Observation of stagnation-flow premixed-spray flame structure by high-speed imaging and local chemiluminescence measurement (Effects of oxygen concentration in gaseous phase on flame behavior)

We conducted an experimental observation of polydisperse premixed-spray flames of kerosene in a stagnation flow. For monitoring behaviors of fuel droplet and flame we adopted laser sheet visualization consisting of a high-speed digital CCD camera and Ar-ion laser, and OH-radical and CH-band emissions detected from local region in the vicinity of propagating flame by using a light-collecting probe. Three flames with different oxygen concentration in gaseous phase (21%, 19% and 17%) were examined. These flames had the same initial droplet size-distribution measured by Phase Doppler Anemometry at the burner exit, and all the other experimental conditions were kept same except oxygen concentration. In the case of oxygen concentration of 21%, various shape of spray boundary was formed depending on time, and combustion reaction zone overlapped considerably with spray area. On the other hand, in the case of 17%, the flame showed relatively flat-shaped spray boundary. Furthermore, we compared these flame behaviors and structures with those of premixed-spray flames we had observed before.