Microscopic geometry changes of a direct-injection diesel injector nozzle due to abrasive flow machining and a numerical investigation of its effects on engine performance and emissions

Abstract

The geometric effects of the abrasive flow machining (AFM), a surface finishing process, on a direct-injection diesel fuel injector nozzle are studied and characterized in this study. To measure the microscopic variations inside the nozzle, before and after the AFM process, several different geometry characterization techniques are used. Empirical correlations that relate nozzle geometrical changes to the AFM process period are derived from the measurements. The resulting impact of the geometric changes of the nozzle on the engine performance and emissions are also assessed with a numerical engine cycle simulation model that is based on a quasi-dimensional multi-zone diesel spray combustion model. This study shows that properly AFM-processed injectors can enhance the engine performance and improve the emissions due to the improved quality of the nozzle characteristics. However, extended process can also cause the enlargement of the nozzle as a side effect and this can adversely affect emissions. Since the enlargement of the nozzle is unavoidable, yet must be minimized, strict control over the process is required. This control can be enforced by either limiting the AFM process, or properly preparing the initial nozzle diameter so as to accommodate the inevitable changes of nozzle geometry.