In internal combustion engines, lean burn is particularly attractive for minimizing pollutant emissions, in particular NOx, with a concomitant improvement in fuel economy. For combustion in lean fuel-air mixtures, achievement of adequate reliability of ignition and sufficiently high burning rate requires special methods. An effective technique is the injection of active radicals by means of the pulsed flame jet (PFJ) ignition system. Presented here is an experimental proof of the action of OH radicals produced by such an ignition system in a swirl flow with varying the spark discharge mode in the cavity of the PFJ igniter. The measuring apparatus used for this purpose was based on the planar laser-induced fluorescence method, and the effects of the spark discharge mode in the cavity of the PFJ igniter on the variation of OH fluorescence area in the jet and its intensity were revealed quantitatively.