A NUMERICAL-MODEL FOR ELASTOHYDRODYNAMIC ANALYSIS OF PLUNGER AND BARREL CLEARANCES IN FUEL-INJECTION EQUIPMENT

This paper describes a numerical model developed to predict the elasto hydrodynamic (coupled solid-fluid) response of unit injector fuel syst ems. These systems consist of a concentric barrel and plunger with a s mall annular clearance. During operating (axial movement of the plunge r), highly nonuniform pressure and clearance fields are developed whic h are strongly coupled with each other. The model simultaneously solve s for the transient response of the fluid film pressure distribution a nd three different structural deformation components in a two-dimensio nal (axial-circumferential) domain. These structural components are th e transverse bending of the plunger, radial expansion of the barrel, a nd radial growth of the plunger from a Poisson effect. The fluid film pressure distribution is governed by the transient Reynolds equation ( i.e., lubrication theory) and the structural deformation components go verned by linear elastic theory. Full account is taken of these hydros tatic, hydrodynamic, and squeeze-film forces generated in the fluid. T he model has been applied to several injector designs. Results have be en compared with known performance characteristics and have been found to be qualitatively accurate, in that locations of plunger/barrel con tact, and potential for failure, ha ve been accurately predicted.