Fuel-nitrogen conversion in the combustion of small amines using dimethylamine and ethylamine as biomass-related model fuels

Laminar premixed flames of the two smallest isomeric amines, dimethylamine and ethylamine, were investigated under one-dimensional low-pressure (40 mbar) conditions with the aim to elucidate pathways that may contribute to fuel-nitrogen conversion in the combustion of biomass. For this, identical flames of both fuels diluted with 25% Ar were studied for three different stoichiometries (Phi = 0.8, 1.0, and 1.3) using in situ molecular-beam mass spectrometry (MBMS). Quantitative mole fractions of reactants, products and numerous stable and reactive intermediates were determined by electron ionization (EI) MBMS with high mass resolution to separate overlapping features from species with different heavy elements by exact mass. Species assignment was assisted by using single-photon vacuum-ultraviolet (VUV) photoionization (PI) MBMS. The results indicate formation of a number of nitrogenated intermediates, including toxic species such as HCN, in appreciable concentrations. Such intermediate species mole fractions may depend not only on stoichiometry, but also on fuel structure. We attempted to analyze the major pathways in the two flames with a detailed combustion model developed for this purpose. For this, thermochemical values for a number of intermediates had to be determined from quantum chemistry calculations. Also, specific sets of reactions were incorporated for the two fuels. While many trends seen in the experiments can be successfully reproduced by the simulations, additional efforts may be needed to reliably describe the fuel-nitrogen chemistry in the combustion of biomass-related model fuels with amine functions. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.