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Combustion, or burning, is a high-temperature
exothermic In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these qu ...

exothermic
redox Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

redox
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...

chemical reaction
between a
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical con ...

fuel
(the reductant) and an
oxidant 125px, Dangerous goods label for oxidizing agents An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize (mild reducing agent) are added to powdered potassium permanganate Potassium perma ...
, usually atmospheric
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
, that produces oxidized, often gaseous products, in a mixture termed as
smoke Smoke is a collection of airborne and es emitted when a material undergoes or , together with the quantity of air that is or otherwise mixed into the mass. It is commonly an unwanted of fires (including s, s, s, s, and s), but may als ...

smoke
. Combustion does not always result in
fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

fire
, because a flame is only visible when substances undergoing combustion vapourise, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g., using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining. Combustion is often a complicated sequence of
elementary In computational complexity theory, the complexity class ELEMENTARY of elementary recursive functions is the union of the classes : \begin \mathsf & = \bigcup_ k\mathsf \\ & = \mathsf\left(2^n\right)\cup\mathsf\left(2^\right)\ ...
radical reactions.
Solid fuel Solid fuel refers to various forms of solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation ...
s, such as
wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. ...

wood
and
coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

coal
, first undergo
endothermic In thermochemistry Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and bo ...
pyrolysis The pyrolysis (or devolatilization) process is the of materials at elevated temperatures in an inert atmosphere. It involves a change of . The word is coined from the -derived s ''pyro'' "fire" and ' "separating". Pyrolysis is most commonly us ...

pyrolysis
to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that
incandescent The incandescent metal embers of the spark used to light this Bunsen burner emit light ranging in color from white to orange to yellow to red or to blue. This change correlates with their temperature as they cool in the air. The flame itself is ...

incandescent
light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nan ...

light
in the form of either glowing or a
flame A flame (from Latin ''wikt:en:flamma#Latin, flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. Very hot flames are hot enough to have ionized gaseous components of ...

flame
is produced. A simple example can be seen in the combustion of
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
into
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
vapor In physics, a vapor (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United St ...
, a reaction commonly used to fuel
rocket engine A rocket engine uses stored rocket propellant Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come ...

rocket engine
s. This reaction releases 242 kJ/ mol of heat and reduces the
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant p ...

enthalpy
accordingly (at constant temperature and pressure): : 2(g) + (g) → 2(g) Combustion of an organic fuel in air is always exothermic because the
double bond In chemistry, a double bond is a between two s involving four s as opposed to two in a . Double bonds occur most commonly between two carbon atoms, for example in s. Many double bonds exist between two different elements: for example, in a group ...

double bond
in O is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in the combustion products and results in the release of energy. The bond energies in the fuel play only a minor role, since they are similar to those in the combustion products; e.g., the sum of the bond energies of CH is nearly the same as that of . The
heat of combustion The heating value (or energy value or calorific value) of a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composi ...
is approximately −418 kJ per mole of O used up in the combustion reaction, and can be estimated from the elemental composition of the fuel. Uncatalyzed combustion in air requires relatively high temperatures. Complete combustion is
stoichiometric Stoichiometry is the calculation of reactants and products in chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical s ...
concerning the fuel, where there is no remaining fuel, and ideally, no residual oxidant. Thermodynamically, the
chemical equilibrium In a chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes th ...
of combustion in air is overwhelmingly on the side of the products. However, complete combustion is almost impossible to achieve, since the chemical equilibrium is not necessarily reached, or may contain unburnt products such as
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
,
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
and even
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
(
soot Soot ( ) is a mass of impure Carbonaceous, carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the resi ...
or ash). Thus, the produced
smoke Smoke is a collection of airborne and es emitted when a material undergoes or , together with the quantity of air that is or otherwise mixed into the mass. It is commonly an unwanted of fires (including s, s, s, s, and s), but may als ...

smoke
is usually toxic and contains unburned or partially oxidized products. Any combustion at high temperatures in
atmospheric An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet A planet is an astronomical body orbi ...

atmospheric
air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the atmosphere (0.04402961% at April 2019 concentration ). Number ...

air
, which is 78 percent
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
, will also create small amounts of several
nitrogen oxidesNitrogen oxide may refer to a binary compound In materials chemistry, a binary phase or binary compound is a chemical compound containing two different elements. Some binary phase compounds are molecular, e.g. carbon tetrachloride (CCl4). More ty ...
, commonly referred to as
NOx In atmospheric chemistry Atmospheric chemistry is a branch of in which the of the and that of other planets is studied. It is a of research and draws on , , , , , and and other disciplines. Research is increasingly connected with other a ...

NOx
, since the combustion of nitrogen is thermodynamically favored at high, but not low temperatures. Since burning is rarely clean, fuel gas cleaning or
catalytic converter A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutant A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resour ...

catalytic converter
s may be required by law.
Fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

Fire
s occur naturally, ignited by
lightning Lightning is a naturally occurring electrostatic discharge Electrostatic discharge (ESD) is the sudden flow of electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan ...

lightning
strikes or by
volcanic A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet ar ...

volcanic
products. Combustion (
fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

fire
) was the first controlled chemical reaction discovered by humans, in the form of
campfire A campfire is a fire at a campsite that provides light and warmth, and heat for cooking. It can also serve as a beacon, and an insect and predator deterrent. Established campgrounds often provide a stone or steel fire ring for safety. Campfires a ...

campfire
s and
bonfire A bonfire is a large and controlled outdoor fire, used either for informal disposal of burnable waste material or as part of a celebration. Regional traditions In many regions of continental Europe, bonfires are made traditionally on 16 Jan ...

bonfire
s, and continues to be the main method to produce energy for humanity. Usually, the fuel is
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
,
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
s, or more complicated mixtures such as
wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. ...

wood
that contains partially oxidized hydrocarbons. The thermal energy produced from combustion of either
fossil fuel A fossil fuel is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structure ...
s such as
coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

coal
or
oil An oil is any nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound ...

oil
, or from
renewable fuelRenewable fuels are fuel A fuel is any material that can be made to react with other substances so that it releases energy as heat energy or to be used for work. The concept was originally applied solely to those materials capable of releasing ...
s such as
firewood Firewood is any wooden Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branche ...

firewood
, is harvested for diverse uses such as
cooking Cooking, cookery, or culinary arts is the art, science, and craft of using heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy ...

cooking
, production of
electricity Electricity is the set of physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia Newton-John song), "Physi ...

electricity
or industrial or domestic heating. Combustion is also currently the only reaction used to power
rocket A rocket (from it, rocchetto, , bobbin/spool) is a spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite alt=, A full-size model of the Earth observation satellite ERS 2 ...

rocket
s. Combustion is also used to destroy ( incinerate) waste, both nonhazardous and hazardous. Oxidants for combustion have high oxidation potential and include atmospheric or pure
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
,
fluorine Fluorine is a chemical element with the Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard conditions for temperature and pressure, standard conditions as a highly toxic, pale yellow Diatomic molecule ...

fluorine
,
chlorine trifluoride Chlorine trifluoride is an interhalogen compound with the formula ClF3. This colorless, poisonous, corrosive, and extremely reactive gas condenses to a pale-greenish yellow liquid, the form in which it is most often sold (pressurized at room tem ...
,
nitrous oxide Nitrous oxide, commonly known as laughing gas or nitrous, is a chemical compound, an Nitrogen oxide, oxide of nitrogen with the Chemical formula, formula . At room temperature, it is a colourless Flammability#Definitions, non-flammable gas, ...
and
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into nitroge ...

nitric acid
. For instance,
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
burns in
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
to form
hydrogen chloride The compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with ...

hydrogen chloride
with the liberation of heat and light characteristic of combustion. Although usually not catalyzed, combustion can be catalyzed by
platinum Platinum is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical el ...

platinum
or
vanadium Vanadium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science tha ...

vanadium
, as in the contact process.


Types


Complete and incomplete


Complete

In complete combustion, the reactant burns in oxygen and produces a limited number of products. When a
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
burns in oxygen, the reaction will primarily yield carbon dioxide and water. When elements are burned, the products are primarily the most common oxides. Carbon will yield
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, sulfur will yield
sulfur dioxide Sulfur dioxide (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the autho ...
, and iron will yield
iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. However, the distinction is ...
. Nitrogen is not considered to be a combustible substance when oxygen is the
oxidant 125px, Dangerous goods label for oxidizing agents An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize (mild reducing agent) are added to powdered potassium permanganate Potassium perma ...

oxidant
. Still, small amounts of various nitrogen oxides (commonly designated

species) form when the air is the oxidative. Combustion is not necessarily favorable to the maximum degree of oxidation, and it can be temperature-dependent. For example,
sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...
is not produced quantitatively by the combustion of sulfur. species appear in significant amounts above about , and more is produced at higher temperatures. The amount of is also a function of oxygen excess.The formation of NOx
Alentecinc.com. Retrieved on 2010-09-28.
In most industrial applications and in
fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

fire
s,
air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the atmosphere (0.04402961% at April 2019 concentration ). Number ...

air
is the source of oxygen (). In the air, each mole of oxygen is mixed with approximately of nitrogen. Nitrogen does not take part in combustion, but at high temperatures some nitrogen will be converted to (mostly

, with much smaller amounts of

). On the other hand, when there is insufficient oxygen to combust the fuel completely, some fuel carbon is converted to
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
, and some of the hydrogens remain unreacted. A complete set of equations for the combustion of a hydrocarbon in the air, therefore, requires an additional calculation for the distribution of oxygen between the carbon and hydrogen in the fuel. The amount of air required for complete combustion to take place is known as pure air. However, in practice, the air used is 2-3 times that of pure air.


Incomplete

Incomplete combustion will occur when there is not enough oxygen to allow the fuel to react completely to produce carbon dioxide and water. It also happens when the combustion is quenched by a heat sink, such as a solid surface or flame trap. As is the case with complete combustion, water is produced by incomplete combustion; however,
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
,
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
, and hydroxide are produced instead of carbon dioxide. For most fuels, such as diesel oil, coal, or wood,
pyrolysis The pyrolysis (or devolatilization) process is the of materials at elevated temperatures in an inert atmosphere. It involves a change of . The word is coined from the -derived s ''pyro'' "fire" and ' "separating". Pyrolysis is most commonly us ...

pyrolysis
occurs before combustion. In incomplete combustion, products of pyrolysis remain unburnt and contaminate the smoke with noxious particulate matter and gases. Partially oxidized compounds are also a concern; partial oxidation of ethanol can produce harmful
acetaldehyde Ethanal (common name acetaldehyde) is an organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
, and carbon can produce toxic carbon monoxide. The designs of combustion devices can improve the quality of combustion, such as
burners Burning Man is a festival A festival is an event ordinarily celebrated by a community and centering on some characteristic aspect of that community and its religion or cultures. It is often marked as a local or national holiday, mela, or M ...
and
internal combustion engines An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combu ...
. Further improvements are achievable by
catalytic that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules ...
after-burning devices (such as
catalytic converter A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutant A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resour ...

catalytic converter
s) or by the simple partial return of the
exhaust gas Exhaust gas or flue gas Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler Poland Poland ( pl, Polska ), officially the Republic ...
es into the combustion process. Such devices are required by
environmental legislation Environmental law is a collective term encompassing aspects of the law that provide protection to the environment. A related but distinct set of regulatory regimes, now strongly influenced by environmental legal principles, focus on the manageme ...
for cars in most countries. They may be necessary to enable large combustion devices, such as
thermal power station A thermal power station is a power station in which heat energy is converted to electricity. Typically, fuel is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam turbine connected to an electric ...

thermal power station
s, to reach legal
emission standards Emission standards are the legal requirements governing Air pollution, air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific Air pollution, air pollutants that may be release ...
. The degree of combustion can be measured and analyzed with test equipment.
HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal rad ...

HVAC
contractors,
firefighters A firefighter is a rescuer extensively trained in firefighting, primarily to extinguish conflagration, hazardous fires that threaten life, property, and the environment as well as to rescue people and in some cases or jurisdictions also animals ...

firefighters
and
engineers Engineers, as practitioners of engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of enginee ...

engineers
use combustion analyzers to test the
efficiency Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and withou ...
of a burner during the combustion process. Also, the efficiency of an internal combustion engine can be measured in this way, and some U.S. states and local municipalities use combustion analysis to define and rate the efficiency of vehicles on the road today.


= Incomplete combustion produced carbon monoxide

= Carbon monoxide is one of the products from
incomplete combustion Combustion, or burning, is a high-temperature exothermic redox (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, ...
. Carbon is released in the normal incomplete combustion reaction, forming soot and dust. Since carbon monoxide is a poisonous gas, complete combustion is preferable, as carbon monoxide may also lead to respiratory troubles when breathed since it takes the place of oxygen and combines with hemoglobin.


=Problems associated with incomplete combustion

= :Environmental problems: These oxides combine with
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
in the atmosphere, creating
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into nitroge ...

nitric acid
and sulfuric acids, which return to Earth's surface as acid deposition, or "acid rain." Acid deposition harms aquatic organisms and kills trees. Due to its formation of certain nutrients that are less available to plants such as calcium and phosphorus, it reduces the productivity of the ecosystem and farms. An additional problem associated with
nitrogen oxidesNitrogen oxide may refer to a binary compound In materials chemistry, a binary phase or binary compound is a chemical compound containing two different elements. Some binary phase compounds are molecular, e.g. carbon tetrachloride (CCl4). More ty ...
is that they, along with
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
pollutants, contribute to the formation of
ground level ozones over the period 1979 to 2000. In June to August, photochemical ozone production causes very high concentrations over the East Coast of the US and China. Ozone Ozone (), or trioxygen, is an inorganic molecule File:Pentacene on Ni(111) STM.jp ...
, a major component of smog. :Human health problems: Breathing
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
causes headache, dizziness, vomiting, and nausea. If carbon monoxide levels are high enough, humans become unconscious or die. Exposure to moderate and high levels of carbon monoxide over long periods is positively correlated with risk of heart disease. People who survive severe
carbon monoxide poisoning Carbon monoxide poisoning typically occurs from breathing Breathing (or ventilation) is the process of moving air out and in the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring ...
may suffer long-term health problems. Carbon monoxide from air is absorbed in the lungs which then binds with
hemoglobin Hemoglobin or haemoglobin (spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two distinct wa ...

hemoglobin
in human's red blood cells. This would reduce the capacity of red blood cells to carry oxygen throughout the body.


Smouldering

Smouldering s of barbecue coal briquettes Smouldering (British English British English (BrE) is the standard dialect of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engla ...
is the slow, low-temperature, flameless form of combustion, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. It is a typically incomplete combustion reaction. Solid materials that can sustain a smouldering reaction include coal,
cellulose Cellulose is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

cellulose
,
wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. ...

wood
,
cotton Cotton is a soft, fluffy staple fiber Fiber or fibre (from la, fibra, links=no) is a natural Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of s ...

cotton
,
tobacco Tobacco is the common name of several plants in the genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defini ...

tobacco
,
peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation Vegetation is an assemblage of species and the they provide. It is a general term, without specific reference to particular , life forms, structure, ...
, duff,
humus In soil science Soil science is the study of soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of ...

humus
, synthetic foams, charring
polymers A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries: ** Poly Property, a Hong Kong inco ...

polymers
(including
polyurethane foam Polyurethane products have many uses. Over three quarters of the global consumption of polyurethane products is in the form of foams, with flexible and rigid types being roughly equal in market size. In both cases, the foam is usually behind othe ...
) and
dust Dust is made of s of solid . On Earth, it generally consists of particles in the that come from various sources such as lifted by wind (an ), , and . Dust in homes is composed of about 20–50% dead . The rest, and in offices, and other ...
. Common examples of smoldering phenomena are the initiation of residential fires on upholstered furniture by weak heat sources (e.g., a cigarette, a short-circuited wire) and the persistent combustion of biomass behind the flaming fronts of
wildfire A wildfire, bushfire, wildland fire or rural fire is an unplanned, unwanted, uncontrolled fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction ...

wildfire
s.


Rapid

Rapid combustion is a form of combustion, otherwise known as a
fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

fire
, in which large amounts of heat and
light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nan ...

light
energy are released, which often results in a
flame A flame (from Latin ''wikt:en:flamma#Latin, flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. Very hot flames are hot enough to have ionized gaseous components of ...

flame
. This is used in a form of machinery such as
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do work (physics), mechanical work. It doe ...

internal combustion engine
s and in
thermobaric weapon A thermobaric weapon, aerosol bomb, or vacuum bomb is a type of explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually ...
s. Such a combustion is frequently called a Rapid combustion, though for an internal combustion engine this is inaccurate. An internal combustion engine nominally operates on a controlled rapid burn. When the fuel-air mixture in an internal combustion engine explodes, that is known as
detonation Detonation () is a type of combustion Combustion, or burning, is a high-temperature exothermic In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relat ...
.


Spontaneous

Spontaneous combustion Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to Exothermic reaction, exothermic internal reactions), followed by thermal runaway (self heating which rapidly acce ...
is a type of combustion which occurs by self-heating (increase in temperature due to
exothermic In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these qu ...

exothermic
internal reactions), followed by thermal runaway (self-heating which rapidly accelerates to high temperatures) and finally, ignition. For example, phosphorus self-ignites at room temperature without the application of heat. Organic materials undergoing bacterial
composting Compost is a mixture of ingredients used to fertilize and improve the soil. It is commonly prepared by decomposing plant and food waste and recycling Recycling is the process of converting waste Waste (or wastes) are unwanted ...

composting
can generate enough heat to reach the point of combustion.


Turbulent

Combustion resulting in a turbulent flame is the most used for industrial application (e.g.
gas turbine A gas turbine, also called a combustion turbine, is a type of continuous Continuity or continuous may refer to: Mathematics * Continuity (mathematics), the opposing concept to discreteness; common examples include ** Continuous probability di ...
s,
gasoline engine Gasoline () or petrol () (see the etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is ...
s, etc.) because the turbulence helps the mixing process between the fuel and
oxidizer An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize other substances — in other words to electron acceptor, accept their electrons. Common oxidizing agents are oxygen, hydrogen peroxi ...
.


Micro-gravity

The term 'micro' gravity refers to a gravitational state that is 'low' (i.e., 'micro' in the sense of 'small' and not necessarily a millionth of Earth's normal gravity) such that the influence of
buoyancy Buoyancy (), or upthrust, is an upward exerted by a that opposes the of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bo ...

buoyancy
on physical processes may be considered small relative to other flow processes that would be present at normal gravity. In such an environment, the thermal and flow transport dynamics can behave quite differently than in normal gravity conditions (e.g., a
candle A candle is an ignitable candle wick, wick embedded in wax, or another flammable solid substance such as tallow, that provides light, and in some cases, a Aroma compound, fragrance. A candle can also provide heat or a method of keeping time. ...

candle
's flame takes the shape of a sphere.). Microgravity combustion research contributes to the understanding of a wide variety of aspects that are relevant to both the environment of a spacecraft (e.g., fire dynamics relevant to crew safety on the
International Space Station The International Space Station (ISS) is a Modular design, modular space station (habitable satellite, artificial satellite) in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (Uni ...

International Space Station
) and terrestrial (Earth-based) conditions (e.g., droplet combustion dynamics to assist developing new fuel blends for improved combustion, materials fabrication processes, Thermal management (electronics), thermal management of electronic systems, multiphase flow boiling dynamics, and many others).


Micro-combustion

Combustion processes which happen in very small volumes are considered micro-combustion. The high surface-to-volume ratio increases specific heat loss. Quenching distance plays a vital role in stabilizing the flame in such combustion chambers.


Chemical equations


Stoichiometric combustion of a hydrocarbon in oxygen

Generally, the chemical equation for Stoichiometry, stoichiometric combustion of a
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
in oxygen is: : C_\mathitH_\mathit + \mathitO2 -> \mathitCO2 + \fracH2O where z = x + \frac. For example, the stoichiometric burning of propane in oxygen is: : \underset + \underset -> \underset + \underset


Stoichiometric combustion of a hydrocarbon in air

If the stoichiometric combustion takes place using air as the oxygen source, the
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
present in the air (Atmosphere of Earth) can be added to the equation (although it does not react) to show the stoichiometric composition of the fuel in air and the composition of the resultant flue gas. Note that treating all non-oxygen components in air as nitrogen gives a 'nitrogen' to oxygen ratio of 3.77, i.e. (100% - O2%) / O2% where O2% is 20.95% vol: : \ce_ \ce_ + z\ce + 3.77z\ce \ x\ce + \frac \ce + 3.77z\ce where z = x + \fracy. For example, the stoichiometric combustion of propane (C3H8) in air is: : \ce + \underset \ce + \underset The stoichiometric composition of propane in air is 1 / (1 + 5 + 18.87) = 4.02% vol. The stoichiometric combustion reaction for CHO in air: : + \left ( \alpha + \frac -\frac \right ) \left ( O_2 + 3.77 N_2 \right ) \longrightarrow \alpha CO_2 + \frac H_2O + 3.77 \left ( \alpha + \frac -\frac \right ) N_2 The stoichiometric combustion reaction for CHOS: : + \left ( \alpha + \frac -\frac + \delta \right ) \left ( O_2 + 3.77 N_2 \right ) \longrightarrow \alpha CO_2 + \frac H_2O + \delta SO_2 + 3.77 \left ( \alpha + \frac -\frac + \delta \right ) N_2 The stoichiometric combustion reaction for CHONS: : + \left ( \alpha + \frac -\frac + \epsilon \right ) \left ( O_2 + 3.77 N_2 \right ) \longrightarrow \alpha CO_2 + \frac H_2O + \epsilon SO_2 + \left ( 3.77 \left ( \alpha + \frac -\frac + \epsilon \right ) + \frac \right ) N_2 The stoichiometric combustion reaction for CHOF: : + \left ( \alpha + \frac -\frac \right ) \left ( O_2 + 3.77 N_2 \right ) \longrightarrow \alpha CO_2 + \frac H_2O + \delta HF + 3.77 \left ( \alpha + \frac -\frac \right ) N_2


Trace combustion products

Various other substances begin to appear in significant amounts in combustion products when the Adiabatic flame temperature, flame temperature is above about . When excess air is used, nitrogen may oxidize to and, to a much lesser extent, to . forms by disproportionation of , and and form by disproportionation of . For example, when of propane is burned with of air (120% of the stoichiometric amount), the combustion products contain 3.3% . At , the Chemical equilibrium, equilibrium combustion products contain 0.03% and 0.002% . At , the combustion products contain 0.17% , 0.05% , 0.01% , and 0.004% .
Equilib-Web
Diesel engines are run with an excess of oxygen to combust small particles that tend to form with only a stoichiometric amount of oxygen, necessarily producing NOx, nitrogen oxide emissions. Both the United States and European Union Emission standard, enforce limits to vehicle nitrogen oxide emissions, which necessitate the use of special
catalytic converter A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutant A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resour ...

catalytic converter
s or treatment of the exhaust with urea (see Diesel exhaust fluid).


Incomplete combustion of a hydrocarbon in oxygen

The incomplete (partial) combustion of a
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
with oxygen produces a gas mixture containing mainly , , , and . Such gas mixtures are commonly prepared for use as protective atmospheres for the Heat treating, heat-treatment of metals and for Carburizing, gas carburizing. The general reaction equation for incomplete combustion of one Mole(unit), mole of a hydrocarbon in oxygen is: : \underset + \underset -> \underset + \underset + \underset + \underset When ''z'' falls below roughly 50% of the stoichiometric value, Methane, can become an important combustion product; when ''z'' falls below roughly 35% of the stoichiometric value, elemental
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
may become stable. The products of incomplete combustion can be calculated with the aid of a material balance, together with the assumption that the combustion products reach Chemical equilibrium, equilibrium.
ExoCalc
For example, in the combustion of one Mole (unit), mole of propane () with four moles of , seven moles of combustion gas are formed, and ''z'' is 80% of the stoichiometric value. The three elemental balance equations are: * Carbon: a + b = 3 * Hydrogen: 2c + 2d = 8 * Oxygen: 2a + b + c = 8 These three equations are insufficient in themselves to calculate the combustion gas composition. However, at the equilibrium position, the water-gas shift reaction gives another equation: : CO + H2O -> CO2 + H2; K_ = \frac For example, at the value of ''K'' is 0.728. Solving, the combustion gas consists of 42.4% , 29.0% , 14.7% , and 13.9% . Carbon becomes a stable phase at and pressure when z is less than 30% of the stoichiometric value, at which point the combustion products contain more than 98% and and about 0.5% . Substances or materials which undergo combustion are called
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical con ...

fuel
s. The most common examples are natural gas, propane, kerosene, diesel, petrol, charcoal, coal, wood, etc.


Liquid fuels

Combustion of a liquid fuel in an oxidizing atmosphere actually happens in the gas phase. It is the vapor that burns, not the liquid. Therefore, a liquid will normally catch fire only above a certain temperature: its flash point. The flash point of a liquid fuel is the lowest temperature at which it can form an ignitable mix with air. It is the minimum temperature at which there is enough evaporated fuel in the air to start combustion.


Gaseous fuels

Combustion of gaseous fuels may occur through one of four distinctive types of burning: diffusion flame, premixed flame, autoignitive reaction front, or as a detonation. The type of burning that actually occurs depends on the degree to which the
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical con ...

fuel
and
oxidizer An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize other substances — in other words to electron acceptor, accept their electrons. Common oxidizing agents are oxygen, hydrogen peroxi ...
are mixed prior to heating: for example, a diffusion flame is formed if the fuel and oxidizer are separated initially, whereas a premixed flame is formed otherwise. Similarly, the type of burning also depends on the pressure: a detonation, for example, is an autoignitive reaction front coupled to a strong shock wave giving it its characteristic high-pressure peak and high detonation velocity.


Solid fuels

The act of combustion consists of three relatively distinct but overlapping phases: * Preheating phase, when the unburned
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical con ...

fuel
is heated up to its flash point and then fire point. Flammable gases start being evolved in a process similar to dry distillation. * Distillation phase or gaseous phase, when the mix of evolved flammable gases with oxygen is ignited. Energy is produced in the form of heat and light. Flames are often visible. Heat transfer from the combustion to the solid maintains the evolution of flammable vapours. * Charcoal phase or solid phase, when the output of flammable gases from the material is too low for persistent presence of flame and the charring, charred fuel does not burn rapidly and just glows and later only Smouldering, smoulders.


Combustion management

Efficient Industrial furnace, process heating requires recovery of the largest possible part of a fuel's
heat of combustion The heating value (or energy value or calorific value) of a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composi ...
into the material being processed.
HeatCalc
There are many avenues of loss in the operation of a heating process. Typically, the dominant loss is sensible heat leaving with the Exhaust gas, offgas (i.e., the flue gas). The temperature and quantity of offgas indicates its heat content (
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant p ...

enthalpy
), so keeping its quantity low minimizes heat loss. In a perfect furnace, the combustion air flow would be matched to the fuel flow to give each fuel molecule the exact amount of oxygen needed to cause complete combustion. However, in the real world, combustion does not proceed in a perfect manner. Unburned fuel (usually and ) discharged from the system represents a heating value loss (as well as a safety hazard). Since combustibles are undesirable in the offgas, while the presence of unreacted oxygen there presents minimal safety and environmental concerns, the first principle of combustion management is to provide more oxygen than is theoretically needed to ensure that all the fuel burns. For methane () combustion, for example, slightly more than two molecules of oxygen are required. The second principle of combustion management, however, is to not use too much oxygen. The correct amount of oxygen requires three types of measurement: first, active control of air and fuel flow; second, offgas oxygen measurement; and third, measurement of offgas combustibles. For each heating process, there exists an optimum condition of minimal offgas heat loss with acceptable levels of combustibles concentration. Minimizing excess oxygen pays an additional benefit: for a given offgas temperature, the
NOx In atmospheric chemistry Atmospheric chemistry is a branch of in which the of the and that of other planets is studied. It is a of research and draws on , , , , , and and other disciplines. Research is increasingly connected with other a ...

NOx
level is lowest when excess oxygen is kept lowest. Adherence to these two principles is furthered by making material and heat balances on the combustion process.
MatBalCalc

HeatBalCalc
The material balance directly relates the air/fuel ratio to the percentage of in the combustion gas. The heat balance relates the heat available for the charge to the overall net heat produced by fuel combustion.
AvailHeatCalc
Additional material and heat balances can be made to quantify the thermal advantage from preheating the combustion air,
SysBalCalc2
or enriching it in oxygen.
SysBalCalc


Reaction mechanism

Combustion in oxygen is a chain reaction in which many distinct Radical (chemistry), radical intermediates participate. The high energy required for initiation is explained by the unusual structure of the dioxygen molecule. The lowest-energy configuration of the dioxygen molecule is a stable, relatively unreactive diradical in a triplet oxygen, triplet spin state. Bonding can be described with three bonding electron pairs and two antibonding electrons, with Spin (physics), spins aligned, such that the molecule has nonzero total angular momentum. Most fuels, on the other hand, are in a singlet state, with paired spins and zero total angular momentum. Interaction between the two is quantum mechanically a "forbidden transition", i.e. possible with a very low probability. To initiate combustion, energy is required to force dioxygen into a spin-paired state, or singlet oxygen. This intermediate is extremely reactive. The energy is supplied as heat, and the reaction then produces additional heat, which allows it to continue. Combustion of hydrocarbons is thought to be initiated by hydrogen atom abstraction (not proton abstraction) from the fuel to oxygen, to give a hydroperoxide radical (HOO). This reacts further to give hydroperoxides, which break up to give hydroxyl radicals. There are a great variety of these processes that produce fuel radicals and oxidizing radicals. Oxidizing species include singlet oxygen, hydroxyl, monatomic oxygen, and hydroperoxyl. Such intermediates are short-lived and cannot be isolated. However, non-radical intermediates are stable and are produced in incomplete combustion. An example is
acetaldehyde Ethanal (common name acetaldehyde) is an organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
produced in the combustion of ethanol. An intermediate in the combustion of carbon and hydrocarbons,
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
, is of special importance because it is a Poison, poisonous gas, but also economically useful for the production of syngas. Solid and heavy liquid fuels also undergo a great number of
pyrolysis The pyrolysis (or devolatilization) process is the of materials at elevated temperatures in an inert atmosphere. It involves a change of . The word is coined from the -derived s ''pyro'' "fire" and ' "separating". Pyrolysis is most commonly us ...

pyrolysis
reactions that give more easily oxidized, gaseous fuels. These reactions are endothermic and require constant energy input from the ongoing combustion reactions. A lack of oxygen or other improperly designed conditions result in these noxious and carcinogenic pyrolysis products being emitted as thick, black smoke. The rate of combustion is the amount of a material that undergoes combustion over a period of time. It can be expressed in grams per second (g/s) or kilograms per second (kg/s). Detailed descriptions of combustion processes, from the chemical kinetics perspective, requires the formulation of large and intricate webs of elementary reactions. For instance, combustion of hydrocarbon fuels typically involve hundreds of chemical species reacting according to thousands of reactions. Inclusion of such mechanisms within computational flow solvers still represents a pretty challenging task mainly in two aspects. First, the number of degrees of freedom (proportional to the number of chemical species) can be dramatically large; second, the source term due to reactions introduces a disparate number of time scales which makes the whole dynamical system stiff. As a result, the direct numerical simulation of turbulent reactive flows with heavy fuels soon becomes intractable even for modern supercomputers. Therefore, a plethora of methodologies has been devised for reducing the complexity of combustion mechanisms without resorting to high detail level. Examples are provided by: * The Relaxation Redistribution Method (RRM) * The Intrinsic Low-Dimensional Manifold (ILDM) approach and further developments * The invariant constrained equilibrium edge preimage curve method. * A few variational approaches * The Computational Singular perturbation (CSP) method and further developments. * The Rate Controlled Constrained Equilibrium (RCCE) and Quasi Equilibrium Manifold (QEM) approach. * The G-Scheme. * The Method of Invariant Grids (MIG).


Kinetic modelling

The kinetic modelling may be explored for insight into the reaction mechanisms of thermal decomposition in the combustion of different materials by using for instance Thermogravimetric analysis.


Temperature

Assuming perfect combustion conditions, such as complete combustion under adiabatic conditions (i.e., no heat loss or gain), the adiabatic combustion temperature can be determined. The formula that yields this temperature is based on the first law of thermodynamics and takes note of the fact that the
heat of combustion The heating value (or energy value or calorific value) of a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composi ...
is used entirely for heating the fuel, the combustion air or oxygen, and the combustion product gases (commonly referred to as the ''flue gas''). In the case of fossil fuels burnt in air, the combustion temperature depends on all of the following: * the Heat of combustion, heating value; * the air-fuel ratio, stoichiometric air to fuel ratio ; * the specific heat capacity of fuel and air; * the air and fuel inlet temperatures. The adiabatic combustion temperature (also known as the ''adiabatic flame temperature'') increases for higher heating values and inlet air and fuel temperatures and for stoichiometric air ratios approaching one. Most commonly, the adiabatic combustion temperatures for coals are around (for inlet air and fuel at ambient temperatures and for \lambda = 1.0), around for oil and for natural gas.
AFTCalc
In industrial Industrial furnace, fired heaters, power station steam generators, and large gas turbine, gas-fired turbines, the more common way of expressing the usage of more than the stoichiometric combustion air is ''percent excess combustion air''. For example, excess combustion air of 15 percent means that 15 percent more than the required stoichiometric air is being used.


Instabilities

Combustion instabilities are typically violent pressure oscillations in a combustion chamber. These pressure oscillations can be as high as 180dB, and long-term exposure to these cyclic pressure and thermal loads reduce the life of engine components. In rockets, such as the F1 used in the Saturn V program, instabilities led to massive damage to the combustion chamber and surrounding components. This problem was solved by re-designing the fuel injector. In liquid jet engines, the droplet size and distribution can be used to attenuate the instabilities. Combustion instabilities are a major concern in ground-based gas turbine engines because of emissions. The tendency is to run lean, an equivalence ratio less than 1, to reduce the combustion temperature and thus reduce the emissions; however, running the combustion lean makes it very susceptible to combustion instability. The Thermoacoustic hot air engine, Rayleigh Criterion is the basis for analysis of thermoacoustic combustion instability and is evaluated using the Rayleigh Index over one cycle of instability
G(x)=\frac\int_q'(x,t)p'(x,t)dt
where q' is the heat release rate perturbation and p' is the pressure fluctuation. When the heat release oscillations are in phase with the pressure oscillations, the Rayleigh Index is positive and the magnitude of the thermo acoustic instability is maximised. On the other hand, if the Rayleigh Index is negative, then thermoacoustic damping occurs. The Rayleigh Criterion implies that a thermoacoustic instability can be optimally controlled by having heat release oscillations 180 degrees out of phase with pressure oscillations at the same frequency. This minimizes the Rayleigh Index.


See also

;Related concepts * Air–fuel ratio * Autoignition temperature * Chemical looping combustion * Deflagration * Detonation * Explosion *
Fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

Fire
* Flame * Heterogeneous combustion * Markstein number * Phlogiston theory (historical) *
Spontaneous combustion Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to Exothermic reaction, exothermic internal reactions), followed by thermal runaway (self heating which rapidly acce ...
;Machines and equipment * Boiler * Bunsen burner * External combustion engine * Furnace (house heating), Furnace * Gas turbine * Internal combustion engine * Rocket engine ;Scientific and engineering societies * International Flame Research Foundation * The Combustion Institute ;Other * List of light sources


References


Further reading

* * * * * * * * {{Authority control Combustion, Chemical reactions