Methodology for developing reduced reaction mechanisms, and their use in combustion simulations

Sammanfattning: Combustion, present in a vast majority of energy and material production as well as in transportation, represents a foundation of our modern society. To improve and optimize the applications relying on combustion demand a high level of knowledge, and an ability to simulate the combustion process. To do so three-dimensional Computational Fluid Dynamic (CFD) combustion simulations can be used, where a reaction mechanism is used for describing the chemical process. The aim of this thesis is to develop more accurate and compact reaction mechanisms using a new development technique, and to implement these reaction mechanisms into CFD simulations. Because of the high computational cost associated with using reaction mechanisms the new development technique aim at creating reaction mechanisms that balances predictability and computational cost as effciently as possible. Previous cheaper, simplerreaction mechanisms are often unable to capture key flame parameters, hence compromising the final CFD simulation results. The new, more chemically correct reaction mechanisms presented in this thesis enables the modelling of a wider array of flame parameters, without demanding a too high computational cost. The development technique builds on the idea of dividing thechemistry into sections, or blocks. The chemical complexity of each individual block depends on its importance to the overall combustion process. By individualizing the chemistry of each block only the most important species and reactions can be included, optimizing the size and predictability. By combining several blocks a complete reaction mechanism can then be produced. With the use of the newly developed improved reaction mechanisms in combustionCFD flame parameters such as flame position, decomposition and final products, ignition time, burning velocity, flame-flame interaction and temperature and pressure distributions can all be improved compared to if simpler reaction mechanisms are used.