A Boundary Lubrication Model and Experimental Study Considering ZDDP Tribofilms on Reciprocating Friction Pairs

Effect of an Aftermarket Additive in Powertrain Wear and Fuel Consumption of Small-Capacity Motorcycles: A Lab and Field Study

“…As shown by Dohner et al [24], new motorcycle oil formulation may cause clutch slippage, severe gear wear and other issues that reduce overall performance. In addition, the incorporation of additives into the fully formulated oil might change its performance due to mutual interactions between the additives [9,12,18,23]. The synergistic and competitive effects among additives is a major tribology field of research since the wear resistance provided by lubricants is not always directly correlated with an increase in antiwear additives content or friction reduction [18,19,22,23].…”

“…In addition, the incorporation of additives into the fully formulated oil might change its performance due to mutual interactions between the additives [9,12,18,23]. The synergistic and competitive effects among additives is a major tribology field of research since the wear resistance provided by lubricants is not always directly correlated with an increase in antiwear additives content or friction reduction [18,19,22,23]. In fact, the presented surface analysis did indicate tribofilm formation with different compositions when MC was added to the engine oil (Figures 6-10), suggesting the MC changes the actuation of the mechanisms of the commercial 10W-30.…”

“…The results obtained with MC showed slight friction reduction in laboratory tribotests (Figure 3), as well as fuel economy increments (Figure 11) without compromising gear protection (Table 9, Figure 10) and clutch operation. The mechanisms behind the observed performance are unknown but might be related to distinct tribofilm formation and wear reduction, which allow components to perform at optimum conditions [18,22,23]. The average improvement in fuel economy of ~2.5% for both oil drain intervals (1000 km-Regime 0 to 1k, 10k to 15k, and 3000 km-Regime 1k to 10k, Figure 11) is assuredly relevant for Motorcycle A [13,24].…”

“…Although lab tests (pin-on-disk, four-ball, copper corrosion, etc.) provide evidence and insights into lubricants' performance, it is challenging to evaluate engine conditions in the laboratory [18,22,23]. In fact, it has been shown that elaborate tests fail to reproduce the tribofilms observed in engine parts [18,21].…”

“…Furthermore, boundary lubrication (Λ < 1), high contact pressure, and sliding motion across the texture direction are ideal conditions to test additives' performance [20,21,27], particularly anti-wear and extreme pressure additives, which are the main constituents of most aftermarket additive packages for engine oils [1,9]. Under these conditions, metal contact under higher stress occurs, leading to asperity deformation and wear, which in turn trigger the additives [23]. Tables 1 and 2 summarize the main lubricant and material properties, respectively.…”