Combustion characteristics and flame stability of propane-air
mixtures in flow tube reactors with heat-recirculating structures
The characteristics of catalytically stabilized combustion in micro-scale heat-recirculating systems remain poorly understood and warrant further study due to extremely complex interactions not only between kinetics and transport but also between heterogeneous and homogeneous reactions. This study is focused mainly upon the essential combustion characteristics of propane-air mixtures in flow tube reactors with a heat-recirculating structure. Computational fluid dynamics simulations are performed to gain a greater understanding of the mechanisms of flame stabilization. The essential factors affecting flame stability and combustion characteristics are determined in order to obtain design insights. The results indicate that both chemical and thermal environments are improved with the catalytically stabilized combustion method and the heat-recirculating structure. The design incorporates the best features of both catalytic combustion and thermal flame methods. The system is essentially free of mass transfer limitations. The flow velocity, wall thermal conductivity, equivalence ratio, exterior heat losses are important factors in determining the performance of the system. Stable operation of the system is limited to a relatively wide flow regime, and the flow velocity is critical to achieving flame stability. There is an optimum wall thermal conductivity in terms of flame stability. The system with a moderate wall thermal conductivity will be most robust against the surrounding conditions. Excess enthalpy combustion can occur in an efficient and rapid manner, resulting from the injection of free radicals and heat produced by the catalytic reaction. Blowout shifts homogeneous combustion downstream significantly without substantially reducing the reaction rate.
Keywords: Combustion characteristics; Flame stability; Heat recirculation; Catalytic combustion; Homogeneous combustion; Computational fluid dynamics