Research On The Effect Of Lubricating Oil On Particulate Emissions Of GDI Engine

Gasoline direct injection(GDI)engine has been widely used for its excellent fuel economy and transient response performance in recent years;however,its particulate emissions problem is serious.Related researches show that because lubricating oil viscosity is large and it is difficult to volatilize and atomize,the combustion of lubricating oil which enters the engine cylinder will have a significant effect on the particulate emissions of the engine.And the particles from engine contain a lot of metal elements,and many of them can cause harm to the heath of human.Related researches and reports point out that GDI engine,especially turbocharged GDI engine has an obvious buring lubricating oil phenomenon.For these reasons,this paper has done series of investigations to explore the effect of buring lubricating oil on the particulate emissions of GDI engine,which includes particle number concentration,mass concentration,particle size distribution,microstructure of particle,elemental compositions of particle,etc.The main conclusions are listed as follows:1.This paper remolded the test GDI engine,and increased the amount of lubricating oil that entered the engine cylinder by increasing the spring rate of the pressure control valve of the oil and gas separator.The lubricating oil consumption under different spring rate was measured by engine bench test.It could be found that lubricating oil burning consumption increased when the spring rate of the pressure control valve increased.2.The GDI engine test bench was built and the engine exhaust was diluted by the second-level exhaust dilution system.The particulate emission characteristics which include particle number concentration,mass concentration,and particle size distribution,etc.were measured by engine exhaust particle sizer(EEPS).The test results suggested that at most working conditions particle number concentration,mass concentration increased when the lubricating oil burning consumption increased,while,the particle size distribution didn’t have aobvious change rule.3.The device for collecting exhaust particulates from GDI engine was designed and the exhaust particulate samples were collected by carbon-coated copper grid for microscopic observing and elemental analyzing.This paper used TECNAI-F20 transmission electron microscope to observe microstructure of particles,and analyzed the primary particle size distribution,overlap coefficient,interlayer spacing,etc.It could be found that with the lubricating oil burning consumption increased,the typical morphology of particles change little,the diameter of primary particles had a tendency to decrease,and the range of overlap coefficient changes was small.At most load conditions of 2000r/min speed,the average size of the interlayer spacing of primary particles tended to be smaller when the lubricating oil burning consumption increased.At 100% load condition,the change of the average size of the interlayer spacing didn’t have an obvious single rule.4.Compared with the particulate characteristics tested by EEPS,the size distribution of primary particle was narrow,and the peak value diameter of primary particle was large.With the lubricating oil burning consumption increased,the results of the changes in the oxidation of particles obtained from the average size of the interlayer spacing were accordant with the changes in the total number concentration of particles,while,the results of 100% load condition were not.5.The elements in particles were examined by energy dispersive X-Ray spectroscopy.It was found that there were many elements,such as: C,O,N,S,Si,P,Fe,Cu,Mn,Ca,Ti,Pb,etc.,in the exhaust particles.Compared with the elements in the lubricating oil from engine oil sump,this paper inferred that many elements of the exhaust particles were probably from the lubricating oil,such as: Mn,Ca,Ti,Pb,etc.In conclusion,the lubricating oil has an obvious influence on the particulate emissions of GDI engine.Decresing lubricating oil not only can increase reliability and service life of engine,but also can reduce the harmful elements emissions.This paper has made a reveal on the effect of lubricating oil on the particulate emissions of GDI engine,and provides theoretical basis and experimental data for improving quality of lubricating oil to reduce particulate emissions.