Experimental study of the effect of nanosecond pulse discharge parameters on the methane-air mixture combustion

Nanosecond pulse discharge (NPD) can generate high-energy, active species, which are favoured in fields such as plasma-assisted combustion. To improve the combustion stability and increase the combustion rate at lean burn, this paper uses the NPD to ignite a methane-air mixture (with an excess air coefficient of 1.4-1.8) in an optical constant volume combustion bomb (CVCB), and conducts experimental study and analysis on the initial flame kernel and flame development at different discharge modes (transistor coil ignition (TCI) and NPD) and discharge parameters (pulse number (PN) and pulse interval (PI)). The results show that, firstly, the initial flame kernel radius and the flame development speed gradually increase with the increase of PN in the NPD ignition. The initial flame kernel shape produced by the NPD discharge is dominated by semilunar and elliptical shapes. With increasing PI, the radius, shape, and displacement distance of the initial flame kernel show a trend of first increasing and then decreasing. Secondly, at the NPD ignition, the flame kernel and the simultaneously engraved flame area are larger than at the TCI ignition. After PN is greater than 10, the flame development speed gradually remains stable. The flame radius shows a first trend of increasing and then decreasing with the increase of PI at the same time. Finally, it is also found that whereas PI mostly affects the combustion duration, PN primarily affects the ignition delay in the NPD ignition.