Study On Effects Of Low Viscosity Alternative Fuels On The Lubricity Of A Diesel Fuel Engine Fuel Supply System

The research center of internal combustion engine is turning to the application of alternative fuels for relieving the stress from energy crisis and environmental protection. The natural gas and LPG are applied to the IC engines by means of new technologies, which, in a manner, realized energy conservation and emission reduction. While the application of biodiesel, methanol and F-T diesel etc. is still in the research stage and there are some problems during the process, such as precise couples’excessive wear and the increased leakage of the fuel injection pump.According to the theory of fluid lubrication and the annular gap liquid flow theory, the paper explains the sealing and lubrication mechanism of diesel precise couples; explores the wear characteristics of three precise couples in the fuel injection pump and changes in fuel injection law; deduces the annular fuel gap leakage general equation when the plunger eccentric and deflected.The simulation and experimental research of the application of F-T diesel to the fuel pump are conducted, and the results show that the annular gap’s leakage is two orders of magnitude larger than that of0#diesel; after the fuel injection pump of F-T diesel running100hours, the pump and nozzle pressure reach a maximum drop, of65.8%compared with before; severe wear occurred at the plunger head and skirt according to the result of microscope scan.New structure of precise couples is designed due to the wear and leakage problems of precise couples caused by the application of low viscosity fuel (like F-T diesel). In the research engine oil was used to lubricate the surface of precise couples, and expected to delay the wear process, meanwhile the oil took the role of sealing. In view of the complexity of flow annular gap flow field, a Fluent multiphase flow model named VOF of CFD software was build to simulate the flow field. The flow field characteristics and leakage of the annular gap with forced lubrication and the friction force between surfaces of precise couples through a series of orthogonal tests. The results show that the annular gap leakage amount of precise couples with forced lubrication is smaller than that without forced lubrication.The fuel injection pump test bench with forced lubrication of low viscosity fuel supply system was designed, on which the fuel injection pressure and the leakage amount of fuel supply system are analyzed after one hundred hours’ durability test. The wear degree is obtained after comparing the injection pressure of pump and nozzle after the durability test with that before the test. The test results show that:with the time extending, the injection pressure doesn’t change on the whole; the peak value of pump pressure decreased gradually early, especially at high speed, and then tends to be stable; while the peak value of nozzle pressure is relatively stable.