热冲击循环台架试验对气体发动机润滑油性能影响规律研究

Effect of Thermal Shock Cycle Bench Test on the Performance of Gas Engine Lubricant

气体发动机与传统燃油发动机相比具有更低的二氧化碳排放、无硫氧化物和颗粒物排放等优势,成为内燃机的研究热点之一.本文中研究了热冲击循环台架试验前后气体发动机润滑油理化性能、摩擦学性能和抗氧化性能等的变化规律.研究发现热冲击循环台架试验后气体发动机润滑油的黏度、色度和碱值等理化性能出现不同程度的劣化,其中碱值下降幅度超过75%,油品的抗氧化性能也出现大幅降低.电感耦合等离子光谱分析(ICP)发现,热冲击过程中发动机的磨损主要集中在富含Fe、Cr等元素的活塞环/缸套与凸轮/挺杆等零部件.SRV摩擦磨损试验表明台架试验后气体发动机润滑油的减摩与抗磨损性能均严重劣化,其中摩擦系数升高26%,磨损体积增大62倍,我们认为试验后油品摩擦学性能的下降主要是由于试验过程中二烷基二硫代磷酸锌(ZDDP)持续消耗以及烟炱等颗粒的产生导致油品不能在摩擦表面形成完整连续的边界润滑保护膜所致.

Gas fuel is considered to be the most competitive alternative fuel for heavy vehicles due to its rich reserves,easy exploitation and low price.Gas engines offer advantages such as lower CO2 emissions,no sulfur oxide and particulate emissions compared with traditional fuel engines,and have become one of the research hotspots for internal combustion engines.Thermal shock test is an important means of engine reliability test,which makes the whole engine and its parts fatigue rapidly by means of fast alternating cold and hot.This paper investigates the changes in the physical and chemical properties,tribological properties and anti-oxidation properties of gas engine oil before and after the thermal shock cycle bench test.The gas engine used in the test is WP12NG460HPDI developed by Weichai Power Co,Ltd.The oil used in the test is 10W-40 gas engine lubricating oil,and the cycle of thermal shock is 8000.It was found that the physicochemical properties of gas engine lubricants,such as viscosity,color,and base number,were deteriorated to some degree after the thermal shock cycle bench test,with the base number declined by over 75%,this was caused by the acidic substances produced during the neutralization and oxidation process of the detergent in the lubricating oil.In addition,pressurized differential scanning calorimeter(PDSC)was used to test the oxidation stability of gas engine lubricating oil before and after the test.It was found that due to the consumption of antioxidants,zinc dialkyl dithiophosphates(ZDDP)and oxidation by-products in the oil,the oxidation resistance of the oil also decreased significantly,the incipient oxidation temperature decreased by 62℃,and the oxidative induction time decreased to 9%of the original oil.Inductively coupled plasma spectroscopy(ICP)analysis revealed that engine wear during thermal shock was mainly found in moving parts such as piston rings/cylinder liners and cams/tappets which were rich in elements such as Fe and Cr.The continuous consumption of ZDDP was found during the experiment.SRV friction and wear experiments showed that the friction reduction and anti-wear performance of gas engine lubricating oil were seriously deteriorated after the bench test,in which the friction coefficient was increased by 26%and the wear volume was increased by 62 times.The wear scar surfaces lubricated by gas engine lubricating oil and thermal shock cycle bench test oil were observed by SEM.The wear scar on the surface lubricated by the original oil was regular and smooth,and no obvious wear or furrow was found on the surface.It can be seen from the EDS test results of the wear scar surface that the surface contains high abundance of Zn,P and S elements,which indicated that under the boundary test conditions,the anti-wear additive in the oil fully reaction on the contact surface,effectively reducing wear.Comparatively,the area of wear under oil after the test increased significantly,and there was obvious furrow wear in the wear marks due to insufficient lubrication.We believed that the deterioration of the tribological performance of the oil after the test was mainly due to the continuous consumption of zinc dialkyl dithiophosphate(ZDDP)and the generation of soot and other particles during the experiment,which resulted in the failure of the formation of a complete and continuous boundary lubrication protective film on the rubbing surface.The above work had a certain reference value for the research,development and application of special lubricating oils for gas engines.