Repetitive Multi-pulses Enabling Lean CH ₄ -Air Combustion Using Surface Discharges

The development of efficient and reliable ignition systems for lean fuel-air mixtures is of great interest for applications associated with the use of combustion in transportation, electricity production, and other heavy industries. In this study, we report the use of repetitive nanosecond pulsed surface discharges for the ignition of lean methane (CH₄)-air mixtures at pressures above 1 bar. Powered by ten 10-ns voltage pulses at 10 kHz, a commercially available non-resistive spark plug was used to generate surface discharges, which were able to ignite CH₄-air mixtures at 1.5 bar and with equivalence ratios (ϕ) ranging from 1.0 to 0.5. At the leanest conditions, e.g., ϕ ≤ 0.6, nitric oxide (NO) and nitrogen dioxide (NO₂) emission were reduced to <10% of their values at ϕ = 1.0, demonstrating the advantage of lean burn in emission reduction. Consistent ignition was obtained under extremely lean conditions (e.g., ϕ = 0.5) with a minimum of five pulses and a minimum Coulomb transfer of 82 μC. Additionally, the surface plug durability was tested for 114 hours or over 12 million pulse trains by operating the surface plug in 3.5 bar of dry air at 30 pulse trains per second. This study shows that the use of repetitive nanosecond pulses with surface discharge-based plugs holds promise for a durable ignition solution.