| OCR Text |
Show combustion time after firing never exceeded three seconds. Especially critical were the regimes of gas supply into the area of the vortex structure epicentres. In this case, it was quite impossible to sustain combustion. Gas supplied into the dimple was immediately ejected out of it not having ignited. In this case, the flame-out was due to short residence time of the air-and-gas mixture in the combustion zone. Experiments displayed that the steady state combustion and flame stabilization could be attained when the natural gas was fed into the downstream area of the dimple. In this case, the residence time of the air-and-gas mixture in the combustion zone was sufficient to sustain the flame. This outcome is in a good agreement with the flow pattern in the dimple. A s the investigations of the flow pattern without combustion demonstrated, it was the downstream section of the dimple that the reverse flow triggered, and so gas entering there passed through the secondary recirculating zone from the back part of the dimple to its front one. In our opinion, the most preferential choices of hole arrangement for gas feeding are the hole positions with the angles ranging in between 135°-225° (Figure 4). It is also worth to note that, in the cases of gas feeding through one or two holes, there are no considerable differences between their combustion processes for these two cases once the holes were situated symmetrically with respect to the longitudinal dimple plane of symmetry. Further all the experiments were performed for the case when the both holes of gas feeding were situated in the downstream section of the dimple, with the angle coordinates 135° and 225°. To visually observe the flow pattern in the dimple, aluminium powder was supplied from the holes situated in front part of the dimple. Aluminium powder particles fluoresce brightly while burning and leave well discernible tracks of their movements in the dimple. The flow visualization showed that the combustion produced a change in the flow pattern of the dimple. While combustion, the other large-scale vortex structures appear and no alternate vortex ejection from the dimple takes place. One of the possible flow patters with large-scale vortices evolving during the combustion is shown on Figure 5. As evident from it, a toroidal vortex appears in the dimple. Such a flow pattern differs essentially from that of without combustion in the dimple (Figure 1). Figure 5. A V E R A G E D F L O W P A T T E R N IN A D I M P L E D U R I NG COMBUSTION (ACCORDING TO VISUALIZATION) 7 |
