BlueBellMouse. A Tool for Kinetic Model Development

Detta är en avhandling från Combustion Physics

Sammanfattning: The simulation of physical phenomena occurring in chemical reactors requires the description of the kinetics involved in the underlying combustion process. Kinetic models are developed for this purpose. A software package, BlueBellMouse, has been developed to facilitate a deeper automatization and ease of simulation, reduction and optimization of kinetic models. A kinetic model is made of a list of chemical reactions and their reaction rate parameters. The range of application of these models is limited by the set of validation cases and physical parameters that have been taken into account during the compilation. Often, their use under different conditions demands a re-optimization. A systematic optimization technique has been developed in the past that consists in adjusting the reaction rate parameters in a mathematically rigorous way using a set of experimental data as constraints. This approach, used so far for the compilation of “general purpose” detailed kinetic models, applies as well to the development of chemical mechanisms for specific tasks, like for example engine simulations. Homogeneous Charge Compression Ignition (HCCI) engine has found in recent years the interest of the scientific community and automotive industry for their ability to provide high thermal efficiencies and low NOx and particulate emissions. The next step in HCCI engine research is to transfer the accumulated knowledge to industrial applications. Some shortcomings are still to be solved to make these engines suitable for commercialization like, for example, the difficulty in control. Various techniques have been investigated in order to overcome those problems; from variation of the fuel composition to exhaust gas recirculation. The need to change fuel characteristics requires the availability of continuously updated kinetic models optimized under engine conditions. In an operative environment, the calculation speed becomes an essential feature. A key factor for the computational time is the dimension of the kinetic model. One way to achieve reasonable dimensions is to strongly reduce the detailed mechanism. Through the optimization techniques, it is feasible to over reduce the original mechanism and re-optimize the coefficients a posteriori to regain accuracy in the model predictions. Using BlueBellMouse a natural gas fuel reference model as developed by Warnatz et al. has been optimized for a set of HCCI engine experimental cases. The model has then been reduced eliminating redundant species and the corresponding reactions until just the most essential components were left and the model predictions showed high discrepancy with respect to the experimental data. The so obtained skeleton mechanism has then been re-optimized to regain the required accuracy. In addition the optimization of a gasoline fuel reference mechanism containing mixture of n-heptane and iso-octane, toward a set of shock tube experimental cases.

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