Structure of Pure Hydrogen Array Microtube Premixed Flame and Measurement of Turbulent Burning Velocity

To investigate the turbulent burning characteristics of pure hydrogen micromix flames at various flow velocities ranging from 45 - - 87 m/s under lean combustion conditions, an arrayed microtube nozzle model combustion chamber is employed. The flame is diagnosed using particle image velocimetry and hydroxyl plane laser-induced fluorescence techniques to examine the structure of the turbulent flame front and the thermal flow field of the flame. Details on the scale of the flame front and turbulent parameters of the micromix combustion chamber are obtained, including flame volume, flame surface density, turbulent intensity, turbulent integral scale, and turbulent burning velocity. The results suggest that the turbulence intensity at the outlet of the micromix combustion chamber linearly increases with the inflow velocity. The probabilities of the flame front protruding towards unburned gas and receding from unburned gas are nearly equal. As turbulent intensity rises, the small-scale structure and wrinkling degree of the flame also increase. These changes lead to an increase in flame surface density, thereby increasing the turbulent flame area and turbulent burning velocity. Additionally, the normalized turbulent burning velocity of the hydrogen micromix flames reaches 7 - 11, approximately twice the flame area ratio of 3. 5-5. 5. This is primarily attributed to the low Lewis number of lean hydrogen flames, causing the local combustion rate of the flame to surpass the laminar burning velocity. Therefore, the increase in burning velocity of lean pure hydrogen micromix turbulent flames is mainly driven by the expansion of the flame area and the enhancement of the local combustion rate. This research provides a theoretical basis and experimental support for optimizing the arrayed microtube nozzle model combustion chamber and micromix combustion technology. © 2024 Xi'an Jiaotong University. All rights reserved.