Preparation Of Nanometer WS₂ Environmental And Energy-saving Engine Lubricating Oil And Its Properties

Along with the increasing shortage of petroleum resources, the sustaining upsurge of petroleum prices, and the policy making of gradually strict energy-saving and emission regulations around the world, energy-saving and emission reduction have become the research hotspot of auto industry. Combining with nano-tribology, this research developed nanometer WS2 green energy-saving engine lubricating oil, which is accommodated the needs of social development, and will play an important role in national resource-saving and environment-friendly society construction.In this thesis, based on the preparation of micrometer WS2 particulates by the method of W-S direct reaction,sheet nanometer WS2 particulates were prepared by the compound thining method of high power ultrasonic/spiral mixing ball-milling, whose average particle size is 95nm. The property contrast analysises between nanometer and micrometer particulates show that, nanometer WS2 particulates have better metal surface adsorption property, dispersion stability, lubricating performances and goodish thermostability. The mechanism analysises preliminarily indicate that, it's mainly through impact comminution and accessorially through friction shearing comminution and the promoter action of-OH free radicals produced by high power ultrasonic for compound thining method of high power ultrasonic/spiral mixing ball-milling to achieve the goal of ultrafine grind micrometer WS2.For the spontaneous glomeration characteristic of nanometer WS2 particulates in lubricating oil, this thesis used surface modifier SA to modify the nanometer WS2 particulates surfaces under compound action of high power ultrasonic/ball-milling stir, and the results show that the modified nanometer WS2 particulates by such method possess excellent dispersion stability in green base oil (PAO6, rapeseed oil, or PriEco3004), and when the additive amount of nanometer WS2 particulates is 2wt%, the best additive amount of SA is 0.5wt%. Mechanism analysises indicate that, compound action of high power ultrasonic/ball-milling stir can break up the nanometer WS2 agglomerations and then strengthen the surfactivity of nanometer WS2 particulates, bringing about the esterification reaction between hydroxide radicals on particulates' surfaces and carboxyl group of the modifier SA, and leading to the change of particulates' surface characteristics from hydrophilicity to lipophilicity. After surface modifying, the long carbon chains on surface can form stereo-hindrance layer, combined with solvation layer formed by lubricant molecule, to prevent nanometer particulates from aggregate, and ultimately make nanometer WS2 particulates dispered in lubricating oil stably for long time.Series of four-ball tribology tests show that,adding 2wt% nanometer WS2 particulates into green base oil PAO6 or rapeseed oil can improve the lubricating performances of base oil under each working condition such as normal temperature, high temperature, low load, high load, low speed, high speed observably, and the improving effect of nanometer WS2 particulates is better than that of nanometer MoS2 particulates or nanometer graphite particulates. And moreover, in PAO6 or rapeseed oil nanometer WS2 particulates have good compatibility with other antiwear additives such as T462A,T202, T323 and T451A, especially when confected with T462A or T202, nanometer WS2 particulates have synergistic effect.Application experiments of nanometer WS2 particulates in engine have been done on the self-designed engine simulant bench and true automobile. The results of engine simulant bench tests show that, nanometer WS2 particulates can reduce the abrasion of piston ring in engine by 27.6%, and reduce fuel consumption by 13%～28%, and decrease the contents of harmful gases such as HC, CO, NOx in tail gas respectively by 18.6%-37.6%,7.7%-14.3%,8.8%-19.7%. The results of road test indicate that, nanometer WS2 particulates can improve the service life of traditional engine lubricating oil by 1.5 times, can reduce the fuel consumption observably(by 38.50% to the greatest extent and by 16.39%to the smallest extent, and the average rate of saving fuel is 20.26%). All of tests illustrate that nanometer WS2 particulates have excellent energy conservation & emission reduction properties.This thesis investigated the auto-reparing properties of nanometer WS2 particulates ulteriorly on four-ball machine, AW-3 anti-wear machine and engine simulant bench. Results indicate that, nanometer WS2 particulates can realize the on line in-situ dynamic repair to the tiny damages on surfaces in PAO6 or rapeseed oil under normal temperature, 100℃and 200℃, but the repairing effect will become unconspicuous under low load. In addition, nanometer WS2 particulates also can reduce the surfaceness of grain wear surface or adhesive wear surface, smoothing the wear surface and avoiding abrasion from worsen, and nanometer WS2 particulates can better the appearance of piston ring's wear surface, and reduce the index of wear severity in engine, lowering engine's interior abrasion, all of which tell us that nanometer WS2 particulates also can realize good repair effect to the existed wear surface.To research the nanometer WS2 particulates'mechanisms of action in green lubricating oil, series of XPS analysises, EDS analysises and argon ion sputtering depth analysises were done. All the results indicate that, in green lubricating oil, the lubricating process of nanometer WS2 can be divided into fluid lubrication stage and mixed lubrication stage. In the former stage, nanometer WS2 particulates mainly increase the thickness of oil film and thus improve the lubrication, and moreover nanometer WS2 particulates can deposit on the friction surface during friction. In the beginning period of the latter stage, friction mainly happens in the nanometer WS2 deposition film, the nanometer WS2 particulates in deposition film occur preferred orientation distribution under the effect of friction shear force, which improves the anti-friction property of the deposition film. In the later period of the latter stage,because of the increasement of friction surface temperature,the deposited nanometer WS2 particulates are activated and transfer from abundant regions (e.g., furrow regions on grain wear surface or concave regions on adhesive wear surface) to perimeter zone, and react with metal convex body affected by tiny area high temperature and high pressure during friction, and generate nanometer FeS and nanometer FeSO4, which are affected by friction shear force and glide on the friction surface, ultimately the wear surfaces are repaired to smooth surfaces, and a compact anti-pressure/anti-wear repair layer which consists of nanometer WO3, nanometer FeS, nanometer FeSO4 and nanometer WS2 is formed, this repair layer not only prevent metal surfaces from direct touch, but also has high carrying capacity, which can limit the elastic deformation and plastic deformation caused by shear stress into the repair layer, and therefore restrain adhesive wear and contact fatigue effectively. In addition, the engine cylinder pressure analysis illustrates that, the repair layer formed by nanometer WS2 particulates on sealing face improves the tightness and increases the cylinder pressure, and then ensures more effective fuel burning, which reduces fuel consumption and emission of the harmful gases such as HC, CO and NOx.Finally, this thesis chose and mixed refined rapeseed oil, PriEco3004, PAO6 and 150BS bright stock proportionally,and added viscosity index improver T618, pour point depressant LZL803B, antioxygen L01, L115, then the green base oil with excellent combination properties was prepared.After that, nanometer WS2 particulates and modifier SA were added into green base oil and treated under the compound action of high power ultrasonic/ball-milling stir, then mixed with other functional additives, nanometer WS2 engine lubricating oil was prepared, whose viscosity meets the requirement of 15W/40 level engine lubricating oil,service properties are equivalent to SL level engine lubricating oil, and biodegradability is good. The performances contrasts with the famous domestic and overseas energy-saving engine lubricating oil show that, nanometer WS2 environmental and energy-saving engine lubricating oil has better lubricating performances and energy conservation & emission reduction properties.