The Impact of Additive Chemistry and Lubricant Rheology on Wear in Heavy Duty Diesel Engines

Increasingly severe emission legislation for heavy duty diesel engines has forced engine builders to modify their engine designs dramatically over the last few years. Some of the design modifications, such as the retardation of injection timing, resulted in higher levels of soot contamination of the crankcase lubricant. Consequently, higher wear levels were observed in the engines as a result of soot abrasion. Despite the more severe environment, there is a demand for increased engine life, which necessitates the search for ways to reduce wear.

This paper describes the results of several wear studies in diesel engines. Valve train wear in engines producing high soot levels in the crankcase oil appears to be a function of soot dispersion and anti-wear film formation. Reducing the abrasiveness of the soot agglomerates and increasing the anti-wear film formation rate both result in lower valve train wear levels. The paper also describes how a Surface Layer Activation (SLA) technique was used to study cylinder liner wear in a diesel engine. The first part of this study was focused on the impact of additive dosage. Increasing the levels of dispersant and anti-wear additive resulted in a liner wear reduction. A follow-up SLA study evaluated the impact of soot level, additive chemistry, and lubricant rheology. Higher levels of soot contamination clearly increased the liner wear relative to non-contaminated oil. The impact of the lubricant's rheo-logical properties appeared to be at least as important as the additive chemistry.