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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, describing the temperature the combustion products theoretically reach if no energy is lost to the outside environment.

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. The constant pressureadiabatic 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).

It is a commonly misunderstood that the adiabatic flame temperature 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. However, since the assumptions inherent in the adiabatic flame temperature assume chemical equilibrium, states in thermal equilibrium but not chemical equilibrium are not constrained by this limit. In fact, several fuel rich acetylene and methane flames have been found to exceed their adiabatic flame temperatures by hundreds of degrees.

Common flames

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 pressure conditions. The temperatures mentioned here are for a stoichiometric fuel-oxidizer mixture (i.e. equivalence ratio \phi = 1).

Note this is a theoretical flame temperature produced by a flame that loses no heat (i.e. closest will be the hottest part of a flame) where the combustion reaction is quickest. And where complete combustion occurs, so the closest flame temperature to this will be a non-smokey, commonly bluish flame


From the first law of thermodynamics for a closed reacting system we have,

{}_RQ_P - {}_RW_P = U_P - U_R

where, {}_RQ_P and {}_RW_P are the heat and work transferred during the process respectively, and U_R and U_P 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,

{}_RW_P = \int\limits_R^P {pdV} = 0

and there is no heat transfer because the process is defined to be adiabatic: {}_RQ_P = 0 . As a result, the internal energy of the products is equal to the internal energy of the reactants: U_P = U_R . 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,

U_P = U_R \Rightarrow m_P u_P = m_R u_R \Rightarrow u_P = u_R .

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,

{}_RW_P = \int\limits_R^P {pdV} = p\left( {V_P - V_R } \right)

Again there is no heat transfer occurring because the process is defined to be adiabatic: {}_RQ_P = 0 . From the first law, we find that,

- p\left( {V_P - V_R } \right) = U_P - U_R \Rightarrow U_P + pV_P = U_R + pV_R

Recalling the definition of enthalpy we recover: H_P = H_R . 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,

H_P = H_R \Rightarrow m_P h_P = m_R h_R \Rightarrow h_P = h_R .

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. CO_2 and H_2O), 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,

{\rm{C}}_\alpha {\rm{H}}_\beta {\rm{O}}_\gamma {\rm{N}}_\delta + \left( {a{\rm{O}}_{\rm{2}} + b{\rm{N}}_{\rm{2}} } \right) \to \nu _1 {\rm{CO}}_{\rm{2}} + \nu _2 {\rm{H}}_{\rm{2}} {\rm{O}} + \nu _3 {\rm{N}}_{\rm{2}} + \nu _4 {\rm{O}}_{\rm{2}}

Rich of stoichiometry there are not enough variables because combustion cannot go to completion with at least CO and H_2 needed for the molar balance (these are the most common incomplete products of combustion),

{\rm{C}}_\alpha {\rm{H}}_\beta {\rm{O}}_\gamma {\rm{N}}_\delta + \left( {a{\rm{O}}_{\rm{2}} + b{\rm{N}}_{\rm{2}} } \right) \to \nu _1 {\rm{CO}}_{\rm{2}

Flame test

A flame test is a procedure used in chemistry to detect the presence of certain metal ions, based on each element's characteristic emission spectrum. The color of flames in general also depends on temperature; see flame color.

The test involves introducing a sample of the element or compound to a hot, non-luminous flame, and observing the color that results. Samples are usually held on a platinum wire cleaned repeatedly with hydrochloric acid to remove traces of previous analytes. Different flames should be tried to avoid wrong data due to "contaminated" flames, or occasionally to verify the accuracy of the color. In high-school chemistry courses, wooden splints are sometimes used, mostly because solutions can be dried onto them, and they are inexpensive. Nichrome wire is also sometimes used. When using a splint, one must be careful to wave the splint through the flame rather than holding it in the flame for extended periods, to avoid setting the splint itself on fire. The use of cotton swab or melamine foam (eraser) as a support have also been suggested. Sodium is a common component or contaminant in many compounds and its spectrum tends to dominate over others. The test flame is often viewed through cobalt blue glass to filter out the yellow of sodium and allow for easier viewing of other metal ions.

The flame test is fast and easy to perform, and does not require any equipment not usually found in a chemistry laboratory. However, the range of detected elements is small, and the test relies on the subjective experience of the experimenter rather than any objective measurements. The test has difficulty detecting small concentrations of some elements, while too strong a result may be produced for certain others, which tends to drown out weaker signals.

Although the test only gives qualitative information, not quantitative data about the actual proportion of elements in the sample; quantitative data can be obtained by the related techniques of flame photometry or flame emission spectroscopy.

Common metals

Some common metals and corresponding colors are:

Uses in industry of flame tests

There are some uses of the flame test in industry; 1. It is particularly useful for the identification of polymers, because many of them give off unique burn patterns. 2. It is also used in salt analysis

Corn ethanol

Corn ethanol is ethanol produced from corn as a biomass through industrial fermentation, chemical processing and distillation. Corn is the main feedstock used for producing ethanol fuel in the United States and it is mainly used as an oxygenate to gasoline in the form of low-level blends, and to a lesser extent, as fuel for E85flex-fuel vehicles.

Production process

There are two main types of corn ethanol production: dry milling and wet milling. The products of each type are utilized in different ways.

In the dry milling process the entire corn kernel is ground into flour and referred to as “meal.� The meal is then slurried by adding water. Enzymes are added to the mash that convert starch to dextrose, a simple sugar. Ammonia is added to control the pH and as a nutrient for the yeast, which is added later. The mixture is processed at high-temperatures to reduce the bacteria levels and transferred and cooled in fermenters. This is where the yeast is added and conversion from sugar to ethanol and carbon dioxide begins.

The entire process takes between 40 to 50 hours, during which time the mash is kept cool and agitated in order to facilitate yeast activity. After the process is complete, everything is transferred to distillation columns where the ethanol is removed from the “stillage�. The ethanol is dehydrated to about 200 proof using a molecular sieve system and a denaturant such as gasoline is added to render the product undrinkable. With this last addition, the process is complete and the product is ready to ship to gasoline retailers or terminals. The remaining stillage then undergoes a different process to produce a highly nutritious livestock feed. The carbon dioxide released from the process is also utilized to carbonate beverages and to aid in the manufacturing of dry ice.

The process of wet milling takes the corn grain and steeps it in a dilute combination of sulfuric acid and water for 24 to 48 hours in order to separate the grain into many components. The slurry mix then goes through a series of grinders to separate out the corn germ. Corn oil is a by-product of this process and is extracted and sold. The remaining components of fiber, gluten and starch are segregated out using screen, hydroclonic and centrifugal separators.

The gluten protein is dried and filtered to make a corn gluten- meals co-product and is highly sought after by poultry broiler operators as a feed ingredient. The steeping liquor produced is concentrated and dried with the fiber and sold as corn gluten feed to in the livestock industry. The heavy steep water is also sold as a feed ingredient and is used as an environmentally friendly alternative to salt in the winter months. The corn starch and remaining water can then be processed one of three ways: 1) fermented into ethanol, through a similar process as dry milling, 2) dried and sold as modified corn starch, or 3) made into corn syrup.

The production of corn ethanol uses water in two ways – irrigation and processing. There are two types of ethanol processing, wet milling and dry milling, and the central difference between the two processes is how they initially treat the grain. In wet milling, the corn grain is steeped in water, and then separated for processing in the first step. Dry milling, which is more common, requires a different process. According to a report by the National Renewable Energy Laboratory, “Over 80% of U.S. ethanol is produced from corn by the dry grind process.�[3] The dry grind process proceeds as follows:

“Corn grain is milled, then slurried with water to create ‘mash.’ Enzymes are added to the mash and this mixture is then cooked to hydrolyze the starch into glucose sugars. Yeast ferment these sugars into ethanol and carbon dioxide and the ethanol is purified through a combination of distillation and molecular sieve dehydration to create fuel ethanol. The byproduct of this process is known as distiller’s dried grains and solubles (DDGS) and is used wet or dry as animal feed.�[4]

Environmental and social issues

Since most U.S. ethanol is produced from corn and the required electricity from many distilleries comes mainly from coal plants, there has been considerable debate about how sustainable corn-based bio-ethanol could be in replacing fossil fuels in vehicles. Controversy and concerns relate to the large amount of arable land required for crops and its impact on grain supply, direct and indirect land use change effects, as well as issues regarding its energy balance and carbon intensity considering the full life cycle of ethanol production, and also issues regarding water use and pollution due to the increase expansion of ethanol production.

The initial assumption that biofuels were good for the environment because they had a smaller carbon footprint is in debate because it is possible that the production of grain alcohol, and therefore E85, may actually have a greater environmental impact than fossil fuel.

That view says that one must consider:

  • The impact of fertilizers and carbon requiring inputs vs carbon offsetting byproducts like distillers grains.
  • The carbon footprint of the agricultural machinery run to plant and harvest, and to spread chemicals in between.
  • The environmental impact of those chemicals themselves, including fertilizers and pesticides necessary for efficient mass-production of the grains used.
  • The larger amount of energy required to ship and process the grains and turn them into alcohol, versus the more efficient process of converting oil into gasoline or diesel.
  • Even resources such as water, needed in huge amounts for grain production, can have serious environmental impact, including ground water depletion, pollution runoff, and algae blooms from waste runoff.

The U.S. Department of Energy has published facts stating that current corn-based ethanol results in a 19% reduction in greenhouse gases, and is better for the environment

From Yahoo Answers

Question:I haev found the adiabatic flame temperature, however while relevant to my question, i would prefer the normal burning temperature in an air environment. =? can ne1 help? =) ty

Answers:Using an alcohol lamp, you can put bends in pyrex glass, get steel wire to a bright orange, and just barely melt copper wire so the temperature I'm estimating about 1100 C. Of course, the temperature an object reaches in the flame depends on the the size of the object as well as the size of the flame.

Question:I've heard some people saying that putting ethanol in gasoline will have detrimental effects on our cars. The rubber fuel lines will diteriorate, and/or clog up like a fat in an artery. Has anyone heard of any thing like this, or any other negatives about ethanol in our gas? Thanks

Answers:rubber parts in any car made since the 70's will not be adversly affected by ethanol. Ethanol is an excellent solvent, and will clean your fuel tank and deliver any crud that was lurking there directly into your engine. E-10 can also hold much more water in suspension than straight gasoline. Water suspended in the gas is not a problem at all (except you get less power from it), but E-10 is more prone to phase separation when the temperature drops, in which the water and ethanol form a layer at the bottom of the tank under a layer of seriously octane-deficient gasoline. Never mix E-10 with MTBE or non-oxygenated fuel in the same tank if you can help it, because of the phase-separation problem. If a gas station doesn't drain and clean their tanks before their first delivery of ethanol-oxygenated fuel, you'll get really crappy gasoline, as the ethanol absorbs the water and cleans all the crud out of the underground storage tanks, and delivers it to your car. Ethanol can't be delivered through pipelines, due to it's propensity to absorb water. Therefore it's trucked in to distribution centers and mixed with the gasoline in the delivery trucks, for delivery to gas stations. Making it cost more due to higher transportation costs. Adding insult to injury, ethanol blended fuels provide less energy per gallon than straight gasoline, so you'll see a 5 or 7% drop in fuel economy when you switch to E-10. And you get to pay a bit more for the privelege. So, if you think E-10 is good for the environment, think about all those diesel-fuel-burning tanker trucks delivering the ethanol to transfer stations already served by pipeline. And of course, thanks to the increased demand for corn, you get to pay more for your meat (cows and chickens eat corn, too, ya know). But Con-Agra and other big corn producers (and congressmen from corn producing states) are behind it 100%!!

Question:AND WHY?

Answers:Ethanol is a liquid at RT Propane is a gas at RT NaCl is a solid at RT These properties are all due to intermoleccular attractions between the molecules in the samples. In gases, molecules are all floating around seperate from one an other. They hardly interact with each other at all. In liquids, molecules are quite close to each other and are held together in a smaller volume then gases. The molecules do not have as much energy as gas molecules. For a molecules to go from liquid to gas phase you have to provide it with enough energy to break away from all the other molecules. In solid phase molecules are very close to each other and hardly move at all. To go from solid to liquid you have to provide enough energy for the molecules to break their attractive forces with each other enough to be able to move around more freely. Propane is a hydrocarbon and is a non-polar compound. There are only very weak attractive forces between 1 propane molecule and another propane molecule. Because of this there are only very small forces holding the molecules in a sample together, so it does not take very much energy for the molecules to be in the gas phase. RT is enough. Ethanol has a polar group on it (OH). Polar groups have a slightly positive and a slightly negative end. The positive and of one molecule is attracted to the negative end of another molecule. So they are held close to each other by these "intermolecular" forces. These forces are moderate in stranght. Because ethanol molecules are attracted to each other like this it takes quite a bit of energy from an individual molecule to break away from these attractions. So ethanol is a liquid at RT. NaCl is an ionic compound. It consists of a cation Na+ and anion Cl- Cations and anions are extremely attracted to each other. In solid NaCl the cations and anions are arranged in a crystal lattice structure with alternating cations and anions that are all very strongly attracted to each other. It takes a large amount of energy to provide enough energy for these bonds to break. For this reason NaCl is solid at RT.

Question:we are doing work on covalent bonds and that is one of the questions in the book pleeease help me the questions are due in tomorrow !! the more detail the better pleeeease thankyou:)!

Answers:Why are they liquids? As opposed to gases? Or maybe solids? The physical state of a substance results from a competition between two factors. (1) molecules are constantly moving, and (2) molecules are attracted to one another. If the "moving about" tendency is greater than the "attraction" tendency, then the substance will be a gas. If the "attraction" tendency is greater than the "molecular motion" tendency, the substance will be a solid. Clearly, somewhere in between produces a liquid. The molecular motion is a function of temperature and molecular mass. The attraction is due to intermolecular forces, called van der Waals forces, of which there are three common ones: London dispersion forces which are present between all molecules, dipole-dipole attraction which occurs between polar molecules and hydrogen bonding, which is a special case where H is covalently bonded to N, O or F and is attracted to a N, O or F of an adjacent molecule. London dispersion forces arise from attractions between molecules because the electrons in molecules are also in motion and allow for the formation of temporary dipoles. Dispersion forces are proportional to the polarizability of a molecule which depends on the number of electrons and the volume over which they are spread. Contrary to popular notions, London dispersion forces can be stronger than hydrogen bonds. Ranges of intermolecular bond strengths: ............................ |------------| ................. hydrogen bonds .................. |-----------| ............................ dipole-dipole attraction ........ |-------------------------------------| ...... London dispersion forces Acetic acid and ethanol exhibit both London dispersion forces and hydrogen bonding. Kerosene exhibits London dispersion forces.

From Youtube

Ethanol or Ethyl Alcohol 1949 :Ethanol is a volatile, colorless liquid that has a strong characteristic odor. It burns with a smokeless blue flame that is not always visible in normal light. Pure ethanol will irritate the skin and eyes. Nausea, vomiting and intoxication are symptoms of acute exposure. Long term exposure can result in serious liver damage. For more on the hazards of ethanol, go to www.cdc.gov . Ethanol was commonly used as fuel in early bipropellant rocket vehicles, in conjunction with an oxidizer such as liquid oxygen. The German V-2 rocket of World War II, credited with beginning the space age, used ethanol, mixed with 25% of water to reduce the combustion chamber temperature. The V-2's design team helped develop US rockets following World War II, including the ethanol-fueled Redstone rocket, which launched the first US satellite. Alcohols fell into general disuse as more efficient rocket fuels were developed. Ethanol fuel is ethanol (ethyl alcohol), the same type of alcohol found in alcoholic beverages. It can be used as a transport fuel, mainly as a biofuel additive for gasoline. Ethanol is widely used in Brazil and in the United States, and together both countries were responsible for 89 percent of the world's ethanol fuel production in 2009. Since 1976 the Brazilian government has made it mandatory to blend ethanol with gasoline. Brazil has the largest and most successful bio-fuel programs in the world, involving production of ethanol fuel from sugarcane, and it is considered to ...

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