A NUMERICAL STUDY ON THE TRANSITION CHARACTERISTICS OF AN INVERSE MICRO-SCALE DIFFUSION FLAME TO MICRO-SCALE PREMIXED FLAME UNDER HEAT RECIRCULATION CONDITIONS

In this investigation, the gaseous hydrogen peroxide (H2O2) is issued at the inner port, and methane (CH4) is injected at the outer port of the sub-millimeter scale burner in order to establish an inverse CH4/H2O2 micro-scale diffusion flame numerically under heat recirculation conditions. The velocity of gaseous H2O2 is considered only as a numerical parameter in this study and the velocity of CH4 is kept constant to examine the flame structure and the transition behavior of an inverse micro-scale diffusion flame. The numerical simulation has been conducted using ANSYS Fluent 14.5 based on Finite Volume Method (FVM) under normal gravity (1G) conditions with low thermally conductive burners. The semi-detailed reaction model, which consists of 58 chemical reactions and 17 chemical species, has been applied in this study. It is found that when the momentum of the gaseous H2O2 is high, then a CH4 /H2O2 inverse micro-scale diffusion flame is formed, and this flame is attached just on the top of the burner by which one can easily analysis an active flame-wall interaction phenomenon. On the other hand, when the momentum of the gaseous H2O2 has been reduced significantly, then H2 /O2 micro-scale premixed flame is established entirely inside the micro-burner. Furthermore, it is found that when the momentum of H2O2 reduces remarkably, then CH4 does not diffuse inside the micro-burner at the flame zone, and consequently only H2 /O2 micro-scale premixed flame is established there as H2O2 is playing the role of a monopropellant, where no extra oxidizer is needed for the survival of flames. This type of flame mode transition phenomenon under micro-burner systems is the first ever reported event in the literature of reacting fluid dynamics (i.e., combustion dynamics). Besides, this is the primary findings of our ongoing research, and hence, the further numerical calculation adopting different pertinent parameters is now under progress with the aim of extracting more profound physical and chemical insights that are associated with the aforesaid transition phenomena.  