Optical and electrical investigation of plasma generated by high-energy self-stabilized spark ignition system

Abstract

Spark discharge plasma is commonly used for ignition in internal combustion engines. The environmental performance of internal combustion engines with forced ignition is improved when operating under lean mixture conditions. High-energy ignition systems are needed to ensure reliable ignition of lean mixtures. The ignition of a combustible mixture is influenced by several plasma parameters, such as the temperature of its various components, the size of the plasma, and the deposited energy. It is, therefore, beneficial to know these parameters. Here, we present optical and electrical investigation of plasma generated in ambient air by a novel high-energy self-stabilized spark ignition system. The electrical investigation showed two high current pulses, with the current amplitude of ∼40 and ∼150 A. The energy is deposited to the spark gap mainly during the second current pulse, and it is increasing from 213 to 541 mJ with the increasing gap size from 3 to 13 mm. The energy efficiency increases with the gap as well, from around 23% to 58%. Time-resolved emission spectra enabled us to estimate the evolution of the gas temperature, electron excitation temperature, and electron density in the generated plasma. It was found that the highest electron density, 3–4 × 1017 cm−3, correlates with the maximum of the second pulse current. We observed a specific plasma evolution between the two current pulses, with an increase in temperature from 4500 to 7500 K and a contraction of the plasma channel diameter from 3.3 to 0.5 mm.