Abstract: Experimental investigation on the laser-induced plasma(LIP)ignition based on direct fuelingschemes was conducted in an ethylene fueled model scramjet combustor with a rear-wall-expansion cavity in aMa=2.92 supersonic inflow with a stagnation pressure of 2.6MPa and a stagnation temperature of 1530K. To studythe effect of cavity direct fueling schemes on LIP ignition processes，flame motions were studied by recording theCH* chemiluminescence images at the frame rate of 50kHz. It is indicated that there exists different stages duringa LIP ignition process，which could be classified into four different periods as laser excitation，initial flame，transi. tion and complete flame periods. As for the cavity direct fueling scheme，it is observed that there always exist simi. lar initial flame formation，weakening，growing and fast transition processes. Furthermore，an initial flame quies.cent phenomenon will occur under the cavity direct fueling scheme with rear-wall injection，during which the CH signal is hardly to be recorded. At global equivalence ratios between 0.03 and 0.07，the cavity direct fueling scheme with fore-wall injection is more favorable for the initial flame propagation，however，it will also cause os. cillations during the flame stabilization process.

Key words: Laser-induced plasma；Ignition；Cavity direct fueling schemes；Rear-wall-expansion cavity

摘要： 针对马赫数 2.92，总压 2.6MPa和总温 1530K的超声速来流条件，基于主动喷注乙烯的燃料喷注方案，在后缘突扩凹腔燃烧室中开展了激光诱导等离子体点火实验研究。通过采集 50kHz的 CH*基自发辐射图像，详细观测了火焰传播过程并进而研究了主动式燃料喷注方案对点火过程的影响。研究表明，在激光诱导等离子体点火以后， CH*基强度沿时间的变化会呈现出不同的阶段性特征，大体可以分为四个不同的发展变化阶段(激光激发阶段、初始火焰阶段、过渡阶段和全局火焰阶段)。对于采用凹腔主动式燃料喷注方案，都会经历一个类似的初始火焰形成、减弱、增长和迅速发展成全局火焰的过程，区别在于采用凹腔后壁面燃料喷注方案的初始火焰要更加微弱，而且要经历一个难以观测到 CH*基信号的初始火焰沉寂阶段。在全局当量比 0.03～0.07的条件下，凹腔前壁面燃料喷注方案要比凹腔后壁面燃料喷注方案更加利于初始火焰的发展，但在形成全局火焰以后会引起较大的波动不利于火焰稳定。

关键词: 激光诱导等离子体；点火；凹腔主动喷注方案；后缘突扩凹腔