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NO, OH, and soot in combustion flame produced from burning at high temperature and pressure diesel fuel spray issuing from a single-hole injection nozzle was measured by laser induced fluorescence (LIF) and laser induced incandescence (LII) methods. The LIF images of OH showed that OH radical, distributed in a band-like zone outside the region of the flame luminescence observed, would persist even after the extinction of flame luminescence. The LIF images of NO showed that NO was located slightly outside the flame luminescence zone and that its region was almost the same as that of OH and would tended to increase in the latter period of the combustion process. Also, the LII images showed that the formation of soot would take place near the flame central zone coincident with the flame luminescence zone.

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.