Recently, fuel injection system has been playing an important part on the performances in diesel engines, and many computer simulations of this system have been developed and reported. There are, however, few papers dealing with a prediction of the zones of abnormal injections such as secondary discharge and periodical fluctuations of injection quantity and of residual pressures.
The objects of this paper are mainly to improve the accuracy and validity of the simulation and to predict the zones of abnormal injections. To confirm the calculated results, they were compared with the transient pressures in a fuel pipe line, the nozzle needle valve lift and the rate of injection as measured of an actual fuel injection system operated on a test bench.
The following conclusions are obtained:
(1) The damping factors at delivery valve and needle valve extremely affected the injection characteristics.
(2) The pressures in a line and the injection quantity decrease with increasing the damping factor at delivery valve.
(3) The damping factor assumed suitably gives the satisfactory agreement with the experimental results.
(4) As for the prediction of abnormal injections, the calculated results agree favorably with the experimental results over a wide range of operating conditions.
Consequently, this simulation may be reasonably enough to use practically for the development and improvement of injection equipment.

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