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Technical Paper

Adaptation of the Penn State Microoxidation Test for the Evaluation of Automotive Lubricants

The Penn State Microoxidation Test has been adapted for use with mineral oil base stocks and fully formulated automotive crankcase oils. Tests under nitrogen and air atmospheres coupled with analyses using gel permeation chromatography (GPC) and clay column adsorption provide for a semiquantitative analysis of the products by elution time (apparent molecular size). This test procedure allows for primary and secondary oxidation reaction rate studies after substantial quantities of the lubricant have been oxidized. Time-temperature studies can show the effectiveness of base oil quality as well as effects contributed by additives. A general time-temperature equivalence in the range of 200 to 225°C has been demonstrated for a series of formulated engine oils. Microoxidation tests have been compared with III-C hot engine tests for a series of ASTM reference oils.
Technical Paper

Comparative Evaluation of Several Hydraulic Fluids in Operational Equipment, a Full-Scale Pump Test Stand, and the Four-Ball Wear Tester

A four-ball wear test has been designed and tested with a series of petroleum based hydraulic fluids. This test procedure comprises a sequence of three 30 minute test segments designed to evaluate “wear in,” steady state wear and the effect of antiwear films produced in the first two parts of the test. Excellent repeatability of this sequential testing has been established. The wear properties of formulated fluids have been shown to be a function of system temperature and bearing load. A series of formulated mineral oil base lubricants that have been evaluated extensively in heavy-duty industrial hydraulic equipment have also been evaluated in a laboratory pump test system and the sequential four-ball wear test. A correlation developed for the heavy-duty industrial hydraulic systems with the laboratory pump test system has been extended to the four-ball wear tester sequential runs under specific load and temperatures.
Technical Paper

Determination of the Viscosity-Shear Behavior of Polymer Containing Fluids Using a Single Pass, High-Shear Capillary Viscometer

A Penn State, single-pass, capillary high shear viscometer redesigned for use at shear rates up to 106 s−1 and viscosity levels as low as 2 cp. is described. The capability of handling the effects of temperature, pressure and kinetic energy changes of Newtonian fluids over a wide range of shear rates and viscosities has been demonstrated by using a series of capillaries of different lengths and diameters. The non-Newtonian characteristics of polymer containing fluids can be obtained with good precision by using the calibrated high-shear viscometer to determine the difference in flow behavior between a Newtonian and a non-Newtonian oil with similar temperature, pressure and kinetic energy corrections. This modified viscometer has been demonstrated with a series of viscosity index improved oils using VI improvers typical of current automotive crankcase lubricants.
Technical Paper

Development and Use of the PSU Microoxidation Test for Diesel Engine Oils

The Perm State Microoxidation Test has been used previously to rate the thermal and oxidative stabilities of III C and III D automotive engine sequence reference oils. These ratings show good correlation with the results in the actual engine tests. In this paper, the oxidative and thermal stabilities of a series of heavy duty diesel engine oils are compared with III C and III D reference oils in the PSU microoxidation test using deposit level and overall production of high molecular weight condensation polymers (sludge precursors). These data show the heavy duty diesel engine oils to be more stable than typical III C and III D reference oils. The ratings of the heavy duty diesel engine oils in the PSU microoxidation test based on high molecular weight condensation polymer (sludge precursor) or deposit show excellent correlation with the ratings of the same oils in a 250 hour test in a heavy duty diesel engine.
Technical Paper

Extension of the Temperature and Shear Rate Range for Polymer Containing Lubricants Using the Cannon HTHS Capillary Viscometer

The Cannon High Temperature High Shear (HTHS) capillary viscometer is currently used in the ASTM D4624 procedure to measure the viscosity of polymer containing lubricants at 150°C and shear rate of 106 sec-1. An expansion of the utility of this Cannon instrument is described in this paper to cover the temperature range of lubricants from 35 to 175°C and shear rates of up to 106 sec-1. A finite difference model is used to solve the transport equations for capillary flow at each temperature. The solution accounted for temperature, pressure, non-Newtonian and kinetic energy effects on viscosity. Fitting these data to a double truncated power law model provides the incipient non-Newtonian shear rate γ̇1, the power law index n, and the incipient second Newtonian shear rate γ̇2. All these parameters can be measured at temperatures of around 100°C or less. The n and γ̇2 were found to be regular functions of temperature while γ̇i is always in the measured range.
Technical Paper

Four-Ball Wear Studies of Steel-on-Steel, Steel-on-Ceramic and Ceramic-on-Ceramic Bearing Systems

Sequential four-ball wear tests have been used to evaluate automotive crankcase oils for use as heavy-duty hydraulic fluids and automotive crankcase lubricants. This test technique has been adapted for use with steel-on-steel, steel-on-ceramic and ceramic-on-ceramic bearing systems. In addition to the conventional “run in” and “steady-state” wear studies, the data produced have been used to interpret bearing unit load levels for the various bearing systems involved. The data produced show that in many cases hybrid bearing systems (steel-on-ceramic) and ceramic-on-ceramic bearing systems may be useful at higher unit loadings than the conventional steel-on-steel systems. These studies focused on achieving low boundary lubricated wear rates. The bearing unit loadings were obtained from the unit bearing pressures after the “run in” of the specific bearing system.
Technical Paper

Friction Characteristics of Vapor Deposited Lubricant Films

Lubricating films were deposited on friction test specimens from a homogeneous gas phase mixture of nitrogen and various lubricant vapors. The lubricants used were tributylphosphate ester (TBP), tricresylphosphate ester (TCP), trimethylolpropane-triheptanoate ester (TMPTH) and mix-bis-(m-phenoxyphenoxy)benzene (PPE). The volume percent of lubricant vapor in nitrogen ranged from 0.5 to 3.0 percent. The friction tests were performed over a temperature range of 245 to 586°C. The lubrication properties of vapor deposited films were found to be controlled by the specimen temperature, vapor exposure time, lubricant vapor concentration and lubricant chemistry. Lubrication of the tribocontact can be optimized by using the deposition parameters to give the optimum film thickness for a given lubricant.
Technical Paper

Improving the Precision of High Temperature High Shear Rate Viscosity Measurements

Capillary viscometers provide a convenient method of measuring the viscosity of polymer containing lubricants at 150°C and 106 sec-1 shear rate as specified in ASTM D4624 Procedure. The commercial Cannon HTHS viscometer and the Penn State HTHS viscometer were used in this study. Improved calibration of the capillaries in the commercial viscometer provided an order of magnitude improvement of the HTHS repeatable values from 4.47% to 0.39% for a typical polymer containing lubricant. The viscosities of seven polymer containing lubricants at 106 sec-1 and 150°C gave an absolute mean percentage difference of 0.62% from measurements made with both capillary viscometers used in this study. The data suggests that substantial improvements can be made in the repeatability of ASTM D4624 HTHS viscosity measurements without changing the design of the current commercial viscometer.
Technical Paper

Low Temperature Rheological Studies of Hydrocarbon Base Lubricants

The low temperature rheological behavior of a number of lubricants was examined in the range of −12 to −37°C over a shear rate range of one to 1000 sec−1. Results are presented for the following fluids: a waxy mineral oil, a synthetic hydrocarbon oil (poly-alpha olefin) and four oils each containing an olefin copol ymer (OCP) viscosity index improver with different additive packages. All samples were subjected to the same cooling history consisting of a 0.56°C/min cooling rate, followed by a one hour soak period before data was collected. These data demonstrate that waxy oils without VI improvers can show non-Newtonian and viscoelastic behavior similar to data at low temperatures for polymer-thickened oils in a non-waxy solvent. Combinations of wax and VI improver can show both shear thinning and shear thickening, as well as viscoelastic properties.
Technical Paper

Microoxidation Evaluation of Automotive Crankcase Oils

The Penn State Microoxidation Tester coupled with gel permeation chromatography and clay column adsorption techniques has been demonstrated to be an effective tool to provide semi-quantitative analysis for automotive crankcase lubricant deterioration. This test simulates engine piston-cylinder zone high-temperature thin-film conditions. Oxidative behavior of a series of ASTM Sequence IIID hot engine test reference oils (with unknown base stocks and additive packages) has been found to be comparable to and consistent with that of a model fluid formulated with a good quality conventionally refined heavy neutral and a simple additive system composed of phenyl alpha naphthylamine and zinc dialkyldithiophosphate. Further simplification of the test procedure for evaluating varnish and deposit formation tendencies proves to be an effective aid in discriminating base oils as well as compounded fluids with a minimum of analytical equipment.
Technical Paper

Paraffinic Resin - A High Quality Lubricant and Newtonian V. I. Improver for Hydraulic Fluids

Paraffinic resins derived from Pennsylvania crude oil are evaluated as viscous lubricants and as blending materials with mineral oils in the preparation of hydraulic fluids and lubricants. The oxidative, thermal, and shear stabilities of the resins and of blends of the resins in mineral oil base stocks have been studied in various rigorous tests from the stand-point of service applications. While the resins provide thickening, the low temperature characteristics of blends show improvement over those prepared with synthetic polymeric additives in that viscosities can be closely approximated on an ASTM viscosity-temperature chart and are unaffected by shearing stresses.
Technical Paper

Predicting Viscosity-Shear Relationships of VI Improved Lubricants

The majority of crankcase lubricants are now formulated to contain polymeric additives to improve the viscosity temperature properties to provide a better lubricating film in the various bearing systems in an internal combustion engine. These VI (viscosity index) improved lubricants are non-Newtonian under the high shear conditions that exist in most automotive bearing systems. The conditions of interest range from starting the engine at temperatures of as low as -40°C to operating the engine at normal operating conditions including bearing temperatures of 150°C or higher. This paper presents a method for predicting the viscosity shear relationship for a series of SAE multigrade engine oils as a function of temperature and shear stress. The method is demonstrated using three types of polymeric VI improvers currently used in SAE multigrade engine oils. The polymer types include olefin copolymers (OCP), polymethacrylates (PMA), and styrene-isoprene copolymers (SI).
Technical Paper

The Effect of Viscosity Index Improvers on the Determination of Zinc Using Atomic Absorption Spectroscopy

Atomic Absorption Spectroscopy is widely used in the petroleum industry for determination of the zinc concentration of new engine oils. Many of the methods in use rely on dilution of the sample with kerosene followed by aspiration into the AA. It has been shown that such methods are subject to matrix interferences from other additive components. One previously identified interferent is the VI improver included in the lubricant formulation. This study is directed at determining the cause of the VI improver generated interference. Included in the study is an examination of the effects of different chemical type and molecular weight polymers. Also included is a comparison of dispersant and non-dispersant VI improvers of similar molecular weight. Some potential methods of eliminating the interference are also examined.
Technical Paper

Vapor Phase Tribology for Advanced Diesel Engines

Delivery of a lubricant as a vapor mixed with a carrier gas provides a method of controlling the delivery rate of the lubricant. Temperatures in the range of 370 to 800 C are high enough to produce a lubricating film from tricresyl phosphate [TCP] vapor delivered in nitrogen as a carrier gas. The solid film lubricant formed by this delivery system provides excellent lubrication for a four-ball wear tester run at 370 °C. Deposit rates are compared for TCP vapor delivered lubrication over a temperature range using stainless steel and quartz surfaces. The deposit rate is sensitive to TCP concentration in the carrier gas. The deposit rates of the TCP decomposition products versus time are reported. Having been demonstrated in laboratory tests, the Vapor Phase [VP] concept is being pursued for hot section lubrication of the advanced (low heat rejection) diesel engines.