Article pubs.acs.org/EF
Assessment of Variability in the Thermophysical Properties of Rocket Propellant RP-1 Tara J. Fortin* National Institute of Standards and Technology, Material Measurement Laboratory, Thermophysical Properties Division, 325 Broadway MS 838.07, Boulder, Colorado 80305, United States ABSTRACT: Density, speed of sound, and viscosity have been measured for 11 orthogonal blends of the rocket propellant RP-1. Density and speed of sound were measured over the temperature range of 278 to 343 K, while viscosity was measured from 263 to 373 K. All measurements were made at ambient atmospheric pressure. The density and sound speed data were used to derive adiabatic compressibilities, and those results are also reported. Different, yet significant, degrees of variability over the 11 RP-1 samples were observed for all reported properties. The largest variability was observed for viscosity. The measurement data were also compared to previously reported results for an additional RP-1 sample and to the predictions of an existing surrogate mixture model. Discrepancies were observed that seem to indicate a need for the development of a more general model to capture the whole range of thermophysical property variability that is possible with the RP-1 fuel.
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INTRODUCTION The liquid propellant rocket engine (LPRE) was conceived of over 100 years ago, but it was Robert H. Goddard who is credited with both the first actual construction of and the first flight of an LPRE in 1921 and 1926, respectively.1 For that flight, Goddard used gasoline as the fuel and liquid oxygen (LOX) as the oxidizer. Since then, various other fuels have been utilized in different combinations, depending on the specific application. In fact, an estimated 170 different fuels have undergone laboratory evaluations as potential liquid propellants.1,2 Every choice of propellant combination is ultimately a compromise between desirable qualities such as high density, low cost, and long-term storage stability, and undesirable qualities such as corrosivity, flammability, and toxicity.1 However, after more than 50 years of operational experience, certain propellants and propellant combinations have proven themselves to be most useful in U.S. space applications; these include hydrazine (as a monopropellant), nitrogen tetroxide/hydrazine, liquid hydrogen (LH2)/LOX, kerosene/peroxide, and kerosene/LOX.1,3 Kerosene is obtained from the fractional distillation of petroleum between approximately 200 and 300 °C.3 Because jet fuels are kerosenes, they were utilized as the initial kerosenes for rocket tests. However, it became clear that the physical property specifications for jet fuels (e.g., their chemical components, density, volatility, etc.) were not sufficiently tight for them to be effective rocket propellants. That problem was ultimately overcome in the mid-1950s with the development of rocket propellant 1 (RP-1).3 Compared to common jet fuels, RP-1 specifications allow for a narrower density range and lower concentrations of certain fuel components thought to cause deposits during regenerative cooling (e.g., sulfur, olefins, and aromatics).4 Specifically, density is allowed to vary from 0.799 to 0.815 g/cm3, and the maximum allowed sulfur, olefin, and aromatic concentrations are limited to 30 mg/kg, 2.0% vol/vol, and 5.0% vol/vol, respectively.5 Typically, RP-1 is formulated by mixing together different blending stocks according to established formulas to produce a This article not subject to U.S. Copyright. Published 2012 by the American Chemical Society
fuel that meets specifications. Despite the strictness of those specifications, there have been indications that some engine manufacturers and launch service providers have encountered an unanticipated degree of variability among RP-1 formulations.6−8 In an effort to evaluate the possible range of compositional variability and the resultant consequences for the fuel’s thermophysical properties, a comprehensive study was undertaken at the National Institute of Standards and Technology (NIST). As part of that study, Lovestead et al. recently reported their assessment of the compositional variability as determined by the advanced distillation curve method.9 In this paper, measurements made at ambient pressure of the thermophysical properties density, speed of sound, and viscosity are reported.
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MATERIALS AND METHODS
A total of 11 separate samples of RP-1 were obtained for this work. Each sample was independently prepared using a distinct recipe while still meeting existing fuel specifications.5 Furthermore, the 11 samples were considered to be orthogonal. In other words, samples were prepared in a manner that ensured there was no correlation or interrelation between samples. Specifically, orthogonal samples are free from carryover or correlation that can occur between batches that are sequentially added to a storage tank. Furthermore, the orthogonal samples were specifically formulated to reflect the full range of variability that could reasonably be encountered with RP-1. All samples were pink in color due to the presence of the dye additive azobenzene-4-azo-2-naphthol. The chemical composition of each sample was previously analyzed using gas chromatography− mass spectrometry (GC−MS),10,11 and the results were reported by Lovestead et al.9 For each of the 11 samples, a subset of the more than 60 reported components is shown in Table 1. Specifically, the top 10 components and their corresponding CAS registry numbers are listed, sorted by the uncalibrated area percent. For each RP-1 sample, the components listed in Table 1 account for approximately 35−42% of the total reported area. As Table 1 shows, the RP-1 samples are composed primarily of linear and branched alkanes (or paraffins) up to C21 (2,6,10,15-tetramethylheptadecane), Received: March 5, 2012 Revised: May 18, 2012 Published: June 14, 2012 4383
dx.doi.org/10.1021/ef3004009 | Energy Fuels 2012, 26, 4383−4394
Energy & Fuels
Article
Table 1. Top 10 Components (by Area %) of the 11 RP-1 Samples compound
CAS no.
area %
compound
Blend 1 n-dodecane n-tetradecane n-tridecane 2,6-dimethylundecane 2-methylundecane 2-methyl decalin 5-methylundecane 3-methylundecane 2,3,6-trimethyloctane cis-decalin
112-40-3 629-59-4 629-50-5 17301-23-4 7045-71-8 2958-76-1 1632-70-8 1002-43-4 62016-33-5 42588-37-2
4.02 3.55 2.98 2.95 2.42 2.34 2.06 2.00 1.87 1.77
17301-23-4 2958-76-1 62016-33-5 112-40-3 7045-71-8 17301-27-8 1632-70-8 629-59-4 4292-75-5 493-02-7
3.00 2.40 2.20 2.00 1.90 1.90 1.80 1.80 1.70 1.60
2958-76-1 17301-23-4 112-40-3 7045-71-8 1632-70-8 493-02-7 17302-28-2 62016-33-5 42588-37-2 1120-12-4
2.65 2.47 2.00 1.96 1.92 1.91 1.81 1.76 1.72 1.60
17301-23-4 62016-33-5 112-40-3 2958-76-1 7045-71-8 17301-27-8 2980-69-0 1632-70-8 1002-43-4 100015-24-7
3.75 2.60 2.41 2.38 2.35 2.06 2.02 2.01 2.00 1.98
17301-23-4 2958-76-1 62016-33-5 7045-71-8 1632-70-8 17301-27-8 100015-24-7 6418-41-3 1002-43-4
3.22 2.61 2.23 2.21 2.08 1.87 1.73 1.73 1.72 1.70
17301-23-4 7045-71-8 62016-33-5 2958-76-1 112-40-3
3.53 2.36 2.35 2.33 2.31
5-methylundecane hexylcyclohexane 2,10-dimethylundecane 2,6-dimethyl decalin 4-methylundecane Blend 7 n-tridecane n-dodecane 2,6-dimethylundecane n-tetradecane 2,3,6-trimethyloctane 2,6,10,15-tetramethylheptadecane 2,y,z-trimethyldodecanea 2,10-dimethylundecane 2-methyl decalin 3-methylundecane Blend 8 2,6-dimethylundecane 2-methyl decalin adamantane 2,y,z-trimethyldodecanea 2,6,10,15-tetramethylheptadecane x,y-dimethylundecanea 2-methylundecane 5-methylundecane 3-methyltridecane 2,10-dimethylundecane Blend 9 n-dodecane n-tridecane n-undecane n-tetradecane 2,6-dimethylundecane 3-methylundecane 2,y,z-trimethyldodecanea 2-methylundecane 3-methyltridecane 5-methylundecane Blend 10 n-undecane n-dodecane 2,6,10,15-tetramethylheptadecane 2,6-dimethylundecane 2,3,6-trimethyloctane 3-methyltridecane 2-methyl decalin 2,10-dimethylundecane 5-methylundecane 2-methylundecane Blend 11 2,6-dimethylundecane 2-methyl decalin n-dodecane 2,6,10,15-tetramethylheptadecane 2,3,6-trimethyloctane 2,y,z-trimethyldodecanea 5-methylundecane 2-methylundecane 3-methyltridecane 2,10-dimethylundecane
Blend 2 2,6-dimethylundecane 2-methyl decalin 2,3,6-trimethyloctane n-dodecane 2-methylundecane 2,10-dimethylundecane 5-methylundecane n-tetradecane hexylcyclohexane trans-decalin Blend 3 2-methyl decalin 2,6-dimethylundecane n-dodecane 2-methylundecane 5-methylundecane trans-decalin 2,6-dimethylnonane 2,3,6-trimethyloctane cis-decalin n-undecane Blend 4 2,6-dimethylundecane 2,3,6-trimethyloctane n-dodecane 2-methyl decalin 2-methylundecane 2,10-dimethylundecane 4-methylundecane 5-methylundecane 3-methylundecane trans-2-methyl decalin Blend 5 2,6-dimethylundecane 2-methyl decalin 2,y,z-trimethyldodecanea 2,3,6-trimethyloctane 2-methylundecane 5-methylundecane 2,10-dimethylundecane trans-2-methyl decalin 3-methyltridecane 3-methylundecane Blend 6 2,6-dimethylundecane 2-methylundecane 2,3,6-trimethyloctane 2-methyl decalin n-dodecane
CAS no.
area %
1632-70-8 4292-75-5 17301-27-8 1618-22-0 2980-69-0
2.18 2.00 1.92 1.91 1.89
629-50-5 112-40-3 17301-23-4 629-59-4 62016-33-5 54833-48-6
3.23 2.84 2.33 2.03 1.94 1.94 1.85 1.68 1.62 1.52
Blend 6
17301-27-8 2958-76-1 1002-43-4 17301-23-4 2958-76-1 281-23-2 54833-48-6 7045-71-8 1632-70-8 6418-41-3 17301-27-8 112-40-3 629-50-5 1120-12-4 629-59-4 17301-23-4 1002-43-4
2.59 2.30 2.18 2.18 2.18 2.02 1.76 1.70 1.69 1.58
7045-71-8 6418-41-3 1632-70-8
4.38 3.00 2.70 2.25 2.21 2.08 1.85 1.78 1.74 1.73
1120-12-4 112-40-3 54833-48-6 17301-23-4 62016-33-5 6418-41-3 2958-76-1 17301-27-8 1632-70-8 7045-71-8
3.50 2.92 2.26 2.09 1.83 1.73 1.71 1.61 1.60 1.56
17301-23-4 2958-76-1 112-40-3 54833-48-6 62016-33-5
2.42 2.31 2.00 1.98 1.79 1.75 1.74 1.71 1.59 1.55
1632-70-8 7045-71-8 6418-41-3 17301-27-8
a
Note that it is not always possible to determine the position of the methyl substitution, and in these instances the position is indicated with a letter rather than a number. 4384
dx.doi.org/10.1021/ef3004009 | Energy Fuels 2012, 26, 4383−4394
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Article
Table 2. Densities of the 11 RP-1 Samples Measured in the Density and Sound Speed Analyzer at Ambient Pressurea Blend 1
a
T (K)
ρ̅ (kg m‑3)
343.15 338.15 333.15 328.15 323.15 318.15 313.15 308.15 303.15 298.15 293.15 288.15 283.15 278.15
770.82 774.50 778.17 781.83 785.48 789.13 792.77 796.41 800.03 803.65 807.27 810.89 814.51 818.13
Blend 2
U(ρ̅) (kg m‑3) 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 Blend 7
ρ̅ (kg m‑3)
Blend 3
U(ρ̅) (kg m‑3)
773.45 777.12 780.77 784.41 788.05 791.68 795.31 798.93 802.55 806.16 809.76 813.37 816.97 820.58
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 Blend 8
Blend 4
ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
769.28 772.96 776.63 780.29 783.93 787.58 791.21 794.84 798.47 802.10 805.75 809.41 813.07 816.73
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.07 0.08 0.10 0.12 0.14
ρ̅ (kg m‑3)
772.38 776.06 779.73 783.38 787.03 790.68 794.31 797.94 801.57 805.19 808.81 812.43 816.05 819.67 Blend 9
Blend 5
U(ρ̅) (kg m‑3) 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06
ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
775.88 779.53 783.18 786.81 790.44 794.06 797.68 801.29 804.89 808.50 812.10 815.70 819.30 822.90 Blend 10
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06
Blend 6 ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
771.90 775.58 779.25 782.92 786.57 790.22 793.86 797.49 801.13 804.75 808.38 812.00 815.62 819.24 Blend 11
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06
T (K)
ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
ρ̅ (kg m‑3)
U(ρ̅) (kg m‑3)
343.15 338.15 333.15 328.15 323.15 318.15 313.15 308.15 303.15 298.15 293.15 288.15 283.15 278.15
773.57 777.22 780.86 784.49 788.11 791.72 795.34 798.95 802.55 806.15 809.75 813.35 816.95 820.55
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06
773.27 776.93 780.58 784.22 787.85 791.47 795.09 798.70 802.31 805.92 809.52 813.12 816.72 820.32
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06
765.00 768.68 772.34 775.99 779.63 783.27 786.90 790.52 794.14 797.76 801.38 805.01 808.64 812.28
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.07 0.08 0.10 0.12 0.13
770.07 773.72 777.35 780.97 784.59 788.20 791.80 795.41 799.00 802.59 806.18 809.77 813.36 816.95
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.07
771.34 775.00 778.64 782.28 785.91 789.54 793.15 796.77 800.38 803.99 807.60 811.24 814.89 818.55
0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.08 0.10 0.15
Ambient pressure during measurements was ∼83 kPa. it vibrates perpendicular to its plane in an electromagnetic field. The resonator in this instrument is constructed of borosilicate glass. The sound speed cell and the density cell are both housed in a thermostated copper block whose temperature is controlled with a combination of thermoelectric Peltier elements and an integrated Pt-100 resistance thermometer. Measurements of air and water performed at 293 K, 313 K, and 333 K are required to adjust the apparatus constants in the instrument’s working equations for both sound speed and density; this is referred to as an adjustment procedure. Additionally, regular calibration measurements are performed to verify the instrument’s performance between adjustment procedures. Our calibration procedure involves measuring water and toluene standard reference material (SRM) 211d14 every 5 K from 343 to 278 K. Additional details about the density and sound speed analyzer can be found in Fortin et al.15 and Laesecke et al.16 A commercial viscodensimeter, the SVM 3000 from Anton Paar, was used to simultaneously measure viscosity and density over the temperature range 263 to 373 K and at ambient pressure. Density is measured with a vibrating-tube densimeter made of borosilicate glass. Viscosity is measured with a Stabinger rotating concentric cylinder viscometer. The horizontally mounted outer cylinder is made of Hastelloy, while the inner cylinder is made of titanium. The inner cylinder contains a small magnet but is otherwise hollow. When sample is injected into the cell, it fills the annular gap between the inner and outer cylinders. During measurements, the outer cylinder is rotated at 3500 rpm by an external electric motor, and the inner cylinder is dragged into rotation by the rotating sample liquid. The revolutions of the rotating field of the magnet in the inner cylinder are measured with a Hall effect sensor, and the dynamic viscosity (η) is ultimately obtained from the ratio of the number of revolutions of the
although 7 of the 11 samples also contain a small amount (
