Spatially resolved measurements of CN, CH, NH, and H 2CO concentration profiles in a domestic gas boiler

Abstract

Spatially resolved measurements of species profiles were performed for CN, CH, NH, and H2CO in a premixed methane/air flame as a function of height above the central slot of a seven-slot atmospheric pressure burner using laser-induced fluorescence (LIF). The burner was constructed to resemble as closely as possible a commercial household boiler with water heat exchanger. For several near-stoichiometric flame conditions, absolute number densities for CN, CH, and NH were obtained using partially saturated LIF with Raman or Rayleigh calibration. For CN, an independent measurement series using linear LIF with quenching corrections applied from known effective fluorescence lifetimes in atmospheric pressure flames verified the results from the saturated LIF measurements. Relative H2CO height profiles in the preheating zone of two flame cases were also obtained with applied quenching corrections from measured effective fluorescence lifetimes at each spatial location. H2CO lifetimes continuously decreased with increasing temperature in the preheating zone (i.e., increasing height above the burner exit). Absolute concentration values and peak concentrations showed striking differences in the two flame cases, which should provide valuable data for detailed numerical simulations of these flames.