| description abstract | In this work, an existing single nozzle FLOX® (FLOX®, WS Wärmeprozesstechnik GmbH, Renningen, Germany) burner was modified with a fuel nozzle that was installed concentrically inside the outer air nozzle and was arranged in two different configurations. In the first, nonpremixed case, the fuel and air nozzles were flush at the nozzle exit. In the second, technically premixed case, the fuel nozzle terminated 50 mm below the air nozzle exit. A third, fully premixed case was also achieved by injecting fuel into the air delivery line via an inline-mixer upstream of the nozzle exit. Additionally, measurements were performed using fuel nozzles with two different sizes. For all these cases, hydrogen volume fraction in the fuel was varied from 0 to 100% at a constant equivalence ratio and thermal power. The resulting flames were characterized using two-dimensional OH-chemiluminescence measurements. In addition, load-flexibility was investigated on the 100 vol. % H2 case by varying the equivalence ratio. Some selected conditions were further investigated using particle imaging velocimetry (PIV) to obtain velocity fields. The experimental results demonstrated a strong influence of nozzle configurations (mixedness), equivalence ratio, and H2-content on flame shapes. First of all, increasing H2-content reduced the flame liftoff height (LOH) above the nozzle exit for all three configurations. Second, for the cases with 100 vol. % H2 and independent of the nozzle configuration, the liftoff height increased drastically when Φ was reduced to below 0.3 while the flame became visibly unstable. Overall, increasing level of mixedness generally caused the flame to stabilize closer to the nozzle exit. A remarkable decrease in the liftoff height was observed for the technically premixed case compared to the nonpremixed case. Increasing H2-content from 0 to 100 vol. % also increased the measured NOx emission by nearly a factor of 4, which was also strongly affected by the level of mixedness. Experimental results from this work are being used in a joint effort to validate numerical models for jet-stabilized hydrogen combustion. | |
