IGNITION AND EXTINCTION OF SURFACE AND HOMOGENEOUS OXIDATION OF NH3 AND CH4

Ignition, extinction and autothermal behavior of surface and homogeneous oxidation reactions of CH4, NH3, and mixed NH3/CH4 fuel systems in air over resistively heated Pt foils was studied in an atmospheric pressure flow reactor. Also examined were the effects of varying fuel concentration on the ignition, extinction, and autothermal surface temperatures. Heterogeneous ignition occurred at approximately 200-degrees-C for NH3 and at approximately 600-degrees-C for CH4. The mixed fuel systems exhibited two surface ignitions (approximately 200-degrees-C and approximately 600-degrees-C), implying a sequential ignition of the two fuels. The effects of removing one of the fuels during autothermal operation gave results consistent with this hypothesis. In homogeneous ignition, two types of flames were observed: a boundary layer flame associated with NH3 systems and an independent flame observed in all systems. Homogeneous ignition of the two fuels and the mixtures occurred at surface temperatures ranging from 1,100-degrees-C to 1,600-degrees-C and appeared to be dominated by CH4 in the mixed systems. A generic behavior is proposed for homogenous-heterogeneous combustion of single and mixed fuels.