An advanced vortex-tube technology for pure ammonia combustion with clean and steady peculiarity

Abstract

The present study investigates the combustion performance of pure ammonia in a stratified vortex-tube reactive flow (SVRF) concerning stability limits, flame topology, pressure fluctuations, and emissions. The results demonstrate that the SVRF enables efficient and stable combustion of ammonia, characterized by uniform flame topology, low NO emissions, and high combustion efficiency. The lean φg stability limits consistently remain below 0.32 within the qf range of 5.0–30.0 l/min. Moreover, the flame topology remains consistently smooth and uniform throughout the process while maintaining a peak heat release above 5.0 × 107 W/m3. Additionally, pressure fluctuation amplitude generally stays within 100 Pa, indicating a remarkably steady combustion process for ammonia burning in the SVRF. The investigation focuses on the multi-field cooperative coupling, which enhances species and enthalpy transport to increase combustion strength, thereby contributing to a larger stability limit. Various criterion numbers are calculated to quantify the aero-/thermo/flame- dynamic stability. It is found that excellent flame-dynamic/thermo-acoustic stability plays a crucial role in achieving steady combustion of pure ammonia, which can be measured by Ra(x) and the “Gain” of the flame transfer function. The degree of synergy between flame disturbance and fluid disturbance, as well as the response of flame disturbance to fluid disturbance in SVRF, is identified as the primary factor influencing different levels of combustion stability performance. Furthermore, a relationship between aero-/thermo-dynamic stability and flame stability has also been discovered. Favorable aero-/thermo-dynamic stability promotes excellent flame-dynamic behavior by suppressing normal direction fluid fluctuation and resulting in more stable intensity and spatial location fluctuations of the flame. Additionally, momentum flux decreases within the interior region, enhancing good flame-dynamic stability when using pure ammonia as fuel.