Density and speed of sound measurements of hexadecane q Stephanie Outcalt * , Arno Laesecke, Tara J. Fortin NIST Mail Stop 838.07, 325 Broadway, Boulder, CO 80305, USA article info Article history: Received 8 July 2009 Received in revised form 6 January 2010 Accepted 7 January 2010 Available online 13 January 2010 Keywords: Adiabatic compressibility Compressed liquid Density Hexadecane Speed of sound abstract The density and speed of sound of hexadecane have been measured with two instruments. Both instru- ments use the vibrating-tube method for measuring density. Ambient pressure (83 kPa) density and speed of sound were measured with a commercial instrument from T = (290.65 to 343.15) K. Adiabatic compressibilities are derived from the density and speed of sound data at ambient pressure. Compressed liquid density was measured in a second instrument and ranged from T = (310 to 470) K with pressures from (1 to 50) MPa. The overall relative expanded uncertainty of the compressed liquid density measure- ments is 0.10–0.13% (k = 2). The overall relative expanded uncertainty (k = 2.3) of the speed of sound measurements is 0.2% and that of the ambient pressure density measurements is approximately 0.04% (k = 2.3). The ambient pressure and compressed liquid density measurements are correlated within 0.1% with a modified Tait equation. Published by Elsevier Ltd. 1. Introduction Hexadecane (C 16 H 34 , CAS No. 544-76-3), also known as cetane, is the namesake of the cetane number that characterizes the com- bustion propensity of a liquid during compression ignition. Hexa- decane was given a cetane number of 100, while a-methyl naphthalene was assigned a cetane number of 0. Diesel fuels can be classified (given a cetane number) based on this reference sys- tem per ASTM Standard D975 [1]. Hence, even though hexadecane is a slightly larger molecule than what is thought of as the average for petrodiesel, it is commonly used as a surrogate to represent the heavier fractions for the purpose of modeling diesel fuel [2]. Diesel fuel produced from petroleum (petrodiesel) is obtained from the fractional distillation of crude oil at temperatures from T = (473 to 623) K at atmospheric pressure [3]. Saturated hydrocar- bons (primarily paraffins including n, iso, and cycloparaffins) make up the majority of the composition of petrodiesel, with lesser amounts of aromatic hydrocarbons (including naphthalenes and alkylbenzenes) commonly present as well. Petrodiesel is consid- ered to consist predominantly of hydrocarbons ranging from C 10 H 20 to C 15 H 28 ; however, it is a complex mixture in which com- ponent fractions can vary considerably, while the fuel is still within specifications. Results of density and speed of sound measurements for hexa- decane are reported in this work. Adiabatic compressibilities have been derived from the ambient pressure density and speed of sound data and are also included in the tables. Compressed liquid density data have been extrapolated to 83 kPa and combined with ambient pressure density data for correlation by a Rackett equa- tion. Additionally, the compressed liquid density data have been correlated with a Tait equation and compared to the existing liter- ature data. 2. Experimental The hexadecane measured in this work was obtained from Sigma–Aldrich Chemicals 1 with a stated minimum purity of 0.99. Prior to measurements of compressed liquid density, the sample was transferred to a stainless steel cylinder and degassed as de- scribed by Outcalt and McLinden [4]. Otherwise, the sample was used as received. A density and speed of sound analyzer, the DSA 5000 from An- ton Paar Company, was used for measurements at ambient pres- sure (83 kPa in Boulder, CO, USA). Details of the instrument and experimental procedures have been reported in [5] and only a brief description will be given here. The instrument contains a sound speed cell and a vibrating quartz tube densimeter connected in ser- ies. Temperature is measured with an integrated Pt-100 thermom- eter with an estimated uncertainty of 0.01 K. The instrument was calibrated with air and deionized water at T = (293.15, 313.15, 0021-9614/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.jct.2010.01.003 q Contribution of the National Institute of Standards and Technology; not subject to copyright in the USA. * Corresponding author. Tel.: +1 303 497 5786; fax: +1 303 497 5224. E-mail address: Outcalt@nist.gov (S. Outcalt). 1 In order to describe materials and experimental procedures adequately, it is occasionally necessary to identify commercial products by manufacturers’ names or labels. In no instance does such identification imply endorsement by the National Institute of Standards and Technology, nor does it imply that the particular product or equipment is necessarily the best available for the purpose. J. Chem. Thermodynamics 42 (2010) 700–706 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct