In the usual elongated carbon black furnace which is provided at one end with a combustion gas entry section, usually of diameter larger than the remainder of the reactor, in lieu of the usual entry port or ports providing hot combustion gases with which to decompose the make oil or gas to carbon black, there are provided independent, double-entry port or pipes. At each double entry there is an outer port and an inner port or pipe. Usually, the pipe approaches the enlarged section or precombustion chamber somewhat tangentially and at a substantial right angle to the longitudinal axis of the elongated reactor or furnace. Thus, viewing the furnace end-on, the outer port or entry will spew its fluid near and onto the walls of the precombustion chamber while the inner port or entry will deliver its gases to a point nearer the longitudinal axis. By feeding so as to obtain a blanket of relatively cool gas adjacent the walls of the precombustion chamber by means of the outer port and a relatively much hotter gas through the inner port, the walls of the chamber are protected while at the same time the make oil or gas can be subjected immediately to a great deal more heat and higher temperature such that higher yields of carbon black are obtained. A novel furnace precombustion zone structure is disclosed.