Effects of H 2 S addition on hydrogen ignition behind reflected shock waves: Experiments and modeling Olivier Mathieu ⇑ , Fiona Deguillaume, Eric L. Petersen Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, USA article info Article history: Received 5 April 2013 Received in revised form 13 July 2013 Accepted 15 July 2013 Available online 10 August 2013 Keywords: H 2 S Hydrogen Ignition delay time Shock tube High pressure abstract Hydrogen sulfide is a common impurity that can greatly change the combustion properties of fuels, even when present in small concentrations. However, the combustion chemistry of H 2 S is still poorly under- stood, and this lack of understanding subsequently leads to difficulties in the design of emission-control and energy-production processes. During this study, ignition delay times were measured behind reflected shock waves for mixtures of 1% H 2 /1% O 2 diluted in Ar and doped with various concentration of H 2 S (100, 400, and 1600 ppm) over large pressure (around 1.6, 13, and 33 atm) and temperature (1045–1860 K) ranges. Results typically showed a significant increase in the ignition delay time due to the addition of H 2 S, in some cases by a factor of 4 or more over the baseline mixtures with no H 2 S. The magnitude of the increase is highly dependent on the temperature and pressure. A detailed chemical kinetics model was developed using recent, up-to-date detailed-kinetics mechanisms from the literature and by chang- ing a few reaction rates within their reported error factor. This updated model predicts well the experi- mental data obtained during this study and from the shock-tube literature. However, flow reactor data from the literature were poorly predicted when H 2 S was a reactant. This study highlights the need for a better estimation of several reaction rates to better predict H 2 S oxidation chemistry and its effect on fuel combustion. Using the kinetics model for sensitivity analyses, it was determined that the decrease in reactivity in the presence of H 2 S is because H 2 S initially reacts before the H 2 fuel does, mainly through the reaction H 2 S+H ¢ SH + H 2 , thus taking H atoms away from the main branching reaction H + O 2 ¢ - OH + O and inhibiting the ignition process. Ó 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved. 1. Introduction It is well known that some impurities, even in very low concen- tration, can induce measurable and sometimes large changes in the combustion properties of a fuel (see [1] for N, S, Cl, and K/Na spe- cies). Amongst these impurities, H 2 S is a common one that can be found in syngas produced from biomass or coal (up to 1% mol. [2]), but can also be present in natural gases (up to 80% v/v [3]) in addi- tion to being a by-product of the oil industry. Hydrogen sulfide and SO 2 are generally removed through a sulfur recovery procedure that uses the modified Claus process (3H 2 S+ 3 / 2 O 2 ? SO 2 +H 2- O + 2H 2 S (1173–1473 K) followed by 2H 2 S + SO 2 ¢ 3 / 2 S 2 + 2H 2 O (440–640 K)). Unfortunately, due to both the limited available lit- erature data (see [3] and reference herein) and the very large num- ber of sensitive reactions with significant rate uncertainty [4], the high-temperature chemistry of sulfur species is still poorly under- stood. This lack of understanding leads to difficulties in the design of emissions control and energy production (gas turbine using syn- gas) processes. To better understand the high-temperature chemistry of H 2 S and to set a base for the comprehension of the interactions be- tween H 2 S and hydrocarbons, a detailed knowledge of the interac- tions between H 2 S and the H 2 /O 2 system is of paramount importance. Indeed, the H 2 /O 2 sub-mechanism is critical for the combustion of hydrocarbons as it contains many important ele- mentary reactions involving radicals (H, O, OH, HO 2 ) which play a great role at every stage of the hydrocarbon oxidation process. However, to the best of the authors’ knowledge, there is only one study on the interactions between H 2 /O 2 and H 2 S. These inter- actions have been investigated in a shock tube at low pressure and high temperatures by Bradley and Dobson [5], with a relatively low level of Ar dilution, 86–88% by volume. Note that the body of work on H 2 S combustion itself is also rather limited. The earliest work (before the 1970s) on sulfur species is summarized in [6] and, more recently, the high-pressure shock-tube ignition delay time mea- surements in air by Frenklach et al. [7] and a few studies on ther- mal decomposition behind reflected shock waves [8,9] or in flow reactors [4,10] have appeared. However, for the latter technique, the study of Zhou [11] proved the possibility of having catalytic ef- fects by silica surfaces on H 2 S, resulting in misleading results such as in [10]. These catalytic effects seem to be suppressed after a 0010-2180/$ - see front matter Ó 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.combustflame.2013.07.011 ⇑ Corresponding author. E-mail address: olivier.mathieu@tamu.edu (O. Mathieu). Combustion and Flame 161 (2014) 23–36 Contents lists available at SciVerse ScienceDirect Combustion and Flame journal homepage: www.elsevier.com/locate/combustflame