Ignition by Nanosecond Repetitively Pulsed Discharges

Abstract

Previous works have shown that nanosecond pulsed plasmas can have strong benefits on ignition, including a reduction of ignition delay times, a decrease of minimum ignition energies, or an extension of lean ignition limits. These effects are highly dependent on experimental conditions such as temperature, mixture, pulse repetition frequency, pulse energy, or discharge size. Therefore, a model allowing for parametric explorations is needed to separate the influence of each variable on plasma-assisted ignition. This work presents the development of both (i) a zero-dimensional (0D) chemical model for plasma-assisted combustion relevant for aircraft engine applications, and (ii) a one-dimensional (1D) radial fluid model of reacting flows describing radial ignition triggered by Nanosecond Repetitively Pulsed discharges (NRP).

The models developed are used to explore the influence of various parameters in an optimization effort. Using the 0D model, the influence of initial gas temperature and energy deposited per pulse on the reduction of ignition delay time is analyzed. Various mixtures of fuel/oxygen/nitrogen are also explored, changing the equivalence ratio and dilution factor, and compared with an instantaneous pure thermal input from the discharge to quantify the chemical effect of the discharge. The 1D model is initially demonstrated in a scenario where no plasma is present, focusing on the ignition of a methane/air mixture by a high-temperature kernel. Additionally, a test case is presented, comparing different NRP ignition strategies. In this case, the total power budget of the discharge is maintained within a narrow range by adjusting the pulse repetition frequency inversely proportional to the square of the plasma region size. Different plasma kernel sizes and pulse repetition frequencies are explored, and their effect on ignition and flame propagation enhancement is discussed.