Energy efficiency of a nanosecond repetitively pulsed discharge for methane reforming

The performance of a nanosecond repetitively pulsed discharge for CH₄ reforming is studied at atmospheric pressure for temperatures ranging from 300 to 700 K. The high-voltage pulser used is capable of producing a voltage pulse with an amplitude of 14 kV and a duration of 40 ns at a repetition frequency of 10 kHz. The discharge energy per pulse is varied in a range from 462 J to 2.47 mJ. The rotational temperature is estimated by fitting synthetic to experimental spectra. Experiments at pulsing frequency of 1 kHz led to temperature profiles that remain unchanged along the axial direction of the reactor. For pulse frequencies between 2–10 kHz, the average temperature of the filament rises from 507 to 777 K. Emission from C₂(A–X) is compared to emission from CH(A–X) along the reactor axis and with respect to the energy input. It is found that as the energy input increases, so does the emission from C₂(A–X), turning the discharges green rather than blue. Results from CH₄ conversion show that the inlet gas temperature has negligible effect on reforming performance. Higher values of energy per pulse improve conversion and energy efficiency. However, increasing the pulse frequency leads to the best performance enhancement with a maximum slope of 0.53% and 0.24% per kJ · mol⁻¹ for conversion and energy efficiency, respectively. The maximum conversion and energy efficiencies were 68.2% and 25.6%, respectively, measured in a CH₄–air mixture. (paper)