566 to help minimize no x formation when the fuel is subsequently burned the flow of air through third port 566 also helps to cool plug 595 once the flamehold condition is extinguished outer tube 570 will begin to cool and return to its original size and position by sliding along the axial direction in manner opposite to that shown by arrow a as a result first port 541 and second port 544 will eventually be disconnected as the nozzle tip 515 returns to its normal conditions of operation the flow of fuel to discharge orifices 145 will then be restored to its original operating flow because the flameholding condition is extinguished before damage occurs fuel nozzle 100 can now continue operation without requiring repair to nozzle tip 515 in addition as with previous embodiments nozzle tip 515 allows nozzle 100 to perform more desirably when natural gas containing hydrogen or higher order hydrocarbons is burned it should also be understood that because of the sliding fit between outer tube 570 and plug 595 a small leakage of fuel from first port 541 to second port 544 and or fourth port 577 may occur during normal operating conditions more specifically even though first port 541 is disconnected from these other ports during normal operation some fuel may leak through the movable interface between the outer tube 570 and plug 595 however by arranging third port 566 to vent curtain or purge air into fourth port 577 as shown in fig5 the formation of undesirable no x will be minimized as the leaking fuel will be mixed with such air before combustion fig6 illustrates another exemplary embodiment of the present invention with a structure and operation similar to that described for the.