A comparison of the multicomponent model and the mixture averaged approximation

University essay from Lunds universitet/Fysiska institutionen; Lunds universitet/Förbränningsfysik

Abstract: In this work the major models for calculating diffusion in simulations of a laminar premixed hydrogen flame, the mixture averaged approximation and the multicomponent model, are explained and compared. This is done in order to see if the accuracy gained in implementing the multicomponent model is enough to warrant the increased workload the transition will cause. The models are used to calculate the mean flame speed for a hydrogen flame, as that is the one most easily measured in experiments. But the results are inconclusive in comparison with experiment, since thermal diffusion was not implemented. Still, it does show a clear distinction between the results produced by the two models, as the mixture averaged model gives the flame speed as 239 cm/s while the multicomponent gives it as 250 cm/s, for a stoichiometric hydrogen flame with standard temperature and pressure. The calculation time is also significantly different, as the multicomponent calculation took 42 minutes, while the mixture averaged calculations only took 17 minutes. Worth noting is that the mixture averaged model was heavily optimized, which explains some of the difference.

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