The Effects of Diesel Injector Needle Motion on Spray Structure

The internal structure of diesel fuel injectors is known to have a significant impact on the steady-state fuel distribution within the spray. However, little experimental or computational work has been performed on the dynamics of fuel injectors. Recent studies have shown that it is possible to measure the three-dimensional geometry of the injector nozzle, and to track changes in that geometry as the needle opens and closes in real time. This has enabled the dynamics of the injector to be compared with the dynamics of the spray, and allows computational fluid dynamics (CFD) simulations to use realistic time-dependent flow passage geometries. In this study, X-ray phase-enhanced imaging has been used to perform time-resolved imaging of the needle seat area in several common-rail diesel injection nozzles. The fuel distributions of the sprays emitted by these injectors were also studied with fast X-ray radiography. Correlations between eccentric motions of the injector needle valve and oscillations in the fuel density as it emerges from the nozzle are examined. CFD modeling is used to interpret the effect of needle motion on fuel flow.