The Effects of Sulfated Ash, Phosphorus and Sulfur on Diesel Aftertreatment Systems - A Review

Bodek, Kristian M.; Wong, Victor

doi:10.4271/2007-01-1922

Cited by 40 publications

(19 citation statements)

References 37 publications

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“…In the 1980s, following the widespread introduction of exhaust aftertreatment systems in road vehicles, it was found that these systems' useful life was limited by components originating from the fuel and lubricant, in particular sulphated ash, phosphorus and sulphur (SAPS) [2]. Refractory sulphated ash particles such as zinc and calcium sulphates accumulated in filters and the narrow channels of catalyst monoliths, phosphorus oxides formed coatings on catalyst surfaces, while sulphur poisoned the catalysts themselves [3]. In response to this, a series of engine oil specifications were introduced between 1994 and 2005 that progressively reduced the permitted maximum level of SAPS precursors in engine oils [1].…”

Section: Zddpsmentioning

confidence: 99%

Tribofilm Formation, Friction and Wear-Reducing Properties of Some Phosphorus-Containing Antiwear Additives

Luiz

Spikes

2020

Tribol Lett

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The film-forming, friction and wear properties of a range of model and commercial ashless P and P/S antiwear additives have been studied. A method has been developed for removing the tribofilms formed by such additives in order to effectively quantify mild wear. In general the P/S additives studied formed thinner tribofilms but gave lower wear than the S-free P ones. In extended wear tests, three P/S additives gave wear as low, or lower, than a primary zinc dialkyldithiophosphate (ZDDP). For almost all lubricants tested the wear rate measured in short tests was considerably higher than that in long tests due to the greater contribution of running-in wear in the former. This highlights the importance of basing antiwear additive choice on reasonably long tests, where running-in becomes only a small component of the wear measured. It has been found that for both P and P/S ashless additives the addition of oil-soluble metal compounds based on Ti and Ca boosts tribofilm formation and can lead to very thick films, comparable to those formed by ZDDP. However, this thick film formation tends to be accompanied by an increase in mixed friction and also does not appear to reduce wear but may even increase it.

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Section: Zddpsmentioning

confidence: 99%

Tribofilm Formation, Friction and Wear-Reducing Properties of Some Phosphorus-Containing Antiwear Additives

Luiz

Spikes

2020

Tribol Lett

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“…Investigations of ash composition have identified inorganic additives in diesel engine lubricants as the primary contributors to ash build-up in the DPF, when fuel-borne catalysts are not used [4,5,6]. These additives primarily consist of calcium-and magnesium-based detergents as well as zinc-based anti-wear additives.…”

Section: Introductionmentioning

confidence: 98%

Characteristics and Effects of Lubricant Additive Chemistry on Ash Properties Impacting Diesel Particulate Filter Service Life

Sappok¹,

Rodriguez²,

Wong³

2010

SAE Int. J. Fuels Lubr.

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Ash accumulation in diesel particulate filters, mostly from essential lubricant additives, decreases the filter's soot storage capacity, adversely affects fuel economy, and negatively impacts the filter's service life. While the adverse effects of ash accumulation on DPF performance are well known, the underlying mechanisms controlling these effects are not. To address these issues, results of detailed measurements with specially formulated lubricants, correlating ash properties to individual lubricant additives and their effects on DPF pressure drop, are presented.Investigations using the specially-formulated lubricants showed ash consisting primarily of calcium sulfates to exhibit significantly increased flow resistance as opposed to ash primarily composed of zinc phosphates. Furthermore, ash accumulated along the filer walls was found to be packed approximately 25% denser than ash accumulated in the channel end-plugs. Both lubricant chemistry and the filter's thermal history were correlated to ash packing density and distribution following DPF post-mortem analysis.In this study, a heavy-duty diesel engine was utilized in conjunction with a rapid lubricant degradation and aftertreatment ash loading system, which has been validated in detail previously against engine-out exhaust and ash accumulated in the field. Results with specially-formulated lubricants containing only calcium-based detergents, only ZDDP additives, and conventional CJ-4 oils were compared utilizing an aging cycle simulating 180,000 miles of on-road use. On-engine DPF performance evaluation, coupled with subsequent filter post-mortem analysis, clearly indicate the manner in which lubricant chemistry and exhaust conditions influence ash properties and DPF performance.The results of this work demonstrate the effects of individual lubricant additives on the resulting ash properties controlling DPF pressure drop, including ash packing density and permeability. Results will be useful in optimizing the design of the combined engine-aftertreatment-lubricant system for future diesel engines, balancing the requirements of additives for adequate engine protection with the requirements for robust aftertreatment systems.

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“…3 However, ZDDP contains high levels of zinc, sulfur, and phosphorus, which are known to degrade exhaust aftertreatment devices. 4 Consequently, zinc-free, low-sulphur, and lowphosphorus alternatives to ZDDP have long been sought. 5 Some promising examples include phosphate esters and thiophosphate esters.…”

Section: Introductionmentioning

confidence: 99%

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

et al. 2020

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Phosphate esters have a wide range of industrial applications, for example in tribology where they are used as vapour phase lubricants and antiwear additives. An atomic-level understanding of phosphate ester tribofilm formation mechanisms is required to improve their tribological performance. A process of particular interest is the thermal decomposition of phosphate esters on steel surfaces, since this initiates polyphosphate film formation. In this study, reactive force field (ReaxFF) molecular dynamics (MD) simulations are used to study the thermal decomposition of phosphate esters with different substituents on several ferrous surfaces. The ReaxFF parameterisation was validated for a representative system using density functional theory (DFT) calculations. During the MD simulations on Fe3O4(001) and α-Fe(110), chemisorption interactions between the phosphate esters and the surfaces occur even at room temperature, and the number of molecule-surface bonds increases as the temperature increases from 300 to 1000 K. Conversely, on hydroxylated, amorphous Fe3O4, most of the molecules are physisorbed and some desorption occurs at high temperature. Thermal decomposition rates were much higher on Fe3O4(001) and particularly α-Fe(110) compared to hydroxylated, amorphous Fe3O4. This suggests that water passivates ferrous surfaces and inhibits phosphate ester chemisorption, decomposition, and ultimately polyphosphate film formation. For the alkyl phosphates, thermal decomposition proceeds mainly through CO and C-H cleavage on Fe3O4(001). Aryl phosphates show much higher thermal stability, and decomposition on Fe3O4(001) only occurs through P-O and C-H cleavage, which require very high temperature. The onset temperature for CO cleavage on Fe3O4(001) increases as: tertiary alkyl < secondary alkyl < primary linear alkyl ≈ primary branched alkyl < aryl. This order is consistent with experimental observations for the thermal stability of antiwear additives with similar substituents. The simulation results clarify a range of surface and substituent effects on the thermal decomposition of phosphate esters on steel that should be helpful for the design of new molecules with improved tribological performance.

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The Effects of Sulfated Ash, Phosphorus and Sulfur on Diesel Aftertreatment Systems - A Review

Cited by 40 publications

References 37 publications

Tribofilm Formation, Friction and Wear-Reducing Properties of Some Phosphorus-Containing Antiwear Additives

Tribofilm Formation, Friction and Wear-Reducing Properties of Some Phosphorus-Containing Antiwear Additives

Characteristics and Effects of Lubricant Additive Chemistry on Ash Properties Impacting Diesel Particulate Filter Service Life

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

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