Study On The Lubrication Of Precision Pairs In The Fule Supply System Of CI Engines Operating With Low Viscosity Fuels

As the world energy crisis and environmental protection issues have become increasingly prominent, it is more significant to develop alternative fuels for automobiles.When the low viscosity fuels are used in CI engines, the precision parts in the fuel supply system has found to have the issues with fast wearing and hence internal leakages. In order to reduce the wear on the precise paired parts, this thesis presents a new technical measure to achieve surface lubrication using engine lubricants based on a theoretical analysis of the lubrication process of the parts.Based on fluid lubrication theory and annular gap flow theory in this article, the mechanism of fuel sealing and lubrication in precision parts in the fuel supply system is understood for developing a basic theory and analytical method. In the mean time, the relationship between pressure distribution of lubricant film in the gap of precision parts and the displacement of plunger with the lateral movement of the plunger is analyzed to obtain the general equation of fuel leakage through the annular gap considering that plunger has possible eccentricity during operation.With the understanding of the lubrication characteristics, a the new structure of plunger parts and needle valve parts to force lubrication is designed based on principle of the annular pressure trough. Engine lubricating oil is introduced into the clearance between precision pairs with certain pressure through adding a lubricating oil path on precise parts, which can form effective oil film on the surface of matching parts and play a role in lubricating and sealing functions. The residual leakage of lubricants can meet the operation requirements because the lubricating oil consumption of fuel supply system is much lower than the national normal value by the theoretical calculation. A numerical simulation has been further performed in order to estimate the influence of stress and strain of plunger parts at the maximum fuel pressure of the plunger cavity using finite element software. The results obtained from the change of matching clearance and cloud chart of the stress distribution indicate that the deformation and stress of plunger parts nearer to the plunger cavity is larger. The plunger has the elastic deformation, and the column sleeve satisfies the intensity request.Finally, the endurance test has been performed on a fully equipped injection pump test bed which was designed. For a operating period of100hours, the injection pressure and leakage of the fuel supply system were studied and degree of wear was determined by measuring surface roughness parameters of the plunger using a microscope. The result shows that injection pressure can be maintained at the required level for100hours. The pump side pressure peak reduces at first then stabilizes with the increase of running time, and the behavior is more obviously at high speed, but curve is relatively flat at low speed; The curve of injector side pressure peak is relatively flat. It is also verified that the amount of lubricant oil leaking to fuel increases gradually with the increase of running time and the growth rate of oil leakage increases with the increase of amount of wear. The worsening of the surface quality of the plunger head been resulted in the emergence of some slight grooves. The surface quality of plunger skirt does not change significantly because of good lubrication. The surface quality of plunger sleeve close to inlet decreases significantly because of fuel erosion, and surface quality of plunger sleeve close to lubricants road has small changes. Due to good lubrication, the surface roughness of needle valve oriented surface is almost not influenced.