Proceedings of the 1 st International Workshop on CFD and Biomass Thermochemical Conversion Leipzig, Germany, 30 September 2014 Paper No. XXX (The number assigned to the abstract) XXX-1 Investigation of Optimum Operating Conditions of Syngas Combustion in Regards to NO x Emissions Khadidja Safer, Mériem Safer Laboratoire des Carburants Gazeux et de l’Environnement/Faculté du Génie Mécanique, Université des Sciences et de la Technologie d’Oran Mohamed Boudiaf, BP1505, Elmanouar,Oran, Algeria khsafer@gmail.com, safer.meriem@gmail.com Fouzi Tabet DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Torgauer Strasse 116, 04347 Leipzig, Germany fouzi.tabet@dbfz.de ABSTRACT Syngas is a hydrogen-rich fuel mainly composed of H 2 and CO. One of the challenges when using syngas for energy production is the high level of NO x emissions. The aim of this study is to identify optimum operating conditions of syngas combustion to minimize NO x emissions. The analysis is performed in counter-flow diffusion flame configuration over a wide range of operating conditions (ambient pressure from 1 to 10 atm, flame strain rate from near equilibrium to near extinction and H 2 /CO molar fraction ratio from 0.4 to 2.0). Results show that H 2 -rich syngas flames produce more NO at low strain rates while NO emissions increase for H 2 -lean syngas at high strain rates. Also, thermal route is the dominant NO formation path. Practical burners like gas turbines should operate at low scalar dissipations (near 1 s -1 ) with H 2 -lean fuel or at very high scalar dissipations (100 to 1000 s -1 ) with H 2 -rich syngas in order to minimize NO emissions. Pressure increase involves more NO emissions and thermal route remains dominant at high pressures. KEYWORDS: Syngas, Syngas composition, Diffusion flames, NO x emissions, Ambient pressure. 1 INTRODUCTION Syngas is a hydrogen-rich fuel, mainly composed of H 2 and CO and may contain other gases such as CH 4 , CO 2 , N 2 and H 2 O. Syngas can be produced from various raw materials such as natural gas, biomass or municipal wastes. This variability of syngas sources induces variability in syngas composition [1]. Syngas is expected to play an increasing role in energy production. However, prior to its implementation, its environmental impact needs to be fully established. In particular, NOx emissions should comply with the current and future emission regulations. Several studies have been reported about NOx emissions of syngas combustion. Giles et al. [2] examined the effect of air-stream dilution on flame structure and NO emissions of syngas diffusion flames with two representative syngas mixtures and three diluents, N 2 , H 2 O and CO 2 in air. Results indicated that syngas flames with CO 2 and H 2 O dilution are more effective in reducing NO emission. Shih et al. [3] numerically studied NOx emissions characteristics of 1D counterflow syngas flames with