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Chemkin 4.1.1 Chapter 2: Combustion in Gas-phase Processes Note that in Table 2-2, the relative moles given will be normalized such that the total mole fractions sum to 1.0. However, it is often more convenient to enter relative moles, as described in Tables 2-3 and 2-4. Table 2-3 N 2 as Added Diluent Equivalence ratio = 1 Name Mole Fraction Fuel C 3 H 8 1.0 Oxidizer O 2 1.0 Added Species N 2 0.758 Complete-combustion Product H 2 O Complete-combustion Product CO 2 Table 2-4 N 2 as Component of Oxidizer Equivalence ratio = 1 Name Mole Fraction Fuel C 3 H 8 1.0 Oxidizer O 2 1.0 Oxidizer N 2 3.76 Complete-combustion Product H 2 O Complete-combustion Product CO 2 Complete-combustion Product N 2 Note that in the second case (Tables 2-3 and 2-4), N 2 can be considered as either an added diluent (Table 2-3), or a component of the oxidizer, i.e., air (Table 2-4). If it is considered part of the oxidizer then it must be included in the complete-combustion products list. Also, the oxidizer composition can be given in relative moles or in mole fractions that sum to one (relative moles will subsequently be normalized to sum to 1.0). If using the equivalence ratio input format (Tables 2-3 and 2-4), the mole fraction of fuel is relative to the total number of moles of fuel and the mole fraction of oxidizer is relative to the total number of moles of oxidizer, they will equal to unity unless more than one species is given for each field of fuel and/or oxidizer. However, the “added species” mole fractions are relative to the total number of moles of the reactants, thus the total mole fraction of added species should not sum up to unity. © 2007 Reaction Design 20 RD0411-C20-000-001
Chapter 2: Combustion in Gas-phase Processes <strong>Tutorials</strong> <strong>Manual</strong> In general, the equivalence ratio is a good parameter for quantification of mixture stoichiometry for combustion of hydrocarbon fuels (composed only of hydrogen and carbon atoms) in air or in oxygen. However, one has to be careful when applying φ to describe fuel stoichiometry for oxygenates (oxygen is chemically bound to the fuel molecule) as well as other non-traditional fuels and oxidizers. Because the definition of the equivalence ratio does not properly account for the oxygen that might be chemically bound in the fuel, it might not be a useful parameter for some fuels. 1 When trying to determine the Complete-combustion or Stoichiometric Products for such fuels, one must remember that a species can be a saturated Stoichiometric Product if and only if the valence orbitals of all of its constituent atoms are filled. That is, if the oxidation numbers of all of the atoms in a given product species sum up to zero. 2.2.2 Example: Stoichiometric Products Table 2-5 Element Determining Stoichiometric Products Oxidation number C +4 H +1 O -2 N 0 Ar 0 The oxidation numbers of the atoms in CO 2 sum up to (+4) + 2 * (-2) = 0 and in H 2 O they sum up to (-2) + 2 * (+1) = 0 as well, thus CO 2 and H 2 O are Stoichiometric Products. However, oxidation numbers of the atoms in O 2 do not sum up to zero (-2 + -2 = -4), thus O 2 can not be entered as a Stoichiometric Product. 2,3 1. C. J. Mueller, M. P. B. Musculus, L. M. Pickett, W. J. Pitz, C. K. Westbrook. “The Oxygen Ratio: A Fuel-Independent Measure of Mixture Stoichiometry”, 30th International Symposium on Combustion (2004). 2. D. W. Oxtoby, H. P. Gillis, and N. H. Nachtrieb, Principles of Modern Chemistry, Thompson Learning, Inc. (2002). 3. S. S. Zumdahl, Chemistry. D.C. Heath and Company, Lexington, Massachusetts (1989). RD0411-C20-000-001 21 © 2007 Reaction Design
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Chapter 2: Combustion in Gas-phase
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Chemkin 4.1.1 3 3 Catalytic Process
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Chemkin 4.1.1 4 4 Materials Problem
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Chemkin 4.1.1 5 5 Chemical Mechanis
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Tutorials Manual 4.1.1 Index Index
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Index Tutorials Manual normalized s
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