| Electronic control is the trend of modern diesel engine development. As the heart and brain of diesel engine, electronic control fuel injection system is the most important part of diesel engine. Therefore, development of appropriate electronic control diesel injection system is being urgently needed by Chinese diesel engine industry.As an important part of new electronic control fuel injection system product development in Chengdu Wit Electric Injection Ltd., system characteristics analysis was done with the combination of experiment analysis and AMESim software numerical simulation. This dissertation presents the whole analysis process, which includes investigation of injection characteristic of injection pressure, cycle fuel quantity, fuel injection rate and high-low pressure system coupling characteristic of pressure, temperature, cycle fuel quantity. Based on the analysis, optimization of new fuel injection system was done by the author. Equipped with the optimized fuel injection system, diesel engines' emissions meet the requirement of China III emission regulation. The main research work of this dissertation is summarized as follows.First, high pressure injection characteristic was studied, which determines the success of engine matching. Through the experiment analysis of high pressure injection characteristic, the author attained injection pressure map of high pressure system, injection temperature map and cycle fuel injection quantity map. Since injection characteristics is basically influenced by five main parameters, which are injection pressure, cycle fuel quantity, injection duration, and fuel supply efficiency respectively, the response analysis and correlation analysis of them were executed. The results show that the fuel injection system is multi-parameters complicated interaction nonlinear system. The complexity of fuel injection system causes cycle-to-cycle variation of fuel injection quantity. In order to realize the stability of fuel injection quantity per cycle, the causes of the variation are classified into three types by the author. They are lifecycle cycle fuel quantity variation which is due to the change of system parameters in lifecycle, individual cycle fuel quantity variance which is caused by the precision of manufacture, and single or multi-cylinder cycle fuel quantity variation which is led by the complicated hydraulic effect of the system. With the application of the correlation analysis in Design Of Experiment (DOE) and Monte Carlo method, the former two types of variation were thoroughly investigated. Finally the author attained the key parameters of influencing on cycle fuel quantity variation, also the quantum index was done, which supplies guarantee to system performance stability and calibrating map coherence, and establishes a foundation for industrialization.Second, considering that fuel injection system is a whole system coupling high and low pressure parts, the author analyzed the influence of low pressure part on fuel injection characteristics and studied the high-low pressure coupling injection characteristic. The investigation provides theory basis of reducing the sensitivity of high injection pressure characteristics to low pressure part and solving the problem of the third type cycle fuel quantity variation. The experiment study of this dissertation revealed the coupling phenomenon of high and low pressure parts' pressure, temperature and injection quantity as well as abnormal injection caused by the intensive coupling phenomenon. In order to eliminate the abnormal phenomenon, the author proposed a decoupling method, which adopts damping delivery valve and optimizing low fuel supply pressure. Through AMESim modeling, parameters of damping delivery valve and low pressure part were optimized. After optimizing, the sensitivity of high pressure part to low pressure part is largely reduced and problem of third type cycle fuel quantity variation is solved. In addition, low pressure part was studied by parameter changing investigation. The results indicate that the influence of relief valve operating pressure on sufficient fuel attraction is bigger than that of supply pump fuel rate, and different low pressure fuel attraction structure has different influence on damping pressure wave and improving next cylinder injection characteristic.Third, to deeply analyze system performance, the linearity analysis of fuel injection system was performed through modern control theory. System matrix eigenvalue analysis shows that fuel injection system is a multi-input, multi-output, nonlinear, time-changing, instability, high complicated system. Model shape analysis of high pressure part indicates that the larger modal shape appears in the fuel injection system pump body cavity and high pressure pipe, and smaller modal shape appears in injector meeting the require of ideal injection fuel rate. Model shape analysis of low pressure part reveals that the eigenfrequency of model shape is more than 1000Hz, which has little influences on pressure wave of every cylinder attraction position; also, the resonance frequency model shape of low pressure part of fuel injection system after high-low pressure decoupling has no influence on high pressure injection characteristic.Finally, for the purpose of proving the feasibility of developed fuel injection system, the optimized fuel injection system was matched with diesel engine through electronic control calibrating. The calibrated diesel engine was tested according to China III ESC emission test procedure. Test results show that the engine's NOx emission is 4.8g/kW·h and PM emission is 0.08g/kW·h, which meet the requirement of China III emission regulation. Furthermore, based on the above conclusions, to reduce the strong coupling characteiristic of high and low pressure parts, the author studied the suction characteristic of low pressure system, and proposed a new fuel suction structure of low pressure part, and proved its feasibility by AMESim modeling. Moreover, to realize ideal fuel injection rate - boot-shape fuel injection rate, the author brought forward two schemes of fuel injection systems, current control system and double plungers system. Numerical simulation proved their capability of realizing the rate.
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