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The impact of passive pre-chamber (PC) internal volume, nozzle hole pattern (i.e. with and without a central axial nozzle), and PC igniter plug type on performance and emissions was investigated in an optically accessible, single-cylinder, gasoline research engine. The two PC igniter plugs investigated were a conventional inductive coil spark plug and a nanosecond repetitively pulsed (NRP) plasma discharge system previously demonstrated to accelerate early flame propagation. The baseline PC design featured a funnel shaped internal volume with a PC tip that contained six radial nozzles and a larger central axial nozzle. Two additional PC tip geometries were evaluated where either the baseline internal volume was increased or the axial nozzle was removed and the radial nozzle diameters were increased. A sweep of charge equivalence ratios ( ϕ) from nearly stoichiometric to the lean limit was performed for a fixed engine speed (1300 revolutions per minute), and engine load (3.5 bar gross indicated mean effective pressure). Time-resolved PC and main chamber (MC) pressure data as well as MC emissions data were collected to analyze engine performance and emissions characteristics. Combustion in the MC was further investigated using high-speed excited methylidyne radical (CH*) chemiluminescence imaging. Collected results highlighted that while all PC tips and ignition systems exhibited similar performance and emissions down to ϕ = 0.8, relevant differences in thermal efficiency and emissions for leaner charge mixtures were observed, with the results highly dependent on the nozzle pattern and ignition system. Major deviations were correlated to preferential de-pressurization of the PC through the axial nozzle for lean conditions that was not observed for mixture conditions closer to stoichiometric. Results show that a combination of radial and axial nozzle patterns in the PC extended lean-stability limits at the low-load condition evaluated. Further benefits were observed with the use of NRP ignition systems due to faster combustion within the PC volume provided that the volume was sufficiently large.

Mitigation of the carbon footprint of internal combustion engines is mandatory to ensure a future for this technology. Within this scope, e-fuels are considered a potential solution to replace conventional fossil fuels. However, in some cases, their physical and chemical properties are so different that its application in conventional engines is complex. For this reason, this work focuses on the study of oxymethylene ethers (OMEX) as a potential low-carbon fuel alternative. The aim is to improve the understanding of the combustion process of these e-fuels when they replace fossil Diesel in internal combustion engines under equivalent operating conditions. To achieve this objective, a computational fluid dynamics model of an optical compression ignition engine has been developed. The operating conditions chosen are representative of a medium load point of the engine, which coincide with experimental work previously done on this platform. n-Heptane was used as surrogate of fossil Diesel while OMEX was simulated as a simpler mixture of oxymethylene ether molecules. Results show remarkable differences between Diesel and OMEX. This fuel provides lower equivalence ratio fields. Thus, oxidation reactions are promoted in wider areas within the combustion chamber, leading to a faster combustion process. Besides, the soot formation is also drastically decreased in comparison to the other fuel. These results have been corroborated with experimental information.

In recent decades, the importance of emerging alternative fuels has increased significantly as a solution to the problems of global warming and air pollution from energy production. In this context, ammonia (NH3) is seen as a potential option and energy vector that may be able to overcome the technical challenges associated with the use of other carbon-free fuels such as hydrogen (H2) in internal combustion engines (ICE). In this research, a numerical methodology for evaluating the impact of using ammonia as a fuel for spark-ignition ICEs has been developed. A combination of a single-cylinder and multi-cylinder numerical experiments has been performed to identify the main challenges and determine correct engine configuration. In addition, the performance of the engine has been evaluated through standard homologation driving cycles, contrasting it with other alternative propulsion configurations. Finally, a simplified life cycle assessment (LCA) has been carried out to compare the global emissions with those of conventional combustion and electric technologies in the European automotive framework.

Fuel film deposits on combustion chamber walls are understood to be the main source of particle emissions in GDI engines under homogenous charge operation. More precisely, the liquid film that remains on the injector tip after the end of injection is a fuel rich zone that undergoes pyrolysis reactions leading to the formation of poly-aromatic hydrocarbons (PAH) known to be the precursors of soot. The physical phenomena accompanying the fuel film deposit, evaporation, and the chemical reactions associated to the injector film are not yet fully understood and require high fidelity CFD simulations and controlled experimental campaigns in optically accessible engines. To this end, a simplified model based on physical principles is developed in this work, which couples an analytical model for liquid film formation and evaporation on the injector tip with a stochastic particle dynamics model for particle formation. The modeling framework is applicable under steady-state engine operating conditions, and can be extended to transient driving cycle simulations, although the former is only presented in this work. Particle number, mass, and size distributions are validated with experimental measurements performed on a steady-state engine test bench for a 2.0L turbocharged gasoline engine under two engine speeds at part and full load. The model is able to qualitatively capture the main trends in particle number concentration values, especially at the higher load conditions. An underestimation of PN and PM at lower loads is observed, which can be attributed to other sources of particle formation.

Pre-chamber spark ignition (PCSI) systems have been proven to improve combustion stability in highly-diluted and ultra-lean natural gas (NG) engine operation by providing spatially distributed ignition initiated by multiple turbulent flame-jets that lead to faster combustion compared to conventional spark ignition. This work investigates the physico-chemical processes that drive the ignition and subsequent combustion in the presence of combustion residuals (internal EGR) within the pre-chamber at varying EGR levels. The over-arching goal is to improve the dilution tolerance of PCSI systems for stoichiometric-operation of on-road heavy-duty natural gas engine. To this end, experiments were performed in a heavy-duty, optical, single-cylinder engine to explore the EGR dilution limits of a pre-chamber, spark-ignited, NG engine operated under stoichiometric conditions. A special skip-fire sequence is utilized to distinguish the effects of in-cylinder combustion residuals from external EGR. Optical diagnostics involving high-speed OH* chemiluminescence imaging and infrared (IR) imaging are acquired simultaneously to probe the ignition, development of pre-chamber jets and the subsequent combustion behavior of the main-chamber charge under various EGR dilution rates. The imaging results and the thermodynamic analysis show that the presence of combustion residuals within the pre-chamber lead to slower spark kernel development resulting in lower ΔP, retarded main-chamber ignition and subsequently slower main-chamber combustion. Cycle-to-cycle variations and tendency to misfire increased with increasing EGR dilution, with combustion residuals making this effect more pronounced. Advancing the spark timing, despite lowering ΔP (due to reduced fuel mass in the pre-chamber and increasing back pressure) can sufficiently compensate for reduced [O2] at low to moderate EGR levels. Failed re-ignition of pre-chamber jets is the main cause of increased cycle-to-cycle fluctuations and misfire under the tested conditions.

Despite recent advances towards powertrain electrification as a solution to mitigate pollutant emissions from road transport, synthetic fuels (especially e- fuels) still have a major role to play in applications where electrification will not be viable in short-medium term. Among e-fuels, oxymethylene ethers are getting serious interest within the scientific community and industry. Dimethoxy methane (OME1) is the smaller molecule among this group, which is of special interest due to its low soot formation. However, its application is still limited mainly due to its low lower heating value. In contrast, other fuel alternatives like hydrogenated vegetable oil (HVO) are considered as drop-in solutions thanks to their very similar properties and molecular composition to that of fossil diesel. However, their pollutant emission improvement is limited. This work proposes the combination of OME1 and HVO as an alternative to fossil diesel, to achieve noticeable soot emission reductions while compensating for the different properties of the first fuel.The aim of this work is to provide insight into the combustion characteristics of blends of these two fuels. For this purpose, experimental and numerical studies are combined. In this context, n-dodecane is proposed as a surrogate for HVO simulation based on the high similarities experimentally observed between both fuels. Then, a compact kinetic mechanism is developed and validated, combining individual OME1 and n-dodecane mechanisms. Results confirm that the numerical approach followed was able to capture the experimental behavior of these blends in terms of heat release rate, in-cylinder pressure and soot formation. An increase of the OME1 content in the blend greatly influences the combustion process. The ignition delay, as well as the premixed combustion phase peak, increase with the OME1 percentage in the blend. However, HVO helps on limiting this effect while remarkable soot formation reductions are still achieved thanks to OME1.

Among the possible electric powerplants currently driving low-payload UAVs (up to around 10 kg of payload), batteries offer certain clear benefits, but for medium-payload operation such as aerotaxis and heavy-cargo transportation UAVs, battery capacity requirements restrict their usage due to high weight and volume. In light of this situation, fuel cell (FC) systems (FCS) offer clear benefits over batteries for the medium-payload UAV segment (> 50 kg). Nevertheless, studies regarding the application of FCS powerplants to this UAV segment are limited and the in-flight performance has not been clearly analysed. In order to address this knowledge gap, a feasibility analysis of these particular applications powered by FCS is performed in this study. A validated FC stack model (40 kW of maximum power) was integrated into a balance of plant to conform an FCS. As a novelty, the management of the FCS was optimized to maximize the FCS efficiency at different altitudes up to 12500 ft, so that the operation always implies the lowest H2 consumption regardless of the altitude. In parallel, an UAV numerical model was developed based on the ATLANTE vehicle and characterized by calculating the aerodynamic coefficients through CFD simulations. Then, both models were integrated into a 0D-1D modelling platform together with an energy management strategy optimizer algorithm and a suitable propeller model. With the preliminary results obtained from the FCS and UAV models, it was possible to ascertain the range and endurance of the vehicle. As a result, it was concluded that the combination of both technologies could offer a range over 600 km and an endurance over 5 h. Finally, with the integrated UAV-FCS model, a flight profile describing a medium altitude, medium endurance mission was designed and used to analyse the viability of FC-powered UAV. The results showed how UAVs powered by FCS are viable for the considered aircraft segment, providing competitive values of specific range and endurance.

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Project management plan for the ALL-IN Zero project

The effects of passive pre-chamber (PC) geometry and nozzle pattern as well as the use of either conventional spark or non-equilibrium plasma PC ignition system on knocking events were studied in an optically-accessible single-cylinder gasoline research engine. The equivalence ratio of the charge in the main chamber (MC) was maintained equal to 0.94 at a constant engine speed of 1300 rpm, and at constant engine load of 3.5 bar indicated mean effective pressure for all operating conditions. MC pressure profiles were collected and analyzed to infer the amplitude and the frequency of pressure oscillations that resulted in knocking events. The combustion process in the MC was investigated utilizing high-speed excited methylidyne radical (CH*) chemiluminescence images. The collected results highlighted that PC volume and nozzle pattern substantially affected the knock intensity (KI), while the use of the non-equilibrium plasma ignition system exhibited lower KI compared to PC equipped with a conventional inductive ignition system. It was also identified that knocking events were likely not generated by conventional end gas auto-ignition, but by jet-related phenomena, as well as jet-flame wall quenching. The relation between these phenomena and PC geometry, nozzle pattern, as well as ignition system has been also highlighted and discussed.

In this paper the acoustic response of a combustion chamber is studied by assuming different pressure field excitation. The viscous effects on the combustion chamber and the finite impedance of the walls have been modeled with a first order system, which damps the resonance oscillation created by combustion. The characterization of the acoustic response of the combustion chamber has been used to identify the source of the excitation in order to distinguish normal combustion from knock. Two engines, a conventional spark ignited (SI) and a turbulent jet ignition (TJI) engine, were used, fueled with gasoline and compressed natural gas (CNG), respectively. The pressure fluctuations in the combustion chambers are analyzed and a pattern recognition system identifies the most likely source of excitation. This new criteria for knock identification permits a more consistent differentiation between knocking and no-knocking cycles, independent on the amplitude of the phenomenon, thus allowing the improvement for knock control algorithms, specially with combustion modes which heavily excite resonance, such as turbulent jet ignition or homogeneous charge compression ignition (HCCI).

[EN] Fuel efficiency improvement and harmful emissions reduction are the main motivations for the development of gas turbine combustors. Numerical computational fluid dynamics (CFD) simulations of these devices are usually computationally expensive since they imply a multi-scale problem. In this work, gaseous non-reactive unsteady Reynolds-Averaged Navier-Stokes and large eddy simulations of a gaseous-fueled radial-swirled lean direct injection combustor have been carried out through CONVERGE (TM) CFD code by solving the complete inlet flow path through the swirl vanes and the combustor. The geometry considered is the gaseous configuration of the CORIA lean direct injection combustor, for which detailed measurements are available. The emphasis of the work is placed on the demonstration of the CONVERGE (TM) applicability to the multi-scale gas turbine engines field and the determination of an optimal mesh strategy through several grid control tools (i.e., local refinement, adaptive mesh refinement) allowing the exploitation of its automatic mesh generation against traditional fixed mesh approaches. For this purpose, the normalized mean square error has been adopted to quantify the accuracy of turbulent numerical statistics regarding the agreement with the experimental database. Furthermore, the focus of the work is to study the behavior when coupling several large eddy simulation sub-grid scale models (i.e., Smagorinsky, Dynamic Smagorinsky, and Dynamic Structure) with the adaptive mesh refinement algorithm through the evaluation of its specific performances and predictive capabilities in resolving the spatial-temporal scales and the intrinsically unsteady flow structures generated within the combustor. This investigation on the main non-reacting swirling flow characteristics inside the combustor provides a suitable background for further studies on combustion instability mechanisms., The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was partly sponsored by the program "Ayuda a Primeros Proyectos de Investigacion (PAID-06-18), Vicerrectorado de Investigacion, Innovacion y Transferencia de la Universitat Politecnica de Valencia (UPV), Spain.'' The support given to Mr. Mario Belmar by Universitat Politecnica de Valencia through the "FPI-Subprograma 2'' grant within the "Programa de Apoyo para la Investigacion y Desarrollo (PAID-01-18)'' is gratefully acknowledged.

During the last years, the sales of vehicles equipped with Spark-Ignition (SI) engines have increased, to the detriment of those powered by Compression-Ignition (CI) engines. However, SI engines provide lower efficiency than CI engines, due to the low compression ratio and stoichiometric mixture operation. A way to increase the efficiency of SI engines is lean combustion, as it allows to increase the specific heats ratio (γ) and reduces pumping losses at part loads. Nevertheless, the operation with extremely lean mixtures deals with ignition issues, promoting Cycle-to-Cycle Variability (CCV) and increasing the probability of misfire. The prechamber ignition concept, also known as Turbulent Jet Ignition (TJI), is a promising solution for enabling the implementation of lean combustion, without its drawback in SI engines. Such a concept can be implemented according to two approaches: In active TJI, there is an additional fuel supply system inside the prechamber, while in passive TJI there isn’t. Therefore, the main advantage of passive TJI is its simplicity, as the prechamber can be installed into a conventional spark plug body, with obvious benefits in terms of packaging and costs. In this work, the benefits of passive TJI on combustion and performance are assessed by simulation analyses. Particularly, a 1-D engine model was developed to simulate the TJI combustion and was validated versus experimental data. Afterward, a 0-D method was applied to assess the impact of the relative air-fuel ratio on CCV. The analysis was carried out in a high speed and load operating condition, namely 4500 rpm and 13 bar of IMEP, under both stoichiometric and lean mixture. Experimental and numerical results demonstrate the effectiveness of the passive TJI concept in promoting faster and more stable combustion also in lean-burn conditions.

[EN] In transport applications, reciprocating internal combustion engines still have important advantages in terms of endurance and refueling time and available infrastructure when compared against fuel cell or battery-based powertrains. Although conventional internal combustion engine configurations produce important amounts of greenhouse gases and pollutant emissions, oxy-fuel combustion can be used to mitigate to a great extent such emissions, mainly producing NOx-free, CO2 and H2O exhaust gases. However, the oxygen needed for the combustion, which is mixed with flue gases before entering the cylinder, has to be stored in an additional tank, which hinders the adoption of this technology. Fortunately, the latest developments in gas separation membranes are starting to produce extremely-high selectivity and high permeability oxygen-separation membranes. Using the waste heat of the exhaust gases to heat up a mixed ionic-electronic conducting membrane, and feeding it with pressurized air, it is possible to produce all the oxygen needed by the combustion process while keeping the whole system compact. This work presents a design of an oxy-fuel combustion engine with in-situ oxygen production. The numerical simulations show also that this concept keeps a competitive brake specific fuel consumption, while the high concentration of CO2 in the exhaust gases facilitates the introduction of carbon sequestration technologies, leading to potentially carbon-neutral internal combustion engines., The authors want to acknowledge the institution "Conselleria d'Educacio, Investigació, Cultura i Esport de la Generalitat Valenciana" and its grant program "Subvenciones para la contratacion de personal investigador de caracter predoctoral" for doctoral studies (ACIF/2020/246) funded by The European Union. This research was partially supported by the institution "Agencia Valenciana de la Innovacion (AVI)" and its grant program "Valorizacion y transferencia de resultados de investigación a las empresas. Línea 1. Valorizacion, transferencia y explotación por las empresas de resultados de I+D. Convocatoria 2021" for project named Demostrador de un motor de oxicombustion con captura de CO2 (DMOCCO2)" INNVA1/2021/38, under the European Regional Development Fund (ERDF) program.

[EN] Experimental results from a study on the evolution of gas jets ejected through the orifices of a pre-chamber in a heavy-duty optical engine are presented. The work examines conditions without fuel inside the main-chamber, which helps to describe the dynamics of the ejected gas jets without the interference of subsequent combustion in the main-chamber. Experimental diagnostics consist of high-speed visible intensified imaging and low-speed infrared imaging. Additionally a one-dimensional gas jet model is used to characterize the spatial distribution of the ejected flow, including parameters such as tip penetration, which are then validated based on experimental results. Different stages in the ejection of pre-chamber jets are identified, with chemical activity restricted to a maximum distance of 5 to 10 orifice diameters downstream of the orifice as indicated by the recorded visible radiation. Sensitivity of cycle-to-cycle variations in pre-chamber jet development to the air-to-fuel ratio in the pre-chamber observed in the experiments is in most part attributed to the variations in the timing of combustion initiation in the pre-chamber. The influence of the ejection flow on the penetration of the gas jet on a cycle-tocycle basis is presented using the one-dimensional model. The one-dimensional model also indicates that the local flow exhibits highest sensitivity to operating conditions during the start of ejection until the timing when maximum flow is attained. Differences that exist during the decreasing mass-flow ejection time-period tend to smear out in part due to the transient slowdown of the ejection process, This research was sponsored by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE). Optical engine experiments were conducted at the Combustion Research Facility, Sandia National Laboratories, Livermore, CA. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. Jose M Garcia-Oliver acknowledges the support of the Generalitat Valenciana government in Spain through Grant Best/2019/176 for his scientific visit to the Combustion Research Facility. P. J. Martinez-Hernandiz is partly supported by an FPI contract (FPI-S2-19-21993) of the "Programa de Apoyo para la Investigacion y Desarrollo (PAID05-19)" of the Universitat Politecnica de Valencia

[EN] Hydrogen is one of the most promising alternative fuels for the transportation industry. The use of hydrogen to enable lean burn in internal combustion engines is an attractive solution for reducing CO2 emissions from two points of views: the substitution of carbon-based fuels and the increased thermal efficiency due to lean operation. Combining this strategy with the passive pre-chamber ignition system with gasoline/hydrogen blends is even more interesting. The main limitations of the passive pre-chamber concept in a high compression ratio spark-ignition engine were shown through engine experiments. A numerical study was then performed to evaluate the chance of extending the dilution limit by using hydrogen along with this technology. Results show how the use of hydrogen provides considerable benefits in the main chamber combustion process by enhancing the thermo-chemical properties of the mixture, increasing the flame speed, and improving the flame structure. Using an adequate gasoline-hydrogen blend proved to enable optimum burning rates at lean conditions, leading to a relevant thermal efficiency gain., Ministerio de Economia, Industria y Competitividad, Gobierno de Espana, Grant/Award Number: TRA2017-89139-C2-1-R; Universitat Politecnica de Valencia, Grant/Award Number: FPI-S1-2019-0033

[EN] The engine oil contamination by both particulate matter (PM) and fuel is becoming an important problem since strategies to control pollutant emissions in internal combustion engines (ICE) significantly increase their presence in engine oil. As a consequence, the engine oil loses its tribological properties compromising engine lubrication and leading to potential problems in engine such as wear, corrosion, etc. For that reason, the study of the oil degradation and contamination due to these strategies have a special interest to the engine manufacturers and engine oil formulators. In this paper, the engine oil soot content and fuel dilution is analysed under real engine conditions. The study is addressed from two different but complementary points of views. First, on-line measurements at several engine operating conditions are performed in order to further understand how the soot generation correlates with the oil soot content and other derived problems on oil performance. Then, experimental data available after the experimental campaign is used to calibrate a numerical model, based on Computational Fluid Dynamics (CFD), that estimate the amount of soot particles settled in the engine oil. Results show that soot particles are more present in oil when operating high load-speed conditions and during the Diesel Particulate Filter (DPF) regeneration cycles. Regarding the fuel dilution, delayed post-injections are critical since they significantly increase the amount of fuel in the engine oil. Numerical results also show the relationships between the soot particles generated during combustion and the amount of soot in engine oil, giving an enhanced comprehension of soot-in-oil deposition mechanisms., A. Garcia-Barbera is partially supported through the Programa Nacional de Formation de Recursos Humanos de Investigacion of Spanish Ministerio de Ciencia e Innovation [grant number BES-2016-078073]. The authors also wish to thank Dr. José M. Pastor for his inestimable assistance in the CFD model implementation and data post-processing.

[EN] Computational fluid dynamics (CFD) modeling has many potentials for the design and calibration of modern and future engine concepts, including facilitating the exploration of operation conditions and casting light on the involved physical and chemical phenomena. As more attention is paid to the matching of different fuel types and combustion strategies, the use of detailed chemistry in characterizing auto-ignition, flame stabilization processes and the formation of pollutant emissions is becoming critical, yet computationally intensive. Therefore, there is much interest in using tabulated approaches to account for detailed chemistry with an affordable computational cost. In the present work, the tabulated flamelet progress variable approach (TFPV), based on flamelet assumptions, was investigated and validated by simulating constant-volume Diesel combustion with primary reference fuels - binary mixtures of n-heptane and iso-octane. Simulations were initially carried out to evaluate and compare the performance of two kinetic models in homogeneous reactors and laminar diffusion flames, followed by turbulent reacting spray simulations considering different fuels, ambient temperatures, and oxygen concentrations. The sensitivity study of the turbulent Schmidt number was then conducted, and results in terms of ignition delay and lift-off length were compared with experimental data to determine a more appropriate global constant. Finally, parametric variations of ambient temperature and oxygen concentration were performed for six fuel blends ranging from PRF0 (n-heptane) to PRF100 (iso-octane), confirming the validity of the TFPV model., Authors acknowledge the financial support from the China Scholarship Council (No. 201806230180) and Natural Science Foundation of China (No. 51961135105) for the first author's study in Politecnico di Milano, Italy

[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., The work has been partially supported by the Spanish Ministerio de Economia, Industria y Competitividad through Grant No TRA2017-89139-C2-1-R "Desarrollo de modelos de combustion y emisiones HPC para el analisis de sistemas de transporte sostenibles" The author C. S. Fernandes thanks the Universitat Politecnica de Valencia for his predoctoral contract (FPI-2019-S2-20-555) , which is included within the framework of Programa de Apoyo para la Investigacion y Desarrollo (PAID)

This paper proposes an educational methodology for the development of the specific instrumental soft skill in Aerospace Engineering degree students. This methodology uses an autonomous and active learning approach to measure, through two different techniques, the local flow velocities around a circular cylinder in a subsonic wind tunnel. The students are directly involved in the complete measuring procedure through practical sessions in a lab, applying directly Hot-Wire Anemometry (HWA) and Particle Image Velocimetry (PIV) techniques, and reporting the analysis of the results after the corresponding data processing. Results show that the proposed lab-based methodology is well received by the students whereas the objective evaluation demonstrates its potential to improve the specific instrumental soft skill acquisition.

[EN] Soot production (including formation and oxidation) is studied in the transient, high-pressure and turbulent n -dodecane Spray A flames from the Engine Combustion Network (ECN) using computational fluid dynamics (CFD) simulations. A two-equation soot-in-flamelet modeling approach is applied within the framework of the Unsteady Flamelet Progress Variable (UFPV) model and results are validated against experimental data. Equations for soot mass fraction and soot number density derived in the mixture fraction space are solved in the context of detailed flamelet calculations. Source terms for the different steps in the soot chemistry are tabulated and incorporated in the flamelet manifold. For the reference condition, the modeling approach based on the tabulated flamelet manifold reduces the computational cost of a CFD calculation by approximately 40 times compared to a non-tabulated well-mixed (WM) modeling approach. The soot-in-flamelet approach is then extended to study the effect of ambient oxygen concentration, ambient mixture composition and ambient temperature on soot production. Results show that the modeling approach is able to capture the experimental trends for the soot volume fraction (SVF) with good quantitative agreement, especially in the soot ramp-up region., This work was partially funded by the Government of Spain through the CHEST Project (TRA2017-89139-C2-1-R) and by Universitat Politecnica de Valencia through Programa de Ayudas de Investigacion y Desarrollo (PAID-01-16) and Ayudas para movilidad dentro del Programa para la Formacion de Personal investigador 2017. We gratefully acknowledge the computing resources provided on Bebop, a computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. The technical support of Convergent Science is also greatly acknowledged.

[EN] To further understand the processes and phenomena taking place in the pre-chamber (PC) ignition concept, many studies under simplified conditions have been carried out in different experimental facilities (e.g. constant volume chambers and rapid compression machines). However limited information is provided about how the volume, orifice diameter and number of orifices were defined, raising the question whether the results are representative of engine-like conditions or not. This novel study arises from the necessity to determine a methodology to reproduce a reference pre-chamber, preserving as much as possible its jet characteristics. A theoretical development based on the first law of thermodynamics has been performed, and a relationship between the effective flow area, pre-chamber volume and engine speed is proposed as the governing parameter of the mass exchange between chambers. Besides, relaying on the know-how of gas jets, a relationship between the orifice diameter, jet tip penetration and engine speed is suggested as the criterion to preserve the relative jet penetration (respect to the distance from the PC hole to the combustion chamber walls). A numerical validation of these assumptions was carried out using a one-dimensional flow calculator to estimate the thermodynamic properties and mass transfer between chambers, and a one-dimensional spray model to estimate the penetration of the PC combustion products jets. Finally, preserving the ratio between the total area of the PC holes and the product of the PC volume and the engine speed for two pre-chamber geometries, an identical pressure rise rate, in an angular basis, is achieved in both pre-chambers. Furthermore, the same relative jet penetration rate, in an angular basis, can be also achieved, even under different engine speeds, when the ratio between the orifice diameter and the product of the square of the jet free length and the engine speed is preserved., The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research has been partially funded by FEDER and the Spanish Government through project RTI2018-102025-B-I00.

[EN] With the rise of cleaner technologies for transport and the emergence of H-2 as a fuel, most of the emissions in the well-to-wheel process are shifting towards the energy carrier production (fuel or electricity). The objective of this study is to perform a simplified cradle-to-grave Life Cycle Assessment (LCA) that compares the greenhouse gases (GHG) and NOX emissions of H-2, electric and conventional technologies for the automotive sector in Europe and to devise the optimum strategy of vehicle fleet renewal to reduce the emissions. In this study the effect of water as GHG was considered and, unless other studies, the current European energy mix and that meeting the objectives for 2050 were considered (while technology level was kept constant) since H-2 from electrolysis and electric vehicles' well-to-wheel emissions are sensitive to the energy mix. To estimate the emissions, the fuel, vehicle production and operation cycles were considered independently for each technology and then put together. For H-2, the best production and distribution strategy was steam methane reforming (SMR) with CO2 sequestration for GHG-100 gases and without capturing CO2 for NOX, both with central plant production and tube trailer transport. Fuel cell vehicles (FCV) with optimum H-2 production always produce the lowest GHG-100 emissions and slightly higher NOX than battery electric vehicles (BEV) in the EU 2050 scenario. In contrast, HICEV would need to reach a fuel consumption of around 30 kWh/100 km to be competitive in emissions against BEV, for that, direct injection (DI) combined with a range extender (REx) hybrid architecture is the recommended powerplant concept. Finally, the optimum strategy to reduce emissions that Europe could follow is presented for the short, mid and long term., This research has been partially funded by FEDER and the Spanish Government through project RTI2018-102025-B-I00 (CLEAN-FUEL).