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This paper studies the effect of nozzle geometry on the flow characteristics inside a diesel fuel injection nozzle and correlates to the subsequent atomization process under different operating conditions, using simple turbulent breakup model. Two kinds of nozzles, valve covered orifice (VCO) and mini-SAC nozzle, with various nozzle design parameters were studied. The internal flow inside the nozzle was simulated using 3-D computational fluid dynamics software with k-ε turbulence model. The flow field at the nozzle exit was characterized by two parameters: the fuel discharge coefficient Cd and the initial amplitude parameter amp0. The latter parameter represents the turbulence characteristics of the exit flow. The effects of nozzle geometry on the mean velocity and turbulent energy distribution of the exit flow were also studied. The characteristics of the exit flow were then incorporated into the spray model in KIVA-II to study the effect of nozzle design on diesel spray behavior.

The effectiveness of scavenging, the displacement of residual combustion gases with fresh air, is examined in an advanced, high power-density diesel engine, consisting of a two-stroke, opposed-piston reciprocator with an ultra-high boost. KIVA-3, a three-dimensional code for modeling reactive flows with fuel injection, is used to study the effect of a variety design choices on scavenging. The parametric study includes the inclined angle of the intake ports, the exhaust port timing and size and the piston stroke-to-bore ratio. A baseline geometry of the opposed-piston engine is examined in detail, which models an existing mono-cylinder test rig. The baseline-design exhibits large asymmetries, nonsteady flow and large recirculation regions that degrade the scavenging. Significant improvement in the scavenging of the baseline design is observed with a uniform inclined angle of the inlet ports of about 20° and with a larger stroke-to-bore ratio (2.0 compared with 1.08).