Enhancement of the transition to detonation of a turbulent hydrogen–air flame by nanosecond repetitively pulsed plasma discharges

This work provides proof of concept for the use of nanosecond repetitively pulsed (NRP) plasma discharges to accelerate a propagating turbulent flame, resulting in enhanced deflagration-to-detonation transition and significant reduction in run-up length. The investigations are conducted on a stoichiometric hydrogen-air mixture at near ambient conditions. The effect of plasma actuation on the flame velocity is investigated using time-of-flight measurements of the propagating flame and detonation wave. The flame velocity shortly after the application of the NRP plasma discharges is more than double that obtained in cases in which no plasma is applied. High-speed imaging of OH* chemiluminescence in the electrode area confirms this result and provides insight about the mechanisms of plasma action. While the volumetric energy deposited during plasma actuation is sufficiently low as to not ignite the combustible mixture prior the arrival of the flame, the chemical and thermal enhancement of the gas is efficient enough to significantly accelerate the transition to detonation. The decrease in the run-up length to transition to detonation is obtained for a plasma power of less than 0.14% of the thermal power of the flame. This result indicates that low-energy active devices using NRP discharges might be suitable for replacing passive devices such as orifice plates or Shchelkin spirals.