Long-gap ignition using femtosecond laser filament-triggered discharge

Abstract

Ignition has a significant impact on combustion efficiency and combustion emissions. Long-gap spark discharge ignition can increase the initial flame kernel and reduce the flame propagation time. However, long-gap spark discharge ignition requires increased discharge voltage and suffers from the fluctuation in ignition time and position. Here, we propose a long-gap ignition technique using femtosecond laser filament-triggered discharge. Femtosecond laser filaments are used to trigger and control long-gap discharges to generate precisely controlled plasma lines in space for ignition. The fluctuation in ignition time can be largely reduced to be on the order of nanoseconds, and the ignition position can be strictly defined by the femtosecond laser filament between the two electrodes. Also, compared with long-gap spark discharge ignition, femtosecond laser filament-triggered discharge ignition can reduce the fluctuation in the flame shape. Femtosecond laser filament-triggered discharge ignition extends the lean ignition limit of methane-air mixtures. In addition, femtosecond laser-triggered discharge can also lower the discharge breakdown threshold, so longer plasma lines can be obtained at the same voltage compared with spark discharge ignition. The extension of the plasma length can generate a larger initial flame kernel. A larger initial flame kernel can increase the flame front area and hence, reduce the flame propagation time.