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The addition of molybdenum dithiocarbamates (MoDTC) to engine oils improves the fuel economy of vehicles. This efficiency is gradually reduced with the depletion of MoDTC and zinc dithiophosphates (ZnDTP) due to oil oxidation. Recent engine oils need more antioxidants than before to fulfill the requirements demanded for oxidation stability, which may influence the duration of friction reduction. Because of this fully formulated oils containing MoDTC were aged and evaluated with engine tests to determine the effect of ashless antioxidants type on friction reduction durability. It revealed that friction reduction durability was strongly influenced by various kinds of antioxidants and hindered phenol (PHE) suppressed the extinction of MoDTC and ZnDTP to retain a low friction property that was two times more stable than diphenylamine. Otherwise, high oxidation stability did not necessarily relate to a long duration of friction reduction.

Emission regulations for diesel-powered vehicles have been gradually tightening. Installation of after-treatment devices such as diesel particulate filters (DPF), NOx storage reduction (NSR) catalysts, and so on is indispensable to satisfy rigorous limits of particulate matter (PM) and nitrogen oxides (NOx). Japan Clean Air Program II Oil Working Group (JCAPII Oil WG) has been investigating the effect of engine oil on advanced diesel after-treatment devices. First of all, we researched the impact of oil-derived ash on continuous regeneration-type diesel particulate filter (CR-DPF), and already reported that the less sulfated ash in oil gave rise to lower pressure drop across CR-DPF [1]. In this paper, impact of oil-derived sulfur and phosphorus on NSR catalyst was investigated using a 4L direct injection common-rail diesel engine with turbo-intercooler. This engine equipped with NSR catalyst meets the Japanese new short-term emission regulations.

Phosphorus levels in engine oil are assumed to be lower than other oils because they cause emission catalyst poisoning. It mainly originates from zinc dithiophosphate (ZnDTP), which is an essential additive for engine oils as an antiwear agent and antioxidant. The reduction of ZnDTP in engine oils will have a great influence on this. On the other hand, fuel efficiency in vehicles is also an important issue and molybdenum dithiocarbamate (MoDTC) is very effective in improving fuel economy. Oils containing MoDTC with phosphorus content from 0.00% to 0.08% were tested using several engine and bench tests to evaluate their antiwear properties, oxidation stability and friction reduction durability. In these tests, oils containing more than 0.02% of phosphorus were able to fulfill ILSAC GF-4 performance standards with optimized additive formulation. MoDTC helped to replace several functions of ZnDTP in low phosphorus engine oils.

The addition of molybdenum dithiocarbamate (MoDTC) to engine oil improves the fuel consumption of vehicles. However, this is also widely known to cause deposit accretion in the Thermo-Oxidation Engine Oil Simulation Test (TEOST 33C). Thus the effects of additives on TEOST 33C and elemental analysis of the deposits were evaluated to analyze the deposit formation mechanism in TEOST 33C by engine oil containing MoDTC. An elemental analysis of deposits revealed that most consisted of carbide and contained small amounts of molybdenum compounds. Deposit accretion was not caused due to the remarkable increase of compounds derived from MoDTC. It was assumed that they acted as a decomposition catalyst under high temperature and induced carbide to be deposited.