combustors are self-contained cylindrical combustion chambers. Each "can" has its own fuel injector, igniter, liner, and casing. The primary air from the compressor is guided into each individual can, where it is decelerated, mixed with fuel, and then ignited. The secondary air also comes from
3111-459: The order of 7%). Most modern engines that use can combustors are turboshafts featuring centrifugal compressors . The next type of combustor is the "can-annular" combustor. Like the can-type combustor, can-annular combustors have discrete combustion zones contained in separate liners with their own fuel injectors. Unlike the can combustor, all the combustion zones share a common ring (annulus) casing. Each combustion zone no longer has to serve as
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#17327805471223172-571: The others. This type of combustor is also lighter than the can type, and has a lower pressure drop (on the order of 6%). However, a can-annular combustor can be more difficult to maintain than a can combustor. Examples of gas turbine engines utilizing a can-annular combustor include the General Electric J79 turbojet and the Pratt & Whitney JT8D and Rolls-Royce Tay turbofans . The final, and most-commonly used type of combustor
3233-465: The overall efficiency of gas turbine engines. Unburned-hydrocarbon (UHC) and carbon-monoxide (CO) emissions are highly related. UHCs are essentially fuel that was not completely combusted. They are mostly produced at low power levels (where the engine is not burning all the fuel). Much of the UHC content reacts and forms CO within the combustor, which is why the two types of emissions are heavily related. As
3294-424: The piston and the valves (which are located beside the piston). IOE engines combine elements of overhead valve and flathead engines; the intake valve is located above the combustion chamber, while the exhaust valve is located below it. The shape of the combustion chamber, intake ports and exhaust ports are key to achieving efficient combustion and maximising power output. Cylinder heads are often designed to achieve
3355-404: The piston), which converts the gas pressure into mechanical energy (often in the form of a rotating output shaft). This contrasts an external combustion engine, where the combustion takes place in a separate part of the engine to where the gas pressure is converted into mechanical energy. In spark ignition engines, such as petrol (gasoline) engines , the combustion chamber is usually located in
3416-420: The same design challenges, like fuel mixing and flame holding. However, as its name implies, a scramjet combustor must address these challenges in a supersonic flow environment. For example, for a scramjet flying at Mach 5, the air flow entering the combustor would nominally be Mach 2. One of the major challenges in a scramjet engine is preventing shock waves generated by combustor from traveling upstream into
3477-490: The same principles hold. One major difference is the lack of rotating machinery (a turbine) after the combustor. The combustor exhaust is directly fed to a nozzle. This allows ramjet combustors to burn at a higher temperature. Another difference is that many ramjet combustors do not use liners like gas turbine combustors do. Furthermore, some ramjet combustors are dump combustors rather than a more conventional type. Dump combustors inject fuel and rely on recirculation generated by
3538-473: The standard annular combustor is the double annular combustor (DAC). Like an annular combustor, the DAC is a continuous ring without separate combustion zones around the radius. The difference is that the combustor has two combustion zones around the ring; a pilot zone and a main zone. The pilot zone acts like that of a single annular combustor, and is the only zone operating at low power levels. At high power levels,
3599-456: The third type, is similar to the air blast injector in that primary air is mixed with the fuel as it is injected into the combustion zone. However, the fuel-air mixture travels through a tube within the combustion zone. Heat from the combustion zone is transferred to the fuel-air mixture, vaporizing some of the fuel (mixing it better) before it is combusted. This method allows the fuel to be combusted with less thermal radiation , which helps protect
3660-461: The use of shorter firetubes . Micro combustion chambers are the devices in which combustion happens at a very small volume, due to which surface to volume ratio increases which plays a vital role in stabilizing the flame. Combustor A combustor is a component or area of a gas turbine , ramjet , or scramjet engine where combustion takes place. It is also known as a burner , burner can , combustion chamber or flame holder . In
3721-433: The velocity results in an unavoidable loss in total pressure, so one of the design challenges is to limit the loss of pressure as much as possible. Furthermore, the diffuser must be designed to limit the flow distortion as much as possible by avoiding flow effects like boundary layer separation . Like most other gas turbine engine components, the diffuser is designed to be as short and light as possible. The liner contains
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