壁面冷却空气对贫油吹熄特性影响的激光诊断研究

The utilization of an air film for cooling the wall in the combustion chamber has an impact on the flow field and changes the structure of the recirculation zone, thus affecting the lean blow-off characteristics. To address this problem, measurements of the lean blow-off limit •were conducted under different -wall cooling air ratios in a swirl combustion chamber -with cooling air. The results indicate that -when the proportion of -wall cooling air reaches 0. 2 , the reduction of the blow-off equivalent ratio of the combustion chamber calculated by the global air flow rate shall range from 0. 09 to 0. 1 under different fuel flow rates. The reduction of the blow-off equivalent ratio calculated by mainstream air shall range from 0. 01 to 0. 028. To further investigate the reasons for this phenomenon, plane laser induced fluorescence laser diagnostic measurements were conducted. The results show that after the addition of wall cooling air, the distribution of OH shall be more concentrated at the flame root near the bottom of the combustion chamber. Under stable flame conditions, a substantial amount of OH distribution is observed in the center of the flame near the bottom of the combustion chamber, compared with near blow-off flame conditions. It facilitates flame stabilization and expands the lean blow-off limit. Results from the Mie scattering experiment show that the addition of wall cooling air can result in an enhanced concentration of fuel droplets near the bottom of the combustion chamber, thus leading to an increase in the local equivalence ratio of the root flame and facilitating the formation of a stable flame. In combination with the experimental findings, it is evident that the addition of wall cooling air at a proportion of 0. 2 can expand the blow-off limit in a swirl combustion chamber and contribute to the flame stability. The research results are expected to provide some theoretical guidance for the control of combustion stability in combustion chambers equipped with cooling air films.