Ignition Characteristics of Scramjet Combustor with Laser Ablation and Laser-Induced Breakdown
Yifu Tian, Zun Cai, Mingbo Sun, Rong Feng, Hang Xing, Bo Yan, Minggang Wan, Yongchao Sun, Hongbo Wang, Jiajian Zhu
Abstract
The ignition characteristics of an ethylene-fueled scramjet combustor with a cavity flame holder were experimentally investigated in a Mach 2.92 inflow using laser ablation (LA) and laser-induced breakdown (LIB). For the LA method, a 532 nm Nd:YAG laser was focused directly on the cavity floor composed of stainless steel. Meanwhile, for the LIB method, the laser was focused at 2 mm above the cavity floor to ignite the combustor. Optical techniques, including optical emission spectroscopy, x-ray diffraction, and schlieren imaging, were utilized to analyze the characteristics of the two different laser-induced plasmas. High-speed chemiluminescence imaging was employed to visualize the ignition process by the LA and LIB methods. The LA plasma could successfully ignite the flame at more positions than the LIB plasma with the same laser energy, showing an improved ignition capability due to the higher energy utilization, longer lifetime, and more components with a longer existence time than that of the LIB plasma. The initial flame kernel ignited by the LIB plasma could propagate faster than the LA plasma once the flame is successfully ignited, possibly due to the direct heat convection in the airflow.