Experimental and numerical study of H2 enrichment on swirl/bluff-body stabilized lean premixed n-butane/air flame

This study focused on the stabilization of lean premixed flames of n-butane/H-2/air 2 /air with swirl/bluff-body. The research explored four different hydrogen fractions (0, 20%, 40%, and 80%) at a constant equivalence ratio and Reynolds number. The turbulent reacting flow was resolved using a combination of Delayed Detached Eddy Simulation (DDES) and Flamelet Generated Manifold (FGM) model. The velocity fields and reaction zones were obtained through Particle Image Velocimetry (PIV) and OH* chemiluminescence measurements respectively. H-2 addition to n-butane significantly enhanced flame characteristics. The chemiluminescence imaging showed that the flame base became stronger with increasing hydrogen addition, reducing the risk of flame lift-off. Hydrogen addition not only increased the overall reaction rate but also changed the combustion intensity at the nozzle exit from weak to strong, which is crucial for flame stabilization. Interestingly, no flashback was observed even at 80% H-2 addition to n-butane at the same level of power rating. The flow strain rate analysis of the PIV measurements showed that the inclusion of hydrogen skewed the strain rate probability density functions towards the positive side, indicating an increase in the burning rate. The results demonstrate a progressive increase in preferential diffusion of H-2 from reactants to products as the H-2 enrichment in the fuel rises and resulted in a more intense flame. Also, the present simulation results were validated with the PIV data, and they showed good agreement. Specifically, an 80% H-2 blend exhibited a 16% peak enhancement in flame surface density compared to pure n-butane while concurrently reducing CO2 2 emissions by 23.2%. The incorporation of H-2 also led to the increased vortex strength and strain rate within the flame.