Plasma jet ignition on lean methane-air mixture in a constant volume combustion chamber

Lean-burn combustion has been widely used in automotive, marine, and power-generation engines because of its advantages in improving thermal efficiency and reducing CO 2 emissions. However, lean conditions can deteriorate combustion stability owing to slower flame propagation and increased cycle-to-cycle variation. To overcome these limitations, plasma-assisted combustion technology has attracted attention as a promising method for enhancing ignition and combustion performance through the generation of high-energy electrons and reactive radicals. In this study, conventional spark ignition (CSI) and plasma jet ignition (PJI) were comparatively applied to methane–air mixtures, and the differences in flame propagation and combustion characteristics were investigated using Schlieren imaging and combustion pressure analysis. The results showed that PJI formed a larger initial flame kernel and promoted faster flame propagation than CSI, even under lean conditions, because of jet-induced flow and possible multi-point ignition effects. Compared with CSI, PJI increased the maximum pressure, heat release rate, cumulative heat release, and pressure rise rate, resulting in enhanced combustion speed and heat release characteristics. In addition, PJI shortened T10, T50, and T90, with the improvement becoming more pronounced under lean conditions. Under λ = 1.6, PJI advanced T90 by approximately 150 ms and maintained about 20% higher heat release per unit fuel mass than CSI, demonstrating improved combustion speed and combustion efficiency under lean-burn conditions.