Isothermal flow field of a technically premixed H2-air double swirl burner

Background-Aim Hydrogen has garnered substantial attention as a potential replacement for conventional fossil fuels in various applications. However, its high flame speed, low ignition energy, and elevated flame temperature present challenges in developing safe, low-emission, and efficient burners/combustors. At Politecnico di Milano, we are currently investigating an original atmospheric burner for 100% H2 combustion featuring a double swirl configuration and employing radially staged combustion air. The objective of the work is to analyze the isothermal mean flow field generated by such burner. Methods The burner comprises a central premixed swirled injector surrounded by an annular swirled airflow, both rotating in the same direction. These streams are axially injected into an octagonal combustion chamber equipped with quartz windows. The burner mean flow field is analyzed by means of the Stereo-PIV technique at a fixed swirl level and flow rate of the annular jet and varying the equivalence ratio of the central premixed jet. For safety reasons, an equivalent air flow rate is used instead of hydrogen. Results Experimental results reveal the occurrence of vortex breakdown with its associated reverse flow region under all tested conditions. The intensity of the reverse flow appears to be influenced by the central swirled jet; the greater the total flow rate of the injector, the more intense the reverse flow, and the wider the swirled jet becomes downstream. A strong turbulent region is observed in the shear layer between the two jets, exhibiting maximum turbulent kinetic energy at approximately 0.9D downstream of the nozzle, where D=36 mm represents the burner diameter. While the position of such maxima seems to remain consistent, the spatial extension of this region increases with the total flow rate of the central injector. Conclusions The results obtained thus far serve as a preliminary step before testing the burner under reactive conditions. Additionally, they will be utilized to validate and refine a numerical simulation, facilitating a deeper understanding of how burner geometry and operating conditions influence the flow field and aiding in the optimization of the burner design.