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Chemkin 4.1.1 Chapter 2: Combustion in Gas-phase Processes Figure 2-41 Jet Flame Network—NO Distribution Figure 2-42 Jet Flame Network—Mole Fractions 2.6.3 Partially Stirred Reactor for Methane/Air 2.6.3.1 Problem description In this tutorial, we want to explore effects of imperfect mixing on the exit flow condition from a premixed gas turbine combustor. © 2007 Reaction Design 64 RD0411-C20-000-001
Chapter 2: Combustion in Gas-phase Processes <strong>Tutorials</strong> <strong>Manual</strong> When chemical kinetics is the limiting factor of the reacting system under investigation, we would model the reactor as a perfectly stirred reactor (PSR). The perfect mixing of reactants and products inside a PSR is usually accomplished by using mixers or multiple-jet injections. However, a gas-turbine combustor normally does not have these mixing mechanisms and has to rely on fluid motions, i.e., largescale eddies and turbulence, to provide the necessary mixing actions. Local turbulence is particularly important as it promotes micro-scale mixing among the gas species. Although it is adequate in many cases to treat the gas-turbine combustor as a PSR, 20 this PSR approach does not always yield proper predictions for the combustor outlet condition. One of the factors that can cause the failure of a PSR approach is the interaction between the turbulence (micro-mixing) and chemical kinetics. If the turbulence is too weak to provide fast mixing among the gas species, the micromixing process will interfere with the chemical kinetics. In some cases, when the reactants (non-premixed cases) or the reactants and the products (premixed cases) fail to mix microscopically before they are blown out of the combustor, no combustion zone can be established inside the combustor. The partially stirred reactor (PaSR) model is a tool that can be used to assess the extent of turbulence-kinetics interaction in a gas-turbine combustor or to provide information on how turbulence intensity will affect the combustor. 2.6.3.2 Problem Setup The project file for this sample problem is located in the samples41 directory and is called pasr__ch4_air.ckprj. A skeletal methane/air combustion mechanism is used to speed the calculation, since we are interested in knowing whether combustion can be sustained inside the combustor by turbulence mixing. Molecular mixing is important to this problem despite the fact that the fuel and air are premixed before entering the combustor. For premixed problems, good and fast mixing between the fresh reactants and the burned products is required to anchor the combustion zone inside the combustor. To provide a good starting point for the back mixing, we need to initialize the PaSR with the burned state. This is similar to starting a gas-turbine combustor with a pilot flame. We can use the equilibrium model or the steady state PSR model to obtain the burned state of the premixed fuel-air mixture. Effects of the initial condition on the solutions will be minimal once the simulation time passes the residence time of the combustor. 20. T. Rutar and P.C. Malte, J of Engineering for Gas Turbines and Power, 124:776-783 (2002). RD0411-C20-000-001 65 © 2007 Reaction Design
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Chemkin 4.1.1 Contents Table of Con
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Chemkin 4.1.1 Tables List of Tables
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Tutorials Manual 4.1.1 Figures List
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List of Figures Tutorials Manual 2-
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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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Tutorials Manual 4.1.1 Index Index
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