The electric discharge generated between the electrodes of a classic spark plug could not assure a fast and total combustion of the air – hydrocarbon mixture. To be able to improve the quality of the combustion process through the ignition system improvement it is necessary to have a complete diagnostic of the discharge produced by a spark plug, from physical and chemical point of view. This work presents a comparative study of the reduced electric field and the vibrational temperature for a classic spark produced in air at atmospheric pressure, as functions of pulses widths applied by the power supply. The reduced electric field was calculated by using the rotational temperature values established by a previous study, considering them as temperature plasma gas temperatures. The vibrational temperature was determined by using the N2second positive molecular emission spectra. The spark plug was supplied with trains of pulses containing one or two pulses having variable widths provided by a special power supply.
The results obtained for the vibrational temperature of nitrogen molecules are close to these obtained for the rotational temperature calculated by using a spectroscopic diagnostic method based on the OH UV molecular band spectra (between 2000 and 3500 K). The electron temperature values, imposed by the reduced electric field (up to 2000 Td), are superior to 10000 K. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)