John J. Truhan

Detecting the onset of localized scuffing in a pin-on-twin fuel-lubricated test for heavy-duty diesel fuel injectors

Abstract Scuffing, usually considered to result from lubrication failure, severely limits the life of heavy-duty diesel fuel injectors. A new method is introduced to detect the onset of localized scuffing and monitor scuffing propagation in a fuel-lubricated ‘pin-on-twin’ reciprocating tribosystem. Tests were conducted on annealed and hardened AISI 52100 steel lubricated by on-highway #2 diesel fuel and ultra-low-sulphur Jet A aviation fuel. Unlike most current reciprocating tests that use changes in the nominal (averaged) friction to detect scuffing, this study analyses the detailed friction traces of individual strokes. The correlation between the change in the friction traces and the onset and progression of scuffing has been validated by examining the surface morphology of wear scars. This method was then applied to study the scuffing characteristics under various test conditions. Generally, scuffing initiated earlier and propagated more rapidly the higher the load, the lower the reciprocating frequency, and the poorer the lubricity of the fuel. The stroke ends, where direction reversal occurred, were especially vulnerable to scuffing due to their low sliding velocity.

The Development of a “Pin-on-Twin” Scuffing Test to Evaluate Materials for Heavy-Duty Diesel Fuel Injectors

In order to meet stricter emissions requirements, advanced heavy-duty diesel fuel injection systems will be required to operate at higher pressures and temperatures and in fuels that have poorer lubricity. Scuffing, as a mode of failure, severely limits injector life, and new materials and processes are required to resist scuffing in these more stringent operating conditions. Consequently, there is a need to test the ability of candidate fuel system materials to resist scuffing in fuel-lubricated environments. This paper describes a pin-on-twin reciprocating wear test in which a cylindrical specimen slides, under load, across two fixed, parallel cylindrical specimens that are perpendicular to the axis of the upper sliding specimen. Cylinders of annealed AISI 52100 were tested dry and lubricated by Jet A fuel and on-highway #2 diesel fuel. The friction force was found to give a reliable real-time determination of the onset of scuffing as verified by the morphology of the wear scar. The scar width and surface roughness profiles either did not reliably detect the onset or were difficult to carry out with this geometry. *Research sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Office of Freedom CAR and Heavy Vehicle Technologies, under contract DE-AC05-00OR22725 with UT-Battelle LLC. Review led by Roger Melley

Measurement of semi-volatiles in used natural gas engine oil using thermogravimetric analysis

Abstract Semi-volatile in internal combustion engine lubricating oil may be responsible for limiting service life and can lead to in-cylinder deposit formation. In order to measure semivolatile content, a new thermogravimetric analysis (TGA) procedure has been adapted from existing soot procedures to determine the levels of semi-volatile compounds in progressively aged lubricating oil samples from a natural gas engine dynamometer test cell run. The per cent weight remaining at 550 °C, while heated at a constant rate in an inert atmosphere, varied linearly with running time, viscosity, and oxidation and nitration. The method yielded reproducible run-to-run results and showed good agreement between helium and argon atmospheres. Mass spectroscopy data confirmed increased levels of high molecular weight species during engine operation. This method may be applicable to diesel engine oil samples.

The Erosion-Corrosion of Intake Valve Sealing Surfaces Due to the Formation of Lubricating Oil Deposits

Intake valves from natural gas-fired reciprocating engines displaying “torching” were examined to determine their failure mechanism. The principal features of the “torched” valves include a relatively thick black deposit on the tulip area of the valve extending to the sealing surface, partial loss of those deposits in various locations, and localized metal loss, oxidation and/or surface cracking in the spalled regions. Electron microprobe, scanning electron microscopy, and optical microscopy were employed to characterize the deposit formation and metal loss mechanisms. The initial cause of the torching appears to be due to the localized spallation of a loosely adherent (Ca,Zn) phosphate oil deposit adjacent to the valve/seat seal which creates a channel of hot, high velocity combustion gases. Within the torched area, significant metal oxidation and metal recession due to erosion/corrosion was observed on the valve sealing face, creating a relatively wide gap where a valve/seat seal should be. In areas where torching is not evident on the valve sealing surface, no appreciable metal recession (but limited metal oxidation) was observed.Copyright