Ignition delay study of moist hydrogen/oxidizer mixtures using a rapid compression machine Apurba K. Das a , Chih-Jen Sung b, *, Yu Zhang b , Gaurav Mittal c a Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, OH 44106, USA b Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269, USA c Department of Mechanical Engineering, The University of Akron, Akron, OH 44325, USA article info Article history: Received 7 October 2011 Received in revised form 21 January 2012 Accepted 24 January 2012 Available online 19 February 2012 Keywords: Autoignition Dry and moist hydrogen Rapid compression machine abstract Autoignition of moist hydrogen/oxidizer mixtures has been studied experimentally using a rapid compression machine (RCM). This work investigated the effect of water addition on ignition delays of stoichiometric hydrogen/oxidizer mixtures in the end of compression temperature range of T C ¼ 907e1048 K at three different end of compression pressures viz. P C ¼ 10 bar (1 MPa), 30 bar (3 MPa), and 70 bar (7 MPa). RCM experiments were conducted with 0%, 10%, and 40% molar percentages of water in the reactive mixture. At P C ¼ 30 bar and 70 bar, the presence of 10% and 40% water vapor was shown to promote autoignition. However, at P C ¼ 10 bar, water addition (10%) was seen to retard the reactivity, thereby increasing the ignition delay. Comparison with different reaction kinetic mechanisms re- ported in literature shows widely different results of simulated ignition delays for the temperature and pressure range studied, although most of the mechanism predictions demonstrate similar trend in ignition delay with water addition. A recent chemical kinetic mechanism, which shows good agreement with the present experiments at higher pres- sure but some discrepancy at lower pressure, was used for brute force sensitivity analysis in order to identify the important reactions for the dry mixtures in the temperature and pressure window investigated. An important reaction identified was further adjusted within the uncertainty limit as an attempt to improve the results from mechanism prediction for the ignition delay at low pressure (P C ¼ 10 bar) without water addition. In addition, the modification in the reaction rate leads to good agreement between the experiment data and the mechanism prediction for the moist mixtures at varying compressed pressures. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Combustion study of hydrogen/oxidizer system has tradi- tionally received substantial attention for multitude of reasons. Having the simplest molecular structure of a naturally occurring fuel, its combustion kinetics forms the fundamental building block in any hydrocarbon fuel chemical kinetics. Owing to its clean burning property, high flame speed and diffusivity, wide flammability range, and substantially lower ignition energy, hydrogen has poised itself in a unique * Corresponding author. Department of Mechanical Engineering, University of Connecticut, Room 484, United Technologies Engineering Building, Storrs, CT 06269, USA. Tel.: þ1 860 486 3679; fax: þ1 860 486 5088. E-mail address: cjsung@engr.uconn.edu (C.-J. Sung). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 6901 e6911 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.01.111