Experiments and Simulations of Lean Methane Combustion

Computational fluid dynamics simulation of methane combustion using chemical kinetics 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 shows promising results. However, to further develop a global reaction model for combustion of methane and other 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. 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 allows little variation in the results. For engineering purposes qualitative methods can be sufficient for error assessment. Here 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 are 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 does not. The second order polynomial fit gives a better goodnessof-fit than obtained when using Richardson. By studying the first and second order terms of the polynomial fitted to the result of the simulations an estimation of the reaction order can be obtained.