| Diesel engine is a sort of indispensable power mechanism for modern society. Recently during increasingly strict standards of energy and emission, as a key technology of diesel engine for meeting the standards, the application and improvement of electronic-control high-pressure common rail injection system (CRS) are important for the sound development of national economy and social environment. In the course of independent innovation of domestic CRS technology, several correlative industrialization problems occur, especially concerning high-pressure common rail diesel injector (CRI) which is a key subassembly of CRS. Therefore, government authorities attach great importance to the problems, and establish a National Science and Technology Major Project of China (Grant No.2011ZX04001-061) in Wuxi Fuel Injection Equipment Research Institute of FAW. The study of this dissertation is supported by the project, and also is supported by the National Natural Science Foundation of China (Grant No.51239005). This dissertation is aimed at investigating those problems, including how to ameliorate the fuel injection consistency and reliability of CRI, and to achieve the independent innovation of CRI which is suitable for domestic actual manufacturing capability.With regard to fuel injection consistency of CRI, it is studied by means of one-dimension modeling in conjunction with the Monte Carlo method of robustness. The CRI modeling is composed of several modules according to subassembly characteristics in structure, dynamics and working principle. The entire modeling and important modules are validated against experimental data; modularized validations are performed in terms of electromagnet force, armature-pin displacement and diesel-nozzle hydrometry. With respect to working curves of energizing time, pressure fluctuation and fuel injection rate, the simulation result corresponds with experimental result basically under different operating conditions. The relative error of fuel injection quantity between simulated and experimental result is equal to about 4.8%.Production test result demonstrates that parameters show variance with normal distribution as a result of large-scale manufacturing and fitting. This study on fuel injection consistency is based upon statistic characteristics of the variance, including mean value μ and standard deviation σ, and thus it is of practical significance to engineering. Single-and multi-factor analysis methodologies are adopted in this study. Using single-factor analysis method can discover the regularity how fuel injection quantity varies with the variation within "±3σ" of each factor under different operating conditions. Research shows that slight effect of fuel-nozzle flow rate or needle-valve lift on the relative variation of fuel injection quantity is revealed under short energizing time operating condition owing to incomplete open of needle-valve, and that the influence of other factors on the relative variation of fuel injection quantity decreases as energizing time or rail pressure increases. Based on central composite designs, multi-factor interaction research discovers a certain coupling effect of factors on fuel injection quantity. Combining the Monte Carlo method of robustness with Response Surface Method (RSM), a Monte Carlo-RSM Method is put forward in this study, and it is able to enhance efficiency in multi-factor research. Adopting the method, investigation demonstrates that fuel injection consistency is governed by a combination of factors, and that three of those factors (electromagnet-valve lift, inlet-and outlet-control-orifice flow rate) carry greater weight, corresponding to 24.76%,24.75% and 15.75% respectively.As concerns fuel injection reliability of CRI, it is investigated by means of Monte Carlo method of structural reliability, and MATLAB is adopted for correlative programming and calculating. A "leakage-shutting" failure model is established. Failure function of the model relates to several random variables, including fuel delivery limitation, fuel injection quantity, fuel dynamic leakage and the structural parameters of command-piston matching parts and nozzle-needle matching parts associated with fuel clearance leakage. Statistical characteristics of those random variables are also obtained by production test. In contrast with Monte Carlo direct sampling mode to satisfy the same calculation precision requirement, Monte Carlo important sampling mode reduces the demand on sampling quantity, signifying higher computational efficiency and applicability. Research indicates that three standard-deviation of variables, including fuel delivery limitation and the working clearances of the two pairs of matching parts, have strong influence on failure rate, and thus suggests that manufacture tolerances of those variables need proper restrictions. Furthermore, the failure rate sensitiveness to the working clearance standard-deviation of nozzle needle matching parts is 3.1 times the value of command-piston matching parts.As for achieving the independent innovation of CRI which is suitable for domestic actual manufacturing capability, fundamental work is accomplished, including conceptional innovation, structural design, patent application and design assessment by means of one-dimension modeling and three-dimension CFD simulation. Originality of the new-type 250MPa CRI consists in a novel control-piston with the outward appearance of a poppet valve. During operation, the poppet control-piston can automatically move downwards or upwards owing to pressure changes in related hydraulic chambers, and consequently appropriately activates or deactivates the function of additional inlet-control-orifices to improve system responsiveness. One-dimension modeling result demonstrates that the new-type CRI is of good injection performance:(1) satisfactory injection flexibility; (2) rapid injection responsiveness that embodies the reductions in opening-delay and closing-delay accounting for about 24.8% and 38.5% respectively under rated rail pressure condition; (3) static fuel leakage avoidance that decreases fuel return quantity by 15.5% approximately. The CFD model is validated against experimental data in terms of flow rate. CFD simulation result indicates that less cavitation occurs in the vicinity of control-valve of new-type CRI, which is beneficial to improve reliability of the control-valve. In key area of the control-valve, average flow rate can be reduced by about 65.36% and average mass exchange rate between vapor-liquid phases is decreased by around 70.22% under rated rail pressure condition.The originality of this dissertation is drawn briefly as follows:(1) a sensibility analysis method on fuel injection consistency of CRI is put forward; (2) a "leakage-shutting" failure model as well as correlative algorithm for reliability analysis is established; (3) a new-type CRI with a poppet control-piston is developed for rapid responsiveness. |
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