Ignition is a challenge for gas turbines, ramjets and scramjets where flow velocities in the combustor are high, resulting in short flow residence times. The success of ignition depends on the flow conditions, as well as the ignition method. In the past years, nanosecond-pulsed high-frequency discharge (NPHFD) plasmas have been pointed out as an optimal alternative ignition method in flowing mixtures, given that they offer several advantages as compared to a long duration DC discharge. Previous works have shown that the interaction between subsequent ignition kernels lead to three different coupling regimes based on their ignition probability (PI): fully-coupled (highest PI), partially-coupled (lowest PI) and decoupled (PI linearly dependent on the number of pulses), which occur at different inter-pulse time conditions.
In the current research, a new experimental platform has been built to explore NPHFD ignition. It has been found that the PI of the aforementioned regimes can be altered by varying the energy per pulse (Epp). In fact, high Epp has resulted in the disappearance of the partially-coupled regime, and low Epp has proven a negligible PI except for the fully-coupled regime. It has also been found that the minimum ignition power – defined as the applied power that results in 50% of PI – decreases linearly as the Epp is lowered. The kernel-growth rate has been found similar in all the tested cases.
Additionally, energy distribution has been optimized by matching the total energy and time of the discharge, and varying the number of pulses and the Epp. It has been concluded that the inter-pulse time is the driving parameter of the ignition probability. Indeed, it has been observed that low total energy and long total time discharges can provide a high PI at the right IPT.