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theses

Spherical diffusion flame experiments in microgravity are slated to be conducted on the space station in the near future. The basic flame configuration adopted for the investigations is the spherically-symmetric diffusion flame generated by issuing a fuel mixture into a quiescent oxidizing environment. Upon ignition, the flame is initially located close to the burner surface, subsequently moving outward to reach the steady-state location. H2/CH4/N2 and H2/CH4/He mixtures are examined in the test matrix. Therefore, to guide the experiments, computational simulations are performed with detailed chemistry and transport, along with optically thick and optically thin radiation models, as well as with no radiative loss. Such flames allow for the investigation of transient flame extinction at the two limits: i.e. radiative and kinetic. A high flow rate can result in a maximum extinction Damkhὅler number (Da) beyond which burning is not possible, caused by the reduction in the flame temperature due to radiative heat loss. By transitioning from a moderate flow rate (for which a diffusion flame can be established) to a low flow rate, a minimum extinction Da may be reached, corresponding to the purely kinetic limit of burning. The dual diffusion flame extinction modes for specific mixture compositions and initial ambient oxygen concentrations are obtained numerically.

ETD_6170

M.S.

Includes bibliographical references

by Tianying Xia

doi:10.7282/T3QC057M

ETD graduate

The author owns the copyright to this work.