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Accurate modelling for spray vapour fields is critical to enable adequate predictions of spray ignition and combustion characteristics of non-premixed reacting diesel sprays. Spray vapour characteristics are in turn controlled by liquid atomization and the KH-RT liquid jet break-up model is regularly used to predict this: with the KH model used for predicting primary break-up given its definition as a surface wave growth model, and the RT model used for predicting secondary break-up due to it being a drag based, stripping model. This paper investigates how the alteration of the switching position of the KH and RT sub-models within the KH-RT model impacts the resulting vapour field and ignition characteristics. The combustion prediction is handled by the implementation of a 54 species, 269 reaction skeletal mechanism utilising a Well Stirred Reactor model within the Star-CD CFD code. Following on from the derivation and implementation of an Ohnesorge based switch between the KH and RT sub-models, this model is now tested in igniting cases for an n-dodecane fuelled single holed injection representing the ECN “Spray A” condition, and is compared to the baseline Reitz-Diwakar model. Differences in flame behaviour, particularly within the temperature distribution, are seen and directly traced from the effect of liquid break-up position and model selection, through atomised droplet size distribution and mixture fraction distribution. Different criteria for judging the ignition delays and lift-off-lengths are compared, with all methods predicting very similar results for both models. The KH and RT sub-models are also tested against each other, with heavy instabilities seen when the RT model is solely applied to the spray. This correlates with the instabilities shown in the vapour fields, suggesting the enabling of the RT model near-nozzle is to be avoided.

[EN] In this study, a macroscopic characterization has been performed on a solenoid diesel injector (2200 bar-8 hole nozzle) under various non-reacting but evaporative conditions. For vapor penetration a two pass Schlieren visualization set up was selected. A high speed camera was used to record high speed images of the injection event to analyze the transient evolution of the vapor phase of the spray. The transient liquid penetration of the spray has been measured via MIE-Scattering imaging technique using a high speed camera as well. Unsteady RANS based CFD Simulations have been performed to simulate the experimental conditions and correlation results are presented. Built-in models from commercial code StarCD have been used to model spray formation which includes submodels for turbulence, nozzle flow, break-up and fuel properties. A novel CAE process using an automation and optimization tool has been used to achieve robust model settings, and the final model prediction are compared with the experimental observation for the injector characterization with respect to the non-reacting spray penetration with change in ambient and injection conditions. The model correlates well with the sensitivities for temperature and injection pressures qualitatively however improvements required to capture the density effects mainly related to the mesh orientation, fixed time step size where further analysis required., This research has been partially funded by FEDER and Spanish Ministerio de Economia y Competitividad through project TRA2015-67679-c2-1-R. Additionally Jhoan Sebastian Giraldo had a grant FPI-SUB 2 from Universitat Politecnica de Valencia.

[EN] Two prototypes multi-hole diesel injector from a high-pressure common rail system were used to operated with diesel and n-Heptane fuels in a high-pressure and high-temperature test rig able to reach 1100 K and 15 MPa under different oxygen concentrations with the goal to study the influence of the boundary conditions on the combustion process evaluating parameters as ignition delay, lift-off length and soot formation. A novel optical set-up was implemented to visualize the soot cloud evolution in the fuel jet between 30 and 85 nun from the nozzle exit using the high-speed color diffused back-illumination technique, it was used as a result of the insertion of a high-pressure window in the injector holder opposite to the frontal window of the vessel allowing an optical arrangement in line-of-sight. The experiments performed in this work used a LED with a wavelength of 460 nm to provide information about physical of the soot properties, the results of varying the operational conditions show the reduction of soot formation with an increase in injection pressure, a reduction in ambient temperature, a reduction in oxygen concentration or a reduction in ambient density. Furthermore, fuel effect on soot formation also has been studied showing a big difference between both fuels, diesel is known to be more prone to produce soot than n-Heptane reducing the ability of the technique implemented, especially in conditions with high temperature and high density., This research has been funded by Jaguar Land Rover. The author Santiago Cardona thanks the Universitat Politecnica de Valencia for his predoctoral contract (FPI-2016-S1), which is included within the framework of Programa de Apoyo para la InvestigaciOn y Desarrollo (PAID -01-2016). We would like to thank Omar Huerta for his collaboration during the measurement campaign and laboratory work.

Spray H (baseline n -heptane) cases of Engine Combustion Network (ECN) are investigated with the Flamelet Generated Manifold (FGM) method. In the FGM method, all thermo-chemical properties are stored as a function of controlling variables, here the mixture fraction and the progress variable. Two approaches are used to construct the FGM tables, igniting counterflow diffusion flamelets (ICDF) and homogeneous reactors (HR). To capture ignition delay times in a reliable way, a sensitivity study is performed to determine the optimal FGM table properties. It is observed that using quadratic discretization in progress variable space, i.e. more points in early stages of chemistry, is essential to predict accurate ignition timings. Once quadratic spacing is applied, the ignition delay time results show good correlation with those of experiments. This is observed with both ICDF- and HR-based FGM tables. The similarity between ignition delay results of two approaches indicates that the effect of mixing on chemistry is low and the diffusion process plays a minor role at elevated ambient conditions such as in conventional diesel engines. Finally, the effect of including the mixture fraction variance is analyzed and the impact is found mainly on the lift-off length. The ignition delay is hardly affected.

A novel solar water heating system, modified cuboid solar integrated-collector-storage (ICS) system with transparent insulation material (TIM) has been designed and developed, which combines collection and storage in a single unit and minimizes the nocturnal heat losses. A comprehensive study has been carried out to evaluate the heat transfer characteristics inside the enclosure of the system to enhance the collection and storage of solar energy. The transient behavior of the modified-cuboid solar integrated-collector-storage system is investigated numerically to evolve optimum configuration. The optimum design for the system is obtained by carrying out a numerical parametric study with different geometry parameters like the depth of the cuboid (d = 2, 5, 8, and 12 cm), and inclination angles (10�, 20�, 30�, and 50�). The inside heat transfer coefficient of the ICS system, stratification factor and water temperature distribution inside the enclosure have been predicted by numerical simulation. Average heat transfer coefficient at the bottom surface of absorber plate is 20% higher for depth of 12 cm as compared to the 2 cm depth of cuboid section, after 2 h of heating. The stratification factor also increases from 0.02 to 0.065 as depth of the system increases from 2 cm to 12 cm. There is a marginal effect of inclination angles of the system on the convection in the enclosure. As the inclination angle increases from 10� to 50�, the average heat transfer coefficient increases from 90 W/m2 K to 115 W/m2 K. But the stratification factor is comparatively high for lower inclination angles. With the optimum design parameters, a field experimental set-up was built and the numerical model was validated for efficient heat collection and storage in a modified cuboid ICS system. The model is in good agreement with the experimental results. � 2006 Elsevier Ltd. All rights reserved.

The Flamelet Generated Manifold (FGM) method is a promising technique in engine combustion modeling to include tabulated chemistry. Different methodologies can be used for the generation of the manifold. Two approaches, based on igniting counterflow diffusion flamelets (ICDF) and homogeneous reactors (HR) are implemented and compared with Engine Combustion Network (ECN) experimental database for the baseline n-heptane case. Before analyzing the combustion results, the spray model is optimized after performing a sensitivity study with respect to turbulence models, cell sizes and time steps. The standard High Reynolds ( Re ) k-e model leads to the best match of all turbulence models with the experimental data. For the convergence of the mixture fraction field an appropriate cell size is found to be smaller than that for an adequate spray penetration length which appears to be less influenced by the cell size. With the optimized settings, auto-ignition and flame lift-off length are analyzed. In general, both techniques capture the qualitative trend of experimental results. However, typically, the HR tabulation method predicts shorter ignition delay and LOL results than the ICDF method. In a quantitative sense, the ICDF and HR methods give better results in LOL and auto-ignition predictions, respectively.