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Show The next example is of the droplet behavior in spray combustion. Figure 14 shows a series of schlieren photographs indicating the behavior of droplets across a typical propagating spray flame[19]. The flame front recorded on the photographs is found to be much smooth like a laminar flame propagating through a gaseous flammable mixture. After the flame front passes, droplets start to evaporate. The process of the droplet evaporation during spray combustion could be discussed on the basis of the schlieren photomicrographs as shown in Fig. 14. t = 1. 02 ms t = 1.77 ms t = 1. 39 ms t= 3 . 28 ms ~ 1mm Figure 14 Series of schlieren photographs representing typical spray flame propagation [ 19] . Fuel: decane; t: time from ignition; Inj ection period = 15 s; Framing rate = 5300 frames/so FlaIIe Shapes and Structures In Fig. 15, direct long-exposure and instantaneous schlieren photographs of a turbulent hydrogen jet diffusion flame, as well as the schlieren photograph of a hydrogen jet without flame, are shown[20,21]. The appearance of the flame zone on the direct long exposure photograph that the flame zone is diffuse and much thicker than a laminar flame is similar to that of the turbulent premixed flame shown in Fig. 6(b), while the detailed flame structure on the instantaneous schlieren photograph shown in Fig. 15(b) is much different from that in Fig. 6(b). Schlieren fronts where the combustion reaction would occur cannot be identified in Fig. 15(b). Since the fine structure of the mixing region of a hydrogen jet where the hydrogen concentration is not uniform can be seen on the instantaneous schlieren photograph shown in Fig. 15 (c), the combustion reaction must occur in the flame zone, although the reaction zone cannot be identified in Fig. 15(b). This implies that the reaction zone of the turbulent diffusion flame shown in Fig. 15 is diffuse in its flame zone. The mixing at the nozzle is closely related to the flame stabilization, so that understanding of the dependence of the mixing process on operating 12 |