Study of Flame Interference of Counterflow Twin Flames

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Concerning the twin flames obtained with a counterflow nozzle burner, the nozzle velocity dependencies of flame temperature, concentration profile, burning velocity, and flame-to-flame distance were investigated for propane/ air mixture, and flame interference effects caused by the existence of two adjacent flames were examined. Furthermore, theoretical analysis was also made on the flammability limits of the twin flames. The obtained results are as follows:1. Some singularities implying the flame strengthening due to flame interference were noticed in the relations of flame temperature and flame distance to the nozzle velocity in a certain velocity range.2. Gas analysis made for the two flames just before and under interference gave no significant differences in the concentration profiles of stable species, which suggests that the active chemical species might play an important role in the flame interference.3. The flammability limits of the twin flames and the one-dimensional-flow flame which is not subjected to interference effects were theoretically compared by the analysis based on a reaction model in which the importance of active species was taken into account, and the limits of the twin flames were found to be more widened owing to the interference.4. The addition effects of hydrogen, well known as an active fuel, to propane was investigated. Though the effect was not so simple, the velocity range of interference was widened (i.e., the interference effect was strengthened ) in the lean side.5. Singularities were noticed also in the relation between the nozzle velocity and the burning velocity obtained by velocity measurements with LDV. However, if the burning velocity is plotted against the velocity gradient normal to the flame surface, the relation becomes monotonous, indicating that the nozzle velocity cannot be regarded as a linear parameter for the flame stretch.