Investigation of Combustion Characteristics of Hydrogen Lifted Flames in a Small Hydrogen Combustion Chamber

Abstract A lifted hydrogen flame combustion process is promising for dry low-NOx combustion systems that mitigate flashback issues in gas turbine combustors. This study investigates some of the key combustion characteristics, including flame base height, tip position, stability limit, formation conditions, and combustion efficiency of a lifted hydrogen flame. NOx emissions were evaluated corresponding to the flame’s base height and length. Experiments were conducted using a tube-type model combustion chamber with a 15 mm diameter and hydrogen injection nozzle diameters ranging from 0.2 to 0.8 mm. The investigation covered both room temperature and preheated air conditions, with the fuel injection positioned at the center of the combustion chamber. Additionally, combustion efficiency and NOx emissions were evaluated across different supplied air temperatures. The experimental results indicate that flame base height and length are functions of air flow velocity, with an overall equivalence ratio of 0.35 for nozzle diameters from 0.4 to 0.8 mm. Both flame base and tip height increase with air flow velocity, while base height decreases, and flame length increases with a higher equivalence ratio. NOx emissions remained below 2 ppm across different nozzle diameters (0.2 to 0.8 mm) and varied minimally with air flow velocity, except for the 0.8 mm nozzle. Longer residence times were associated with high NOx emissions. Low NOx emissions (< 2 ppm) were achieved with preheated air, where higher preheated air temperatures enhanced reactivity and resulted in a more stable lifted flame. This study established the static combustion stability of a hydrogen lifted flame in a single burner, achieving low emissions and avoiding flashback.