汽油润滑性研究 V.汽油的弹性流体润滑性能

STUDY ON THE LUBRICITY OF GASOLINE FUELS Ⅴ. Elastohydrodynamic behaviour of gasolines

汽油模型化合物的高频往复试验机 ( HFRR)试验表明 ,汽油主成分的粘度对磨损的影响可能比其化合物类型的影响还要大。这可能反映了 HFRR试验中粘度对汽油弹性流体润滑膜的形成的贡献。为了进一步研究汽油的润滑行为 ,测量了汽油及 MTBE的弹流润滑牵引力和油膜厚度 ,考察作为粘度最低的液体燃料的汽油生成的弹流膜究竟有多薄 ,以及如何由弹流润滑向边界润滑转变。结果表明 ,在高速下汽油、MTBE及柴油的弹流行为均遵循 Hamrock-Dowsen公式 ,而在低速下汽油的弹流膜极薄 ,在薄膜润滑区其弹流行为明显偏离理论直线。微牵引力试验台架试验表明 ,柴油的弹流润滑行为与十六烷和润滑油相似 ,而汽油和 MTBE则有很大的不同。在固定滑滚比下 ,汽油和 MTBE在低滚动速度下的摩擦系数很高 ,但在很高速度下的摩擦系数却降到比柴油和矿物润滑油更低的水平。可变滑滚比试验表明 ,在线性区 ,汽油的摩擦系数对滑滚比的增加十分敏感。对于汽油和MTBE,由于粘度太低以及目前的牵引力试验台滚动速度的限制 ,无法进入全膜润滑区 ,因此无法得到完整的Stribeck曲线。

Wear measurements using model gasolines revealed that the HFRR wear depends more strongly on viscosity than on chemical type of the main gasoline components This is probably because of the contribution of viscosity to EHD film thickness in the HFRR test To make further progress in understanding gasoline lubricating behaviors, EHD traction and optical film thickness measurements of gasolines and MTBE in point contacts were carried out and compared with those of diesel fuels and hexadecane Research is directed to understand how thin the films will be formed by gasoline fuels, and how is the transition from elastohydrodynamic to boundary lubrication It was found in ultra thin film measurement that at high speed, the EHD behaviour of gasolines, MTBE, and diesel fuels obeys Hamrock Dowson theory At low speed, gasolines give very thin films and show significant boundary film formation Mini traction machine (MTM) test further revealed that diesel fuels exhibited EHD behaviors similar to that of hexadecane and other lubricants, but gasolines gave EHD Stribeck curves and traction curves significantly different from those of lubricants Fixed slide roll ratio (SRR) traction tests showed that gasolines and MTBE gave high friction coefficient at low rolling speed and that it was not possible to reach full EHD condition even at much higher entrainment speed Variable SRR traction test revealed that in the linear region, traction coefficient was very sensitive to the increase of SRR, and at high SRR, traction coefficient increased Results suggest that the Stribeck curves of gasolines and MTBE obtained in this study are incomplete Due to their extremely low viscosity and the rolling speed limitation of the current MTM test device, it was not possible to enter the full fluid film region