正癸烷在模型超燃燃烧室中的燃烧特性研究

Combustion Behavior of n-Decane in a Scramjet Model Combustor

为探究正癸烷在双凹腔结构的模型超燃燃烧室中的燃烧特性,试验采用蓄热式加热器提供高焓纯净空气,燃烧室进口的Ma数为2.03,来流总温在800K^1100K,常温液态的正癸烷经凹腔上游的直射式燃料喷嘴进入燃烧室。通过对试验过程中燃烧室壁面压力和流场中的CH*基分布的分析,发现了正癸烷的两种稳焰模式:双凹腔稳焰模式和单凹腔稳焰模式。双凹腔稳焰模式是通过射流形成的尾迹区和凹腔中的回流区共同作用实现稳焰;单凹腔稳焰模式则是通过主流中的激波与边界层干涉形成分离区与凹腔中的回流区实现稳焰。随着试验来流总温的降低,正癸烷的稳焰模式从双凹腔稳焰转变为单凹腔稳焰,直到稳焰失败,模式转变温度和临界稳焰温度分别为876K和842K。还利用一维分析方法对两种稳焰模式的燃烧效率、Ma数分布以及总压恢复系数进行了比较,结果发现双凹腔稳焰模式的燃烧效率和总压恢复系数均大于单凹腔稳焰模式。

This study carried out experiments to investigate the combustion behavior of n-decane at Mach2.03 and stagnation temperature between 800 and 1100 K using a supersonic combustion with two serial cavities flame holder. All experiments were performed in the direct-connect supersonic combustion facility with regenerative storage air-heater. n-decane with ambient temperature was directly injected into a supersonic crossflow upstream of the first cavity. CH chemiluminescences was performed along with measurements of the combustor wall pressure. Two flameholding modes of n-decane,flame held with two cavities and flame held with one cavity were identified by the location of a rise in wall pressure and the CH chemiluminescence emission. The flame held with two cavities was stabilized through the interaction between the jet wake and a recirculation zone in the cavity. On the other hand,the flame held with one cavity was stabilized through the interaction between the separation of boundary layer,which was induced by shock wave,and a recirculation zone in the cavity. As the stagnation temperature decreased,the flame held with two cavities turned to one cavity until it couldn＇t be stabilized. The transition temperature from flame held with two cavities to one cavity and the flameholding temperature of n-decane were 876 K and 842 K,respectively. The result of the one-dimensional analysis show that the combustion efficiency and stagnation pressure recovery coefficient are higher when the flame held at two cavity.