| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 88 === An experimental study is performed in order to investigate the roles of triple flames and flamefront instabilities in the blowout transient process. Two dimensional laser LIPF(laser induced predissociative fluorescence) OH and PIV (particle image velocimetry) diagnostic techniques are used for measurements of instantaneous flame structure and velocity data. Initial conditions are controlled by external acoustic excitation and beginning the blowout transien process. The blowout transient process can be divided into four regions: the pulsating, onset of receding, receding and extinction regions, according to the dynamic characteristics of the flame. In the pulsating region, the flame base is basically pulsating at two specific heights with jittering. Flamefront instability may play a role in leading the onset of blowout process. Both LIPF OH image and PIV results show the possible existence of the triple (or edge) flame structures in the flame base for cases in the pulsating and onset regions. High strain rate, higher than the extinction strain rate, in the flame base in the onset region should be considered as a prominent factor for the blowout process. Moreover, according to the instability in the pulsating and onset regions, we predicts the value of Lewis number would decrease from more than one to less than one. As to the experiment apparatus, PIV system in the experiment can supply two dimensional instantaneous velocity data, and it has the advantages of the low cost, so it deserves to be popularized.
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