| As one of the most important friction pair in diesel engine,the work conditions of cast iron-cylinder liner are terrible and lubrication conditions change periodically with the rotation of crank shaft.Friction modifiers can form regular,closed poly-molecular layers on the metal surface.The molecules in the outer adsorption layer adsorbed loosely,which can be sheared easily,so that they can reduce friction coefficient efficiently.With a reduced friction coefficient,we can save fuel,improve economy and lower down mechanical lost.As a kind of green friction modifier,glycery monooleate has excellent friction-reduction performance.However,when focus on friction performance of cylinder liner and piston ring,there are little researches relate to the friction-reduction performance and mechanism of glycery monooleate..Therefore,in order to lower down friction loss and improve mechanical efficiency,it is of great importance to research friction-reduction performance of glycery monooleate.In this paper,contraposition reciprocating test rig was used to study the friction-reduction performance of glycery monooleate under boundary lubrication,and cast iron cylinder liner and PVD piston ring are selected as friction sample.The loading is 10 MPa,the rotated speed is 200 r/min,the test time is 4 h,the work temperature changes from 70℃ to 150℃.Fluid lubrication test rig is used to study the friction-reduction performance of glycery monooleate under fluid lubrication.Molecular dynamics simulation is used to model the lubrication system.The radial distribution function,radius of gyration,temperature,stress of Fe atom walls,shear viscosity and relative concentration were analyzed.The results show that glycery monooleate has obvious friction reduction performance under boundary lubrication.When the temperature is low,the physic-adsorption ability is strong,which is the mechanism of friction reduction performance,because the functional groups are at the end of carbon chain of glycery monooleate and the structure is of straight chain.When the temperature is high,it can form chemic-adsorption films,which is the main reason of friction reduction.Carbonyl reacts with Fe,and unbounded hydroxy reacts with fractured carbon chain.Also,glycery monooleate can reduce friction under fluid lubrication.Molecular dynamics simulation shows that shear thin effect and boundary slipping are main factors to reduce friction. |
