Transient Turbulent Gaseous Fuel Jets for Diesel Engines

TLDR

Transient turbulent jet injection in large chambers shows self‑similar behavior, with penetration distance scaling as the square root of time and the fourth root of the nozzle exit momentum flow rate to chamber density. The penetration constant was derived by modeling the jet as a steady jet with a spherical vortex (Turner) and validated through experiments with under‑expanded nozzles in chambers where the jet impinges at a small angle to a wall. Experiments confirm a penetration constant of 3 ± 0.1 for transient turbulent jets, valid for both incompressible and compressible flows with significant diffusion, and show that high nozzle pressure ratios maintain this constant while low ratios lead to wall‑induced penetration retardation.

Abstract

Existing data on transient turbulent jet injection in to large chambers demonstrates self-similar behavior under a wide range of conditions including compressibility, thermal and species diffusion, and nozzle under expansion. The Jet penetration distance well downstream of the virtual origin is proportional to the square root of the time and the fourth root of the ratio of nozzle exit momentum flow rate to chamber density. The constant of proportionality has been evaluated by invoking the concept of Turner that the flow can be modeled as a steady jet headed by a spherical vortex. Using incompressible transient jet observations to determine the asymptotically constant ratio of maximum jet width to penetration distance, and the steady jet entrainment results of Ricou and Spalding, it is shown that the penetration constant is 3 ± 0.1. This value is shown to hold for compressible flows also, with substantial thermal and species diffusion, and even with transient jets from highly under-expanded in which, as in diesel engine chambers with gaseous fuel injection, the jet is directed at a small angle to one wall of the chamber. In these tests, with under expanded nozzles. Observations of transient jet injection have been made in a chamber in which, as in diesel engine chambers with gaseous fuel injection, the jet is directed at a small angle to one wall of the chamber. In these tests, with under-expanded nozzles it was found that at high nozzle pressure ratios, depending on the jet injection angle, the jet penetration can be consistent with a penetration constant of 3. At low pressure ratios the presence of the wall noticeably retards the penetration of the jet.