A numerical assessment of the novel concept of crevice containment in a rapid compression machine Gaurav Mittal a,⇑ , Mandhapati P. Raju b , Anil Bhari a a Department of Mechanical Engineering, The University of Akron, Akron, OH 44325, USA b Optimal Inc., Plymouth, MI, USA article info Article history: Received 13 August 2010 Received in revised form 27 February 2011 Accepted 20 April 2011 Available online 9 May 2011 Keywords: Rapid compression machine Two-stage ignition Crevice containment abstract Rapid compression machines (RCMs) typically incorporate creviced pistons to suppress the formation of the roll-up vortex. The use of a creviced piston, however, can enhance other multi-dimensional effects inside the RCM due to the crevice zone being at lower temperature than the main reaction chamber. In this work, such undesirable effects of a creviced piston are highlighted through computational fluid dynamics simulations of n-heptane ignition in RCM. Specifically, the results show that in an RCM with a creviced piston, additional flow of mass takes place from the main combustion chamber to the crevice zone during the first-stage of the two-stage ignition. This phenomenon is not captured by the zero- dimensional modeling approaches that are currently adopted. Consequently, a novel approach of ‘crevice containment’ is introduced and computationally evaluated in this paper. In order to avoid the undesirable effects of creviced piston, the crevice zone is separated from the main reaction chamber at the end of compression. The results with ‘crevice containment’ show significant improvement in the fidelity of zero-dimensional modeling in terms of predicting the overall ignition delay and pressure rise in the first-stage of ignition. Although the implementation of ‘crevice containment’ requires a modification in RCM design, in practice there are significant advantages to be gained through a reduction in the rate of pressure drop in the RCM combustion chamber and a quantitative improvement in the data obtained from the species sampling experiments. Ó 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved. 1. Introduction Rapid compression machines (RCMs) are valuable tools for investigating chemical kinetics at low-to-intermediate tempera- tures and elevated pressures. Until few years ago, interpretation of RCM data was plagued with uncertainties arising from the influ- ence of temperature non-uniformity due to the presence of piston motion induced roll-up vortex, and facility dependent heat loss characteristics [1,2]. The CFD evidence of the roll-up vortex in the context of RCMs and its consequences on ignition were first discussed by Griffiths and coworkers [3,4]. Lee and Hochgreb [5] made a remarkable contribution and developed upon the idea of incorporating a crevice on the periphery of piston, which was ini- tially proposed by Park and Keck [6], and computationally showed the efficacy of the creviced piston in suppressing the vortex. The phenomenon of the roll-up vortex and its suppression was subse- quently investigated by many groups [7–14] and the importance of a creviced piston in RCMs for obtaining quality experimental data is now well recognized. Another important aspect is to correctly model RCM experi- ments to properly account for the facility dependent heat loss characteristics, so that the experimental data can be used for vali- dating detailed chemical kinetic mechanisms. Such modeling is usually conducted with a zero-dimensional (Zero-D) code, such as SENKIN [15], while accounting for the heat loss effects [16–18]. However, not all approaches that are used to account for heat loss effects are appropriate. It was highlighted in Ref. [19] that the assumptions of adiabatic core and Newtonian heat loss results in severe discrepancy in the modeled temperature, whereas the ‘adiabatic volume expansion’ provides a much better way of dealing with the heat loss. As such, the use of the creviced piston goes a considerable way to the attainment of the homoge- neous temperature field within the main body of the reaction chamber, and hence enables a closer approximation of the Zero- D modeling to the reality [20]. In our previous investigation with hydrogen ignition in an RCM [21], it was shown that SENKIN sim- ulations in conjunction with the Zero-D modeling approach with an ‘adiabatic volume expansion’ perform very well in adequately predicting the ignition delay, as compared with the results obtained from computational fluid dynamics (CFD) simulations. Recognizing that the ignition characteristics of hydrocarbon fuels, 0010-2180/$ - see front matter Ó 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.combustflame.2011.04.013 ⇑ Corresponding author. E-mail address: gaurav@uakron.edu (G. Mittal). Combustion and Flame 158 (2011) 2420–2427 Contents lists available at ScienceDirect Combustion and Flame journal homepage: www.elsevier.com/locate/combustflame