Large Eddy Simulation of Hydrogen/Natural Gas/Air Premixed Swirling Flames and CIVB Flashback Risks

The desire to develop gas turbines (GTs) that can utilise natural gas (NG) blended with hydrogen (H2) often encounters operability challenges related to combustion-induced vortex breakdown (CIVB) flashback issues. Hence, a detailed Large Eddy Simulation (LES) was employed in this study to examine the impact of H2-NG co-firing on central recirculation zones (CRZs), combustion properties, and the risk of CIVB flashback in a pilot-scale swirl burner facility. The LES model successfully replicated the swirling component of the flame observed in the experiment with reasonable accuracy. The findings revealed that the introduction of H2 into the burner increased the velocity and temperature of the burned gases. The higher reactivity of H2 resulted in faster burning rates and a shift in the reaction zone, indicating that NG-H2 firing burns more rapidly than pure NG firing. Additionally, H2 was found to enhance the velocity gradient, pushing the CRZ upstream. Changes in the location of the CRZ can disrupt density and velocity gradients, affecting the generation of vorticity by the baroclinic torque and potentially increasing negative axial velocity, thereby increasing the risk of CIVB flashback. Further research is necessary to comprehensively assess the CIVB flashback risk, particularly when the proportion of H2 exceeds 30 %.