INVESTIGATION OF THE IGNITION PROCESS IN LEAN MIXTURES

Abstract

Experimental studies of the new ignition system performance were carried out. A special model of a combustor, equipped with optical quality windows, was build to allow interferometrie and Schlieren visualization of combustion front propagation under a different location of electrodes, a different size of nozzle and a different mixture composition. Also pressure variations inside the combustor's chamber, under a different modes of ignitions, were measured.In the system, ignition of the lean charge is initiated by chcmically active radicals and the combustion is executed in vortices. Chemically active radicals are produced in the combustor, where combustion of a rich charge occurs. Combustion  products, rich in radicals, are ejected through a nozzle into the main chamber, where they mix with the lean mixture. The strong jet of radicals produces intensive mixing of partially burned rich mixture from the combustor with a fresh lean charge. This mixing occurs in created vortices and leads to volumetric ignition and makes the combustion similar to that in well stirred reactors.Two different models of combustor were used in the course of the research. The electrodes could be positioned at three different locations, e.g. at the chamber ccnter, close to the nozzle or at the close end of the chamber. Nozzles of 1,6 mm, 2,5 mm or 4 mm diameter could be separately installed at one end of the chambcr. The first chamber was equipped with optical quality windows for visualization and the second one was equipped with Kistler pressure transducer for pressure measurement. Combustion process inside the modelling chamber was visualized and recorded by the CCD camera, or pressure variations in the chamber were measured. Experiments were conducted for methane-air mixture of different air excess coefficients λ, (1, 0,8 and 0,6). For these three mixtures, experiments were conducted for three different locations of electrodcs and for three different nozzle diameters.