نشریه تحقیقات موتور
پیاپی 34 (بهار 1393)

Increasing the injection pressure and using blend fuels are two strategies for ‎reducing the emission of diesel engines. Accordingly, in the present study, by ‎using the CFD analysis, the influence of high injection pressures on the non-‎reacting behavior of the liquid HFO and HFOn-butanol blend spray as an ‎alternative fuel is studied. Three different injection pressures of 1000, 2000 ‎and 3000 (bar) in a constant volume chamber of the medium speed diesel ‎engine at the temperature of 298 K have been considered. Furthermore, an ‎Eulerian-Lagrangian multiphase scheme has been used for simulating the ‎interaction of the discrete liquid phase of the fuel with continuous air phase, ‎while the Reitz-Diwakar scheme has been utilized for modeling the secondary ‎breakup. Furthermore, numerical results of spray characteristics are validated ‎with experimental data and a favorable agreement has been achieved. Based on ‎obtained results, increasing the injection pressure would cause an increase in ‎the spray penetration length and the spray cone angle and a decrease in the ‎Sauter mean diameter (SMD). However, increasing the injection pressure from ‎‎1000 to 2000 (bar) has more significant effect on improving spray ‎characteristics than an increase from 2000 to 3000 (bar).‎

In this paper, the effect of the injector geometry has been investigated on ‎characteristics of the internal nozzle flow and the cavitation phenomenon. To ‎this end, the cavitational flow inside a multi-hole diesel injector was simulated ‎using the computational fluid dynamics. The flow inside the nozzle was ‎considered transient and biphasic (liquid phase and vapor phase) and was ‎simulated using the Eulerian two-fluid model, which is a non-homogeneous ‎model. In this model, governing equations were solved for each phase ‎separately. The interaction between phases was modeled using relevant ‎interfacial exchange terms. To investigate the effect of the nozzle geometry on ‎the cavitational flow, the number of injector holes was varied from 2 to 8. ‎Results showed that by increasing the number of nozzle holes, the structure ‎and the intensity of the vortex flow in the nozzle sac and holes are extremely ‎varied. From the nozzle flow characteristics point of view, an increase in the ‎number of nozzle holes, resulted in a reduction in the injection velocity and the ‎mass flow rate and an increase in the cavitation intensity. Furthermore, the ‎discharge coefficient and the effective area of the nozzle fall with increasing the ‎number of nozzle holes. The simulation method was validated by comparing ‎numerical results with experimental data and a good agreement was achieved.‎