Experimental Study On Failure Degradation Process Of Diesel Engine Oil Based On Grey System Theory

Diesel engine is the main power source of all kinds of ships.With the increase of diesel engine power,the increase of operating temperature and the extension of service cycle,higher technical requirements are put forward for the lubrication and oxidation stability of diesel engine oil.Due to the pollution of high temperature,high pressure,metal catalysis,combustion by-products and abrasives,the failure and degradation of diesel engine oil are inevitable.The internal mechanism of failure and degradation of diesel engine oil is very complex,including oxidation,nitrification,vulcanization,pollution(fuel dilution,moisture,grinding debris),etc.The failure and degradation of diesel oil will affect many physical and chemical properties,especially tribological properties,including the change of viscosity,the decline of metal protection properties,the deterioration of tribological properties and the decrease of oxidation life.The purpose of this paper is to conduct an experimental study on the failure degradation process of diesel engine oil,and to explore the influence of the degradation process on the physicochemical and tribological properties and the corresponding mechanism by applying the grey system theory.This is of great significance to the fault diagnosis of active diesel engines and the development of long-life diesel engine oil in the future.The effects of single physical and single chemical action on the performance of diesel engine oil were studied by simulated fuel dilution test and high temperature oxidation test.In the simulation test,the grey correlation degree values of fuel dilution with acid value,alkali value and oxidation induction period were the highest,which were 0.84,0.86 and 0.84 respectively.When the diesel content reaches 10%,the kinematic viscosity of 40? decreases by 31.3%,far exceeding the oil change index(20%).The flash point of the oil sample opening of 20%dilution concentration is only 126?,lower than the oil change index of diesel engine oil(130?).Low concentration(?10%)of fuel dilution has little effect on the tribological properties of diesel engine oil under boundary lubrication conditions,and the friction coefficient and wear amount change little.High concentration of fuel dilution(>10%)will lead to the deterioration of the anti-friction and anti-wear properties of diesel engine oil under boundary lubrication conditions.High temperature oxidation has a significant effect on the acid and alkali value of diesel engine oil.When the temperature is set at 150? and the copper wire is added as a catalyst,the acid value increases by 2 times and the alkali value decreases by 58.5%after 48 hours.The correlation degree between the physical and chemical properties of diesel engine oil and Cu and Fe elements is not obviously different,and the correlation degree between them is obviously higher than that between them and Cu elements.The four-ball friction test shows that high temperature oxidation is an important factor to reduce the anti-friction performance of diesel engine oil.By analyzing the correlation between the physical and chemical properties of the oil samples in bench test and the elements,the conclusion of the simulation test is verified,which indicates that the grey correlation analysis has a broad prospect in the study of diesel engine oil degradation mechanism.