Characterization of Flow Structures in a Diesel Injector for Different Needle Lifts and a Fluctuating Injection Pressure

Abstract

This paper aims at analyzing the needle lift's influence on the internal flow of singlehole diesel injector to identify flow structures. A numerical ReynoldsAveraged Navier–Stokes (RANS) model of a singlehole diesel injector was developed and validated to study the flow's dynamic for different needle's lifts and subjected to realistic injection pressure. The main findings are: (1) under steady injection pressure, flow coefficients reached a steadystate value and maximum injected fuel mass flow rate is reached at intermediate needle's lifts. (2) The sac volume is the area with several vortex structures due to the throttling between the needle body and the injector body. (3) The frequency of the fluctuating injection pressure can excite the initial jet entering the sac volume similarly to the Coanda effect. Finally, using a proper orthogonal decomposition (POD) allowed extracting coherent structures within the sac volume and putting in evidence a reorganization of the flow.