In the present study, different regimes of wall impingement in biodiesel spray were investigated in terms of emissions of diesel engines and performance and the best model for simulating the DI diesel engines fueled by biodiesel blends was presented. As shown by the findings, all aspects of wall impingement were considered in Walljet model, and it properly predicted the fuel droplet size generated by decomposition and penetration. Thus, it is possible to use it for simulating the biodiesel fuel spray atomization at varying engine operating conditions through the adjustment of the model constants.

Background and aims. The condensation silicone impression materials are available, but there is little knowledge of their accuracy after disinfection. The objective of this study was to evaluate the effect of the disinfection by spray atomization on dimensional accuracy of condensation silicone impressions.Materials and methods. Impressions were made on a stainless steel master model containing a simulated two complete crown preparation with an edentulous space interposed using Spidex® and Rapid® impression materials. 44 impressions were made with each material, of which 16 were disinfected with 5.25% sodium hypochlorite, 16 were disinfected with 10% iodophor and 12 were not disinfected. Three dimensional measurements of working casts, including interpreparation distance, height, and diameter, were calculated using a measuring microscope graduated at 0.001 mm. Dimensional changes (mm) between the disinfected and non-disinfected working casts were compared. One-way analysis of variance (ANOVA) was employed to analyze the data (α=0.05).Results. Disinfection of each condensation silicone material by spraying atomization with two different disinfectant material resulted in significant change in interpreparation distance (p< 0.05). Changes in height and diameter were only significant in Spidex® impressions (p< 0.05). Conclusion. Significant changes in the mean dimensions were seen as a result of disinfection by spraying; however, the dimensional changes do not seem great enough to cause critical positional distortion of teeth when fixed partial denture restorations are made.

Numerical modeling of internal nozzle flow can be regarded as an essential investigation in the field of gasoline direct injection system of combustion engines since it is directly connected with fuel spray atomization and subsequently efficiency of exhaust gas emission. Internal nozzle flow can be changed and formed according to several parameters such as; system pressure, chosen fuel type, the orientation of spray holes according to injector axis, conicity of spray holes and distribution of spray holes on valve-seat, etc. The changes in these parameters also affect the formation of cavitation inside of whole domain, spray angle and create wall-wetting on the spray hole surfaces. The present work investigates the parameter and design analysis in the valve-seat region of direct gasoline injection (GDI) injector using Computational Fluid Dynamics (CFD) and Design of Experiments (DOE). CFD is employed to study the behaviors of internal flow inside the valve-seat region according to several design parameters, whereas a mixed-level factorial design is used to test the significance of the effects on the response variables. In conclusion, the effects of the most significant factors on response parameters as amount of vapor formation, spray (Tau) angle, and pre-hole wall wetting are determined for further efficient design.

This paper investigates the effects of swirling air stream on a viscous hollow cone spray atomization with sinuous instabilities. The dimensionless dispersion equation of wave growth rate was derived with linear stability analysis. The dispersion equation is solved by numerical method and swirling air stream effect on maximum growth rate and its corresponding unstable wave number is investigated. The results show that the maximum growth rate of a swirling liquid sheet subjected to purely outer axial air is more pronounced compared to its counterpart subjected to purely inner axial air. In swirling air stream، swirling of outer air has more effect compared to inner air on maximum growth rate and improves the atomization. The combination of inner and outer air stream swirling has the highest effect on wave growth rate. The growth rate can be related to the breakup length of the liquid sheet and when the growth rate increases، breakup length is shorter. The drop diameter is dependent to the wave number and decreases with the increase of the wave number that can afford improvement of combustion and decrease the specific fuel consumption.

In this study, the combustion process and emission formation using a blend of biodiesel and diesel fule in the in-direct-injection diesel engine) Lister 8.1(at full load states have been simulated with a computational fluid dynamics (CFD). The utilized model was included detailed spray atomization, mixture formation and distribution model which are enable to modeling the combustion process in spray/wall and spray/swirl interactions along flow configurations. Simulation of combustion and expansion stroke was done, therefore qualitative analysis was presented. The results revealed that increasing the percentage of biodiesel in the fuel caused to increase indicated power, indicated specific fuel consumption and peak cylinder temperature. Also results showed that UHC and soot emissions decreased but NOx emission was increased. The results of this research in compare with the corresponding results in the literature and showed a good agreement.

The combustion processes and emission formation in pre and main chambers of a Lister 8.1 IDI diesel are simulated with the Computational Fluid Dynamics (CFD) code. The model includes spray atomization, mixture formation and distribution and subsequently the combustion processes and emissions formation modeling are carried out with considering of flow configurations in two chambers. A part load (50% load) and a full load simulation of engine are carried out. Also, the amount of mass burning rate of fuel, temperature, heat losses and emissions formation in pre and main chamber are presented with more details. The simulation results, such as the mean in-cylinder pressure and exhaust emissions are compared with the measured values and show good agreement. This work demonstrates that multidimensional modeling can be used at complex chamber geometry to gain more insight into the flow field, combustion process and emissions formation. The simulation results show that the CFD combustion simulation tool works quite correctly for the predicting combustion process and emission formation in Lister 8.1 IDI diesel engine.

A newly developed heavy duty diesel engine in dual fuel mode of operation has been studied in detail. The main fuel would be natural gas and diesel oil as pilot injection. The importance and effects of mixture preparation and formation through ports, valves and in cylinder flow field with different swirl ratio and tumble on diesel combustion phenomena is an accepted feature which has been studied using a developed CFD model together with a KIVA3-V2 code. This analysis is capable to investigate engine geometry, valves lift, and valves timing turbo charging, and its effects on dynamic flow field with variable dual fuel ratio on power and emission levels output. This complete open cycle study of a dual fuel engine has been carried out originally and for the first time and by considering complete grid consisted of four moving valves, two intake ports, two exhaust ports, and the port runners. It is found that important complex flow structures are developed during the intake stroke. While many of these structures decay during the compression stroke, swirl and tumble can survive. The effect of increased swirl ratio at the end of the compression stroke for the D87 engine with a piston bowl is clearly observed in this study. This is important for aiding in good fuel spray atomization. The formation, development, and break-up of tumble flow are seen, contributing to an increase in turbulent kinetic energy at the end of the compression stroke. The complete engine flow field, i.e. the inlet jet, and formation of swirl in the intake ports, is also clearly shown in the study. Results of these simulations assist in the improved understanding of the intake process and its influence on mixture formation and flow field in a dual fuel engine.

The prediction of the droplets diameter and the velocity distribution in a spray is very difficult، since its processes and mechanisms are not completely known and depends on many parameters. The early stage of the atomization process (Primary Breakup) is clearly deterministic، whereas the final stage of the spray formation (Secondary Breakup) is random and stochastic and deals with the stochastic aspect of the droplet size and the velocity distribution which is done using the maximum entropy principle (MEP). The MEP predicts the atomization process while satisfying constrain equations of the mass، the momentum and the energy. Finally، experimental results for an annular jet and a swirl nozzle were used to verify the modeling results for the size and the velocity distribution of spray droplets which shows a good agreement between modeling and experiments. The effect of some atomization parameters like Weber number، momentum and energy source terms were investigated on the droplets distribution.

In present work، the spray characterization and mixture formation in MAN B&W L16/24 DI diesel engines are studied by using FIRE CFD Code. In addition، the effect of WAVE، KH-RT and TAB different spray breakup models in prediction of performance and pollutants of diesel engines has been investigated. Finally، the accuracy of each model in comparison with experimental data was reported. Results showed that the WAVE model are the better ability to predict the decomposition of the fuel spray’s droplets and predicts the droplet size produced by penetration and decomposition، correctly. Therefore، it can be used for simulation of spray’s wall impingement at engine’s operating conditions.

In the present work the spray characteristics of bio-ethanol and its blends have been experimentally and theoretically investigated. To have a comprehensive study, the effects of ambient condition and injection pressure on the spray of different blends have been considered. Macroscopic and microscopic characteristics of spray such as tip penetration length, cone angle, projected area, volume, Sauter Mean Diameter (SMD), and Ohnesorge number are investigated precisely. Besides, air entrainment and atomization analysis have been carried out to improve mixture formation process. Using curve fitting and least squares method, theoretical correlations have been suggested in such a way to predict experimental results with the accuracy of 9.9%. To have a good estimation for the calculated parameters, uncertainty analysis has been performed. The results demonstrate enhancing the injection pressure or decreasing the ambient pressure, improve the atomization characteristics of spray. Moreover outcomes of this study indicate, spray tip penetration is enhanced by increasing the injection pressure or bio-ethanol percentage in the blend, while spray cone angle showing opposite behavior.