Experimental investigation of flame stabilization inside the quarl of an oxyfuel swirl burner

- New generic oxycoal burner optimized for simulations and detailed experiments.
- Measurements in oxyfuel and air atmospheres.
- Measurements of flow field and reaction zone inside quartz quarl.
- Flame regime switches from non-premixed to premixed.

A more detailed understanding of coal combustion as required for predictive engineering is still lacking. To gain insights into physically relevant sub-processes the community follows a stepwise approach. Experiments have been conducted starting from lab-scale gas-assisted coal flames up to self-sustaining industrial-scale coal combustors in the MW-range. In the intermediate range, however, experiments are sparse. To close this gap in this contribution a new generic test rig is presented that is suitable for operating gas-assisted coal flames. In close similarity to a burner designed for oxycoal combustion the nozzle and quarl assembly exhibit most important characteristics of a state-of-the-art combustor. Quarl and combustion chamber provide excellent optical access such that advanced laser diagnostic methods can be applied for detailed studies of flow and scalar fields. Geometrical requirements for future numerical simulations such as easy meshing of the nozzle have been considered during the re-design of the burner. Although prepared for gas-assisted oxycoal firing, in a first step various gas flames operated in air and oxyfuel atmospheres are investigated here. The focus of the present study is on flame stabilization. The leading edge of the flame is located inside the quarl such that the optical access to this most important region is a mandatory requirement. For non-reacting and reacting conditions flow fields inside the quarl and the combustor are studied using stereoscopic particle image velocimetry (SPIV). To visualize reaction zones and flame stabilization regions planar laser induced fluorescence of the OH molecule (OH-PLIF) and broadband chemiluminescence (CL) measurements are performed for reacting conditions. It is observed that close to the nozzle the leading edge of the flame stabilizes as a diffusion flame in the slow moving shear layer located between the central recirculation zone and the fuel inlet. Further downstream the flame stabilizes in the high-momentum annular jet flow generated by the primary and secondary flow. Most probably it has switched to the premixed regime.