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Chemkin 4.1.1 Chapter 2: Combustion in Gas-phase Processes mesh points are added in regions where the solution or its gradients change rapidly. The initial guess for the solution on the finer mesh is obtained by interpolating the coarse mesh solution. This procedure continues until no new mesh points are needed to resolve the solution to the degree specified by the user. The simulation also needs a starting estimate of the solution from which to begin its iteration. This estimate is given in terms of a reaction zone in which the reactants change from their unreacted values (the unburned composition) to the products. Intermediate species are assumed to have a Gaussian profile that peaks in the center of the reaction zone with the width such that the profile is at 1/10 of its peak value at the edges of the reaction zone. The user provides estimates for the location and thickness of this reaction zone on the Initial Grid Properties tab of the C1_ Pre-Mixed Burner panel. Starting estimates for the gas composition in various parts of the flame are input on the Species-specific Properties tab of the C1_ Pre-Mixed Burner panel. The species on the Intermediate Fraction tab are generally short-lived radical species, or species that are expected to be present throughout the flame. The species on the Product Fraction sub-tab are those expected to be present in the fully burned state. If no product species estimates are given, an equilibrium composition will be used for the product estimate. Within the reaction zone the model uses straight lines between the initial and final values for both the reactants and products. On the cold side of the reaction zone the reactant species profiles are flat at the unburned values. On the hot side, the product species are flat at the estimated product values. Note that any given species can be both a reactant and a product species. For example, the nitrogen in an air flame will be both a reactant and a product, while the excess fuel in a rich flame will also be both a reactant and a product. Parameters pertaining to the incoming gas are input on the C1_Inlet1 panel. The input mass flow rate (4.6 mg cm -2 sec -1 ), which corresponds to an experimental value, is the only input on the Stream Properties Data tab. The composition of the fuel-rich input gas (28% H 2 , 9% O 2 and 63% Ar) is input on the Species-specific Data tab of the C1_Inlet1 panel. The Solver panel has some inputs where the default settings are being replaced. There are no inputs on the Output Control or Continuations panels for this project. 2.3.4.3 Project Results Figure 2-11 shows the experimental gas temperature profile as a function of distance imposed on the simulation. The gas composition in Figure 2-12 exhibits the expected behavior of the primary combustion species as a function of distance above the burner, with most of the oxygen reacting away within the first 2 cm. At the larger © 2007 Reaction Design 34 RD0411-C20-000-001
Chapter 2: Combustion in Gas-phase Processes <strong>Tutorials</strong> <strong>Manual</strong> distances, some of the H atoms recombine to form molecular hydrogen. This would not have been important in a fuel-poor flame, but does occur in this fuel-rich situation. An inspection of the text file shows that the simulation now has 33 grid points, a significant increase from the initial six. The grid is more dense at the lower distances, as needed to resolve the more rapid changes in chemical composition and temperature occurring in that region. Figure 2-11 Burner-stabilized Flame—Experimental Gas Temperature Profile Figure 2-12 Burner-stabilized Flame—Mole Fractions RD0411-C20-000-001 35 © 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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Chapter 3: Catalytic Processes Tuto
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Chemkin 4.1.1 4 4 Materials Problem
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Chapter 4: Materials Problems Tutor
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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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Tutorials Manual

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