Experimental study on the spark ignition characteristics at elevated temperature and pressure under flow conditions

Abstract

This study investigates the fundamental spark-ignition characteristics under engine-relevant environments, focusing on spark discharge energy and the shapes of spark channels. The pressure, temperature, and mean flow velocity conditions were independently controlled (up to 20 bar, 567 K, and 18 m/s, respectively) to study the individual effects on spark channels. In terms of analyzing spark discharge energy, the breakdown and arc/glow phases were individually examined. Results showed that the breakdown voltage and energy are predominantly affected by ambient density, which is consistent with Paschen's law. During the arc/glow phases, the total discharge energy increased with an increase in mean flow velocity, whereas relatively minor effects on the total discharge energy were observed with pressure and temperature variances. In terms of the shapes of spark channels, it was found that the shapes vary significantly under different thermodynamic and flow conditions. Specifically, ambient pressure and spark channel stretching by flow had considerable effects on the shapes of spark channels, such as the thickness of spark channels and the extent of corrugation. This study also proposes a mechanism for forming short circuits, which explicates the spark behaviors under flow conditions, based on the prior analyses of spark characteristics. In the process of examining the mechanism, the formulae for the required voltage for short circuits and the resistance of spark channels are additionally suggested.