Exploration of spark discharge characteristics for ignition of scramjet engines

Ignition in a model scramjet engine is explored experimentally, using Mach 2 combustor inlet conditions, a backwards facing step geometry, in-cavity ethylene fueling, and a nanosecond-pulsed high-frequency discharge (NPHFD) source with a standard automotive spark geometry. Chemiluminescence imaging at 40 kHz is used to capture ignition events. It is found that the NPHFD source can ignite a wider range of mixtures and is more energy efficient than a conventional capacitive ignition source. In addition, a relationship between ignition probability, ignition rate, and the power of the ignition source is found. It is found that the power deposition rate of the NPHFD source, controlled by pulse repetition frequency, is the most critical factor affecting ignition dynamics, and that ignition energy is a secondary consideration.