Ignition of a parallel hydrogen injection into a supersonic hot air stream and ignition of a cold premixed combustible hydrogen/air stream heated by a hot air jet were investigated by a high-resolution TVD LU-SGS numerical algorithm. The present two-dimensional simulation included detailed chemistry in terms of elementary reactions, as well as a multispecies molecular transport model and the Baldwin Lomax algebraic turbulent model. In the case of a cold hydrogen injection into a hot air stream, numerical simulation showed that, with a decrease of the width of fuel jet, ignition point moves upstream quickly. The present results also showed that ignition distance was linearly dependent on the logarithmic function of the width of the fuel jet. Furthermore, the phenomenon could be still observed even for a very low concentration of hydrogen in the fuel jet. In the case of a premixed hydrogen/air stream ignited by a hot air jet, with a decrease of the width of air jet, ignition point moved very slightly downstream. However, there existed an ignition limit for the width of air jet, that is, if the width of the air jet was less than this limit, ignition became impossible. Furthermore, this ignition limit depended strongly on the initial temperatures of air stream and premixed hydrogen/air stream.
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