382 research outputs found
The Influence of Actual Layout and Off-Axis Needle Stroke on Diesel Nozzle Flow Under Ballistic Needle Displacement
No full textThe injection of small amount of diesel fuel relies on the shortening of energizing signal. In such injection conditions, the needle does not reach the mechanical stroke-end and its displacement is defined as ballistic. Some specific experimental work has been performed on how the dynamics of injector needle is reflected on the fuel flow pattern within the nozzle. Due to the intrinsic difficulties of the field, just single axial hole injectors have been optically investigated in real time, by means of the most advanced X-ray techniques. In the current study, based on 3D-CFD modeling, the investigation has been extended to multi-hole injector layouts, under typical pilot/split injection conditions, namely high injection pressure and low needle lift. The role of different factors on the flow development within the nozzle has been shown and discussed; the investigations have taken into account actual injector tip layouts and the response to the needle off-axis operating conditions. Results are presented highlighting the flow features within the nozzle and their reflects on the hole-to-hole differences
Hole Cross Section Shape Influence on Diesel Nozzle Flow
No full text"Progress in hole drilling technique is opening new perspectives in diesel nozzle design. In such a scenario, research on unconventional hole shapes looks worthwhile, in order to evaluate their influence on fuel flow features within the nozzle. In the present paper, investigations have been based on modeling. Moving from a standard hole configuration towards oval shaped holes, 3D-CFD campaigns have been devoted to highlight the hole layout influence on diesel nozzle flow. The investigations have been focused both on the fuel flow pattern at hole inlet and on the flow features at hole exit section; in such a modeling process, transient data concerning spatial distribution of velocity, turbulent kinetic energy and cavitation behavior at hole exit have been computed, highlighting the perturbations induced by the unconventional hole shape on the fuel flow; once the flow behavior has been explored, results have been resumed indicating how flow pattern properties are reflected at hole exit, quantitatively
Influence of Actual Injector Tip on Multi-Hole Diesel Nozzle Flow
No full textFlow rate imbalances among the nozzle holes are responsible for undesirable effects, as hole to hole differences, that worsen the regular fuel spray development. Multi hole injectors for common rail-equipped small diesel engines have been investigated by 3D-CFD modeling, under ballistic needle motion; simulation campaigns have been devoted to highlight, on one side, how the actual nozzle layout influences the fuel flow pattern upstream the nozzles; on the other side, the role of actual operating conditions of the injector has been studied. Relating to geometrical layout, different factors define the actual injector tip features; here, the effects of specific details have been taken into account; in the modeling of the actual nozzle layout, the effects of hole key-shape, inlet edge radius and hole diameter have been investigated, pointing out their influence on the fuel flow development. Then, regarding the modeling of injector actual operation, needle eccentricity and injector axis inclination have been considered, as well. Once the modeling details have been described, the fuel flow features are shown and discussed, both for VCO and Micro-Sac nozzle types, addressing the role of the different driving factors on the flow development
On a Modified VCO Nozzle Layout for Diesel Common Rail Injectors under Actual Needle Displacement
No full textThe mechanical-hydraulic behavior of the nozzle and the features of the internal flow are two fundamental factors in the spray formation process. In the current multi-injection strategies, short injections with reduced values of the needle lift are usual. In these cases, the nozzle can give rise to abnormalities in spray development, highlighted by irregularities and asymmetries. The main hole to hole differences are encountered in the rate of injection, in the spray shape and in the atomization process. The off-axis of the needle, the characteristics of the volume upstream of the holes and their geometry play a key role in causing such anomalies. In the paper, an unconventional VCO nozzle layout has been defined and analyzed by modeling. The study is oriented at evaluating its capability on reducing the dispersion among the flow features of the holes, when the pure axial needle displacement is perturbed. The investigated nozzle is based on a multihole layout but, referring to the injector axis, nozzle holes have a non-radial arrangement. In comparison with the standard VCO nozzle configuration, 3D-CFD simulations have been devoted to highlight the influence of the alternative nozzle layout on the internal flow and on the resulting spray features in the external ambient. In the modelling process, data concerning rate of injection, spatial distribution of velocity and cavitation behaviour at hole exit have been computed; specific attention has been focused on the fuel flow distribution among the holes; the computations have evidenced the behaviour of the unconventional layout when off-axis needle displacement is considered. Results have been resumed indicating how the internal flow pattern properties are reflected by the spray features
Pilot Injection Model for Small Diesel Cylinder
No full text"Pilot spray formation process has been analyzed by simulation. Investigating the influence of injection phasing and engine speed on vapor preparation process, the attention has been focused on fuel evaporation within cylinder. Once such a phase had been concluded, the indications on fuel shot evolution have been extrapolated and the obtained results have been used in the lumped parameter modeling of pilot spray evaporation. As the main driving factors regard both the injection system operation (injection pressure, needle opening, nozzle hole diameter and shape, fuel properties) and the in-cylinder conditions (in terms of pressure, temperature and charge motion), different simulation tools have been used. The complete injection system operation has been modeled with a 0-1D approach; the effect of nozzle flow conditions have been investigated by 3D-CFD transient simulations; the in-cylinder conditions and pilot shots evolution have been modeled by detailed 3D-CFD simulation of intake and compression strokes, in order to quantify the intensity of swirl-squish structures and their interaction, as well. The details of model approach have been described and the obtained results have been presented and discussed.
Coupling Codes for Nozzle Flow Modeling in Diesel Injection Systems
No full textThis paper deals with a numerical investigation of a single cylinder diesel engine equipped with mechanical fuel direct injection system and focuses on the fuel injection system modelling with the aim of predicting the performance of the entire injection system, the spray characteristics, the interaction among spray-cones, combustion chamber flows and geometry. In the simulations, two different codes have been used. With the former one, AMESim code, the complete injection system has been analysed and the single components have been selected and modelled. The results obtained from the injection system simulation, in terms of injection needle lift, injection flow rate, pressure time evolution, have been used to initialize the latter computation tool, FIRE code, in which 3D flow numerical investigation of the internal injector flow has been performed. Since such a flow is directly linked to the spray modelling, the primary break-up effects have been taken into account. The details of the adopted modelling strategy have been shown and the results of each simulation step have been presented. In order to highlight the relationship among the nozzle flow condition and the spray formation-vaporization characteristics, a comparison between two different calculation setups has been shown. Moreover, a qualitative comparison among predictions and experimental data has been discussed
Actual Tip Layout and Off-Axis Stroke In Nozzle Flow Modeling Under Ballistic Needle Displacement
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