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While standardized laboratory-scale wear tests are available to predict the lubricity of liquid fuels under ambient conditions, the reality is that many injection systems operate at elevated temperatures where fuel vaporization is too excessive to perform the measure satisfactorily. The present paper describes a High Pressure High Frequency Reciprocating Rig (HPHFRR) purposely designed to evaluate fuel lubricity in a pressurized environment at temperatures of up to 300°C. The remaining test parameters are identical to those of the widely standardized High Frequency Reciprocating Rig (HFRR). Results obtained using the HPHFRR indicate that wear rate with poor lubricity fuels is strongly sensitive to both temperature and oxygen partial pressure and may be orders of magnitude higher than at ambient conditions. Surprisingly however, wear rate was found to decrease dramatically at temperatures above 100°C, possibly due to evaporation of dissolved moisture.

A study has been made of the lubricant film-forming properties of viscosity index improver-containing oils in non-steady state, high-pressure contacts. Two types of non-steady speed condition have been investigated, sudden halting of motion and cyclically-varying entrainment speed. Film thickness has been measured in a ball on flat contact using ultra-thin film interferometry. It has been shown that viscosity index improver polymers in solution exhibit an enhanced squeeze behavior during halting and a viscoelastic response to acceleration/deceleration.

Recent work by the authors has indicated that some types of viscosity index improver polymers can form thick boundary films in lubricated contacts. These films appear to result from the adsorption of molecules of polymer on metal surfaces to produce layers, about 20 nm thick, having higher polymer concentration and thus higher viscosity than the bulk solution. In the current paper it is shown that these VII boundary films are able to separate rubbing surfaces in both rolling and sliding contacts and that they make a significant contribution towards reducing friction and wear at temperatures up to at least 140°C. The mechanism by which these polymers reduce friction and wear is elucidated.

This paper describes the development of a thin film rheometer able to measure the viscosity of lubricant films of the order of 200 μm thickness on flat, solid surfaces. The rheometer consists of a small cylinder mounted on a piezo bimorph which is divided electrically into two halves. When an AC voltage is applied to the one half of the piezo it causes the flat surface of the cylinder to oscillate in its own plane with an amplitude of a few microns. This motion produces an AC output from the other half of the piezo. The flat face of the cylinder is held parallel to an oily test surface and the latter is supported on a micrometer stage so that the gap between the two surfaces can be adjusted. As the gap is narrowed the oil film dampens the sinusoidal motion of the cylinder and the extent of this damping can be used to determine the viscosity of the oil film between the surfaces.

Four bench oxidation tests, the penn state microoxidation test, the thin film oxygen uptake test (TFOUT), ASTM D-2112 and ASTM D-2272 rotating bomb tests (RBOT), were evaluated for their ability to predict the oxidation performance of motor oils in the ASTM Sequence III-D and III-E engine tests. Based on comparative results for a series of oils for which we have III-D, III-E or other engine test data, the Penn State microoxidation test gave the best overall prediction.

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.