Effect of injection dynamic behavior on fuel spray penetration of common-rail injector

Abstract

The spray tip penetration is an important parameter to evaluate the fuel injection quality. This study presents an experimental investigation on the high-pressure diesel injection process of a common-rail injector under condition of varying pressures, particularly on the effect of the dynamic injection behavior on the fuel spray penetration. The injector delivery process is tested on a common-rail test rig, with an optical test rig to examine the diesel spray based on a constant-volume bomb (CVB) system. This process includes two stages: i.e., the opening stage and the keeping stage, while the two-stage injection momentum causes crucial influence on the fuel spray. Correspondingly, the fuel spray penetration also has two stages. In Stage I (the dynamic stage), the spray penetration sharply increases. In Stage II (stable stage), the spray penetration stably increases. When the injection pressure rises, the spray tip penetration increases, and the two-stage turning-point time is shorter. Considering this two-stage characteristic, an equation is proposed to predicate the spray tip penetration: it is based on the dynamic injection pressure for the dynamic period but the constant pressure differential for the stable period. The predicated spray tip penetration has good agreement with the test data.