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We have investigated the fundamental characteristics of unit injectors and pump-line-nozzle systems theoretically by a graphical analysis of characteristic lines. We have confirmed the higher potential of unit injectors for higher injection pressure, compared with pump-line-nozzle systems. It can be said that the unit injector has the ability to reach higher injection pressures with smaller drive system and less power loss than that of pump-line-nozzle systems. Furthermore, we have obtained basic views on how to improve the defective delivery characteristics in the low-speed region by a simulation method and with experiments. We have confirmed that modulus of rigidty in the driving system influences not only injection pressure but also injection mode.

A new system developed by the authors to predict the cavitation erosion of the fuel injection system utilizes ultrasonic wave issued by collapse of cavities in the system. This prediction system can replace the conventional time-consuming endurance test and thus greatly contributes to the saving of cost and time. The technical features of this system include: (1) Detection of ultrasonic wave through the fuel injection pipe wall using a piezoelectric sensor, with the ultrasonic wave signal intensity in a higher frequency range increasing with the cavitation intensity, i.e., the leval of energy released by the collapse of cavities; (2) the system output representing effective cavitation intensity which is given after being processed from the raw state in a high pass filter; and (3) capability of dealing with a higher level of accuracy than by the conventional method.