The Brayton cycle is a constant-pressure cycle named after George Brayton (1830–1892), the American engineer who developed it. It is also sometimes known as the Joule cycle. It was originally invented 18 years earlier by John Ericsson in externally heated, both open and closed, piston engines, see Ericsson Cycle. A cyclic process is a thermodynamic process which begins from and finishes at the same thermostatic state. ... George Brayton (October 3, 1830 - December 17, 1892) was a British-born American mechanical engineer from Boston, who is noted for introducing the continuous combustion process that is the basis for the gas turbine, and which is now referred to as the Brayton cycle. ... Look up engineer in Wiktionary, the free dictionary. ... James Joule - English physicist James Prescott Joule, FRS (December 24, 1818 – October 11, 1889) was an English physicist, born in Sale, Cheshire. ... John Ericsson (1803-1889) This article is about John Ericsson, the Swedish and American inventor. ... This article or section seems not to be written in the formal tone expected of an encyclopedia entry. ...

History

In 1790 Barber proposed a heat engine in which a bellows (compressor) and a turbine (expander) were connected to a common shaft. The bellows compressed the air, then the air was passed through a fire and heated finally the hot air was expanded through a turbine wheel where work was realized.

In 1872, Brayton filed a patent for his "Ready Motor" which, unlike the Otto or Diesel cycles, used a separate compressor and expansion cylinder. Today the Brayton cycle is generally associated with gas turbines. Year 1872 (MDCCCLXXII) was a leap year starting on Monday (link will display the full calendar) of the Gregorian Calendar (or a leap year starting on Saturday of the 12-day slower Julian calendar). ... For other uses, see Patent (disambiguation). ... Today Internal combustion engines in cars, trucks, motorcycles, construction machinery and many others, most commonly use a four-stroke cycle. ... This article does not cite any references or sources. ... Compressor has several meanings: A gas compressor is a mechanical device that takes in a gas and increases its pressure by squeezing a volume of it into a smaller volume. ... This machine has a single-stage centrifugal compressor and turbine, a recuperator, and foil bearings. ...

Like other internal combustion power cycles, The Brayton cycle is an open system, though for thermodynamic analysis it is conventionally assumed that the exhaust gases are reused in the intake, enabling analysis as a closed system. An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. ... This article is about systems theory. ... Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dunamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ...

Model

A Brayton-type engine consists of three components: An engine in the broadest sense, is something that produces an output effect from a given input. ...

• A gas compressor
• A mixing chamber
• An expander

In the original 19th-century Brayton engine, ambient air is drawn into a piston compressor, where it is compressed; ideally an isentropic process. The compressed air then runs through a mixing chamber where fuel is added, a constant-pressure isobaric process. The heated(by compression), pressurized air and fuel mixture is then ignited in an expansion cylinder and energy is released, causing the heated air and combustion products to expand through a piston/cylinder; another theoretically isentropic process. Some of the work extracted by the piston/cylinder is used to drive the compressor through a crankshaft arrangement.[ Bold text Wiktionary has related dictionary definitions, such as: compressor, compression inthe wkjhrlfidhb;g/df == Compressor may refer to: Gas compressor, a mechanical device that compresses a gas e. ... An isentropic process (a combination of the Greek word iso -same- and entropy) is one during which the entropy of working fluid remains constant. ... An isobaric process is a thermodynamic process in which the pressure stays constant; . The heat transferred to the system does work but also changes the internal energy of the system: according to the first law of thermodynamics, where W is work done by the system, E is internal energy, and...

[1]

The term Brayton cycle has more recently been given to the gas turbine engine. This also has three components: This machine has a single-stage centrifugal compressor and turbine, a recuperator, and foil bearings. ...

• A gas compressor
• A burner (or combustion chamber)
• An expansion turbine

Ideal Brayton cycle: A combustion reaction taking place in a igniting match Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... A turboexpander (also referred to as turbo expander, expansion turbine or simply expander) is a centrifugal or axial flow turbine through which a high pressure gas is expanded to produce work that is typically used to drive a compressor. ...

• isentropic process - Ambient air is drawn into the compressor, where it is pressurized.
• isobaric process - The compressed air then runs through a combustion chamber, where fuel is burned, heating that air—a constant-pressure process, since the chamber is open to flow in and out.
• isentropic process - The heated, pressurized air then gives up its energy, expanding through a turbine (or series of turbines). Some of the work extracted by the turbine is used to drive the compressor.
• isobaric process - Heat Rejection (in the atmosphere).

Actual Brayton cycle: An isentropic process (a combination of the Greek word iso -same- and entropy) is one during which the entropy of working fluid remains constant. ... An isobaric process is a thermodynamic process in which the pressure stays constant; . The heat transferred to the system does work but also changes the internal energy of the system: according to the first law of thermodynamics, where W is work done by the system, E is internal energy, and... An isentropic process (a combination of the Greek word iso -same- and entropy) is one during which the entropy of working fluid remains constant. ...

• adiabatic process - Compression.
• isobaric process - Heat Addition.
• adiabatic process - Expansion.
• isobaric process - Heat Rejection.

Since neither the compression nor the expansion can be truly isentropic, losses through the compressor and the expander represent sources of inescapable working inefficiencies. In general, increasing the compression ratio is the most direct way to increase the overall power output of a Brayton system. ^[1] In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid. ... An isobaric process is a thermodynamic process in which the pressure stays constant; . The heat transferred to the system does work but also changes the internal energy of the system: according to the first law of thermodynamics, where W is work done by the system, E is internal energy, and... Image File history File links Brayton_cycle. ... Thermodynamic efficiency (e) is defined as: where W is the absolute value of the work done in one thermodynamic cycle. ... Bold text The compression ratio is a single number that can be used to predict the performance of any engine (such as an internal-combustion engine or a Stirling Engine). ...

Here are two plots, Figure 1 and Figure 2, for the ideal Brayton cycle. One plot indicates how the cycle efficiency changes with an increase in pressure ratio, while the other indicates how the specific power output changes with an increase in the gas turbine inlet temperature for two different pressure ratio values.

In 2002 a hybrid open solar Brayton cycle was operated for the first time consistently and effectively with relevant papers published, in the frame of the EU SOLGATE program. The air was heated from 570°K to over 1000°K into the combustor chamber.

Figure 1: Brayton cycle efficiency

Figure 2: Brayton cycle specific power output

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Methods to improve efficiency

The efficiency of a Brayton engine can be improved in the following manners:

• Reheat, wherein the working fluid—in most cases air—expands through a series of turbines, then is passed through a second combustion chamber before expanding to ambient pressure through a final set of turbines. This has the advantage of increasing the power output possible for a given compression ratio without exceeding any metallurgical constraints. (Although use of an afterburner can also be referred to as reheat, it is a different process that increases power while markedly decreasing efficiency.)

• Intercooling, wherein the working fluid passes through a first stage of compressors, then a cooler, then a second stage of compressors before entering the combustion chamber. While this requires an increase in the fuel consumption of the combustion chamber, this allows for a reduction in the specific heat of the fluid entering the second stage of compressors, with an attendant decrease in the amount of work needed for the compression stage overall.

• Regeneration, wherein the still-warm post-turbine fluid is passed through a heat exchanger to pre-heat the fluid just entering the combustion chamber. This allows for lower fuel consumption and less power lost as waste heat.

• A Brayton engine also forms half of the combined cycle system, which combines with a Rankine engine to further increase overall efficiency.

• Cogeneration systems make use of the waste heat from Brayton engines, typically for hot water production or space heating.

Working mass is a mass against which a system operates in order to produce acceleration. ... Georg Agricola, author of De re metallica, an important early book on metal extraction Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. ... For other uses of afterburner, see Afterburner (disambiguation). ... The specific heat capacity (symbol c or s, also called specific heat) of a substance is defined as heat capacity per unit mass. ... In a combined cycle power plant, or combined cycle gas turbine (CCGT) plant, a gas turbine generator generates electricity and the waste heat from the gas turbine is used to make steam to generate additional electricity via a steam turbine, this last step enhances the efficiency of electricity generation. ... The Rankine cycle is a thermodynamic cycle. ... Cogeneration (also combined heat and power or CHP) is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat. ...

Reverse Brayton cycle

A Brayton cycle that is driven in reverse, via net work input, and when air is the working fluid, is the air refrigeration cycle or Bell Coleman cycle. Its purpose is to move heat, rather than produce work. This air cooling technique is used widely in jet aircraft. Refrigeration is the process of removing heat from an enclosed space, or from a substance, and rejecting it elsewhere for the primary purpose of lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. ...

References

1. ^ Lester C. Lichty, Combustion Engine Processes, 1967, McGraw-Hill, Inc., Lib.of Congress 67-10876

See also

Wikimedia Commons has media related to:

Brayton cycle

• Gas turbine
• jet engine
• Heat engines
• thermodynamics
• power
• HVAC
• engineering

External links

• Today in Science article on Brayton Engine
• http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JSEEDO000126000003000872000001&idtype=cvips&gifs=yes
• http://elib.dlr.de/46328/
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V50-4GP6WDN-1&_user=10&_coverDate=10%2F31%2F2006&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b7c7869ea69813a7397758263df4667c

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