Optical and electrical diagnostics of a spark-plug discharge in air

Optical and electrical diagnostics were used to investigate a spark discharge using a commercial spark-plug operating in the glow phase regime. Voltage and current were measured in order to characterize the discharge. The gas temperature was estimated as a function of time and duty cycle using ro-vibrational spectra of the second positive system of nitrogen by comparison between experimental and simulated spectra. It was found that 1600 K Tg 2800 K. The reduced electric field varied between 1 and 1000 Td after the end of the current pulse. Using the line intensity method between one line from the ionic argon and the other from the neutral atom, the electronic temperature was measured and found to be between 17 000 and 20 000 K. The electron density was determined from the broadening of Hα line and was found to be 4.0 × 1014 cm−3 ne 1.7 × 1015 cm−3.