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  • 1. Lindberg, Jenny
    Experiments and simulations of lean methane combustion2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computational fluid dynamics of methane combustion using chemical kinetics for description of the chemistry is studied. Linear least squares data fit to measured concentrations and temperatures is used to modify reaction rate parameters in the Arrhenius rate equation for combustion of methane. The modification of reaction rate parameters influences the result of CFD-simulations to predict combustion at experimental conditions where the Fluent rate equation failed. This first test show promising results but to further develop a global reaction model for combustion of methane and more complex fuels, a more extensive experimental study is required.The reaction rate for combustion of methane is rapid making ordinary sampling techniques for measuring to crude to collect sufficient amount of data for modification. Numerical simulation of fast chemistry using the Arrhenius theory often suffer from convergence difficulties as a result of the stiffness in the chemistry formulation. An alternative method for assessing the space discretization error is proposed. Richardson extrapolation is the most common model used for assessment of solution accuracy but the rigidity of the method allow little variation in the results. For engineering purposes qualitative methods can be sufficient for error assessment. The space discretization error of a two-dimensional axisymmetric simulation of combustion of methane in turbulent flow is studied. Profiles of temperature and carbon dioxide concentration is investigated and a second order polynomial fit is compared to the Richardson extrapolation. The profiles indicate grid independency of the solution but the Richardson method do not. The second order polynomial fit gives a better goodness of fit than obtained using Richardson, and by studying the first and second order term of the solution an estimation of the reaction order can be obtained and used to evaluate the accuracy of solution where the rigidity of the Richardson method provide unrealistic results.

  • 2. Lindberg, Jenny
    et al.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Space discretization error of methane combustion simulations in turbulent flow2005In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 19, no 5, p. 1873-1878Article in journal (Refereed)
    Abstract [en]

    Numerical investigation of methane combustion in a pipe with turbulent flow is studied. The space discretization error is investigated quantitatively and qualitatively, using the Richardson extrapolation and profiles comparisons. Comparison of the profiles indicates that the solution converges to a grid-independent solution. The Richardson method gives unsatisfactory results to determine the grid error, because of the rigidity of the method. A second-order polynomial is used as an alternative to the Richardson method. The results are more stable and have a better goodness of fit. The results of the simulations are compared with those of a similar experiment and the corresponding analytical solution.

  • 3. Lindberg, Jenny
    et al.
    Hermansson, Roger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Modification of reaction rate parameters for combustion of methane based on experimental investigation at furnace-like conditions2004In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 18, no 5, p. 1482-1484Article in journal (Refereed)
    Abstract [en]

    A method for modifying reaction rate parameters in the Arrhenius rate equation for combustion of methane is proposed. Linear least-squares data fit to measured concentrations and temperatures is used to modify reaction rate parameters in the Arrhenius rate equation for combustion of methane in one step. The modified equation is compared to the one provided by the software Fluent by implementing both into a three-dimensional Fluent simulation. The modification of reaction rate parameters influences the result of computational fluid dynamics simulations to predict combustion at experimental conditions where the Fluent rate equation failed. With modified parameters, the size of the reaction zone increases to give better agreement with experiments than that obtained using the Fluent rate equation. This first test indicates that the method has the contingency of becoming a useful tool for modification of reaction rate parameters though it still needs further development.

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