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.

Scuffing transition diagrams for heavy duty diesel fuel injector materials in ultra low-sulfur fuel-lubricated environment

“…Therefore, we might expect the rise in the plowing component of the friction force to reflect an increased incidence of surface deformation and hence become an indicator of scuffing. This correlation has been verified by surface morphology examination [12]. By monitoring the progressive changes in the friction traces of individual strokes, this method reveals when and where local scuffing initiates, and how the scuffed area grows during reciprocating sliding.…”

“…It had good agreement with industrial field experience [13]. In this paper, this scuffing detection technique [12] is enhanced by mapping scuffing in both space and time domains in a unique 3D plot, which is then used to generate scuffing transition diagrams for fuel injector materials to exemplify the effects of surface finish and sliding velocity on scuffing characteristics. The worn surface morphology and tribochemical surface films are examined to help understand the scuffing mechanisms in fuel-lubrication.…”

“…In our previous study [12,13], a crossed-cylinders arrangement, which we shall call the 'pin-on-twin test', has been developed. A schematic drawing of the 'pin-on-twin' reciprocating test configuration is shown in Fig.…”

“…The averaged friction coefficient was proven not sensitive enough to detect scuffing for hardened steel or other high scuffing-resistant materials in reciprocating sliding [12]. A new method using detailed friction information of individual strokes to reveal scuffing has been reported [12].…”

“…In our previous studies, a friction transition-based scuffing detection method has been developed [12] and used to evaluate the scuffing resistance of fuel injector candidate materials. It had good agreement with industrial field experience [13].…”