Abstlact : 工n this stLldy, visllal investigation of spyays ayld naIyles has been peyfbyilrled and soot fbrl― nation in Diesel and GTL f’ uels has been coyylpayed in a specially designed Rapid Charging Coynb11stion Vesse1 (RCCV) uyldey vayious aiI rlbient gas ○2 concentrations and two irJection pyess11yes. 工t has been concluded that soot iil― L the Inixing― controlled cOInbustion of Diesel and GTL fUels has silrlilay tendency to be fbrlned in the leading poytion of the jet bolHldaries. Auto― ignition delay fbr GTL fUel is shoyter than that fby diesel fUe1. The teil― rlpoyal and special variation of soot concentration in the diesel flayne j ets at vayious O2 concentrations ''vas coyrelated ''vith the heat release yate. Soot concentyation appeays in the regions when diffUsion coynbustion stayts, and its concentyatioll yeaches Iylaxiil― n1그Iyl at the peak of heat release cLLrve and then decreases d1그 e to oxidation. Vis1그 alizatioyl by shado''vgyaph Irlethod showed that soot decyeases 、vith lo、ver ○2 concentyation, and higher iⅲ ection pressuye.