Intermediate species detection in a morpholine flame: contributions to fuel-bound nitrogen conversion from a model biofuel

Abstract

A slightly fuel-rich (Φ = 1.3) premixed laminar flat morpholine/oxygen/argon flame at 40 mbar was studied with cavity ring-down spectroscopy (CRDS). Morpholine as a secondary amine was considered as a prototypical nitrogenated biofuel. To contribute to the investigation of fuel-nitrogen conversion chemistry in this flame, absolute mole fraction profiles of CH, CN, and NH2 were determined. To our knowledge, this is the first study reporting quantitative mole fractions of these radicals from CRDS in a low-pressure flame of a model biofuel. The species profiles are discussed in combination with some relevant intermediates from molecular beam mass spectrometry, determined in this flame very recently (Lucassen et al., Proc Combust Inst 32(1):1269–1276, 2009). Some relative species profiles were also determined in flames of further amines to facilitate comparison. The results demonstrate that NH3- and HCN-related chemistry occurs in different regions of this flame. HCN production is considerable, and NO is found in the exhaust gases in percent-level concentrations. To monitor the combustion status, chemiluminescence is increasingly being applied as an intrinsic low-cost sensor. We believe to present the first chemiluminescence measurements in a flame of a prototypical nitrogenated biofuel, reporting relative emission intensities for five excited-state species. The shapes and maximum positions of the ground- and excited-state profiles show interesting differences, especially for the CN radical, which must be the consequence of different reaction pathways.