Experimental and chemical kinetic study of CO and NO formation in oxy-methane premixed laminar flames doped with NH 3 Manuel Barbas a , Mário Costa a,⇑ , Stijn Vranckx b,c , Ravi X. Fernandes b,d a IDMEC, Mechanical Engineering Department, Instituto Superior Técnico, University of Lisboa, Lisboa, Portugal b Physico Chemical Fundamentals of Combustion, RWTH Aachen University, 52056 Aachen, Germany c Flemish Institute of Technological Research (VITO), Boeretang 200, 2400 Mol, Belgium d Physikalisch Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany article info Article history: Received 16 July 2013 Received in revised form 28 October 2014 Accepted 29 October 2014 Available online xxxx Keywords: Oxy-fuel combustion Experimental Kinetic study CO NO abstract The present work focuses on the oxy-fuel combustion of methane doped with ammonia in a premixed laminar burner operating at atmospheric pressure, and includes both experiments and a chemical kinetic study. CO and NO formation/emission were examined as a function of the stoichiometry and oxidizer composition. The experimental results showed that, for all oxidizer compositions studied, an increase in the excess oxygen coefficient generally decreases both the CO and NO emissions. Moreover, for the O 2 /CO 2 environments, decreasing the oxygen concentration in the oxidizer, for a given excess oxygen coefficient, leads to higher CO emissions, but lower NO emissions. In air firing, the CO emissions were found to be significantly lower than those measured under oxy-fuel conditions, while the NO emissions were higher than those from the oxy-fuel cases. The chemical kinetic study allowed to identify the main reactions that directly (with the aid of a rate-of-production analysis) and indirectly (through a sensitivity analysis) influence both the CO and NO emissions. Under oxy-fuel conditions, CO 2 +H M CO + OH and 1 CH 2 + CO 2 M CH 2 O + CO significantly contribute to CO formation additionally to those reactions found in air-fired combustion, while CO oxidation takes place through CO + OH M CO 2 + H for all studied conditions. Formation of NO occurs for all conditions mainly with HNO as intermediate, particularly through HNO + H M H 2 + NO. Once NO is formed, interconversion to NO 2 occurs. Ó 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. 1. Introduction It seems to be consensual [1] that the current energy demand will be largely supplied by the combustion of fossil fuels in the near future, despite the limited reserves and the environmental issues. Renewable energy sources are being introduced to the energy scenario and, hopefully, will be the major contributor in the future, solving both issues, particularly the increase in CO 2 emissions. For the time being, the so-called oxy-fuel combustion technology is one of the most promising solutions to enable CO 2 capture and sequestration. In this technology combustion takes place with pure oxygen instead of atmospheric air, which, com- bined with flue gas recirculation, generates combustion products rich in CO 2 that greatly facilitates its sequestration. This study concentrates on CO and NO formation during oxy- methane combustion in a laboratory burner. Related previous studies include those reported in Refs. [2–12]. Amato et al. [2] investigated the CO (and O 2 ) emissions from a methane fired labo- ratory combustor operating under oxy-fuel conditions. The authors performed measurements and thermodynamic equilibrium and chemical kinetics calculations. They concluded that CO emissions are higher in combustion with O 2 diluted with CO 2 than in com- bustion with air. Moreover, for a given residence time, the CO emissions from oxy-fuel combustion are higher than the equilib- rium values because of the slow oxidation of the intermediate CO formed in the flame. Also, they found that CO emissions increase exponentially with the flame temperature, and predicted that an increase in pressure would lower the emissions. Glarborg and Bentzen [3] evaluated the chemical effects of the presence of high CO 2 concentrations in the oxy-fuel combustion of methane in a laboratorial flow reactor. Their experimental results were inter- preted with the aid of a detailed chemical kinetic mechanism for hydrocarbon oxidation. They concluded that the presence of high CO 2 concentrations lead to a significant increase in the CO concen- trations, in the near burner region. The high levels of CO 2 prevent complete oxidation of the fuel at higher temperatures despite the presence of excess oxygen. Heil et al. [4] investigated experimen- tally the effect of the N 2 and CO 2 (as bulk gases) on the burning http://dx.doi.org/10.1016/j.combustflame.2014.10.020 0010-2180/Ó 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. ⇑ Corresponding author at: Mechanical Engineering Department, Instituto Supe- rior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal. E-mail address: mcosta@ist.utl.pt (M. Costa). Combustion and Flame xxx (2014) xxx–xxx Contents lists available at ScienceDirect Combustion and Flame journal homepage: www.elsevier.com/locate/combustflame Please cite this article in press as: M. Barbas et al., Combust. Flame (2014), http://dx.doi.org/10.1016/j.combustflame.2014.10.020