Combustion chemistry

Following Equation (6.1), combustion will be a chemical reaction between fossil fuel atoms (predominantly carbon and hydrogen, i.e., hydrocarbon) and oxygen in air to form carbon dioxide and water vapor. Methane, CH4, is the major constituent of most natural gases and undergoes combustion reaction 

For coal with C H N 0 S as constituents, the individual combustible fuel fraction molecules will undergo combustion described by the 

Suffice it to say that carbon dioxide is the product formed by complete combustion. Incomplete combustion will yield CO, a toxic compound, which can further be oxidized to CO2. The toxicity of CO comes from the fact that when inhaled it forms oxy-hemoglobin in the bloodstream which prevents hemoglobin from absorbing oxygen. 

The coefficients in the chemical reactions of combustion may be interpreted as the number of moles of the substances required for the reactions to occur. For example, in the methane combustion reaction, 1 mole of methane reacts with 2 moles of oxygen to form 1 mole of carbon dioxide and 2 moles of water. Although the number of atoms of each element must be conserved during a reaction, the total number of moles or molecules need not. Because the number of atoms of each element cannot change, it follows that the mass of each element and 

Additionally, there are 2 moles of water and 1 mole of CO2 in the 3 moles of combustion products. Therefore the mole fraction of water and carbon dioxide in the combustion products are 

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Gardiner W C Jr (ed) 2000 Gas-Phase Combustion Chemistry 2nd edn (Heidelberg Springer)... 

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

Combustion chemistry in diffusion flames is not as simple as is assumed in most theoretical models. Evidence obtained by adsorption and emission spectroscopy (37) and by sampling (38) shows that hydrocarbon fuels undergo appreciable pyrolysis in the fuel jet before oxidation occurs. Eurther evidence for the existence of pyrolysis is provided by sampling of diffusion flames (39). In general, the preflame pyrolysis reactions may not be very important in terms of the gross features of the flame, particularly flame height, but they may account for the formation of carbon while the presence of OH radicals may provide a path for NO formation, particularly on the oxidant side of the flame (39). 

Emissions Control. From the combustion chemistry standpoint, lean mixtures produce the least amount of emissions. Hence, one pollution prevention alternative would be to use lean premixed flames. However, lean mixtures are difficult to ignite and form unstable flames. Furthermore, thek combustion rates are very low and can seldom be appHed dkectly without additional measures being taken. Consequently the use of lean mixtures is not practical. 

E. J. Badin, Coal Combustion Chemistry—Correlation Fispects Elsevier, New York, 1984, Chapt. 6, p. 68. 

Computer simulation techniques offer the ability to study the potential energy surfaces of chemical reactions to a high degree of quantitative accuracy [4]. Theoretical studies of chemical reactions in the gas phase are a major field and can provide detailed insights into a variety of processes of fundamental interest in atmospheric and combustion chemistry. In the past decade theoretical methods were extended to the study of reaction processes in mesoscopic systems such as enzymatic reactions in solution, albeit to a more approximate level than the most accurate gas-phase studies. 

Roesler, J. F., An Experimental and Two-Dimensional Modeling Investigation of Combustion Chemistry in a Laminar Non-Plug-Flow Reactor, Proc. 27th Symp. (Int.) Combust., 1, 287-293 (1998). 

Diagnostics in Combustion Measurements to Unravel Combustion Chemistry... 

With the discussion of oxygenafe, pofentially bioderived, fuels and fuel additives such as alcohols, ethers, or esters, the need for defailed information on their combustion chemistries is becoming acute. Additional functional groups in the fuel molecule lead to a larger number of possible structural isomers. The influence of the chemical structure of the fuel molecule... 

Ofiwald, P. et al.. Isomer-specific fuel destruction pathways in rich flames of methyl acetate and ethyl formate and consequences for the combustion chemistry of esters, /. Phys. Chem. A, 111, 4093,2007. 

Chapter 2 is devoted to combustion diagnostics. The majority of the novel diagnostic techniques have already been presented in Applied Combustion Diagnostics (2002) by the same author and in a number of survey papers (e.g.. Proceedings of the Combustion Institute, 2005 Progress in Energy and Combustion, 2006). In this book, K. Kohse-Hoinghaus presents work on how to make measurements in combustion chemistry, since this is an area where there have been many recent developments. 

Colorimetry, See Analytical techniques Combustion chemistry, 40 products, 41, 42, 502 spontaueous, 18, 41, 43, 214, 216 Communicatious, 427, 428 Compound specific analyzers, 311 Compressed gases colour coding, 271 construction materials, 266 first aid measures, 280 hazards, 265 precautions, 272, 403... 

Pope, S. B., Computationally efficient implementation of combustion chemistry using in situ adaptive tabulation. Combust. Theory Model. 1 (1997)... 

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