Friction performance of MoDTP and ester‐containing lubricants between CKS piston ring and cast iron cylinder liner

Abstract

The friction performance of MoDTP in the existence of ester was investigated. Tribological experiments were performed on reciprocating test rig between CKS piston ring and cast iron cylinder liner. Experimental results show that ester concentration is a key factor that influences the performance of MoDTP, the competitive effects between MoDTP and ester also vary with test temperature and load, and the "V" shape friction coefficient curve is caused by the change in friction surface states. During friction, when the surface roughness decreased and liner surface is covered by the friction layer, fresh metal is less likely to expose to lube oil, which reduces the activity of MoDTP in the existence of high concentration ester. | INTRODUCTIONEngine lube oil has been designed as a complex mixture, which is mainly composed of base oil and various functional additives. Among different additives, friction modifier (FM) is important for engine lube oil. FM is the component that reduces the friction coefficient on the friction surface. A better friction reduction performance will improve the energy efficiency and emission reduction performance.Basically, there are four main classes of FM additives applied to liquid lubricants, which are organic FMs, organic-molybdenum compounds, functionalized polymers, and dispersed nanoparticles.1 Among these additives, organic FMs (OFM) and organic-molybdenum compounds are most widely used in modern engine lube oil. Synthetic ester is typical OFM, which contain polar group and form adsorption film on friction surface. Different from OFM, organic-molybdenum compounds will form tribo-chemical film on the metal surface, reduce friction coefficient, and increase fuel economy. MoDTC/MoDTP have been used as FM for a long time.12,13 Significant friction reduction performance was shown in engine performance. Mistsuaki et al developed engine oil with excellent fuel economy performance. The low friction formulation contains molybdenum compound and phosphorus extreme-pressure agent. The fuel economy can improve up to 7% compared with commercial oil. 14 Grossiord et al studied the friction reduction mechanism of MoDTP; it is found that the MoDTP tribofilm is mainly composed of an amorphous phosphate glass containing flexible and highly dispersed MoS 2 single sheets. 15Martin et al investigated the friction reduction film formed by MoDTP in ultra high vacuum tribometer (UHV). 16Results indicate that molybdenum disulphide (MoS 2 ) contributes to the friction reduction performance, and the metal phosphate glass is responsible for the anti-wear action. The tribochemical reaction of MoDTP can be separated into 2 steps. Firstly, the phosphate reacted with iron oxide. Secondly, the nascent iron surface reacted with sulfide species, which decrease the friction coefficient. 17,18When MoDTP mixed with other additives, most studies focus on the performances in the presence of MoDTC, zinc dithiophosphate (ZnDTP an interesting phenomenon is found that the friction coefficient drops down first and is fol...

Design and experimental development of a new electronically controlled cylinder lubrication system for the large two-stroke crosshead diesel engines

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Preparation and performance evaluation of an ester‐bridged antioxidant used as multifunctional additive in ester oil

“…Owing to their excellent properties such as high thermal-oxidative stability, low-temperature fluidity, outstanding viscosity-temperature performance and lubricating properties, synthetic esters have attracted considerable interest. [1][2][3][4] However, with the rapid advancement of equipment, synthetic ester oils fail to satisfy operations demand under increasingly harsh working conditions, especially the high temperature of the lubrication system. 5,6 The high-temperature status inevitably caused rapid thermal oxidation of the synthetic ester oils to form some degradation products and/or polymerised large molecules; consequently, the harmful substances deteriorate their comprehensive performance, resulting in a short service life of the lubricants.…”

Friction reduction mechanism of glycerol monooleate-containing lubricants at elevated temperature - transition from physisorption to chemisorption

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