Loop Fuel Injection System Fault Simulation And Characteristic Analysis

So far, diesel engine is still the most efficient and the most widely used power plant. As the important sub-system, fuel oil system affects directly the performance behavior and determines the operation functions of diesel engine. Any performance failure of fuel oil system can undoubtedly induce the abnormal condition of diesel engine. Investigations show that almost 113 of diesel engine failures are caused by fuel injection system. Those failures are usually accompanied by two-injecting-in-one-cycle, injecting disjointedly, unstable injection or intermittent injection, oil leakage etc, which worsen diesel engine combustion condition, reduce power output, decrease economy function and reliability function and increase harmful emissions. So the failure detection of fuel oil system in due time can be of great significance to diesel engine. This paper firstly analyzes the structural characters of diesel engine fuel oil system, summarizes the working process, performance functions and structural requirements of all kinds of fuel oil injection system, especially the circulating fuel oil system. On the basis of current research on the numerical simulation of diesel engine fuel injection system, this paper secondly establishes the mathematical models which use compressible fluid equation, continuous fluid equation, Newton's second law and flow velocity equation to describe the fuel pressure inside the fuel pump, fuel injector, high pressure pipes and fuel distributor etc.. Calculations were made concerning normal condition and 585 kinds of typical performance failures of fuel oil system under 3 performance conditions of diesel engine. Calculated results show out 3 unique characters of circulating fuel oil system in fuel pressure waveforms: ~1D high pressures still remain in the fuel pump cavity and nozzle cavities after fuel injection, which is called remaining pressure; @~ there are two valve opening points in the fuel pressure waveforms because of the existence of inner and outer fuel valves; ?the valve seating character is not obvious during the process of fuel oil discharge, which is due to the rapid decrease of fuel oil pressure. Symptomatic information can be obtained from the fuel pressure waveforms which is useful in failure detection of fuel oil system. These symptomatic parameters can reflect the working condition of circulating fuel oil system such as oil supplying advance angle, fuel injection duration angle, injector nozzle pressure, fuel valve opening pressure, fuel remaining pressure, maximum injection pressure, fuel injection rate, injection timing and so on. Any performance failure of fuel oil system will change the injection condition and bg about corresponding change in the pressure waveforms and symptomatic parameters. Thirdly this paper introduces a new method which can detect the symptomatic parameters from the pressure waveforms of circulating fuel oil system. With this method this paper studies the propagation features of pressure waveforms inside the fuel pump, high pressure pipes and fuel injector and reveals the internal relationship between performance failure and symptomatic parameters. The symptomatic parameters are analyzed about the typical failure of different fuel oil viscosities, different fuel oil densities, blocked injector nozzles, loosen valve springs, deposited nozzle, injector leakage, worn- out fuel pump, too late or too early injection timing, etc. On the basis of symptomatic identification of fuel pressure waveforms, this paper finally conducts the an...