弱旋流喷嘴的污染排放和燃烧稳定性分析

基于弱旋流喷嘴(LSI)的弱旋流燃烧技术具有极低的NOx污染排放能力.分析了弱旋流燃烧的稳定燃烧和降低污染排放的原理,发现其特殊的流动形式及其与湍流火焰传播的匹配是决定其燃烧稳定性和污染排放的主要因素.而弱旋流喷嘴的旋流叶片角度、直径比和流量比等关键参数会影响LSI的下游流动特征,进而影响其燃烧性能.燃料对LSI燃烧稳定性和污染排放的影响主要是通过火焰传播速度和绝热火焰温度发挥作用.为了将液体燃料应用于LSI,目前主要采用了预混预蒸发的方式,试验结果表明:其NOx排放可比采用常规强旋流喷嘴的燃烧室降低10%~60%,但存在自燃和回火的风险.而LSI喷雾燃烧的方式,则需要针对弱旋流液雾燃烧开展更深入的基础研究.只有解决了液体燃料的LSI应用问题,才能发展出不同于传统强旋流燃烧的新一代航空发动机超低排放燃烧室.

Analysis of low-swirl injector emissions and combustion stabilization

Low-swirl combustion technology based on low-swirl injector (LSI) has an ability of ultra-low emission. The principle of the low-swirl combustion stabilization and emissions reduction was analyzed; it was found that its special flowfield structure matching the turbulent flame propagation was a key factor for combustion stabilization and pollution emissions. Key parameters such as the vane angle, radius ratio and mass flow ratio, could impact the downstream flow characteristics of LSI, which would further affect the combustion performance. Fuels impact the combustion stabilization and pollution emissions of LSI by the flame speed and adiabatic flame temperature. To apply the liquid fuel in LSI, the premixed prevaporised combustion was adopted at present, and the experimental results indicated that it could reduce 10%-60% of NOx emissions compared with the traditional high swirl injector combustor, along with a risk of autoignition and flashback. And for LSI spray combustion, more basic researches on the liquid spray combustion in low-swirl flow shall be required. It is difficult to develop next-generation ultra-low emission combustor for aero-engines different from the traditional high-swirl combustion, unless solving the application problem of LSI using liquid fuel.