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Research Papers: Internal Combustion Engines

Kinetic Study of the Thermo-Oxidative Degradation of Squalane (C30H62) Modeling the Base Oil of Engine Lubricants

[+] Author and Article Information
Moussa Diaby

Ecole Polytechnique, Laboratoire des Mécanismes Réactionnels, CNRS 91128 Palaiseau Cedex, Francemoussa@dcmr.polytechnique.fr

Michel Sablier

Ecole Polytechnique, Laboratoire des Mécanismes Réactionnels, CNRS 91128 Palaiseau Cedex, Francemichel.sablier@dcmr.polytechnique.fr

Anthony Le Negrate

PSA Peugeot Citroën, Centre Technique de Vélizy, 78943 Vélizy-Villacoublay Cedex, Franceanthony.lenegrate@mpsa.com

Mehdi El Fassi

PSA Peugeot Citroën, Centre Technique de Vélizy, 78943 Vélizy-Villacoublay Cedex, Francemehdi.elfassi@mpsa.com

J. Eng. Gas Turbines Power 132(3), 032805 (Nov 30, 2009) (9 pages) doi:10.1115/1.3155797 History: Received March 09, 2009; Revised April 07, 2009; Published November 30, 2009; Online November 30, 2009

On the basis of ongoing research conducted on the clarification of processes responsible for lubricant degradation in the environment of piston grooves in exhaust gas recirculation (EGR) diesel engines, an experimental investigation was aimed to develop a kinetic model, which can be used for the prediction of lubricant oxidative degradation correlated with endurance test conducted on engines. Knowing that base oils are a complex blend of paraffins and naphthenes with a wide range of sizes and structures, their chemistry analysis during the oxidation process can be highly convoluted. In the present work, investigations were carried out with the squalane (C30H62) chosen for its physical and chemical similarities with the lubricant base oils used during the investigations. Thermo-oxidative degradation of this hydrocarbon was conducted at atmospheric pressure in a tubular furnace, while varying temperature and duration of the tests in order to establish an oxidation reaction rate law. The same experimental procedures were applied to squalane doped with two different phenolic antioxidants usually present in engine oil composition: 2,6-di-tert-butyl-4-methylphenol and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. Thus, the effect of both antioxidants on the oxidation rate law was investigated. Data analysis of the oxidized samples (Fourier transform infrared spectroscopy and gas chromatography/mass spectrometry) allowed rationalization of the thermo-oxidative degradation of squalane. The resulting kinetic modeling provides a practical analytical tool to follow the thermal degradation processes, which can be used for prediction of base oil hydrocarbon aging. If experiments confirmed the role of phenolic additives as an effective agent to lower oxidation rates, the main results lie in the observation of a threshold temperature where a reversed activity of these additives was observed.

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Figures

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Figure 1

Mechanism of low-molecular weight material formation (8)

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Figure 2

Antioxidant mechanism for radical scavengers

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Figure 3

Chemical structures of (a) BHT and (b) OBHP

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Figure 4

Chemical structure of squalane (C30H62)

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Figure 5

Mass loss of squalane versus the test duration without antioxidant additives

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Figure 6

FTIR spectra of oxidized sample at 180°C and different durations of the tests

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Figure 7

Plot of ln(1−XC=O) against time of oxidation tests without antioxidant additives

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Figure 8

Chromatogram of an oxidized sample at 180°C and different durations of the tests without antioxidant additives

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Figure 9

(a) Mass loss and (b) percentage of oxidation products versus time for increased test duration time at 180°C with squalane doped with OBHP

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Figure 10

(a) Mass loss and (b) percentage of oxidation products versus time for increased test temperature at 205°C with squalane doped with OBHP

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Figure 11

The model reaction and the kinetic rate equations proposed by Naidu (42) for the modeling of paraffin hydrocarbon oxidative thermal degradation

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Figure 12

The simplified model and the kinetic rate equations proposed for the modeling of squalane thermal oxidative degradation

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Figure 13

Fictitious steps of oxidation products’ formation for squalane oxidative thermal degradation

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Figure 14

Variations of squalane and degradation products’ experimental percentages versus test duration time at a temperature of 180°C (dots) and their theoretical variations (thick lines) applying the simplified model presented here for the oxidative thermodegradation of squalane

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