The Influence of Varying Fuel Composition and Flowfield on Turbulent Biogas-Like Flame Characteristics

The flame stability of biogas surrogate flames subjected to variations in fuel composition and flow stabilization mechanisms are experimentally investigated in a non-premixed variable swirl burner (IIST-GVS1) with an axial-plus-tangential swirler. OH* chemiluminesce measurements along with 2D-PIV and probe measurements are performed to get insight into the flame characteristics and the emission levels at different operating conditions of the burner. Fuels with pure CH\(_4\) and with 20-40 % CO\(_2\) dilution are tested. 2D-PIV measurements reveal recirculation zones BRZ and ORZ due to the bluff body and combustor walls, respectively, and a central swirl-induced inner recirculation zone (IRZ). The recirculation of hot product gases plays a significant role in flame stabilization. Depending on the global equivalence ratio (\(\phi _g\)), the flame stabilized close to the burner exit, at the boundary of BRZ, or downstream in the swirl-induced region. Though the swirl enhanced the flame stabilization, the region of a stable operating zone (in terms of \(\phi _g\)) reduced with a high amount of swirl. Increasing CO\(_2\) dilution weakened the flame under all flow conditions with an enlargement of the heat release zone area. For a fixed \(\phi _g\), changes in fuel type led to local flowfield modification under similar inflow conditions. Also, with increasing CO\(_2\) dilution, the flame stabilized further downstream in locations with higher turbulence fluctuations and lower axial velocities. The burner, in general, produced deficient levels of NO\(_x\) emissions. However, higher levels of CO are seen with increasing CO\(_2\) dilution and at low \(\phi _g\).