EXPERIMENTAL INVESTIGATION OF A BLUFF BODY BURNER FOR DISTRIBUTED HYDROGEN INJECTION

A novel concept for injection of gaseous hydrogen (fuel) into a stream of air (oxidant) within low-NOx gas turbine combustion systems is proposed and tested experimentally in a laboratory bluff body (BB) burner. Instead of conventional injection nozzles, that represent undesired point sources of the highly reactive fuel, the injection concept presented in this paper employs porous steel components, with anticipation to achieve hydrogen injection into air in a compositionally diluted and spatially distributed fashion. The BB burner is tested with four different bluff bodies: three bluff bodies manufactured of solid steel and characterized by different diameters are used to chart the burner behavior in conventional, fully premixed operation with respect to flame stoichiometry and bulk velocity; one bluff body of porous steel is used to implement and demonstrate the distributed fuel injection (BB-DFI) concept. The experimental setup consists' of OH* chemiluminescence (CL) and luminescence of flame measured at kHz repetition rate (4 kHz OH* CL and 14 kHz luminescence of flame) using high-speed cameras. Stable operation of the BB-DFI burner configuration with distributed hydrogen injection is demonstrated in the equivalence ratio range of 0.3-0.5 for three bulk velocities of 15, 25 and 35 m/s with the flame anchoring downstream of the distributed injection section, on the tip of the bluff body, according to design. The flame shape observed during the initial tests suggests inadequate mixing between the fuel and carrier air in the mixing section. For comparison, three different arrangements of vortex generators are designed and manufactured to improve fuel-oxidant mixing. The effectiveness of the vortex generators in terms of mixing is investigated using laser induced fluorescence (LIF) technique and one of the vortex generator arrangement show promising improvement in fuel-oxidant mixing.