Stabilization and soot/NOx emission of hydrogen-enriched methane flames in a turbulent jet with coaxial air under elevated pressures

Abstract

Adding hydrogen to methane has gained interest as a means of reducing CO2 emissions from combustion systems. However, this process can lead to several issues, such as flashback and NOx emissions. Therefore, it is essential to determine the optimal conditions for flame stabilization and emission to design effective hydrogen burners. This study chose a turbulent fuel jet with coaxial air as the basic configuration, and its combustion characteristics were investigated under elevated pressures. Additionally, the depth of the fuel tube in the coaxial air tube was actively controlled to regulate flame stabilization, and its effects were examined for various pressures, velocities, and hydrogen concentrations. Three flame stabilization modes were observed clearly, i.e., inner-attached, outer-attached, and inner-lifted modes. Furthermore, the parameters that influenced the flame modes were identified, and the characteristics of soot and NOx emissions were studied. The inner-lifted mode demonstrated the best combustion performance, and the corresponding conditions were predicted to be extended through hydrogen enrichment and pressure elevation. Therefore, the inner-lifted flame is recommended as the conceptual design goal for hydrogen-enriched high-pressure burners.