Evaluation of Instability Phenomena in a Common Rail Injection System for High Speed Diesel Engines

An existing simulation code of a COMMON RAIL Diesel fuel injector, named UNIJET, has been revised and completed, with the aim to predict injection characteristics and to investigate on the instabilities which appeared in experimental tests. Particular attention has been given to the injector control valve modeling, to understand the influence of cavitation on discharge flow characteristics. The valve residual motion, after a Pilot Injection cycle, is responsible for the clear and sudden injected quantity variations of subsequent Master injection, as the time delay between the two cycles decreases. Numerical predictions have been compared with valve lift measurements, and with experimental relation among fuel injected quantity, injection pressure and duration.