Observation of combustion characteristics of droplet clusters in a premixed-spray flame by simultaneous monitoring of planar spray images and local chemiluminescence

• Published in: Symposium, International, on Combustion Vol. 27; no. 2; pp. 1967 - 1974
• Main Authors: Tsushima, Shohji, Saitoh, Hiroyasu, Akamatsu, Fumiteru, Katsuki, Masashi
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1998
• ISSN: 0082-0784
• DOI: 10.1016/S0082-0784(98)80041-6

In order to better understand the combustion behavior of spray flames, simultaneous measurments of droplet cluster visualization using laser tomography and local OH chemiluminescence and CH-band emission using a newly develped optical probe system named the Multi-color Integrated Cassegrain Receiving Optics (MICRO) are applied to a premixed-spray flame. Time-series planar images of droplet clusters and their transient structures during combustion are examined using an Ar-ion laser and a high-speed digital CCD camera. By observing the droplet clusters and local chemiluminescence simultaneously in the premixed-spray flame, it is confirmed that some portions of the spray stream disappear very rapidly due to preferential flame propagation, while other portions of the spray stream survive over a long period to form droplet clusters, disappearing gradually from their outermost portions, which seems similar to a diffusion flame. The disappearance speed of individual droplet clusters in the premixed-spray flame, instead of a conventional evaporation rate of a single droplet, is defined and calculated by processing the obtained droplet-cluster planar images. The disappearance speed for rapid preferential flame propagation through easy-to-burn regions in the upstream region of the flame is about 2.5 m/s. On the other hand, the disappearance speed when droplet clusters burn dominated by a diffusion combustion mode in the downstream region of the flame is approximately 0.45 m/s.