Numerical study of premixed turbulent propagating flames

Turbulent premixed combustion occurs in a variety of technical applications including spark ignition engines, gas turbine combustion chambers, and accidental explosions of chemical plants. This research aims to achieve an understanding of the relevant physical and chemical processes involved and to enhance the predictability of these processes. A flamelet model for premixed turbulent combustion was investigated. As a turbulent combustion model is ultimately aimed at the design process, numerical simulations were used to give results in relatively fast turnover times without the sacrifice of physical accuracy.

The numerical study was carried out using a commercial Computational Fluid Dynamics (CFD) code, Star-CD, to investigate the interaction between the propagating turbulent premixed flames and solid obstacles to quantify the role of generated turbulence in flame acceleration and structure, based on Flame Surface Density (FSD) model. In addition, the investigation, examines the validity of the numerical models used.

This research used experimental measurements obtained for a stoichiometric mixture of Liquefied Petroleum Gas (LPG) that filled a rectangular duct of dimensions 545mm x 195mm x 195mm. A blockage ratio of 55.4% (of cross-sectional area) was embodied in the model to enhance the turbulence interaction aimed at accelerating the reaction rate.

Analysis was performed to the regimes of combustion in the paradigm of the experimental set-up. The predicted results obtained were found to agree well with the experimental results of flame speed and pressure histories. Both suggest that initially the flame is mostly in the corrugated flamelet combustion regimes. The increase in turbulence intensities results in change of combustion regime from broken flamelet to the distributed reaction zone.

Further numerical/computational investigations of the different obstructions are an essential necessity in order to comprehend fully the flame-solid interactions for different obstacle shapes.