LES modelling of spray combustion

Detta är en Master-uppsats från Lunds universitet/Institutionen för energivetenskaper

Sammanfattning: Computational fluid dynamics is a powerful method for understanding the flow and combustion that occurs inside aircraft engines and will be a key tool in the transition from conventional fossil-based fuel to sustainable alternatives. Because conventional fuels have been more widely researched, an attempt at simulating the combustion of alternative fuels should be preceded by the development of a method that is capable of accurately simulating the combustion of a conventional fuel. In this thesis, the combustion of the conventional jet fuel Jet A-1 in a gas turbine combustor is simulated with the software OpenFOAM and two different chemical reaction mechanisms: F2 and Z77. The results are compared with experimental data to validate the simulation method, and the performance of the reaction mechanisms is compared. The reaction mechanisms are also used in supplementary chemical kinetics simulations in CHEMKIN to compute laminar flame speed and ignition delay time, two characteristic combustion features, to assist in explaining the phenomena observed in the CFD simulations. The simulations produced generally realistic results, but overestimated the lift-off distance of the flame at low pressure. The Z77 mechanism produced higher and more pressure-sensitive temperatures than the F2 mechanism. At high pressure, there was an instability in the simulations in the form of a pressure oscillation. It was shown that this instability was driven by the combustion process, but it could not be determined whether this was the sole cause of the instability. Finally, the simulations showed that CH concentration is better than OH concentration as an indicator of high heat release.

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