Information about Adiabatic Flame Temperature
In the study of combustion, there are two types of adiabatic flame temperature depending on how the process is completed: constant volume and constant pressure. The constant volume adiabatic flame temperature is the temperature that results from a complete combustion process that occurs without any work, heat transfer or changes in kinetic or potential energy. This is the maximum temperature that can be achieved for given reactants because any heat transfer from the reacting substances and/or any incomplete combustion would tend to lower the temperature of the products. The constant pressure adiabatic flame temperature is the temperature that results from a complete combustion process that occurs without any heat transfer or changes in kinetic or potential energy. Its temperature is lower than the constant volume process because some of the energy is utilized to change the volume of the system (i.e., generate work).
In daily life, the vast majority of flames one encounters are those of organic compounds including wood, wax, fat, common plastics, propane, and gasoline. The constant-pressure adiabatic flame temperature of such substances in air is in a relatively-narrow range around 1950°C. This is because, in terms of stoichiometry, the combustion of an organic compound with n carbons involves breaking roughly 2n C–H bonds, n C–C bonds, and 1.5n O2 bonds to form roughly n CO2 molecules and n H2O molecules.
Because most combustion processes that happen naturally occur in the open air, there is nothing that confines the gas to a particular volume like the cylinder in an engine. As a result, these substances will burn at a constant pressure allowing the gas to expand during the process.
).
From the first law of thermodynamics for a closed reacting system we have,
and 
are the heat and work transferred during the process respectively, and 
and 
are the internal energy of the reactants and products respectively.
In the constant volume adiabatic flame temperature case, the volume of the system is held constant hence there is no work occurring,
. As a result, the internal energy of the products is equal to the internal energy of the reactants: 
.
Because this is a closed system, the mass of the products and reactants is constant and the first law can be written on a mass basis,
In the constant pressure adiabatic flame temperature case, the pressure of the system is held constant which results in the following equation for the work,
. From the first law, we find that,
. Because this is a closed system, the mass of the products and reactants is constant and the first law can be written on a mass basis,
We see that the adiabatic flame temperature of the constant pressure process is lower than that of the constant volume process. This is because some of the energy released during combustion goes into changing the volume of the control system. One analogy that is commonly made between the two processes is through combustion in an internal combustion engine. For the constant volume adiabatic process, combustion is thought to occur instantaneously when the piston reaches the top of its apex (Otto cycle or constant volume cycle). For the constant pressure adiabatic process, while combustion is occurring the piston is moving in order to keep the pressure constant (Diesel cycle or constant pressure cycle).
If we make the assumption that combustion goes to completion (i.e.
and 
), we can calculate the adiabatic flame temperature by hand either at stoichiometric conditions or lean of stoichiometry (excess air). This is because there are enough variables and molar equations to balance the left and right hand sides,
Rich of stoichiometry there are not enough variables because combustion cannot go to completion with at least
and 
needed for the molar balance (these are the most common incomplete products of combustion),
However, if we include the Water Gas Shift reaction,
Different fuels with different levels of energy and molar constituents will have different adiabatic flame temperatures.
We can see by the following figure why nitromethane
is often used as a power boost for cars. Since it contains two moles of oxygen in its molecular makeup, it can burn much hotter because it provides its own oxidant along with fuel. This in turn allows it to build-up more pressure during a constant volume process. The higher the pressure, the more force upon the piston creating more work and more power in the engine. It is interesting to note that it stays relatively hot rich of stoichiometry because it contains its own oxidant. However, continual running of an engine on nitromethane will eventually melt the piston and/or cylinder because of this higher temperature.
In real world applications, complete combustion does not typically occur. Chemistry dictates that dissociation and kinetics will change the relative constituents of the products. There are a number of programs available that can calculate the adiabatic flame temperature taking into account dissociation through equilibrium constants (Stanjan, NASA CEA, AFTP). The following figure illustrates that the effects of dissociation tend to lower the adiabatic flame temperature. This result can be explained through Le Chatelier's principle.
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Common Flames
)
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In daily life, the vast majority of flames one encounters are those of organic compounds including wood, wax, fat, common plastics, propane, and gasoline. The constant-pressure adiabatic flame temperature of such substances in air is in a relatively-narrow range around 1950°C. This is because, in terms of stoichiometry, the combustion of an organic compound with n carbons involves breaking roughly 2n C–H bonds, n C–C bonds, and 1.5n O2 bonds to form roughly n CO2 molecules and n H2O molecules.
Because most combustion processes that happen naturally occur in the open air, there is nothing that confines the gas to a particular volume like the cylinder in an engine. As a result, these substances will burn at a constant pressure allowing the gas to expand during the process.
Common Flame Temperatures
Assuming initial atmospheric conditions (1 bar and 20°C), the following table list the adiabatic flame temperature for various gases under constant volume conditions. The temperatures mentioned here are for a stoichiometric fuel-oxidizer mixture (i.e. equivalence ratio).
| Fuel | Oxidizer |  (°C) |
(°F)
|
|---|---|---|---|
Acetylene  | air | 2,500 | 4,532 |
| Acetylene | Oxygen | 3,100 | 5,612 |
Butane  | air | 1,970 | 3,578 |
| Butane | Oxygen | 2,718 | 4,925 |
Methane  | air | 1,950 | 3,542 |
| Natural gas | air | ~1,950 | ~3,542 |
Propane  | air | 1,980 | 3,596 |
| Propane | Oxygen | 2,526 | 4,579 |
MAPP gas  | air | 2,010 | 3,650 |
| MAPP gas | Oxygen | 2,927 | 5,301 |
Thermodynamics
)
First law of thermodynamics for a closed reacting system
and are the heat and work transferred during the process respectively, and and are the internal energy of the reactants and products respectively.
In the constant volume adiabatic flame temperature case, the volume of the system is held constant hence there is no work occurring,
. As a result, the internal energy of the products is equal to the internal energy of the reactants: .
Because this is a closed system, the mass of the products and reactants is constant and the first law can be written on a mass basis,
-
.
)
Internal energy versus temperature diagram illustrating closed system calculation
)
Enthalpy versus temperature diagram illustrating closed system calculation
In the constant pressure adiabatic flame temperature case, the pressure of the system is held constant which results in the following equation for the work,
. From the first law, we find that,
. Because this is a closed system, the mass of the products and reactants is constant and the first law can be written on a mass basis,
-
.
We see that the adiabatic flame temperature of the constant pressure process is lower than that of the constant volume process. This is because some of the energy released during combustion goes into changing the volume of the control system. One analogy that is commonly made between the two processes is through combustion in an internal combustion engine. For the constant volume adiabatic process, combustion is thought to occur instantaneously when the piston reaches the top of its apex (Otto cycle or constant volume cycle). For the constant pressure adiabatic process, while combustion is occurring the piston is moving in order to keep the pressure constant (Diesel cycle or constant pressure cycle).
)
Adiabatic flame temperatures and pressures as a function of stoichiometry (relative ratio of fuel and air)
)
Constant volume flame temperature of a number of fuels
If we make the assumption that combustion goes to completion (i.e.
and ), we can calculate the adiabatic flame temperature by hand either at stoichiometric conditions or lean of stoichiometry (excess air). This is because there are enough variables and molar equations to balance the left and right hand sides,
Rich of stoichiometry there are not enough variables because combustion cannot go to completion with at least
and needed for the molar balance (these are the most common incomplete products of combustion),
However, if we include the Water Gas Shift reaction,
Different fuels with different levels of energy and molar constituents will have different adiabatic flame temperatures.
)
Constant pressure flame temperature of a number of fuels
)
Nitromethane versus isooctane flame temperature and pressure
We can see by the following figure why nitromethane
is often used as a power boost for cars. Since it contains two moles of oxygen in its molecular makeup, it can burn much hotter because it provides its own oxidant along with fuel. This in turn allows it to build-up more pressure during a constant volume process. The higher the pressure, the more force upon the piston creating more work and more power in the engine. It is interesting to note that it stays relatively hot rich of stoichiometry because it contains its own oxidant. However, continual running of an engine on nitromethane will eventually melt the piston and/or cylinder because of this higher temperature.
)
Effects of dissociation on adiabatic flame temperature
In real world applications, complete combustion does not typically occur. Chemistry dictates that dissociation and kinetics will change the relative constituents of the products. There are a number of programs available that can calculate the adiabatic flame temperature taking into account dissociation through equilibrium constants (Stanjan, NASA CEA, AFTP). The following figure illustrates that the effects of dissociation tend to lower the adiabatic flame temperature. This result can be explained through Le Chatelier's principle.
See also
External links
- Adiabatic flame temperature program
- Gaseq, program for performing chemical equilibrium calculations.
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.
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trillion fold).]]
Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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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.
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In thermodynamics, work is the quantity of energy transferred from one system to another without an accompanying transfer of entropy. It is a generalization of the concept of mechanical work in mechanics.
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In thermal physics, heat transfer is the passage of thermal energy from a hot to a cold body. When a physical body, e.g. an object or fluid, is at a different temperature than its surroundings or another body, transfer of thermal energy
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Kinetic may refer to:
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- Kinetic theory
- Kinetic energy
- Kinetic Motor Company of India; also Kinetic Group, Kinetic Engineering.
- Kinetic Suspension Technology of Western Australia.
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Potential energy can be thought of as energy stored within a physical system. This energy can be released or converted into other forms of energy, including kinetic energy.
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A reactant or reagent is a substance consumed during a chemical reaction.[1] Solvents and catalysts, although they are involved in the reaction, are usually not referred to as reactants.
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Flame is burning gas or vapor, the visible part of fire. Flame may also refer to:
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- Flaming (internet), a message sent over the internet with the deliberate intent to insult.
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organic compounds]] An organic compound is any member of a large class of chemical compounds whose molecules contain carbon; for historical reasons discussed below, a few types of compounds such as carbonates, carbon oxides and cyanides, as well as elemental carbon are
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The WOOD callsign may refer to:
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- WOOD-TV – an NBC-affiliated television station in Grand Rapids, Michigan
- WOOD (AM) – an AM radio station in Grand Rapids, Michigan
- WOOD-FM - an FM radio station in Grand Rapids, Michigan
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Wax has traditionally referred to a substance that is secreted by bees (beeswax) and used by them in constructing their honeycombs.
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Fat
Fat may refer to:- Fat, a group of compounds that are generally soluble in organic solvents and largely insoluble in water
- Adipose tissue, an anatomical term for loose connective tissue composed of adipocytes
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Plastic is the general term for a wide range of synthetic or semisynthetic polymerization products. They are composed of organic condensation or addition polymers and may contain other substances to improve performance or economics.
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Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. It is derived from other petroleum products during oil or natural gas processing. It is commonly used as a fuel for engines, barbecues, and home heating systems.
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Gasoline or petrol is a petroleum-derived liquid mixture consisting mostly of aliphatic hydrocarbons and enhanced with aromatic hydrocarbons toluene, benzene or iso-octane to increase octane ratings, primarily used as fuel in internal combustion engines.
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Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry) is the calculation of quantitative (measurable) relationships of the reactants and products in chemical reactions (chemical equations).
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Acetylene (systematic name: ethyne) is a hydrocarbon belonging to the group of alkynes. It is considered to be the simplest of all alkynes as it consists of two hydrogen atoms and two carbon atoms.
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Acetylene (systematic name: ethyne) is a hydrocarbon belonging to the group of alkynes. It is considered to be the simplest of all alkynes as it consists of two hydrogen atoms and two carbon atoms.
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2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1
Atomic radius 60 pm
Atomic radius (calc.
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(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1
Atomic radius 60 pm
Atomic radius (calc.
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Butane, also called n-butane, is the unbranched alkane with four carbon atoms, CH3CH2CH2CH3. Butane is also used as a collective term for n
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Butane, also called n-butane, is the unbranched alkane with four carbon atoms, CH3CH2CH2CH3. Butane is also used as a collective term for n
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2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1
Atomic radius 60 pm
Atomic radius (calc.
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(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1
Atomic radius 60 pm
Atomic radius (calc.
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Methane is a chemical compound with the molecular formula CH4. It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.
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gas, especially when compared to other energy sources such as electricity. Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane.
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Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. It is derived from other petroleum products during oil or natural gas processing. It is commonly used as a fuel for engines, barbecues, and home heating systems.
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Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. It is derived from other petroleum products during oil or natural gas processing. It is commonly used as a fuel for engines, barbecues, and home heating systems.
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2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1
Atomic radius 60 pm
Atomic radius (calc.
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(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1
Atomic radius 60 pm
Atomic radius (calc.
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MAPP gas is liquefied petroleum gas (LPG) mixed with methylacetylene-propadiene. MAPP is the tradename for a product of the Dow Chemical Company. In Australia it is known as RazorGas and is a trademark of ELGAS.
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MAPP gas is liquefied petroleum gas (LPG) mixed with methylacetylene-propadiene. MAPP is the tradename for a product of the Dow Chemical Company. In Australia it is known as RazorGas and is a trademark of ELGAS.
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