Ignition by plasma jet

Abstract

IN order to improve the emission characteristics and efficiency of internal combustion engines, the trend is to leaner mixtures. Successful combustion at lower fuel : air ratios requires increased rates of flame propagation and, in spark-ignited engines, more effective and reliable ignition sources. Various avenues of research are being pursued towards these aims. One which shares the philosophy of radical injection with the present work is the stratified charge or torch-ignition concept (see ref. 1 for review). This is based on burning a rich mixture in a cavity small by comparison with the cylinder volume so that the free radicals generated therein are ejected into the main charge, there to increase the propagation rate in a leaner mixture. In the work described here the radicals are generated in the igniting plasma, rather than by using chemical energy, and the volume of the ‘pre-chamber’ of the stratified charge or torch ignition concept is shrunk to a very small space within the plug, where a very high temperature, resulting in high ejection velocity, is produced by means of a small amount of electrical energy.