Triboligical Behavior And Friction-induced Structure Change Mechanisms Of Biofuel Soot Particles

Due to the low sulfur, eco-friendly and renewable characters, the biomass pyrolysis fuel can be regarded to replace the fossil fuel as an alternative fuel. The biomass fuel could be used in a diesel engine directly via a micro-emulsified method. At present, the exhaust emission performance of diesel engine fueled with the biomass fuel has been focused extensively. However, it is shown that the limited research for the morphology, structure and composition of biomass fuel soot particles (BS), and the tribological behavior of biomass fuel soot particles is also vacant.The composition of fuel is a key factor which decides the morphology, structure and composition of BS particles. Besides, the tribological behavior of BS particles depends on their physical and chemical properties that are related with the using life of engine tribological parts. In the present thesis, the morphology, structure and composition of BS particles were firstly further studied by a series of modern analysis technologies, and then the tribological behavior of BS particles was investigated using a four-ball tribometer. It was detailed with the structure variation of BS particles during rubbing by an end-face tribometer. The experimental results not only help the proper application of biomass fuels in diesel engine, but also understand the soot-induced wear of diesel engine well.BS particles were prepared by the combustion of micro-emulsified biomass fuel (5wt%emulsified refined biomass pyrolysis fuel) using a self-manufactured soot trapper. The morphology, structure and composition of BS particles were investigated by comparison those of carbon black particles (CB) which were selected to simulated the engine fuel soot particles. The results showed that the average particle diameter of BS particles was approximate30-50nm, and the carbon black was approximate30-40nm. The agglomerate dimension of BS particles was25μm, and the agglomerate dimension of carbon particles was about10μm. The degree of graphitization of BS particles (IG/ID1=0.4273) was higher than that of CB particles (IG/ID1=0.3545) with the analysis of Raman Spectroscopy. The composition of BS particles was almost same as compared to that of CB particles. The C-OH and C=C functional groups were detected on the surface of BS particles, and the acid and basic sites were higher than those of CB particles. The discrepancy between BS and CB particles was ascribed to the complex compositions of biomass pyrolysis fuel.It was investigated the effects of the content of BS particles (1,3and5wt%), load (196,296and396N) and rotation speed (1000,1200,1450and1600rpm) on the lubrication properties of liquid paraffin (LP) and fully formulated engine oil (CD SAE15W-40) using a four-ball tribometer. The results showed that the BS particles can enhance the strength of oil film. The PB value increased by38.6%when5wt%BS was added into LP. As for CD SAE15W-40, the PB value increased by29.5%in case of5wt%BS. The increase of PB values was ascribed to the increase of kinematic viscosity of oil samples. BS particles could degrade the anti-wear of lubricating oils, but promote the friction reduction. The degradation of anti-wear property of lubricating oils was ascribed to the agglomerate particles which could absorb the lubricating oil or additives resulting in the serious wear. The occurrence of depleted oil lubrication was ascribed to the dimension of BS particles was greater than that of oil film thickness. The promotion of friction reduction was ascribed to the "rolling ball" effect and BS particles took part in the formation of the boundary lubrication film when the particle dimension of BS particles was smaller than that of oil film thickness.It was found the different effects of load and rotation speed on the BS-contaminated LP and CD SAE15W-40through the four-ball tribometer. The average wear scar diameter (AWSD) increased with the increase of loads (196,296and396N) for the same levels of BS-contaminated oil samples at the same rotation speed of1450rpm. Variation in the friction coefficient for two oil samples was not regularity. What is more, the ablation was easy to be produced with the BS-contaminated oil samples under high load and rotation speed.The effects of polyisobutylene succinimide dispersant (trade name T154A) and zinc dialkyl dithiophosphate (trade name T203) on the tribological properties of3wt%BS-contaminated LP were investigated, and effect of solid catalyst TiF3particles on tribological properties of LP and CD SAE15W-40was also investigated by a four-ball tribometer. Results showed that effect of T154A on the anti-wear and anti-friction properties of BS-contaminated LP was ascribed to the dispersion role. There was a little effect of T154A on the anti-wear property of BS-contaminated LP, but there was a great effect on the anti-friction property of BS-contaminated LP. Regarded to T203, the low contents of T203could strengthen the anti-wear and anti-friction properties of BS-contaminated LP which was ascribed to the BS particles absorb ZDDP molecular to take part in the formation of boundary lubrication film. However, in case of LP with higher content of T203, the serious wear took place which was ascribed to the increase of agglomerate diameter of BS particles. TiF3can enhance the strength of oil film for BS-contaminated LP. The PB value increased by46.4%from560N to820N when3wt%BS particles was added into LP. However, the BS particles had a little effect on the variation of PB value. The TiF3can enhance their anti-wear and friction reduction of LP and CD SAE15W-40which was ascribed to the active elements Ti, C and F contributed to the formation of boundary lubrication film.Finally, the structure variation of BS particles was investigated using an end-face tribometer under the different loads (1000,1500and2000N) and rotation speeds (196,296and396rpm) conditions. Both effects of TiF3and FeF3on the structure variation of BS particles were also investigated. Results showed that both TiF3and FeF3could enhance the anti-wear and friction reduction of BS-contaminated LP and CD SAE15W-40. The above efficacy decreased when the load increased to2000N for two oil samples which was consistent to the four-ball experimental results. Friction induced the variation in the structure of BS particles on the wear zones. Low load and rotation speed had a little effect on the structure variation of BS particles, and high load and rotation speed had a great effect on the structure variation of BS particles. The structure variation of BS particles showed the amorphous carbon content (R3) decreased, the order graphene content (ID2/IG’ increased and the surface defect sites of graphene (ID1/IG,) increased on the wear zones. The structure variation of BS particles mechanism was ascribed to the friction induced the peeling of outer layer of BS particles on the wear zones resulting in the formation of the better boundary lubrication film. The friction heat can cause the transform between Csp3and Csp2hybrid carbon each other. TiF3and FeF3have the varying degrees of impact on the structure variation of BS particles on the wear zones. TiF3and FeF3could promote degree of graphization of BS particles on the wear zones at some conditions. Friction induced the structure variation of BS particles on the wear zones which depended on the friction heat and initial structure of BS particles.