COMBUSTIOn & carbon Dioxide
By Rabon Hutcherson II.
Combustion and carbon dioxide, what are they? When people think of combustion they probably think of simple just bursting into flames; and for carbon dioxide you probably think of what we breath out and what plants take from the air and turn to oxygen. Even though these thoughts are true there is much more to combustion and carbon dioxide. Things you might not think of about combustion are, mathematical equations, models, solutions and chemical reactions, and for carbon dioxide dry ice, combustion and it being a solid. All of these factors you may not have known are now here for you to see.
One of the things that has lead the way for the study of combustion is the Combustion Theory. Combustion Theory is the use of theoretical methods (mathematics, modeling, numerics, etc. in the study of combustion phenomena. Although Faraday and others in the middle of the 19th century and around beginning of the 20th century laid some early foundations, it was not until the middle of the 20th Century that von Karman and a Russian School, involving Frank-Kamenetskii and Zeldovich, prepared a sound basis for the theory. Von Kerman referred to this as “aerothermochemistry”, in which every imaginable physical transport, chemical and thermodynamic process is thrown into the melting pot – a vast field of developing knowledge in Physics, Chemistry, Engineering and Mathematics. The development of systematic asymptotic techniques in Caltech during the 1960s opened the way towards revealing an underlying simplicity in many combustion processes, involving fairly simple mathematical models and solutions. Computers have also made it possible to treat many problems in their fuller, more complicated form. It can also be stated that Combustion Theory has provided a rich range of equations with fascinating mathematical properties. These include the Sivashinsky equation which approximates the destabilizing effect of density change in flames; the Kuramoto-Sivashinsky equation which approximates an anti-diffusive destabilizing effect that some flames possess; and Clarke’s equation which describes chemical and pressure-wave interactions in a detonable chemical mixture. These equations, and some milestone solutions and dimensionless numbers that have helped to punctuate the growth of this field of research can be spotted in the following artistic impression of “Combustion Theory?. The three fundamentals for combustion are fire, fuel and heat. Fire is a chemical reaction involving rapid oxidation or burning of a fuel. It needs three elements to occur, fuel can be any combustible material – solid, liquid or gas. Most solids and liquids become a vapor or gas before they will burn. The air we breathe is about 21 percent oxygen. Fire only needs an atmosphere with at least 16 percent oxygen. Heat is the energy necessary to increase the temperature of the fuel to a point where sufficient vapors are given off for ignition to occur. Heat of combustion, heat released during combustion. In particular, it is the amount of heat released when a given amount (usually 1 mole) of a combustible pure substance is burned to form incombustible products (e.g., water and carbon dioxide); this amount of heat is a characteristic of the substance. Heats of combustion are used as a basis for comparing the heating value of fuels, since the fuel that produces the greater amount of heat for a given cost is the more economic. Heats of combustion are also used in comparing the stabilities of chemical compounds. For example, if equal quantities of two isomeric hydrocarbons burn to produce equal amounts of carbon dioxide and water, the one releasing more energy is less stable, since it was the more energetic in its compounded form. Certain combustible metals, such as magnesium, titanium, potassium and sodium burn at high temperatures and give off sufficient oxygen to support combustion. They may react violently with water or other chemicals, and must be handled with care. Combustion, rapid chemical reaction of two or more substances with a characteristic liberation of heat and light; it is commonly called burning. The burning of a fuel (e.g., wood, coal, oil, or natural gas) in air is a familiar example of combustion. Combustion need not involve oxygen; e.g., hydrogen burns in chlorine to form hydrogen chloride with the liberation of heat and light characteristic of combustion. Combustion reactions involve oxidation and reduction. Before a substance will burn it must be heated to its ignition point, or kindling temperature. Pure substances have characteristic ignition points. Although the ignition point of a substance is essentially constant, the time needed for burning to begin depends on such factors as the form of the substance and the amount of oxygen in the air. A finely divided substance is more readily ignited than a massive one; e.g., sawdust ignites more rapidly than does a log. The vapors of a volatile fuel such as gasoline are more readily ignited than is the fuel itself. The rate of combustion is also affected by these factors, particularly by the amount of oxygen in the air. The nature of combustion was not always clearly understood. The ancient Greeks believed fire to be a basic element of the universe. It was not until 1774 that the French chemist A. L. Lavoisier performed experiments that led to the modern understanding of the nature of combustion. Spontaneous combustion, phenomenon is when a substance unexpectedly bursts into flame without apparent cause. In ordinary combustion, a substance is deliberately heated to its ignition point to make it burn. The most famous cases of spontaneous combustion is the mysterious phenomenon of human combustion. This is when a person just starts to burn; they don?t have to burst into flames they could just simple smoke are burn internally outward. This is a very true event, but also very rare.
Joseph Black, a Scottish chemist and physician, first identified carbon dioxide in the 1750s; carbon dioxide is a colorless, odorless gas. It occurs in the atmospheres of many planets, including that of the earth. On the earth, all green plants must absorb carbon dioxide from the atmosphere to live and grow. Green plants convert carbon dioxide and water into food and oxygen. Plants and animals, in turn, “burn” the food by combining it with oxygen to release energy for growth and other life activities. This process, called respiration is the reverse of photosynthesis. Oxygen is used up and carbon dioxide and water are used to produce more food and oxygen. The cycle of photosynthesis and respiration maintains the earth’s natural balance of carbon dioxide and oxygen. Carbon dioxide is essential in the role of internal respiration. Internal respiration refers to the process by which oxygen is transported to body tissues and carbon dioxide is carried away from them. This carbon dioxide is also a chief guardian of the pH of the blood, which is essential for survival. This buffer system – called the carbonate buffer – is made up of bicarbonate ion and dissolved carbon dioxide plus carbonic acid. The carbonic acid can neutralize hydroxide ions which if added, would increase the pH of the blood and cause alkalosis. The bicarbonate ion can neutralize hydrogen ions that, if added, would cause a decrease in the pH of the blood and lead to acidosis. Both changes in pH are life threatening. The carbon dioxide in the earth’s atmosphere helps regulate the planet’s temperature. When sunlight reaches the earth, some of it is converted into heat. The carbon dioxide absorbs some of the heat and so helps keep it near the earth’s surface. If all the heat from the sunlight escaped into outer space, the earth would become very cold. The amount of carbon dioxide in the atmosphere has been increasing since about 1890, chiefly as a result of the burning of fuels that contain carbon. This increase has caused a slight rise in the earth’s average temperature. Carbon dioxide has important uses in the home and in industry. For example, carbon dioxide released by baking powder or yeast makes cake batter rise. Carbon dioxide in soft drinks, beer, and sparkling wines gives the beverages their fizz. Some fire extinguishers use carbon dioxide because it does not bum and because pure carbon dioxide is denser than air. Carbon dioxide’s heaviness enables it to blanket a fire and prevent oxygen from getting to the fire thus starving the burning material of the oxygen it needs to continue burning. Dry ice is solid carbon dioxide. Carbon dioxide becomes a solid at -78.5 0C. The name dry ice refers to the fact that the substance changes from a solid to a gas without first becoming a liquid. Because of this property, dry ice is widely used in industry to refrigerate food, medicine, and other materials that would be damaged by the melting of ordinary ice. Carbon dioxide is one of the most important compounds on earth. Its importance to industry and the survival of all life are well documented. Without it, all human life would cease to exist. We all owe a debt of gratitude to our friend CO2 of burning, releases heat. If the heat so released cannot escape the substance, the temperature of the substance rises until ignition takes place. Spontaneous combustion often occurs in piles of oily rags, green hay, leaves, or coal; it can constitute a serious fire hazard. Carbon dioxide CO2, chemical compound, occurs as a colorless, odorless, tasteless gas that is about 1 1/2 times as dense as air under ordinary conditions. It does not burn and will not support combustion of ordinary materials. Its weakly acidic aqueous solution is called carbonic acid. The gas, easily liquefied by compression and cooling, provides the sparkle in carbonated beverages. Solid carbon dioxide, or dry ice, is a refrigerant. Dough rises because of carbon dioxide formed by the action of yeast or baking powder. Carbon dioxide is a raw material for photosynthesis in green plants, and is a product of animal respiration and of the decay of organic matter. Carbon dioxide occurs both free and combined in nature, and makes up about 1% of the volume of dry air. It can cause death by suffocation if inhaled in large amounts. Carbon dioxide is a gas that occurs in the atmosphere and is produced in body tissues as a waste product of energy-generating processes. Dissolved in the blood, carbon dioxide is carried to the lungs, and from there it is exhaled as a gas. Some carbon dioxide also leaves the body in urine and in perspiration. If the level of carbon dioxide in the blood rises above normal, the brain automatically stimulates the lungs into working faster. The increase in breathing rate is necessary to rid the body of the extra carbon dioxide, but it may be harmful in other ways. CO2, a colorless gas having a faint, sharp odor and a sour taste; it is a minor component of the Earth’s atmosphere (about 3 volumes in 10,000), formed in combustion of carbon-containing materials, in fermentation, and in respiration of animals and employed by plants in the photosynthesis of carbohydrates. The presence of the gas in the atmosphere keeps some of the radiant energy received by the Earth from being returned to space, thus producing the so-called greenhouse effect. Industrially, it is recovered for numerous diverse applications from flue gases, as a by-product of the preparation of hydrogen for synthesis of ammonia, from limekilns, and from other sources. Carbon dioxide was recognized as a gas different from others early in the 17th century by a Belgian chemist, Jan Baptist van Helmont, who observed it as a product of both fermentation and combustion. By the mid-20th century, most carbon dioxide was sold as the liquid. If the liquid is allowed to expand to atmospheric pressure, it cools and partially freezes to a snow like solid called Dry Ice that sublimes (passes directly into vapor without melting) at -78.5? C (-109.3? F) at the pressure of the normal atmosphere. At ordinary temperatures, carbon dioxide is quite unreactive; above 1,700? C (3,100? F) it partially decomposes into carbon monoxide and oxygen. Hydrogen or carbon also converts it to carbon monoxide at high temperatures. Ammonia reacts with carbon dioxide under pressure to form ammonium carbonate, then urea, an important component of fertilizers and plastics. Carbon dioxide is slightly soluble in water (1.79 volumes per volume at 0? C and atmospheric pressure, larger amounts at higher pressures), forming a weakly acidic solution. This solution contains the dibasic acid called carbonic acid (H2CO3). Carbon dioxide is used as a refrigerant, in fire extinguishers, for inflating life rafts and life jackets, blasting coal, foaming rubber and plastics, promoting the growth of plants in greenhouses, immobilizing animals before slaughter, and in carbonated beverages. Ignited magnesium continues to burn in carbon dioxide, but the gas does not support the combustion of most materials. Prolonged exposure of humans to concentrations of 5 percent carbon dioxide may cause unconsciousness and death.
Combustion & Carbon dioxide
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World Book Encyclopedia, 1992 edition, see “Carbon dioxide”.
Science and Invention, 1983 edition, see “Carbon dioxide”.
McGraw-Hill Encyclopedia of Science and Technology, 1987 edition, see “Carbon dioxide”.