Simulation of a syngas counter-flow diffusion flame structure and NO emissions in the pressure range 1–10 atm K. Safer a , F. Tabet b, ⁎, A. Ouadha c , M. Safer a , I. Gökalp d a Laboratoire des Carburants Gazeux et de l'Environnement, Faculté du Génie Mécanique, Université des Sciences et de la Technologie d'Oran Mohamed Boudiaf, BP. 1505 Elmenaouer, Oran 31000, Algeria b European Institute for Energy Research (EIFER) — EDF R&D, Emmy-Noether-Strasse 11, D-76131 Karlsruhe, Germany c Laboratoire d'Energie et de Propulsion Navale, Faculté du Génie Mécanique, Université des Sciences et de la Technologie d'Oran Mohamed Boudiaf, BP. 1505 Elmenaouer, Oran 31000, Algeria d Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), Centre National de la Recherche Scientifique (CNRS), 1C avenue de la recherche scientifique, Orléans 45071 Cedex 2, France abstract article info Article history: Received 9 March 2012 Received in revised form 26 November 2012 Accepted 28 October 2013 Available online 15 December 2013 Keywords: Syngas Counter-flow diffusion flame Flame structure Radiation Pressure NO emissions This paper reports a numerical investigation of syngas flame structure and NO reaction pathways over a wide range of operating conditions (H 2 /CO ratio between 0.4 and 2.4, scalar dissipation rate from equilibrium to ex- tinction and ambient pressure from 1 to 10 atm) in mixture fraction space. An analysis of optimal operation con- ditions for syngas combustion in regard to NO index emissions is also provided. Flame structure is characterized by solving flamelet equations with the consideration of radiation. The chemical reaction mechanism adopted is GRI-Mech 3.0. The computational predictions showed that flame temperature exhibits a peak at an intermediate scalar dissipa- tion rate for a given value of H 2 /CO ratio. From hydrogen-lean syngas to hydrogen-rich syngas fuels, maximum flame temperature increases for scalar dissipation rate values lower than the intermediate value whereas de- creases at higher values. Zeldovich route is found to be the main NO formation route and its contribution to the NO production continually increases with the increase of hydrogen content and pressure. Hydrogen-rich syn- gas flames produce more NO at lower scalar dissipation rates while NO levels increase towards hydrogen-lean syngas flames at higher scalar dissipation rates. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen-rich alternative fuels such as syngas are expected to serve as a clean energy in power generation systems. The combustion of these blended fuels is an important component of the IGCC (Integrated Gasi- fication Combined Cycle) concept. Synthetic gas fuels are primarily composed of H 2 and CO and may also contain N 2 , CO 2 ,H 2 O, CH 4 and other higher order hydrocarbons, which depend on the fuel source and processing technique [1]. It is then natural that these variations of synthetic gas are the largest barriers towards the usage of synthetic gas. One challenging aspect for use of syngas as a fuel is the composition variability in production of syngas from coal and biomass through the gasification process, which complicates the design and operation of modern power generation systems [2]. This variation in composition of syngas has a direct impact on combustor performance and emissions. Characterization of syngas combustion in terms of flame structure, extinction limits, and emissions based on fuel composition plays an im- portant role in determining combustor-operating conditions. Research activities on syngas diffusion flames in open literature are often conducted using counter-flow configuration both experimentally and theoretically. A thorough understanding of strained laminar flames is a prerequisite to achieve improved knowledge of more complex system. The literature on counter-flow H 2 /CO diffusion flames is abundant. The purpose of these studies is, in general, to analyze the influence of main parameters such as dilution (with CO 2 or H 2 O), preheating, oper- ating pressure and radiation on the flame structure and NOx emissions. A recent paper [3] has summarized various existing numerical studies in this subject area. Drake and Blint [4] numerically investigated the effect of flame stretch on the flame structure and NOx formation in opposed- flow diffusion flames with CO/H 2 /N 2 mixture as a fuel. They showed that flame structure is very sensitive to H 2 amount and NO concentra- tion decreased dramatically as flame stretch increased. The most of NO is found to be formed by thermal route at low stretch, while domi- nated by N 2 O-intermediate pathway at very high stretch rates. Park et al. [5] conducted a numerical study to understand the impact of fuel composition on flame structure in H 2 /CO synthetic gas diffusion flame Fuel Processing Technology 123 (2014) 149–158 ⁎ Corresponding author. Tel.: +49 721 6105 1483; fax: +49 721 6105 1332. E-mail address: tabet@eifer.org (F. Tabet). 0378-3820/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fuproc.2013.10.019 Contents lists available at ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc