http://hdl.handle.net/10379/138 2017-10-29T22:39:58Z http://hdl.handle.net/10379/6943 Experimental and numerical assessment of MRI-induced temperature change and SAR distributions in phantoms Colgan, Niall; Van der Putten, Wil; Tuohy, Brendan Eskola, H., Väisänen, O., Viik, J., Hyttinen, J. During an MR procedure, most of the transmitted RF power is transformed into heat within the patient’s tissue and implants as a result of resistive losses which is referred to as the specific energy absorption rate (SAR) (1). The European committee for electrotechnical standardisation (CENELEC) has mandated that all scanners must measure the specific absorption rate of radiofrequency in patients and develop system safeguards to ensure that the limits set out IEC 60602-3-33 are not exceeded. Accurate estimation of SAR is critical to safeguard in unconscious/sedated patients, patients with compromised thermoregulation, implant patients, pregnant patients and neonates who require an MRI procedure. The increased static field strength and RF duty cycle capabilities in modern MRI scanners means that systems can easily exceed safe SAR levels for patients (2). Advisory protocols routine used to establish QA protocols do not have advise on the testing of SAR levels in MRI and this is not routinely measured in annual medical physics QA. There is increasing need to verify the manufacturers SAR estimations. 2017-06-01T00:00:00Z http://hdl.handle.net/10379/6900 Ignition characteristics of 2-methyltetrahydrofuran: An experimental and kinetic study Tripathi, Rupali; Lee, Changyoul; Fernandes, Ravi X.; Olivier, Herbert; Curran, Henry J.; Sarathy, S. Mani; Pitsch, Heinz The present paper elucidates oxidation behavior of 2-methyltetrahydrofuran (2-MTHF), a novel second-generation biofuel. New experimental data sets for 2-MTHF including ignition delay time measurements in two different combustion reactors, i.e. rapid compression machine and high-pressure shock tube, are presented. Measurements for 2-MTHF/oxidizer/diluent mixtures were performed in the temperature range of 639-1413 K, at pressures of 10, 20, and 40 bar, and at three different equivalence ratios of 0.5, 1.0, and 2.0. A detailed chemical kinetic model describing both low-and high-temperature chemistry of 2-MTHF was developed and validated against new ignition delay measurements and already existing flame species profiles and ignition delay measurements. The mechanism provides satisfactory agreement with the experimental data. For identifying key reactions at various combustion conditions and to attain a better understanding of the combustion behavior, reaction path and sensitivity analyses were performed. (C) 2016 by The Combustion Institute. Published by Elsevier Inc. This work was performed as part of the Cluster of Excellence “Tailor-Made fuels from Biomass”, which is funded by the Excellence Initiative by the German federal and state governments to promote science and research at German universities. The work performed by the Clean Combustion Research Center was supported by competitive research funding from King Abdullah University of Science and Technology (KAUST). The work at NUI Galway was kindly supported by Saudi Aramco under the FUELCOM program. 2016-10-10T00:00:00Z http://hdl.handle.net/10379/6899 An RCM experimental and modeling study on CH4 and CH4/C2H6 oxidation at pressures up to 160 bar Ramalingam, Ajoy; Zhang, Kuiwen; Dhongde, Avnish; Virnich, Lukas; Sankhla, Harsh; Curran, Henry J.; Heufer, Alexander The oxidation of CH4 and CH4/C2H6 mixtures were studied at pressures relevant to knocking in large bore natural gas engines. The experiments were carried out in a rapid compression machine (RCM) at end of compression (EOC) temperatures ranging between 885 and 940 K at compressed gas pressures of 105, 125, 150, and 160 bar at varying equivalence ratios (0.417, 0.526, and 1.0) and dilution percentages (0, 10, and 30% Exhaust Gas Recirculation - EGR) that were defined in a test matrix. This study describes the method and limitations of performing high-pressure experiments of this magnitude in an RCM, modeling, and validation of the kinetic mechanism against experimental data. While the recently published AramcoMech 2.0 could well predict the ignition delay times (IDTs) for CH4 within the uncertainty ranges at comparatively higher pressures and lower temperatures (885-940 K), the predicted reactivity is, in general, lower than that of AramcoMech 1.3 as shown in our previous screening study. Based on the comparison between both mechanisms as well as sensitivity analysis on the predicted IDTs, the reaction rate constant for (H) over dot-atom abstraction from CH4 by H(O) over dot(2) radical was optimized in order to achieve better agreement with the new data while maintaining the agreement to the previous data sets. The modified mechanism predicts well the IDTs and the trend of their variation caused by the change in pressure, equivalence ratio, dilution percentage, and mixture variation with C2H6. (C) 2017 Elsevier Ltd. All rights reserved. 2017-06-13T00:00:00Z http://hdl.handle.net/10379/6882 Simplified approach to the prediction and analysis of temperature inhomogeneity in rapid compression machines Yousefian, Sajjad; Gauthier, François; Morán-Guerrero, Amadeo; Richardson, Robert R.; Curran, Henry J.; Quinlan, Nathan J.; Monaghan, Rory F.D. Substantial progress has been made in understanding and reducing temperature inhomogeneity in rapid compression machines (RCMs) with the help of computational modeling. To date, however, it has not been possible to investigate and map the full range of possible RCM designs, working gases, and, operating conditions. In this work,, we present a framework which simplifies the task of comprehensive and general RCM performance prediction. A set of thermophysical and geometrical parameters has been defined to characterize the design and operating conditions of a general RCM. Dimensional analysis was applied to reduce the number of variables, and a sensitivity analysis, based on computational simulations, was used to rank the dimensionless parameters and eliminate unimportant-ones. The results of this analysis show that Reynolds number,, Prandtl number, aspect ratio,: and crevice volume ratio are the most important parameters determining temperature inhomogeneity. A further set of computational simulations was conducted to predict postcompression temperature inhomogeneity over the full range of RCM design and operating parameters. These results are well-represented by a simple power-law equation that correlates a dimensionless temperature inhomogenity parameter (mass-averaged over the main chamber) as a function of postcompression time with just three parameters-Peclet number (the product of Reynolds and, Prandtl numbers), aspect ratio, and crevice volume ratio. This equation-can serve as a simple and general tool for RCM designers and users who wish to determine optimal configurations that minimize temperature inhomogeneity for combustion experiments. 2015-11-03T00:00:00Z