A numerical and experimental study of counterflow syngas flames at different pressures S. Som, A.I. Ramı ´rez, J. Hagerdorn, A. Saveliev, S.K. Aggarwal * Department of Mechanical and Industrial Engineering, University of Illinois, 842 West Taylor Street, Chicago, IL 60607-7022, USA Received 5 October 2006; received in revised form 2 April 2007; accepted 3 May 2007 Available online 11 June 2007 Abstract Synthesis gas or ‘‘Syngas’’ is being recognized as a viable energy source worldwide, particularly for stationary power generation due to its wide availability as a product of bio and fossil fuel gasification. There are, however, gaps in the fundamental understanding of syngas combustion and emissions characteristics, especially at elevated pressures that are relevant to practical combustors. This paper presents a numerical and experimental investigation of the combustion and NO x characteristics of syngas fuel with varying composition, pressure and strain rate. Experiments were performed at atmospheric conditions, while the simulations considered different pressures. Both exper- iments and simulations indicate that stable non-premixed and partially premixed counterflow flames (PPFs) can be established for a wide range of syngas compositions and strain rates. Three chemical kinetic models, GRI 3.0, Davis et al., and Mueller et al. are examined. The Davis et al. mechanism is found to agree best with the experimental data, and hence used to simulate the PPF structure at different pres- sure and fuel composition. For the pressure range investigated, results indicate a typical double flame structure with a rich premixed reaction zone (RPZ) on the fuel side and a non-premixed reaction zone (NPZ) on the oxidizer side, with RPZ characterized by H 2 oxi- dation, and NPZ by both H 2 and CO oxidation. While thermal NO is found to be the dominant route for NO production, a reburn route, which consumes NO through NO + O + M! NO 2 + M and H + NO + M ! HNO + M reactions, becomes increasingly important at high pressures. The amount of NO formed in syngas PPFs first increases rapidly with pressure, but then levels off at higher pressures. At a given pressure, the peak NO mole fraction exhibits a non-monotonic variation with syngas composition, first decreasing to a minimum value, and then increasing as the amount of CO in syngas is increased. This implies the existence of an optimum syngas composition that yields the lowest amount of NO production in syngas PPFs, and can be attributed to the combined effects of thermal and reburn mechanisms. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: High pressure; Syngas flames; Partially premixed; NO x emissions 1. Introduction In the wake of increasingly strict emission laws imposed by the US Environmental Protection Agency and limited fossil fuel availability, there is a worldwide interest in the utilization of alternative and environmentally benign energy sources. Hydrogen represents potentially an unlimited source of energy since it can be produced through electrolysis of water as well as partial oxidation and reforming of natural hydrocarbons. However, due to its high flammability and low volumetric energy density, many critical issues pertaining to hydrogen safety and storage still need to be addressed. Consequently, blending hydrogen with other hydrocarbon fuels is an attractive option. In this context, synthesis gas (mainly a mixture of CO/H 2 ) or ‘‘syngas’’ is being recognized as a viable energy source worldwide, especially for stationary power generation. Syngas is formed through gasification pro- cesses, and can be produced from virtually any fossil fuel, including coal, biomass, organic waste, and refinery residual [1,2]. It is particularly attractive for stationary power gener- ation, since it allows for a wide flexibility in fossil fuel sources, 0016-2361/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2007.05.023 * Corresponding author. Tel.: +1 312 996 2235; fax: +1 312 413 0441. E-mail address: ska@uic.edu (S.K. Aggarwal). www.fuelfirst.com Available online at www.sciencedirect.com Fuel 87 (2008) 319–334