Flame stability of a micro can-type afterburner for a SOFC

This paper is fundamental studies on an afterburner for a 20kW class home cogeneration solid oxide fuel cell (SOFC) hybrid system. The proposed burner is a micro size can-type with a baffle plate having multi air holes set annularly and an opposite arranged single fuel and air nozzle in the center. This geometry is suitable to enhance the fuel and air mixing and to stabilize the flame in the ultra lean fuel of the effluent from SOFC stack in the MGT. The blow off limits and flame shape are discussed with the flow structure behind the baffle plate which measured by using a particle image velocimetry (PIV). The formed flames can be classified into four groups which are a premixed flame, a partially premixed flame, a partially nonpremixed flame, and a nonpremixed flame depend on the pilot air jet velocity, the baffle plate holes air jets velocity, and the clearance of the fuel nozzle exit and baffle plate, even when the flow rate of the fuel is same. When the premixed flame formed side by the fuel nozzle, the fuel is preheated approximaiely 750K. The counter-rotating vortices are formed behind the baffle plate and the vortices play a key role for the fuel and air mixing as well as the flame stabilization. The pilot jet not only controlled the flame position but also enhanced the fuel and air mixing. Especially, the pilot jet is important to form the premixed flame near the blow off conditions, and the desirable velocity is close to the air jets velocity of the baffle plate holes. However, there are some ineffective conditions for the pilot air jet.