Investigation of the flow characteristics and NOx formation mechanism of hydrogen micromix diffusion combustion with vortex generator

It is well established that hydrogen has become one of the most promising fuels for achieving zero-carbon emissions. However, hydrogen combustion still faces many challenges, particularly the flashback issue and high NOx emissions, which necessitate the exploration of hydrogen combustion technologies and pollution control measures. This paper proposes a micromix diffusion combustion scheme with a disturbance vortex generator (DVG). The flow characteristics of the micromix element were analyzed, including the velocity distribution, penetration depth, jet vortex length, and vortex structure. It was found that DVG would create an air streamwise vortex within the main airflow, thus accelerating the axial velocity decay and facilitating the penetration of hydrogen. The hydrogen jet vortex rolls up the mainstream air, forming a coupled vortex system, which further enhances mixing. Sensitivity analysis was carried out to study the influences of the key parameters of the micromix element. The hydrogen injection hole diameter and the DVG height were found to be the most influential factors. The interactions between vortex, flame, and NOx were investigated to obtain the mechanism of NOx formation. By conducting a comparative analysis of the effects of the hydrogen orifice diameter and the vortex generator height, it has been observed that augmenting the length of the jet vortex can significantly promote the mixing of hydrogen with the mainstream air, playing an essential role in reducing emissions. This study establishes a solid foundation for future research endeavors in the development of micromix diffusion combustors.