Effect Of Engine Soot On The Wear And Friction Performances Of Lubricating Oil

In recent years, diesel engine manufacturers had to adopt new engine technology withstrict regulation releasing, such as electric common rail, waste gas circulation (EGR)system and so on. The application of these technology produced more soot particles duringdiesel engine operation. Although more soot was discharged through the engine exhaustpipe, but higher contents of soot still remained in diesel engine oil. Through the dieselengine combustion process, a part of soot particles were expelled from the atmosphere aftergenerated, the other part were absorpt in the engine oil. Relevant literature pointed out thatthe oil containing soot will generate obvious wear in the engine. In this thesis the effect ofsoot on the antifriction and antiwear property of different lubrication and wear mechanismwere explored, to understand the engine soot internal area, to help predict the wear modeldevelopment of future engine friction parts design.(1) Soot decreased antifriction property of32~#oil. Soot was easy to agglomeratewithout dispersant, to block the oil flow, to increase oil shear force, friction coefficient rosefrom0.055to0.075. The influence of the soot amounts on the antiwear property of32~#oilwas dependent on the load change. When load was100-200N, the influence was minimum.When the amount of soot was more than6%,(147N,1450rpm)wear of the steel balldiameter (WSD) variation was no longer obvious. Using scanning electron microscope(SEM) the steel ball surface morphology was observed. Wider ravines in the ball surfacethat added carbon black was viewed. Local areas had gelling signs, and carbon blacksubsidence in the ravines was found.(2) Soot impacted on the antifriction of15W/40CD oil very seriously. Along withcarbon black contents increased, the WSD of15W/40CD oil had ascending tendency, butthe friction coefficient change was not obvious. The effect of soot on the antifriction andantiwear property of lubrication was related to the physical and chemical properties of theoil itself and the additives. Energy Dispersive Spectrometer (EDS) observed that carbonblack hindered the formation of boundary films. The experimental results showed that ZDDP film adsorption by carbon black was not found.(3) Under experimental conditions of the piston ring-cylinder bore bench test, Sootdecreased antifriction property of lubrication. When the contents of carbon black was2%,oil surface temperature rose to about50℃rapidly, anti-wear film was weaken. However,carbon black of high graphitization degree has some of the thermal conductivity andabrasion resistance. The Raman spectra measurement showed that the carbon structure ofthe friction surface had a higher degree of carbon graphitization in4wt%carbon black,thatcaused temperature decreased. In the experimental conditions the anti-wear layer wasweaken by carbon black, but mixing layer graphite structure in the friction surface alsoreduced wear.(4) Oil viscosity has a nonlinear grow during the soot amount increasing, and oilviscosity increased one times when8%carbon black contents. The main soot-wearmechanism is abrasive wear, but under different lubrication states, the impact of carbonblack amount on antifriction and antiwear property of lubrication was also different. Alongwith soot level in the lubricant enhanced, the weakening of the anti-wear layer will appearon the contact surface, this would deepen the further wear.