An asymptotic approach to heat recirculation in diffusion flames fueled by organic particles

Abstract

Owing to their safety, stability and controllability, diffusion flames have found extensive applications in medicine and power generation. Regarding the significance of recirculation impact on micro-combustors, an efficient method should be developed for better analysis of the micro-combustors performance. In this paper, an asymptotic method is developed to model diffusion flames propagation through a biofuel in counterflow configuration with the consideration of heat recirculation effect. The flame structure includes pre-heat, post-vaporization and oxidizer zones. Micron-sized lycopodium particles and air can be regarded as biofuel and oxidizer, respectively. Mass and energy conservation equations are investigated in each zone. For evaluation of the thermal recirculation impact, a specific term is included in the energy conservation equation. Furthermore, the effects of changes in the flame temperature, mass fraction of the gaseous fuel and oxidizer (relative to fuel and oxidizer Lewis numbers), mass particle content, particle radius and equivalence ratio were examined considering and ignoring the thermal recirculation effect. The results indicate that increase of heat recirculation coefficient will rise the flame temperature and shift the flame position to the fuel nozzle side. Also, consideration of thermal heat recirculation will enhance the gaseous fuel production in the pre-heat and post-vaporization zones.