Research On Coating Anti-wear Technology Of Injector’s Sealing Cone In Diesel

The injector needle couples is a core component of diesel fuel injection system, and itsperformance has a direct impact on the fuel spray effects, thereby affecting the engine’s power,economy and reliability. Because the injector needle couples are used in extremely harshenvironment, the sealing cone of needle couples is prone to wear and tear.The abrasion of sealing cone is mainly caused by the combined effects of the impactforce generated by the needle, when it hit the nozzle holder, and the impurities entrained inthe fuel. After the sealing cone was worn, it will occur deformation, the surface roughnesswill increase, and its sealing effect will be deteriorated, resulting in spray effect reduced, evenfuel dripped. So that the diesel cannot be fully burn, a lot of cokes accumulated in spray hole,combustion chamber and piston. The spray holes will be blocked if the abrasion is serious.Finally, the engine power will decrease, and the fuel consumption will increase.For this problem, we propose a coating solution. We use surface coating technology tospray coating on the sealing cone of needle, in order to improve its anti-wear properties. Inthis paper, we verified this solution by finite element simulation and experiment. UsingANSYS, we make a series of contact analysis for the needle couples, compare the stressdistribution between the original needle couples and Al2O3coating, TiN coating and DLCcoating needle couples. Simulation results show that: the maximum contact stress of originalneedle couples is208MPa, after addition of coating, all the maximum contact stress of coatingneedles are greater than208MPa, but all of them occur on the coating, and all are within theirmaterial allowable intensity range. In addition, all the coating needle couples’ stressconcentrated areas are smaller than the original needle couples, and the stress concentratedarea mainly occur on the coating.Based on the simulation results, and consideration of material performance parameters,we select DLC to be the injector needle coating material, and the thickness is10um. We usemagnetron sputtering PVD to manufacture the DLC coating needle.By engine bench and injector test bench, we make experiments for the original needleand DLC coating needle. And then, using SEM(scanning electron microscopy), we observedthe worn morphology of sealing cone. The results show that: in the early stage of theexperiment, DLC coating has a good protective effect for the needle. Significantly, there arefewer abrasions on the DLC coated needle than the original needle. With the extension of theexperimental time, the original needle occurs lots of clear scratches, cracks, and severe spallings. The DLC coating needle also occurs several slight spallings, since the DLC coatingbond strength is weakened, but the rest of coating is still relatively intact. These experimentsprove that DLC coating has a good protective effect for the needle, and improve the anti-wearperformance of the needle’s sealing cone, but its bonding strength with W6Mo5Cr4V2needto be improved.