Olivier Mathieu e-mail: olivier.mathieu@tamu.edu Eric L. Petersen e-mail: epetersen@tamu.edu Texas A&M University, College Station, TX 77843 Alexander Heufer e-mail: aheufer@gmx.de Nicola Donohoe e-mail: n.donohoe1@nuigalway.ie Wayne Metcalfe e-mail: waynemetcalfe@gmail.com Henry J. Curran e-mail: henry.curran@nuigalway.ie National University of Ireland Galway, Galway, Ireland Felix G € uthe Alstom, Baden, 5242-CH Switzerland e-mail: felix.guethe@power.alstom.com Gilles Bourque Rolls-Royce Canada, Montreal, QC H8T 1A2, Canada e-mail: gilles.bourque@rolls-royce.com Numerical Study on the Effect of Real Syngas Compositions on Ignition Delay Times and Laminar Flame Speeds at Gas Turbine Conditions Depending on the feedstock and the production method, the composition of syngas can include (in addition to H 2 and CO) small hydrocarbons, diluents (CO 2 , water, and N 2 ), and impurities (H 2 S, NH 3 , NO x , etc.). Despite this fact, most of the studies on syngas com- bustion do not include hydrocarbons or impurities and in some cases not even diluents in the fuel mixture composition. Hence, studies with realistic syngas composition are neces- sary to help in designing gas turbines. The aim of this work was to investigate numerically the effect of the variation in the syngas composition on some fundamental combustion properties of premixed systems such as laminar flame speed and ignition delay time at re- alistic engine operating conditions. Several pressures, temperatures, and equivalence ratios were investigated for the ignition delay times, namely 1, 10, and 35 atm, 900–1400 K, and / ¼ 0.5 and 1.0. For laminar flame speed, temperatures of 300 and 500 K were studied at pressures of 1 atm and 15 atm. Results showed that the addition of hydrocarbons generally reduces the reactivity of the mixture (longer ignition delay time, slower flame speed) due to chemical kinetic effects. The amplitude of this effect is, how- ever, dependent on the nature and concentration of the hydrocarbon as well as the initial condition (pressure, temperature, and equivalence ratio). [DOI: 10.1115/1.4025248] Introduction Synthetic gas or syngas, a gaseous mixture composed ideally of CO and H 2 , can be produced from a large variety of feedstock (coal, biomass, waste, and natural gas) and production methods. These characteristics make syngas an attractive fuel to produce clean energy efficiently, with fuel supply flexibility and security for power systems such as gas turbines. However, this large vari- ety of feedstock and production methods induces a large variation in the syngas composition where, in addition to CO and H 2 , can be found reasonable amounts of small hydrocarbons, CO 2 ,H 2 O, N 2 , and impurities such as NH 3 , HCN, COS, NO x , and H 2 S. A literature survey on the two types of feedstock considered for this study, coal and biomass, highlighted this high variation in the syngas composition. For instance, a total of 23 different composi- tions were found for a real biomass-derived syngas where the H 2 mole percentage varies between 5 and 50.4% and the CO percent- age between 8.1 and 50% [1–4]. Overall, the average CO/H 2 mole ratio in these bioderived syngases was 50/50. Several other com- pounds such as N 2 , CH 4 ,C 2 H 2 ,C 2 H 4 ,C 2 H 6 , CO 2 ,H 2 O, and impurities such as NH 3 , NO x , and SO 2 have been reported as well. The same exercise has been done for a coal-derived syngas with an average composition determined from 40 real, coal-syngas mixtures [1,3–16]. The H 2 /CO mole ratio was determined to be 40/60 for this average coal-syngas. It has been found that the proportion of hydrocarbons was typically higher for the biomass- derived syngas and that the impurities can be different among specific blends. This trend was confirmed by the study of Xu et al. [15], where the nature and maximum concentration of hydrocar- bons and contaminants reported in the literature were listed for both types of syngas. Although the laminar flame speed (S L ) [14–27] and ignition delay time (s ign )[28–37] of basic H 2 /CO mixtures have been investigated thoroughly in recent years, there is very little information on the fundamental combustion of more complex and realistic mixtures. Thus, only the influences of CO 2 [20,26], steam [17], and nitrogen [25] on flame speed have been studied whereas the addition of hydrocarbons to a H 2 /CO mixture is still an area requiring investigation. For the ignition delay time, except for a recent study on an average bio-syngas mixture by the authors [38], only CO 2 addition effects have been investigated over the past few years [38–40]. Results from Ref. [38] showed that the composition of the syngas can induce noticeable varia- tions in s ign , especially at temperatures above 1250 K and for pres- sures of 12.5 atm or lower, indicating a need for more studies on the effect of syngas composition on combustion properties such as ignition delay time. Consequently, because of this lack of experimental background on realistic syngas blends, it is difficult for gas turbine manufac- turers to design engines that can operate efficiently and safely with this wide range of fuel compositions. Using a state-of-the-art C0–C5 detailed kinetics mechanism, the aim of this study was to investigate numerically the effect of syngas composition on some Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 8, 2013; final manuscript received August 5, 2013; published online October 21, 2013. Editor: David Wisler. 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