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[EN] In this study, a numerical methodology for the optimization of the combustion chamber in compression ignited engines using OME as fuel is presented. The objective is to obtain a dedicated combustion system for an engine that is fueled with this alternative fuel improving the efficiency and reducing the emissions of NOx. This article proposes the integration between the optimization algorithm and CFD codes to evaluate the behavior of an engine fuelled with the low sooting fuel OME. Based on a diesel model validated against experimental data, a further model for OME fuel was implemented for evaluating the performance of the engine. The particle swarm algorithm (PSO) was modified based on the Novelty Search concepts and used as optimization algorithm. Several tools are coupled in order to create each CFD case where all the tools and optimization algorithm are coupled in a routine that automates the entire process. The result is an optimized combustion system that provides an increase of the efficiency (about 2.2%) and a NOx reduction (35.7%) in comparison with the baseline engine with conventional fuel. In addition, a neuronal network was trained with all the results of all simulations performed during the optimization process, studying the influence of each parameter on the emissions and efficiency. From this analysis it was concluded that the EGR rate and injection pressure affects the NOx emissions with a range of variability of 63% and 38% respectively.

[EN] The selective catalytic reduction (SCR) is a technology employed for NOx reduction purposes which is based on the injection of an Urea Water Solution (UWS) into the exhaust line. Conversion of this injected urea into ammonia is a key step to ensure high SCR efficiency. In order to study this phenomenon, a three-dimensional model of the urea-water injection process has been created to recreate realistic conditions. A Lagrangian-Eulerian approach has been followed to model liquid and gas phases, respectively. Droplet evaporation as well as relevant chemical processes have been included to recreate the thermolysis and hydrolysis phenomena, and the results have been validated against literature data. Then, the validated model has been applied to recreate an in-house experimental facility that measured spray macroscopic and microscopic characteristics by means of diffused back illumination (DBI) visualization. Probability density functions of the UWS droplet sizes as well as the velocity distributions have been obtained at three different regions of interest to be compared with the experimental data set. Contours of isocyanic acid and ammonia mass fractions have been included to show the chemical transformation from urea into its products. The model accurately replicates the experimental results, and it stands as a good methodology to predict the main spray characteristics as well as the chemical processes that take place in actual SCR systems.

[EN] The Selective Catalytic Reduction (SCR) technology allows the transformation of the Nitrous Oxide emissions present in exhaust gases into gaseous nitrogen and water. For a proper operation of the SCR, a urea-water solution (UWS) injector must dose an adequate amount of liquid into the exhaust pipe in order to avoid deposit formation and to guarantee the SCR system efficiency. This task requires the knowledge of the performance of the injector. Then, the goal of this work is to study the hydraulic performance of a UWS injector, by means of measuring the spray momentum flux in order to understand the influence of different variables as injected fluid, injection pressure, counter pressure and cooling temperature of the injector on the flow characteristics. The tested injector was cooled at three different temperatures, 60, 90 and 120 degrees C, the injection pressure of the UWS was set at 5, 7 and 9 bar, with counter pressures of 750, 900, 1000 and 2000 mbar for the two tested fluids, water and UWS. The measurements were carried out using an experimental facility developed at CMT-Motores Termicos for the determination of spray momentum flux, where a piezoelectric pressure sensor was located near the nozzle exit of the injector, which measures the impact force of the spray. Additionally, the proposed methodology allowed to determine the injected mass flow and to capture the transient injection events, such as the opening and closing stages. Moreover, mass flow rate measurements of the injector were performed under the same operating conditions, determining the influence of the injection pressure, cooling temperature, counter pressure and fluid properties. Regarding the pressure, the tendency was as expected, the higher the injection pressure the higher the Momentum flux and flow rate. Results showed that an increment of the cooling temperature of the injector induces the appearance of flash boiling conditions, having an impact on the total injected mass and momentu

[EN] Due to environmental problems, research on fuel economy and pollutant emissions in internal combustion engines has drawn the attention of automobile manufacturers and researchers. The diesel engine is one of the most efficient alternatives and one of the main areas of the study in these engines is spray mixing, recognized as a critical factor in combustion control and the reduction of its related contaminants. The studies about fuel sprays rely on experimental data of the rate of injection, which can only be obtained with high-cost equipment. The aim of this paper is to validate for different fuels a method for the determination of the rate of injection based on spray momentum measurements and the total injected mass. After a proper tuning of the test momentum flux device, the injection rate results were validated using the Bosch tube method. The technique was validated for four different fuels, diesel, biodiesel, GTL (Gas-to-liquid) and Farnesane, in order to identify the consequences of the fuel properties on the injection performance characteristics and the estimation method. The results of rate of injection following the procedures presented showed good accuracy when compared to experimental values. These methods can be employed to estimate this parameter when experimental facilities for this purpose are not available.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Industrial & Engineering Chemistry Research, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.iecr.0c02494., [EN] Exhaust after-treatment devices for NOx reduction have become mandatory for achieving the strict diesel emission standards. The selective catalytic reduction (SCR) method has proven to be efficient in this task. Nonetheless, in order to improve the efficiency of the system, the urea-water solution (UWS) injection process needs to be properly characterized due to the limited geometry of the exhaust line and its flow conditions. In combination with the experimental analysis into the system in a dedicated test rig, computational fluid dynamics studies provide better insights into the physical phenomena. Therefore, the main objective of this investigation is to achieve validated droplet size and velocity distributions in the simulation when compared to experiments. Three different positions along the spray are evaluated for that. The methodology adopted includes an Eulerian-Lagrangian approach to study the UWS spray. The results obtained with it show a proper experimental validation as well as the Sauter mean diameter distribution for the conditions tested. The proposed model accurately reproduces the main spray characteristics for different injection pressures and ambient conditions. Thus, the main conclusions obtained sum up in a good methodology for predicting UWS sprays in SCR-like conditions.

[EN] The injection process of the urea-water solution (UWS) determines the initial conditions for the mixing and evaporation of the fluid in the selective catalytic reduction system. In this study, the liquid atomization process of a UWS dosing system is investigated using optical diagnosis through back-light imaging. The droplet diameter distribution and the droplet velocity (in the axial and tangential components) of the liquid spray are quantified under different air flow and injection conditions. A new test facility was designed to study UWS spray under conditions that resemble those of the engine exhaust pipe, which is capable of reaching an air flow of 400 kg/h and air temperatures up to 400 degrees C. The test matrix consisted of variations in the air flow temperature, air mass flow and UWS injection pressure. A high speed camera was used for capturing the images of the liquid spray, comparing the atomized liquid behaviour in three different regions of the plume: the first one near the nozzle exit, and the other two in the developed region of the spray (one aligned with the injector axis and the other at the spray periphery). Increasing the injection pressure affected the atomization process producing smaller particles with higher velocities in the axial and tangential components, promoting wider global spray angles, that combined with high air flow temperatures could improve the evaporation and mixing process in the SCR system. The main contribution is the development of an alternative technique for the quantification of the droplet size and velocity.

[EN] Currently, diesel engines are calibrated using more and more complex multiple injection strategies. Under these conditions, the characteristics of the flow exiting the fuel injector are strongly affected by the transient interaction between the needle, the sac volume and the orifices, which are not yet clear. In the current paper, a methodology combining a 1D injector model and 3D-CFD simulations is proposed. First, the characteristics of the nozzle flow have been experimentally assessed in transient conditions by means of injection rate and momentum flux measurements. Later, the 3D-CFD modeling approach has been validated at steady-state fixed lift conditions. Finally, a previously developed 1D injector model has been used to extract the needle lift profiles and transient pressure boundary conditions used for the full-transient 3D-CFD simulations, using adaptive mesh refinement (AMR) strategies to be able to simulate the complete injection rate starting from 1 mu m lift.

[EN] Awareness of climate change, fossil fuel availability, and pollutants has been growing which have pushed forward the effort in cleaner engines. In this aspect, the gasoline engines have more improving margin than diesel engines. To have a more efficient combustion, injection systems had evolved from old Port Fuel Injectors to modern Gasoline direct injections which are the used by engine manufacturers nowadays. In this study, within the framework of the Engine Combustion Network (ECN), the so named Spray G is modelled. This gasoline direct injector was developed by Delphi with the intention of getting a better understanding of the gasoline spray. The model is focused on the Rate of Injection (ROI) signal, whose results are presented in order to help engine calibration and modelling for an extensive range of configurations without the need for experimental measurements.

[EN] The use olschlieren imaging at high acquisition rate has been adopted as a standard optical technique for the analysis of vaporizing diesel sprays under engine-like conditions. A single-pass schlieren arrangement is typically used for the study of axially drilled single-orifice nozzles, as vessels with multiple optical accesses regularly allow line of sight visualization. Contrarily, for multi-spray nozzles, measurements are commonly performed through a single,optical access, in which case a double-pass arrangement is employed. As a consequence, the light beams pass through the test section twice, increasing the optical sensitivity of the schlieren setup. However, the influence this has on the macroscopic spray characteristics is still unclear. The scope of this study is to analyze the differences in vapor phase penetration and spreading angle measured for the same injection event, through high-speed imaging, for both single and double-pass schlieren configurations. Experiments were carried out with a three hole nozzle with a nominal orifice diameter of 90 mu m, named Spray B from the Engine Combustion Network, using commercially available diesel fuel and in non-reactive conditions. The impact of different injection pressures, chamber temperatures and densities on the spray captured by each setup was assessed. On the results, vapor. phase penetration and spreading angle followed the expected trend found in the literature, for the different boundary conditions tested. Comparing the optical setups, vapor phase penetration and spreading angle results obtained with the double-pass arrangement were marginally higher than those from the single-pass. The deviation was observed throughout all tested conditions. For spray tip penetration, although the discrepancy was approximately constant for different injection pressures and chamber temperature, it increased with increasing density. These results highlight the importance of a proper understanding regarding the limitat

[EN] Accurate experimental data are often needed to validate computational fluid dynamics models. These models regularly rely on experimental results from single-orifice axially drilled nozzles that do not fully represent real injectors, as the difference in inclination angles creates turbulent conditions at the nozzle outlet, consequences of which on the spray development are not yet fully understood. In this work, near-field visualization was done for two nozzle inclination angles in non-vaporizing conditions. Spray tip penetration, spreading angle, and axis angle fluctuations are reported. Three hypotheses are analyzed: liquid jet breakup mechanism, internal flow development, and cavitation. Experiments were carried out using n-Dodecane, testing a single orifice axially drilled and a three-orifice injector, from the Engine Combustion Network. The spray was observed with a diffused back-illumination technique and a long distance microscope, only visualizing the first 6 mm of spray tip penetration, for three injection pressures and four gas densities at ambient temperature. The multi-orifice injector produced a spray with wider spreading angle, which resulted in smaller penetration values. Additionally, higher spray axis angle fluctuations were observed for the multi-orifice injector, which increased for higher injection pressure and, to a lesser extent, with decreasing chamber density. Further analysis was performed with spreading angle fluctuations measurements, where results showed good agreement with spray axis angle fluctuations trends, implying that complex internal flow structures, and even incipient cavitation, could be present in the multi-orifice injector and be the cause of these spray axis angle fluctuations.

In this research, two Engine Combustion Network (ECN) mono-orifice nozzles, referred to as Spray C and Spray D. respectively, were analyzed by performing visualization tests through Schlieren and Diffused Backlight Illumination (DBI) techniques under a wide range of ambient conditions in a non-reactive atmosphere. Spray C presents a straight nozzle designed with a sharp fillet in opposition to Spray D that has similar hydraulic properties, but with a convergent nozzle construction and a smoother corner. The experiments were carried out injecting two distinct fuels at different injection pressure ranges, from 50 MPa to 150 MPa with n-dodecane and to 200 MPa for diesel. The images were processed with Matlab home-built routines to calculate parameters as spray penetration, spreading angle, quasi steady liquid length, as well as the spray penetration derivative respect to the square root of time, presented in this document as R-parameter. The results showed a clear influence of nozzle geometry in all measured parameters, due mainly to the nature of Spray C to cavitation, which increase the spreading angle and consequently a reduction in vapor penetration. On the other hand, fuel properties also affected spray penetration due to its dependency on viscous forces expressed in terms of the Reynolds number and its volatility in case of liquid length. This last parameter was calculated employing two processing methodologies, finding a good general agreement between them.

A lot of effort has been put in the past years into the understanding of the delivery and development of diesel sprays in engine-like conditions as it has been proved to be a very important step for the design of better and cleaner commercial engines. Due to the bigger share of passenger cars engines over heavy duty engines, the research has been mainly focused on the investigation using small nozzles. This paper studies two nozzles with diameters representative of those that can be encountered in heavy duty engines, with the objective of corroborating the conclusions gathered for small nozzles representative of passenger car engines. The experimental data have been acquired by state-of-the-art techniques and equipment, and serves two purposes: further the understanding of the physics involved in the injection event and spray evaporation; and provide a dataset to CFD models that can accurately predict the behavior of the injection event. The tests were performed in a constant pressure flow vessel that allows to simulate engine-like conditions (1000 K and 15 Mpa) with continuous flow. The injection system tested is a novel, common-rail, solenoid-actuated injector for heavy duty applications which operates up to 220 Mpa. All experiments were performed in non-reacting conditions. The extended test matrix allowed to determine the influence of several parameters such as rail pressure, gas temperature, gas density, and nozzle geometry on the air-fuel mixing and evaporation process, by analyzing the spray penetration and spreading angle. Mie scattering and double-pass Schlieren optical configurations have been used to measure global liquid and vapor penetration, respectively. The data proves that spray penetration at low temperature can be up to 15% faster than spray penetration at high temperature conditions at the same density for the nozzles experi-mented, which limits the usability of low temperature experiments to infer the behavior of the injector at high temperature

[EN] The present study gives a general outline for the fluid-dynamical calculation of flows at high pressure conditions. The main idea is to present a mathematical description of high pressure processes in liquids at compressible conditions, quantifying the effect of density variations on the flow pattern due to those pressure variations. The improved mathematical approach is coupled to a Large Eddy Simulation (LES) solver. The main code was developed by OpenSource Ltd. for OpenFOAM, and the authors have introduced the additional expressions in order to calculate particular variables. For validating the code improvement, the LES solver is applied to a modern common-rail nozzle injector used in diesel engines. Results have been compared against other calculations that assumed constant properties and simultaneously validated with experimental data. © 2010 Elsevier Ltd.

The current work focuses on the study of the influence of pressure and temperature on three important thermodynamic properties: speed of sound, compressibility and density of common diesel fuels. The sample fuels studied were conventional diesel (Repsol Elite), Rape Methyl Ester (typical bio-diesel used in Spain) and a fuel used especially for winter season (Arctic). Speed of sound and densities has been determined experimentally. The third property, bulk modulus, has been calculated from the other two. Speed of sound measurements have been carried out in wide range of temperatures (298 < T/K < 343) and pressures (15 < p/MPa < 180), which represent the typical values used in injection systems for diesel engines. Hence, a particular configuration was coupled to the high-pressure injection system, obtaining accurate measurements at these extreme conditions. A detailed description of the method is presented; also, the obtained results are listed, with an uncertainty of ~0.3%. Density measurements have been performed over a broad range of temperatures (298 < T/K < 343), using two commercial devices, obtaining an overall uncertainty of ~0.6%. © 2010 Elsevier Ltd. All rights reserved.