Tsuyoshi Nakajima

Multi-point time-series observation of optical emissions for flame-front motion analysis

A simple optical diagnostic technique to analyse flame-front movement is proposed. Time-series, multi-point optical emission measurements using an aberration-free Cassegrain probe coupled with multiple fibres were performed successfully in turbulent premixed flames. The spatial resolution of the Cassegrain optics was examined using a CCD camera in free space and also in turbulent flame conditions. Spatial intensity distributions of OH, CH and C2 chemiluminescence measured in a two-dimensional laminar flame were compared with the numerical calculation of one-dimensional profiles of these species, demonstrating the ability of the present optical technique to detect a flame front. The probability density of the instantaneous speed and orientation angle of flame-front displacement were determined locally through a geometric motion analysis of simultaneous, time-evolutional OH* signals at three points. Flow fields measured by PIV were compared with the flame-front velocities to examine differences between gas flow and flame-front dynamics. Errors due to flame curvature, thermal density change and inclined propagation were also estimated.

An Experimental Study on Low Frequency Oscillation and Flame-Generated Turbulence in Premixed/Diffusion Flames

Abstract Experimental studies were carried out on turbulences in open premixed jet flames by using a double coaxial type burner with propane-air mixtures. Shadow and schlieren graphs showed that low frequency oscillations of the flame occur in the vicinity of the boundary between the outer flame and the surrounding air stream. The phenomena are surely caused by the hydrodynamic instability and it was also asserted from the fact that the phenomena could never be seen in the case of the surrounding flow velocity being large enough in measurement by a counter-type laser doppler velocimeter (LDV). Moreover, the organized motion with periodic vortices was entirely common in premixed, rich-premixed, and diffusion flames in the open atmosphere. The normalized frequencies had a tendency similar to the results obtained by some workers On the other hand, from the measurement of velocity fields by LDV, it was found that strong turbulences occurred on the flame front mainly by the velocity gradient, not |∂∪|∂r| but |...

Laser diagnostics and spectroscopy for combustion flow

Flame propagation speed and flame front structure have been measured and investigated by finite focal length Cassegrain optics developed to measure local chemiluminescence. This method can be a powerful tool for combustion flow diagnostics.