Evaluation Of The Transient Plasma Ignition Of Methane/Air Under Lean-Burn Conditions

Abstract

Transient plasma ignition (TPI) has recently been attracting more attention due to the combination of its much larger volume ignition kernels and the generation of active radicals, which stabilizes the initial stage of the combustion by the enhancement of flame propagation rates compared with conventional spark ignition. In this study, TPI early flame propagation characteristics were investigated for near-atmospheric stoichiometric and lean mixtures of methane and air. Transient plasma was generated by applying nanosecond (pulse duration 10 – 12 ns), high-voltage (6 – 10 kV) pulses between two opposed pin-to-pin configurations with a gap distance of 3 mm residing within a custom-built constant volume combustion vessel. The delay to ignition and peak pressure as a function of voltage, air-fuel mixture rate (ϕ = 0.6 – 1.0), and pulse repetition frequency (PRF) of 1 – 10 kHz were evaluated. The early flame propagation and the discharge streamer phenomena were investigated via high-speed schlieren images as well as examining nanosecond pulses’ voltage-current waveform sequences. It is showed that a leaner mixture could reduce the ignition voltage range. The experiment results showed that higher PRF has potential advantages such as higher peak pressure, shorter ignition delay, faster flame propagation speed, smaller energy consumption, and leaner condition compared to conventional spark ignition.