Transient turbulent gaseous fuel jets for diesel engines

Existing data on transient turbulent jet injection into large chambers demo nstrates self-similar behavior under a wide range of conditions including c ompressibility thermal and species diffusion, and nozzle under expansion. T he jet penetration distance well downstream of the virtual origin is propor tional to the square root of the time and the fourth root of the ratio of n ozzle exit momentum flow rate to chamber density. The constant of proportio nality has been evaluated by invoking the concept of Turner that the flow c an be modeled as a steady jet headed by a spherical vortex. Using incompres sible transient jet observations to determine the asymptotically constant r atio of maximum jet width to penetration distance, and the steady jet entra inment results of Ricou and Spalding, it is shown that the penetration cons tant is 3 +/- 0.1. This value is shown to hold for compressible flows also, with substantial thermal and species diffusion, and even with transient je ts from highly under-expanded nozzles. Observations of transient jet inject ion 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 o f 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.