Investigation on soot dispersant properties and wear effects in the boundary lubrication regime

Diatto, Paolo; Anzani, Marilena; Tinucci, L.; Tripaldi, Giuseppe; Vettor, A.

doi:10.1016/s0167-8922(99)80099-6

Cited by 13 publications

(4 citation statements)

References 20 publications

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“…Jao et al reported that soot leads to engine wear via an abrasive wear mechanism. Moreover, the same workers showed that higher levels of abrasive contaminants within the oil inhibits boundary film formation. − This excessive build-up of soot particles in engine oil is highly undesirable because it accelerates engine wear, which ultimately leads to lower fuel efficiency and reduced engine lifetimes. − Fortunately, this soot-related wear problem can be mitigated by the addition of various copolymers to engine oil formulations. ,− Such copolymers can act as dispersants and confer steric stabilization, thus maximizing the degree of dispersion of the diesel soot. However, genuine diesel soot is prohibitively expensive for optimization studies because it can only be generated by running an engine over an extended period under suboptimal conditions.…”

Section: Introductionmentioning

confidence: 99%

Is Carbon Black a Suitable Model Colloidal Substrate for Diesel Soot?

et al. 2015

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Soot formation in diesel engines is known to cause premature engine wear. Unfortunately, genuine diesel soot is expensive to generate, so carbon blacks are often used as diesel soot mimics. Herein, the suitability of a commercial carbon black (Regal 250R) as a surrogate for diesel soot dispersed in engine base oil is examined in the presence of two commonly used polymeric lubricant additives. The particle size, morphology, and surface composition of both substrates are assessed using BET surface area analysis, TEM, and XPS. The extent of adsorption of a poly(ethylene-co-propylene) (dOCP) statistical copolymer or a polystyrene-block-poly(ethylene-co-propylene) (PS-PEP) diblock copolymer onto carbon black or diesel soot from n-dodecane is compared indirectly using a supernatant depletion assay technique via UV spectroscopy. Thermogravimetric analysis is also used to directly determine the extent of copolymer adsorption. Degrees of dispersion are examined using optical microscopy, TEM, and analytical centrifugation. SAXS studies reveal some structural differences between carbon black and diesel soot particles. The mean radius of gyration determined for the latter is significantly smaller than that calculated for the former, and in the absence of any copolymer, diesel soot suspended in n-dodecane forms relatively loose mass fractals compared to carbon black. SAXS provides evidence for copolymer adsorption and indicates that addition of either copolymer transforms the initially compact agglomerates into relatively loose aggregates. Addition of dOCP or PS-PEP does not significantly affect the structure of the carbon black primary particles, with similar results being observed for diesel soot. In favorable cases, remarkably similar data can be obtained for carbon black and diesel soot when using dOCP and PS-PEP as copolymer dispersants. However, it is not difficult to identify simple copolymer-particle-solvent combinations for which substantial differences can be observed. Such observations are most likely the result of dissimilar surface chemistries, which can profoundly affect the colloidal stability.

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Section: Introductionmentioning

confidence: 99%

Is Carbon Black a Suitable Model Colloidal Substrate for Diesel Soot?

et al. 2015

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“…Soot promotes oil degradation that in turn promotes wear [5]. 4 Soot competes with antiwear additives for adsorption at metal surfaces [6] 5 Soot induces a transition of the metal surfaces from anti-wear Fe 3 O 4 to prowear FeO [7] 6 Corrosive wear is caused by increased SO x re-circulated by EGR, and there is a correlation between soot level and SO x [8] 7 Soot accumulates in the contact inlet and restricts oil supply [9]- [11] The first proposed mechanism for the detrimental effect of soot on wear was by Rounds, who suggested that soot particles adsorb ZDDP or its active intermediates, thereby preventing these forming an effective antiwear film [2]- [4]. However in the Discussion to [2] it was noted that removal of most of the soot from an oil restored the wear properties back to those of the fresh oil, which would not be expected if ZDDP were removed by the soot.…”

Section: Introductionmentioning

confidence: 99%

Antagonistic Interaction of Antiwear Additives and Carbon Black

2009

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SUMMARYIt is well known that the presence of soot in engine oils can lead to an increase in wear of engine parts. This is a growing problem as soot levels in diesel engine oils are rising due to a combination of extended drain intervals and the various methods employed to reduce NOx formation such as retarded ignition and exhaust gas recirculation.Several different mechanisms have been proposed by which soot might lead to an increase in wear in mixed lubrication conditions, of which the most widely favoured is abrasion by soot, either of the rubbing metallic parts in engines or of the antiwear additive films formed on rubbing metal surfaces.In this study it is shown that the combination of mixed alkyl ZDDP and carbon black (used as soot surrogate) is strongly antagonistic in terms of wear. In a lubricant containing carbon black, the presence of ZDDP leads to considerably more wear than if ZDDP is left out. A similar, though less severe antagonism is also seen with primary ZDDP and other antiwear and EP additives. By varying the lubricant film thickness it is shown that the effect of carbon black in ZDDP-containing oils is to promote wear up to quite thick hydrodynamic film conditions, approaching the secondary carbon black particle size.It is proposed that the antagonistic wear effect results from a corrosion-abrasive mechanism in which the reaction film formed by antiwear additive and rubbing metal surface is very rapidly and continually abraded by carbon black. At most carbon black concentrations, wear rate then becomes controlled by the rate of initial antiwear additive film formation, which for secondary ZDDP is very rapid, rather than by the kinetics of the abrasive process.From this understanding, strategies for reducing the impact of engine soot on wear can be deduced.

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“…The increasing request by laws and customers for abatement of pollutant emissions has also favored the development of several technologies to eliminate soot, mostly produced by obstruction of injectors and accumulation of carbon particles in manifolds [4]. Soot particulate emissions are known to reduce wear and fatigue resistance of diesel engine components due to the interactions between soot, metal and lubricant additives or among soot particles [5][6][7][8]. Recently, modeling and simulation in engine designing have emerged as important tools for optimizing and predicting wear of mechanical systems under variable load and/or sliding speed.…”

Section: Introductionmentioning

confidence: 99%