Measurement of temporal and spatial resolved rotational temperature in ignition sparks at atmospheric pressure

In this work, the temporal and spatial rotational temperature, as an indicator of spark temperature in the gas, of an ignition spark at ambient pressure is determined. With optical emission spectroscopy, the rotational bands of the nitrogen C³Π_u → B³Π_g transition at a wavelength of 337 nm are for determination. In addition, the electrical values of the current and the voltage are measured with a digital storage oscilloscope. All measurements are performed with a common nickel spark plug and a commercial 90 mJ ignition coil. The dwell time of the coil is varied in four steps from 100 to 25% and the influence on the rotational temperature is measured. The results are split into the three spark phases: breakdown, arc discharge, and glow discharge. The results show a cold breakdown, which is independent from the dwell time. On average, arc discharge is the hottest discharge phase, while the glow discharge has a medium rotational temperature.