58699 - Spark Ignition of Spp Injector under Sub-Atmospheric Conditions 

The sub-atmospheric ignition performance of an SPP (Stratified Partially Premixed) injector and combustor was experimentally investigated at the sub-atmospheric test facility in Institute of Engineering Thermophysics, Chinese Academy of Sciences. The experiments were conducted under different inlet air pressure ranging from 19 kPa to 101 kPa. The inlet temperature and pressure drop of the injector (△P_sw/P_3t) were kept constant at 303 K and 3%. The transparent quartz window mounted on sidewall of the model combustor provides optical access of flame signals. Ignition fuel-air ratio (FAR) under different inlet pressure was experimentally acquired. The spark ignition processes, including the formation of flame kernel, the flame development and stabilization were recorded by a high-speed camera at a rate of 5 kHz. Experiment results indicate that the minimum ignition FAR grows rapidly as the inlet air pressure decreases. It was observed that the successful ignition of single injector generally comprises two phases: (1) The initial flame kernel excited by sparks moves radially towards the injector centerline and enters the central recirculation zone (CRZ). This phase is accompanied by breakup of the kernel and attenuation of the flame intensity. (2) The flame kernels expand around and establish stable swirling flame in CRZ. This phase is quick and the flame intensity increases rapidly. An algorithm was developed to track the trajectory of flame kernels within 25 ms following the spark during its breakup and motion processes. The intensity-weighted centroids of each flame zones in the instantaneous images were extracted as the flame skeleton points. The flame trajectory was obtained through the correlation of two adjacent frames. Results show that the calculated trajectory provides an approximate description of the flame evolution process. Under different inlet air pressures, the propagation trajectories of flame kernels share similarities in the first phase. It is pivotal for a successful ignition that the initial flame kernel keeps enough intensity and moves into CRZ along radial direction. While the initial flame kernels that move downstream with airflow usually extinguish gradually and cause ignition failure. Finally, the time-averaged non-reacting flow field under inlet pressure of 54 kPa and fuel mass flow of 8 kg/h was simulated. The basic effects of flow structure and fuel spatial distribution on kernel propagation and flame evolution were analyzed.