A novel ignition device for the internal combustion engine

Abstract

Although the recent rapid proliferation of research into plasma jet ignition^1–16 has partly been prompted by the requirements of continuous combustion and pollutant removal^17–25, the main motive has been to extend the lean operability limit of the internal combustion engine. This trend to leaner mixtures has been stimulated by the need to improve engine emission characteristics and efficiencies. Because optimum conditions occur near the lean misfire limit, a plug providing increased rates of flame propagation and more effective and reliable ignition has been sought; pulsed plasma jets offer much promise but use too much power. In these devices, the igniting jet is generated by explosive gas expulsion through an orifice, engendered by a short-duration arc discharge to which the plasma medium is exposed while confined by the walls of a cavity within the plug. Such plasma jets, and particularly those fed with specific plasma media, have proved capable of extending the flammable fuel–air mixture range both at the fuel lean and at the rich limit, and increase the speed at which flames propagate following ignition. This is thought to be due to the generation of turbulence and free radicals. We report here the development and testing of an ignition plug based on two sparks at the extremities of an internal cavity. This design combines much of the effectiveness of a plasma jet with the small power consumption, and consequently low rates of wear, of a conventional sparking plug.