Improving the geometry and quality of a micro-hole fuel injection nozzle by means of hydroerosive grinding

Abstract

Hydroerosive grinding of small orifice components often creates a feature known, for the purposes of this paper, as a keyhole. The keyhole is created by undesirable erosion close to the entry of a hole, which results in an asymmetrical geometrical form and poor quality. This paper details how the keyhole problem can be eliminated and applied to diesel fuel injection nozzle manufacture. The hydroerosive grinding process consists of a low viscosity fluid, similar to the viscosity of diesel fuel, containing abrasive particles such as silicon carbide and boron carbide. A fuel injection nozzle tends to have five to seven injection holes ranging in diameter from 100 μm to 200 μm. This fluid is passed through the injection holes in a fuel injection nozzle to calibrate the nozzle flowrate, improve surface finish, pre-age the nozzle radius and micro-deburr the hole edge at the fuel inlet, and to improve the flow efficiency of the hole. The paper addresses problems associated with hydroerosive grinding, such as the keyhole feature and asymmetrical holes, and describes a solution to eliminate the keyhole effect and to increase the flowrate of the nozzle without resulting in poor hole geometry. The paper contains a study on the process development, understanding of the two-phase flow characteristics, and practical implementation of the technique.