Intracavity laser absorption spectroscopy of NH₂ in methane/air flames doped with N₂O, NO and NH₃

Intracavity Laser Absorption Spectroscopy (ICLAS) was used to measure concentration profiles of NH₂ in low pressure (30 Torr) methane/oxygen/nitrogen flames doped with small amounts of N₂O, NO, NH₃. The effective optical length of ICLAS, which dictates the sensitivity of the method, was controlled by the generation time of the quasi cw-laser. The effective optical length of 0.87 km, reached at generation time of 75 μsec, provided very high sensitivity: from 5 × 10¹⁰ molec/cc at 500 K in the vicinity of burner ≤ 2 × 10¹¹ molec/cc in the burnt gas zone. The radial profile of NH₂, measured using a tomographic technique, indicated that the radical is located mainly inside a cylinder with diameter equal to the burner diameter. In the ammonia doped flame the calculations predicted an additional concentration maximum located close to the burner. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).