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56-424: Burning is combustion, a high-temperature reaction between a fuel and an oxidant. Burning or burnin' may also refer to: Burning Combustion is often a complicated sequence of elementary radical reactions . Solid fuels , such as wood and coal , first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion

112-817: A 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 ) and terrestrial (Earth-based) conditions (e.g., droplet combustion dynamics to assist developing new fuel blends for improved combustion, materials fabrication processes , thermal management of electronic systems , multiphase flow boiling dynamics, and many others). Combustion processes that happen in very small volumes are considered micro-combustion . The high surface-to-volume ratio increases specific heat loss. Quenching distance plays

168-412: A detonation . The type of burning that actually occurs depends on the degree to which the fuel and oxidizer 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

224-399: A triplet spin state . Bonding can be described with three bonding electron pairs and two antibonding electrons, with 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

280-444: A cigarette, a short-circuited wire) and the persistent combustion of biomass behind the flaming fronts of wildfires . Spontaneous combustion is a type of combustion that occurs by self-heating (increase in temperature due to 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

336-548: A given offgas temperature, the 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. The material balance directly relates the air/fuel ratio to the percentage of O 2 in the combustion gas. The heat balance relates the heat available for the charge to the overall net heat produced by fuel combustion. Additional material and heat balances can be made to quantify

392-463: 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

448-414: A strong shock wave giving it its characteristic high-pressure peak and high detonation velocity . The act of combustion consists of three relatively distinct but overlapping phases: Efficient process heating requires recovery of the largest possible part of a fuel's heat of combustion into the material being processed. There are many avenues of loss in the operation of a heating process. Typically,

504-400: A tower with multiple catalyst beds, and are converted to SO 3 , achieving the first stage of conversion. The exit gases from this stage contain both SO 2 and SO 3 which are passed through intermediate absorption towers where sulfuric acid is trickled down packed columns and SO 3 reacts with water increasing the sulfuric acid concentration. Though SO 2 too passes through the tower it

560-426: 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

616-445: A vital role in stabilizing the flame in such combustion chambers . Generally, the chemical equation for stoichiometric combustion of a hydrocarbon in oxygen is: For example, the stoichiometric combustion of methane in oxygen is: If the stoichiometric combustion takes place using air as the oxygen source, the nitrogen present in the air ( Atmosphere of Earth ) can be added to the equation (although it does not react) to show

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672-460: Is acetaldehyde produced in the combustion of ethanol . An intermediate in the combustion of carbon and hydrocarbons, carbon monoxide , is of special importance because it is a poisonous gas , but also economically useful for the production of syngas . Solid and heavy liquid fuels also undergo a great number of pyrolysis reactions that give more easily oxidized, gaseous fuels. These reactions are endothermic and require constant energy input from

728-454: Is stoichiometric concerning the fuel, where there is no remaining fuel, and ideally, no residual oxidant. Thermodynamically, the chemical equilibrium 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 , hydrogen and even carbon ( soot or ash). Thus,

784-400: 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 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.,

840-419: Is 1 / (1 + 2 + 7.54) = 9.49% vol. The stoichiometric combustion reaction for C α H β O γ in air: The stoichiometric combustion reaction for C α H β O γ S δ : The stoichiometric combustion reaction for C α H β O γ N δ S ε : The stoichiometric combustion reaction for C α H β O γ F δ : Various other substances begin to appear in significant amounts in combustion products when

896-463: Is converted to 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 is known as the "theoretical air" or "stoichiometric air". The amount of air above this value actually needed for optimal combustion

952-581: Is greatly preferred especially as carbon monoxide is a poisonous gas. When breathed, carbon monoxide takes the place of oxygen and combines with some of the hemoglobin in the blood, rendering it unable to transport oxygen. These oxides combine with water and oxygen in the atmosphere, creating 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

1008-532: Is harvested for diverse uses such as cooking , production of electricity or industrial or domestic heating. Combustion is also currently the only reaction used to power rockets . 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 , chlorine , fluorine , chlorine trifluoride , nitrous oxide and nitric acid . For instance, hydrogen burns in chlorine to form hydrogen chloride with

1064-428: Is known as the "excess air", and can vary from 5% for a natural gas boiler, to 40% for anthracite coal, to 300% for a gas turbine . 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

1120-482: Is often hot enough that incandescent light in the form of either glowing or a flame is produced. A simple example can be seen in the combustion of hydrogen and oxygen into water vapor , a reaction which is commonly used to fuel rocket engines . This reaction releases 242   kJ/mol of heat and reduces the enthalpy accordingly (at constant temperature and pressure): Uncatalyzed combustion in air requires relatively high temperatures. Complete combustion

1176-438: Is positively correlated with the risk of heart disease. People who survive severe carbon monoxide poisoning may suffer long-term health problems. Carbon monoxide from the air is absorbed in the lungs which then binds with hemoglobin in human's red blood cells. This reduces the capacity of red blood cells that carry oxygen throughout the body. Smoldering is the slow, low-temperature, flameless form of combustion, sustained by

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1232-548: Is produced by incomplete combustion; however, carbon and carbon monoxide are produced instead of carbon dioxide. For most fuels, such as diesel oil, coal, or wood, 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 , and carbon can produce toxic carbon monoxide. The designs of combustion devices can improve

1288-416: Is removed when the gas is exposed to ferric hydroxide . The next step to the contact process is double contact double absorption (DCDA). In this process the product gases (SO 2 ) and (SO 3 ) are passed through absorption towers twice to achieve further absorption and conversion of SO 2 to SO 3 and production of higher grade sulfuric acid. SO 2 -rich gases enter the catalytic converter, usually

1344-462: Is susceptible to reacting with arsenic impurities in the sulfur feedstock, vanadium(V) oxide (V 2 O 5 ) has since been preferred. This process was patented in 1831 by British vinegar merchant Peregrine Phillips. In addition to being a far more economical process for producing concentrated sulfuric acid than the previous lead chamber process , the contact process also produces sulfur trioxide and oleum . In 1901 Eugen de Haën patented

1400-417: Is the source of oxygen ( O 2 ). In the air, each mole of oxygen is mixed with approximately 3.71  mol of nitrogen. Nitrogen does not take part in combustion, but at high temperatures, some nitrogen will be converted to NO x (mostly NO , with much smaller amounts of NO 2 ). On the other hand, when there is insufficient oxygen to combust the fuel completely, some fuel carbon

1456-510: 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 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. Combustion of gaseous fuels may occur through one of four distinctive types of burning: diffusion flame , premixed flame , autoignitive reaction front , or as

1512-648: Is theoretically needed to ensure that all the fuel burns. For methane ( CH 4 ) 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

1568-539: Is unreactive and comes out of the absorption tower. This stream of gas containing SO 2 , after necessary cooling is passed through the catalytic converter bed column again achieving up to 99.8% conversion of SO 2 to SO 3 and the gases are again passed through the final absorption column thus achieving not only high conversion efficiency for SO 2, but also enabling production of a higher concentration of sulfuric acid. The industrial production of sulfuric acid involves proper control of temperatures and flow rates of

1624-457: The efficiency 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. Carbon monoxide is one of the products from incomplete combustion . The formation of carbon monoxide produces less heat than formation of carbon dioxide so complete combustion

1680-410: The flame temperature is above about 1600  K . When excess air is used, nitrogen may oxidize to NO and, to a much lesser extent, to NO 2 . CO forms by disproportionation of CO 2 , and H 2 and OH form by disproportionation of H 2 O . For example, when 1  mol of propane is burned with 28.6  mol of air (120% of the stoichiometric amount),

1736-446: The heat-treatment of metals and for gas carburizing . The general reaction equation for incomplete combustion of one mole of a hydrocarbon in oxygen is: When z falls below roughly 50% of the stoichiometric value, CH 4 can become an important combustion product; when z falls below roughly 35% of the stoichiometric value, elemental carbon may become stable. The products of incomplete combustion can be calculated with

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1792-525: The United States and European Union enforce limits to vehicle nitrogen oxide emissions, which necessitate the use of special catalytic converters or treatment of the exhaust with urea (see Diesel exhaust fluid ). The incomplete (partial) combustion of a hydrocarbon with oxygen produces a gas mixture containing mainly CO 2 , CO , H 2 O , and H 2 . Such gas mixtures are commonly prepared for use as protective atmospheres for

1848-424: The aid of a material balance , together with the assumption that the combustion products reach equilibrium . For example, in the combustion of one mole of propane ( C 3 H 8 ) with four moles of O 2 , seven moles of combustion gas are formed, and z is 80% of the stoichiometric value. The three elemental balance equations are: These three equations are insufficient in themselves to calculate

1904-499: The air and sulfur dioxide (SO 2 ) is necessary to avoid catalyst poisoning (i.e. removing catalytic activities). The gas is then washed with water and dried with sulfuric acid. To conserve energy, the mixture is heated by exhaust gases from the catalytic converter by heat exchangers. Sulfur dioxide and dioxygen then react as follows: According to the Le Chatelier's principle , a lower temperature should be used to shift

1960-418: The application of heat. Organic materials undergoing bacterial composting can generate enough heat to reach the point of combustion. Combustion resulting in a turbulent flame is the most used for industrial applications (e.g. gas turbines , gasoline engines , etc.) because the turbulence helps the mixing process between the fuel and oxidizer . The term 'micro' gravity refers to a gravitational state that

2016-431: The basic process involving combining sulfur dioxide and oxygen in the presence of vanadium oxides , producing sulfur trioxide which was easily absorbed into water, producing sulfuric acid . This process was improved remarkably by shrinking the particle size of the catalyst (e.g. ≤ 5000 microns), a process discovered by two chemists of BASF in 1914. The process can be divided into four stages: Purification of

2072-405: The chemical equilibrium towards the right, hence increasing the percentage yield. However too low of a temperature will lower the formation rate to an uneconomical level. Hence to increase the reaction rate, high temperatures (450 °C), medium pressures (1-2  atm ), and vanadium(V) oxide (V 2 O 5 ) are used to ensure an adequate (>95%) conversion. The catalyst only serves to increase

2128-408: The combustion gas composition. However, at the equilibrium position, the water-gas shift reaction gives another equation: For example, at 1200  K the value of K eq is 0.728. Solving, the combustion gas consists of 42.4% H 2 O , 29.0% CO 2 , 14.7% H 2 , and 13.9% CO . Carbon becomes a stable phase at 1200  K and 1  atm pressure when z is less than 30% of

2184-457: The combustion products contain 3.3% O 2 . At 1400  K , the equilibrium combustion products contain 0.03% NO and 0.002% OH . At 1800  K , the combustion products contain 0.17% NO , 0.05% OH , 0.01% CO , and 0.004% H 2 . 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 nitrogen oxide emissions. Both

2240-400: The dominant loss is sensible heat leaving with the offgas (i.e., the flue gas ). The temperature and quantity of offgas indicates its heat content ( 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

2296-403: The gas is washed with water, and dried by sulfuric acid. In the dusting tower, the sulfur dioxide is exposed to a steam which removes the dust particles. After the gas is cooled, the sulfur dioxide enters the washing tower where it is sprayed by water to remove any soluble impurities. In the drying tower, sulfuric acid is sprayed on the gas to remove the moisture from it. Finally, the arsenic oxide

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2352-486: 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 smoldering reaction include coal, cellulose , wood , cotton , tobacco , peat , duff , humus , synthetic foams, charring polymers (including polyurethane foam ) and dust . Common examples of smoldering phenomena are the initiation of residential fires on upholstered furniture by weak heat sources (e.g.,

2408-402: The liberation of heat and light characteristic of combustion. Although usually not catalyzed, combustion can be catalyzed by platinum or vanadium , as in the contact process . In complete combustion, the reactant burns in oxygen and produces a limited number of products. When a hydrocarbon burns in oxygen, the reaction will primarily yield carbon dioxide and water. When elements are burned,

2464-420: The maximum degree of oxidation, and it can be temperature-dependent. For example, sulfur trioxide is not produced quantitatively by the combustion of sulfur. NO x species appear in significant amounts above about 2,800 °F (1,540 °C), and more is produced at higher temperatures. The amount of NO x is also a function of oxygen excess. In most industrial applications and in fires , air

2520-425: 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. Contact process The contact process is a method of producing sulfuric acid in the high concentrations needed for industrial processes. Platinum was originally used as the catalyst for this reaction; however, because it

2576-576: The produced smoke is usually toxic and contains unburned or partially oxidized products. Any combustion at high temperatures in atmospheric air , which is 78 percent nitrogen , will also create small amounts of several nitrogen oxides , commonly referred to as 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 converters may be required by law. Fires occur naturally, ignited by lightning strikes or by volcanic products. Combustion ( fire )

2632-463: The productivity of the ecosystem and farms. An additional problem associated with nitrogen oxides is that they, along with hydrocarbon pollutants, contribute to the formation of ground level ozone , a major component of smog. Breathing 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

2688-425: The products are primarily the most common oxides. Carbon will yield carbon dioxide , sulfur will yield sulfur dioxide , and iron will yield iron(III) oxide . Nitrogen is not considered to be a combustible substance when oxygen is the oxidant . Still, small amounts of various nitrogen oxides (commonly designated NO x species) form when the air is the oxidative. Combustion is not necessarily favorable to

2744-644: The quality of combustion, such as burners and internal combustion engines . Further improvements are achievable by catalytic after-burning devices (such as catalytic converters ) or by the simple partial return of the exhaust gases into the combustion process. Such devices are required by environmental legislation for cars in most countries. They may be necessary to enable large combustion devices, such as thermal power stations , to reach legal emission standards . The degree of combustion can be measured and analyzed with test equipment. HVAC contractors, firefighters and engineers use combustion analyzers to test

2800-401: The rate of reaction as it does not change the position of the thermodynamic equilibrium . The mechanism for the action of the catalyst comprises two steps: Hot sulfur trioxide passes through the heat exchanger and is dissolved in concentrated H 2 SO 4 in the absorption tower to form oleum Note that directly dissolving SO 3 in water is impractical due to the highly exothermic nature of

2856-469: The reaction. Acidic vapor or mists are formed instead of a liquid. Oleum is reacted with water to form concentrated H 2 SO 4 . This includes the dusting tower, cooling pipes, scrubbers, drying tower, arsenic purifier and testing box. Sulfur dioxide has many impurities such as vapours, dust particles and arsenous oxide . Therefore, it must be purified to avoid catalyst poisoning (i.e.: destroying catalytic activity and loss of efficiency). In this process,

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2912-422: The real world, combustion does not proceed in a perfect manner. Unburned fuel (usually CO and H 2 ) 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

2968-499: The stoichiometric composition of the fuel in air and the composition of the resultant flue gas. Treating all non-oxygen components in air as nitrogen gives a 'nitrogen' to oxygen ratio of 3.77, i.e. (100% − O 2 %) / O 2 % where O 2 % is 20.95% vol: where z = x + y 4 {\displaystyle z=x+{y \over 4}} . For example, the stoichiometric combustion of methane in air is: The stoichiometric composition of methane in air

3024-414: The stoichiometric value, at which point the combustion products contain more than 98% H 2 and CO and about 0.5% CH 4 . Substances or materials which undergo combustion are called fuels . The most common examples are natural gas, propane, kerosene , diesel , petrol, charcoal, coal, wood, etc. Combustion of a liquid fuel in an oxidizing atmosphere actually happens in the gas phase. It

3080-404: The thermal advantage from preheating the combustion air, or enriching it in oxygen. Combustion in oxygen is a chain reaction in which many distinct 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

3136-456: Was the first controlled chemical reaction discovered by humans, in the form of campfires and bonfires , and continues to be the main method to produce energy for humanity. Usually, the fuel is carbon , hydrocarbons , or more complicated mixtures such as wood that contain partially oxidized hydrocarbons. The thermal energy produced from the combustion of either fossil fuels such as coal or oil , or from renewable fuels such as firewood ,

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