An extinction analysis of counterflow diffusion flames in supersonic airflow is presented. The flow configuration consists of supersonic airflow coming from infinite distance and opposing a fuel stream ejected from the surface of a porous body. (It is well known as the Tsuji-burner, but airflow is supersonic.) If airflow velocity is subsonic, the flame temperature decreases as airflow velocity increases because the flame stretch rate increases, and finally flame extinction takes place at a certain airflow velocity. However, in the case of supersonic airflow, the region in which a diffusion flame can be established between a detached shock wave and a porous body reappears, and flame extinction occurs when the airflow velocity decreases. This indicates shock heating has a stronger effect than high stretch-rate flow. Moreover, the flame temperature changes increasingly with the Mach number when the airflow velocity is supersonic, in contrast with the case of subsonic airflow.
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