Characteristics of Plasma Ejection of Expulsion-Type Semiconductor Spark Plugs of Gas-Turbine Engines

Many variants are known of expulsion-type semiconductor plugs for capacitive ignition systems for gas-turbine engines, which differ in the design of discharge chambers. A distinctive feature of serial-produced expulsion-type plugs, which are manufactured by domestic industry, is the relative arrangement of semiconductor element and side electrode, at which the working surface of semiconductor is located not along the plug axis, but at an angle. The working surface of the side electrode is near the discharge-chamber base. There is no systematized information on research on discharge processes in the expulsion-type plugs in the technical literature. This work is dedicated to the study of interrelation between the energy parameters of spark discharges, space–time characteristics of plasma ejection from the discharge chambers of plugs, and plug-ignition effectiveness. The oscillography, together with plasma-ejection high-speed photographing methods, are used as research techniques. A serial-produced semiconductor plug and a specially developed model of expulsion-type plug with a window made of organic glass were chosen as the objects of research. The organic-glass window made it possible to photograph the process of plasma-discharge development within the discharge chamber. The oscillograms of discharge current and voltage drops in the plugs were recorded with a two-beam oscilloscope using a noninductive coaxial shunt and a resistive voltage divider. The parameters of plasma ejection were correlated with the plug-ignition effectiveness. The obtained results complement the general understandings of the regularities of development of plasma ejection from the discharge chambers of semiconductor plugs and confirm that the discharge parameters have an effect on the initial ignition speed from the standpoint of thermal and chain igniting mechanisms. © 2018, Allerton Press, Inc.