THE GOVERNING ROLE OF PRE-EXISTING LUBRICANT DEPOSITS IN SUBSEQUENT DEPOSIT GROWTH: A UNIFORM LAYER MODEL
Open Access
- Author:
- Kouame, Sylvain-Didier Brou
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 27, 2011
- Committee Members:
- Randy Vander Wal, Dissertation Advisor/Co-Advisor
Randy Lee Vander Wal, Committee Chair/Co-Chair
Andre Louis Boehman, Committee Member
Yaw D Yeboah, Committee Member
Joseph Manuel Perez Sr., Committee Member - Keywords:
- Deposits
Uniform layer
Dehydrogenation
Lubricant
Deoxygenation
Polymeric deposit
Aged Film Test
Carbon
Micro- Oxidaton
Aged Oil Test - Abstract:
- Deposit formation on pistons, valves, fuel pumps and injectors is universally recognized as undesirable, because engine performance will degrade. Across several lubricant formulations including mineral, synthetic, bio-based and fully formulated lubricants, the Penn State Micro-Oxidation (PSMO) test has shown that mass deposition, regardless of the nature of the lubricant, follows a similar trend. A lacquer or varnish type of deposit initially forms followed by transformation to a dark carbon deposit. Yet each of these very different deposits (lacquer or dark carbon) results from degradation of the same lubricant. To provide a reference frame for mass deposition, the standard mass deposition profile was mapped using the PSMO method. Sets of substitutional tests were performed using a second stage of PSMO. Aged film substitution tests were performed using differently aged pre-deposits re-inserted within fresh lubricant to gauge the effect of deposit chemistry upon deposit growth. Similarly, aged oil experiments were conducted to test for any potential synergy between aged oil and evolving deposits. Each test strategy provides a means by which to decouple the lubricant from the deposit so as to gauge the role of deposit chemistry upon continued deposit growth. To provide a baseline for comparison, heat treatments were applied to films extracted from various stages of the mass deposition curve. To characterize film chemistry and its evolution, FTIR and EDS spectroscopy were applied PSMO deposits formed during the course of this study. The former measures alkyl sp3 C-H and carbonyl C=O bond stretching vibrations and their relative concentration as films/deposits age. The latter provides a more global measure of C- and O-atom content as the deposit undergoes deoxygenation and dehydrogenation reactions. Results obtained in this study showed a declining activity towards mass deposition with film age. Chemical characterization of these series of films by EDS for global elemental composition and by FTIR for chemically specific bond concentration correlate well with each other, specifically comparison of the chemical composition rates shows correspondence between C and O atom concentration changes. Also mass deposition rates decrease with increasing film age, within the proviso for times past induction and accelerative stages. Aged film studies demonstrate a consistent reactivity decline with increasing film. The significance of these studies is that they are the first to consider the deposit as not only chemically active, but governing subsequent deposition. Traditionally, deposits have been considered as inert, the end product of a series of complex liquid phase radical driven processes, decoupled from the film. Further distinguishing this work from prior studies, referencing the film is the presumption of homogeneous chemistry, albeit time-varying under heated, oxidizing conditions. Hence in this context, the uniform layer deposition model is advanced.