Design And Cycle Fuel Injection Quantity Characteristics Research Of Double-Valve Electronically Controlled Fuel Injection System For Marine Low-Speed Diesel Engines

Low-speed diesel engines are the primary power source of ocean-going ships.Improving the performance is of great significance to reduce pollutant emissions.As the core component of marine low-speed diesel engines,the fuel injection system has a decisive impact on the operational performance of the whole engine.However,China’s independent design ability of the fuel injection system for marine low-speed diesel engines is lacking due to long-term dependence on foreign companies to provide patent production.The technical problems concerning the consistency and stability of cycle fuel injection quantity have not been solved.In order to break through the technical bottleneck of the fuel injection system for marine low-speed diesel engines and change the passive situation that the critical parts of the fuel injection system for marine low-speed diesel engines are subject to others in China,the design method of double-valve electronically controlled fuel injection system for marine low-speed diesel engines is put forward for the first time in this thesis.The characteristics of the cycle fuel injection quantity are studied.The thesis mainly includes the following aspects.The investigation on the design of the double-valve electronically controlled fuel injection system for marine low-speed diesel engines is carried out.An innovative design method of a double-valve electronically controlled fuel injection system is proposed,in which the pressure amplification control valve controls the pressure building process,and the injection control valve controls the injection process.According to the basic principles of electromagnetism,mechanics,and hydraulics in fuel injection systems,the key components are designed in detail.The structural parameters of the double-valve electronically controlled fuel injection system for marine low-speed diesel engines are determined and the test bench of the fuel injection system for marine low-speed diesel engines is built.Through the special test of injection characteristics of the system,it is found that there are nonlinear phenomena in injection duration and cycle fuel injection quantity of the system under low load conditions.Under main operating conditions,the system fuel supply coefficient could be stabilized at the level of 0.8.The deviation between injection duration and injection pulse width is about 4 ms.The variation coefficient of cycle fuel injection quantity is less than 6%.The fuel injection pressure of the system could be adjusted under the synergistic control of double-valve,but the fuel injection pressure during stable fuel injection stage is not affected.In order to obtain the crucial influential parameters of cycle fuel injection quantity,a multi-disciplinary coupled simulation model of the double-valve electronically controlled fuel injection system for marine low-speed diesel engines is established based on the bond graph theory.Compared with the experimental data,it is concluded that the model could accurately predict the critical performance indicators such as cycle fuel injection quantity,driving pressure,fuel pressure after amplification,and injection pressure.The simulated and experimental values of the injection characteristics of the system are tested by F-test.The results show that the F value and F critical value of the simulated and measured cycle fuel injection quantity are 1.384 and 3.522,respectively.The F values of the simulated and experimental driving pressure,fuel pressure after amplification,and injection pressure are 1.019,1.005,and 1.006,respectively,all less than the F critical value of 1.037,which indicates that there is no significant difference between the model calculation results and the test data.Thus,the calculation results of the simulation model of the double-valve electronically controlled fuel injection system for marine low-speed diesel engines have high reliability.On this basis,the nonlinear characteristics of cycle fuel injection quantity are studied in view of the nonlinear phenomenon between the cycle fuel injection quantity and the injection pulse width of the double-valve electronically controlled fuel injection system for marine low-speed diesel engines.The nonlinear degree of cycle fuel injection quantity is defined,and the effects of structural parameters on cycle fuel injection quantity and its nonlinear degree are explored.Meanwhile,the D-optimal experimental design method is used to conduct the correlation analysis upon the nonlinear degree of cycle fuel injection quantity in the full range of injection pulse width.Taking the absolute value of a correlation coefficient greater than 0.5 as the standard,the quadratic interaction factors that have a significant impact on the nonlinear degree of cycle fuel injection quantity are screened out,which lays a foundation for the improvement of system structure.In order to improve the consistency of the cycle fuel injection quantity of the system,an evaluation method for the robustness of the cycle fuel injection quantity is proposed.The mean value,standard deviation,skewness,and kurtosis of cycle fuel injection quantity are used as quantitative indexes.The effects of the sizes of moving parts and the precision orifice holes on the robustness of cycle fuel injection quantity are analyzed.The quantitative analysis of the influential factors on the robustness of cycle fuel injection quantity is carried out.The results show that,for different injection pulse widths,the nozzle hole diameter is the most crucial factor affecting the mean value of cycle fuel injection quantity.The control orifice diameter is the least important factor affecting the mean value of cycle fuel injection quantity.The change in working conditions greatly influences the quantitative rate of the standard deviation of cycle fuel injection quantity,and the influential degree of each factor on the standard deviation of cycle fuel injection quantity varies under different injection pulse widths.The diameters of the needle ring,control plunger,and nozzle hole are the most critical factors affecting the skewness of cycle fuel injection quantity.As for the kurtosis of cycle fuel injection quantity,when the injection pulse width is less than 17 ms,the diameter of the needle ring has a decisive effect on the cycle fuel injection quantity kurtosis.When the injection pulse width reaches 17 ms,the nozzle hole diameter is the most crucial factor affecting the kurtosis of cycle fuel injection quantity.After structural improvement,the nonlinear characteristics and the robustness of cycle fuel injection quantity of the double-valve electronically controlled fuel injection system for marine low-speed diesel engines are improved.The cycle fuel injection quantity enters the linear range when the injection pulse width is over 4 ms,and the maximum variation coefficient of cycle fuel injection quantity decreased from 29.98% before structural optimization to 4.78% after structural optimization.As for the whole engine test verification,the maximum coefficients of variation of maximum explosion pressure and exhaust temperature for each cylinder under different loads are 2.39% and 2.48%,respectively.The fuel consumption rate is lower than the design index.The double-valve electronically controlled fuel injection system for marine low-speed diesel engines could meet the performance requirements of the marine low-speed diesel engine with independent brand.