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Récemment, les constructeurs automobiles se sont intéressés au développement des catalyseurs appelés quatre voies, destinés à diminuer simultanément les émissions polluantes des moteurs diesels par l'intermédiaire d'un seul monolithe catalytique. Dans cet objectif, plusieurs études ont montré que la capacité de stockage des NOx de ces catalyseurs est inhibée par la présence de suies. Les travaux présentés dans ce manuscrit s'inscrivent dans la compréhension des phénomènes en cause. Les résultats obtenus montrent que la présence de noir de carbone entraîne une diminution de la stabilité des nitrates adsorbés par les systèmes catalytiques étudiés et, ainsi, de leur capacité de stockage des NOx. Ce phénomène a été attribué à une réduction des espèces nitrates adsorbées à la surface des matériaux par les particules de carbone adjacentes. La présence d'une particule Pt à proximité d'un site de carbone favorise la formation de complexes oxygénés de surface, limitant l'effet réducteur du carbone envers les nitrates adsorbés. La perte de capacité d'adsorption des NOx des catalyseurs étudiés, observée lors de leur mise en contact avec du noir de carbone, s'est révélée irréversible à l'issue de l'oxydation du carbone. La caractérisation des matériaux par microscopie à transmission (MET) a révélé une modification importante de la structure des matériaux. Un frittage des particules de platine et une modification de la structure des particules de Ba entraînent en effet la perte irréversible de l'activité des matériaux vis-à-vis de l'adsorption des NOx. / Recently, car manufacturers have developed "4 way" catalytic converters in order to couple hydrocarbon and CO oxidation, soot combustion and DeNOx fonctions on a single monolith. Several studies showed that the NOx storage capacity of NSR catalysts is reduced in the presence of soot. The aim of this work is to investigate the effect of carbon­ NSR catalyst contact on the ability of the catalyst to store NOx. The results show that the presence of carbon black in the catalytic bed involves a decrease of adsorbed nitrates stability and of the NOx storage capacity of materials. It is proposed that the proximity of the carbon particles and NOx adsorbents sites leads to a reduction of the stored nitrates species. The decrease of the NOx storage capacity is Jess important when platinum is present in the catalytic material composition. In agreement with previous studies on the catalytic combustion of soot, it is suggested that platinum increases the number of surface-oxygen complexes -C(O), which thus led to a decrease in the reducing character of carbon. Our study reveals that the deactivation of the NOx storage activity due to carbon-catalyst contact is an irreversible phenomena, and thus even when all carbon is burnt. Characterization of materials by transmission electron microscopy (TEM) showed that sintering of the platinum particles and a structural modification of the barium particles occurs after that the catalysts was in contact with carbon. The decrease in the NOx storage activity of the materials is then assigned to a lesser proximity of the oxidizing sites (Pt) and adsorption sites (Al or Ba).

The horizontal and vertical distributions of ozone and its precursors over North America during spring and summer are frequently determined by several factors: cloud convection, lightning NOx production, mixing depth, and long-range transport. The critical factors that contribute to the spatial distribution of air pollutants are studied using the Regional chEmical trAnsport Model (REAM) with diverse satellite measurements as well as in-situ surface and aircraft measurements. Surface and aircraft measurements show a large amount of reactive nitrogen tracers over the Antarctic plateau during summer. These enhanced measurements are investigated, and their photochemical impact is accessed by 1-D CTM and REAM.

One major aspect of environmental pollution affecting human life and climate is air pollution. The harmful pollutants in the air include mostly hydrocarbons, carbon monoxide, carbon dioxide, nitrogen oxides as well as soot and other particulate matter. These pollutants result in several damaging effects on environment and living beings which include acid rain, photochemical smog, global warming and various health hazards in human beings even cancer. Major contribution of these pollutants is from man-made sources such as industrial and automotive emissions that employ fossil fuels. In our country, diesel constitutes more than 40% of the fossil fuel consumption. Studies show that diesel engine emissions contribute to 80% of nitrogen oxides amongst other air pollutants. In the context of stringent emission regulations being implemented all over the world, exhaust emission control, in general and nitrogen oxide emission in particular, is gaining significant importance. A review of recent literature indicates the significance and popularity of electrical discharge based non thermal plasma for exhaust cleaning applications in general, and NOx cleaning in particular. While the existing pre-combustion and catalyst based post-combustion nitrogen oxides (NOx) abatement techniques have inherent disadvantages owing to short shelf life, saturated engine modifications, cost concerns etc., the electrical discharge based non- thermal plasma techniques offer certain advantages in terms of cost and life factors. Several non-thermal plasma techniques viz., pulsed plasma, surface plasma, dielectric barrier discharge plasma etc., have been studied under different laboratory conditions. Interestingly, due to the high oxidizing environment that prevails in the discharge plasma zone, complete reduction of NOx by the plasma alone is becoming a challenging task. This has led the researchers to utilize additional processing techniques in cascade with discharge plasma. This additional gas cleaning technique may involve the use of adsorbents, catalysts or some other secondary treatment for eliminating the nitrogen oxides produced due to oxidizing reactions in the plasma chamber. One such additive can be an adsorbent, which can be commercially obtained or prepared from industrial wastes. In this thesis the adsorption properties of two industrial wastes were explored for the first time in conjunction with discharge plasma. The synergistic effect of plasma combined with an adsorbent shows promising results in NOx removal thus offering an effective solution to two environmental issues namely air pollution and open waste dumping. While the plasma, generally, refers to direct plasma treatment of exhaust, it can also be used for generation of ozone in a separate reactor which can subsequently be injected into the exhaust stream resulting in indirect plasma treatment. The current work focuses on both direct and indirect dielectric barrier discharge plasma treatment for NOx reduction in diesel engine exhaust cascaded with either oyster shells, a mariculture waste or lignite ash from lignite coal fired plant. Instead of conventional petro-diesel, biodiesel produced from the seeds of pongamia pinnata is used as the fuel. This biofuel, on one hand, causes considerable reduction in volatile organic compounds, particulate matter, soot, oil mist etc., but on the other hand may have higher concentrations of nitrogen oxides, an aspect that has motivated us to take up the research work envisaged in this thesis. It was observed in the laboratory environment that for a given power, both direct and indirect plasma treatments have resulted in NOx removal to the tune of 85 to 95% when cascaded with the adsorbents studied.

[ES] Las actuales y futuras normativas, en términos de emisiones contaminantes y movilidad sostenible, continuarán fijando una difícil etapa para el desarrollo y mejoramiento de los motores de combustión interna alternativos (MCIA). Los nuevos parámetros conocidos como, emisiones reales de conducción, los cambios de altitud y las condiciones extremas de operación a bajas temperaturas, son los mayores desafíos para cumplir bajo estas nuevas normativas. Por esta razón, la academia y los fabricantes de la industria de la automoción continúan trabajando en colaboración, tratando de desarrollar más eficientes y menos contaminantes sistemas de propulsión. En este trabajo experimental de investigación, los principales resultados de un proyecto de colaboración llevado a cabo entre la empresa Valeo Systèmes Thermiques y la Universitat Poltècnica de València son presentados. La recirculación de gases de escape, en sus dos configuraciones, de alta y de baja presión, y la desactivación de cilindros, son las principales estrategias que se estudiarán en este trabajo, debido a su alto potencial y su bajo costo de implementación. Estas estrategias son evaluadas en un motor Diesel, instalado en una cámara de ensayos climática y operando a bajas temperaturas ambiente (-7°C). La primera estrategia, es la activación de la EGR de alta presión desde el inicio de un arranque de motor y el desarrollo de un modelo de condensación simple capaz de predecir si hay o no condensación dentro de la línea de EGR bajo estas condiciones. En particular, el ratio de humedad y las condiciones internas del motor que caracterizan la aparición de este fenómeno son calculadas por el modelo. Este modelo es validado por medio de cámaras instaladas en el rail de EGR con el objetivo de visualizar la evolución de la condensación dentro de los componentes. El ratio de humedad calculado y el comportamiento de la condensación observado a través de las cámaras, muestran que durante un arranque de motor en frío, las condiciones de condensación en los gases están presentes hasta que se alcanzan aproximadamente 50°C, mientras que en las paredes sólidas y en los componentes, las condiciones se mantienen hasta que se alcanzan aproximadamente 30°C. En la segunda estrategia, una nueva línea de EGR compacta, equipada con un sistema de bypass para el intercambiador de calor es usada con el objetivo de acelerar el proceso de calentamiento del motor en comparación a la línea de EGR de baja presión original del motor. El objeto de esta estrategia es evaluar el impacto en el comportamiento del motor de realizar EGR de baja presión a bajas temperaturas con la activación del sistema de bypass para deshabilitar el intercambiador de calor. Siguiendo esta estrategia, una notable reducción en emisiones de NOx de aproximadamente 60% con respecto a un caso de referencia sin activación de la EGR de baja presión es lograda. Además, el proceso de calentamiento del motor ha sido reducido en aproximadamente 60 segundos y la temperatura de admisión del motor ha sido aumentada en 30°C, liderando una reducción en las emisiones de CO de aproximadamente 12%. En la tercera estrategia, el impacto de usar una nueva configuración de la desactivación de cilindros con el propósito de acelerar el proceso de calentamiento del motor es evaluada. Los resultados muestran un incremento en la temperatura de escape de alrededor de 100°C, el cual permite reducir la activación del catalizador en 250 segundos además de reducir el proceso de calentamiento del motor en aproximadamente 120 segundos. Esto permite reducir las emisiones de CO y HC en un 70% y 50%, respectivamente. Y finalmente, la última estrategia experimental realizada, evalúa el impacto de usar la EGR de alta presión mientras el filtro de partículas está en el modo activo de regeneración. Siguiendo esta posible condición de calibración de motor, una reducción en emisiones de NOx de aproximadamente 50% con respecto a un caso de referencia ha sido alcanzada. / [CA] Les actuals i futures normatives, en termes d'emissions contaminants i mobilitat sostenible, continuaran fixant una difícil etapa per al desenvolupament i millorament dels motors de combustió interna alternatius (MCIA). Els nous paràmetres coneguts com, emissions reals de conducció, els canvis d'altitud i les condicions extremes d'operació a baixes temperatures, són els majors desafiaments per a complir les noves normatives. Per aquesta raó, l'acadèmia i els fabricants de la indústria de l'automoció continuen treballant en col·laboració, tractant de desenvolupar més eficients i menys contaminants sistemes de propulsió. En aquest treball experimental d'investigació, es presenten els principals resultats d'un projecte de col·laboració dut a terme entre l'empresa Valeo Systèmes Thermiques i la Universitat Politècnica de València. La recirculació de gasos del motor, en les seues dues configuracions, d'alta i de baixa pressió, i la desactivació de cilindres, són les principals estratègies que s'estudiaran en aquest treball, a causa del seu alt potencial i el seu baix cost d'implementació. Aquestes estratègies són avaluades en un motor Dièsel, instal·lat en una cambra d'assajos climàtica i operant a baixes temperatures ambient (-7 °C). La primera estratègia, és l'activació de la EGR d'alta pressió des de l'inici d'una arrancada de motor i el desenvolupament d'un model de condensació simple capaç de predir si hi ha o no condensació dins de la línia de EGR. En particular, el ràtio d'humitat i les condicions internes del motor que caracteritzen l'aparició d'aquest fenomen són calculades pel model. Aquest model és validat per mitjà de càmeres instal·lades a el rail de EGR amb l'objectiu de visualitzar l'evolució de la condensació dins dels components. El ràtio d'humitat calculat i el comportament de la condensació observat a través de les càmeres, mostren que durant una arrancada de motor en fred, les condicions de condensació en els gasos són presents fins que s'aconsegueixen aproximadament 50 °C, mentre que a les parets i als components, les condicions es mantenen fins que s'aconsegueixen aproximadament 30 °C. En la segona estratègia, una nova línia de EGR compacta, equipada amb un sistema de bypass per a l'intercanviador de calor és usada amb l'objectiu d'accelerar el procés de calfament del motor en comparació a la línia de EGR de baixa pressió original del motor. L'objecte d'aquesta estratègia és avaluar l'impacte en el comportament del motor de realitzar EGR de baixa pressió a baixes temperatures amb l'activació del sistema de bypass per a evitar l'intercanviador de calor. Seguint aquesta estratègia, s'aconsegueix una notable reducció en emissions de NOx d'aproximadament 60% respecte a un cas de referència sense activació de la EGR de baixa pressió. A més, el procés de calfament del motor ha sigut reduït en aproximadament 60 segons i la temperatura d'admissió del motor ha sigut augmentada en 30 °C, produint una reducció en les emissions de CO d'aproximadament 12%. Per a la tercera estratègia, és avaluat l'impacte d'usar una nova configuració de la desactivació de cilindres amb el propòsit d'accelerar el procés de calfament del motor. Els resultats mostren un increment a la temperatura dels gasos de al voltant de 100 °C, el qual permet reduir l'activació del catalitzador en 250 segons a més de reduir el procés de calfament del motor en aproximadament 120 segons. Això permet reduir les emissions de CO i HC en un 70% i 50%, respectivament. Finalment, l'última estratègia experimental realitzada, avalua l'impacte d'usar la EGR d'alta pressió mentre el filtre de partícules està en la manera activa de regeneració. Seguint aquesta possible condició de calibratge de motor, ha sigut aconseguida una reducció en emissions de NOx d'aproximadament 50% respecte a un cas de referència sense activar la EGR d'alta pressió. / [EN] Current and future legislations, regarding pollutant emissions reduction and green mobility, will continue fixing a difficult stage for the development and improvement of internal combustions engines (ICEs). The Real Driving Emissions (RDE) parameters, the changes of altitude, and the extreme ambient temperature conditions in operation, are the major challenges to fulfill under these new legislations. By these reason, academy and automotive manufacturers continue working in collaboration, trying to develop more efficient and less polluting powertrains. In this experimental research work, the main results of a collaboration project between the private company Valeo Systèmes Thermiques and the Universitat Poltècnica de València are presented. Exhaust gas recirculation (EGR), in both configurations, high-pressure and low-pressure, and Cylinder Deactivation (CDA), are the main strategies studied in this work due to its high potential and low-cost implementation. These strategies are evaluated in a Light-duty Diesel engine, fitted in a climatic test bench and operating under low ambient temperature (-7ºC). The first strategy is the High-pressure EGR activation from the beginning of the engine start and the development of a simple condensation model able to predict whether or not there is condensation inside the EGR line under these conditions. In particular, the humidity ratio and the internal engine conditions that characterize the appearance of this phenomenon are estimated by the model. This model is validated by means of cameras fitted on the EGR rail in order to visualize the condensation evolution. The humidity ratio estimate and the condensation behavior observed through the cameras, shows that during an engine cold start, condensation conditions in the gases are present until reach approximately 50ºC, while in solid walls and components, the conditions remains until reach approximately 30ºC. In the second strategy, a new compact line fitted with a bypass system for the cooler is used with the aim of accelerating the engine warm-up process as compared to the original low-pressure EGR line. The aim of this strategy is to evaluate the impact on the engine behavior of performing Low-pressure EGR at cold conditions and to activate the bypass system in order to disable the cooler. Following this strategy, a noticeable NOx emissions reduction of approximately 60% with respect to a reference case without low-pressure EGR has been achieved. In addition, the engine warm-up process has been reduced in approximately 60 seconds and the engine intake temperature has been increased 30ºC, leading a CO emissions reduction of approximately 12%. In the third strategy, the impact of using a new cylinder deactivation configuration with the aim of improving the engine warm-up process is evaluated. The results show an increase of the exhaust temperatures of around 100ºC, which allows to reduce the diesel oxidation catalyst light-off by 250 seconds besides of reducing the engine warm-up process in approximately 120 seconds. This allows to reduce the CO and HC emissions by 70% and 50%, respectively. And finally, the last experimental strategy evaluates the impact of using the high-pressure exhaust gas recirculation while the diesel particulate filter is under active regeneration mode. Following these possible engine calibration conditions, a NOx emissions reduction of approximately 50% with respect to a reference case without high-pressure EGR during a DPF regeneration process has been achieved. / Miguel Ángel Bernal Maldonado has been partially supported through contract FPI-S1-2017-2377 of "Programa de Ayudas de Investigación y Desarrollo (PAID-01-17) de la Universitat Politècnica de València". The support of Valeo Systèmes Thermiques through projects CN-2016-99 and CN-2018-08 is also greatly acknowledged. / Bernal Maldonado, MÁ. (2023). Study of Different Strategies to Improve the Internal Combustion Engine (ICE) Operating at Cold Conditions [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/192652

Although Large Eddy Simulation (LES) has demonstrated its potential for modelling the reaction in simple academic combustors, it is more computationally expensive than Reynolds Averaged Navier-Stokes (RANS) which has been used widely for industrial cases. The aim of this research is to employ LES at minimal grid resolution and computational resource requirements to capture the main characteristics of the reacting flows in a helicopter combustor and exhaust plume with the focus on NOx emissions. Test cases have been carried out to validate the current LES code for non- reacting jet, non-premixed combustion and unstructured grids. Despite the moderate grid refinement and simple chemistry models employed, the findings from these test cases have demonstrated good capabilities of the current LES to capture the mixing, flame and flow characteristics. In a farther test case, a key gas-phase chemical reaction selected for the helicopter exhaust plume modelling has also been tested. The validated LES code is then employed in the numerical study of the reaction in the helicopter combustor. The LES predictions in terms of the temperature and EINOx agree generally well with the combustor design, analytical solutions, previous LES and test measurements. Subsequently, the potential application of LES for the calibration of simpler models has been assessed for the generic and helicopter combustors. The results obtained from LES are compared with those from a one-dimensional combustor performance and emissions code, HEPHAESTUS, developed within the Cranfield University Power and Propulsion Department. The discrepancies between the results are found to be primarily due to specific simplification and assumptions established in the HEPHAESTUS model which can be addressed. Finally, LES has been employed to model the transformation of NO to NO2 in the helicopter exhaust plume. The findings from this research have demonstrated that, even without the implementation of highly dense mesh or advanced reaction model, LES is able to provide results with an acceptable level of fidelity at relatively low computational costs. These advantages make it a powerful predictive tool for future design and emissions optimisation investigations, and calibration of other simpler modelling approaches.

Coal firing power stations represent the second largest source of global NOx emissions. The current practice of predicting likely exit NOx levels from multi-burner furnaces on the basis of single burner test rig data has been proven inadequate. Therefore, to further improve current NOx reduction technologies and assist in the assessment of NOx levels in new and retrofit plant cases, an improved understanding of the impact of burner interactions is required. The aim of this research is two-fold: firstly, to experimentally investigate isothermal flow interactions in multi-burner arrays for different swirl directions and burner pitches in order to gain a better understanding of burner interaction effects within multi-burner furnaces. Secondly, to carry out numerical modelling in order to determine turbulence models which give the best agreement to experimental data. Experimental investigations were carried out using flow visualisation for qualitative and 3D laser Doppler anemometry for quantitative measurements. Numerical modelling was performed using the computational fluid dynamics software, Fluent, to compare performance between k-ε, k- ω and RSM turbulence models. Experimental investigation showed that the recirculation zone of the chequerboard configuration is more sensitive to the change in pitch than that of the columnar configuration. Further, it was found that the smaller pitch is more sensitive to change in configuration than the wider pitch. The analysis of fluctuating components, u’, v’ and w’ showed that the burner flow is highly anisotropic at burner exit. Numerical investigation showed that the k-ω turbulence model consistently performed below the other two models. The statistical comparison between k-ε and RSM turbulence models revealed that, for prediction of the swirl velocity profiles, the RSM model overall performed better than the k-ε turbulence model. The visual and statistical analyses of turbulent kinetic energy profiles also showed that the RSM turbulence model provides a closer match to the experimental data than the k-ε turbulence model.

NOx-bildning från ljusbågsugn påverkas av:  Temperaturen  Ugnstrycket  Skrotdensiteten  Efterbränningen  Exponeringen av ljusbågarna  Stålsorternas respektive körsätt Den ökade efterfrågan på ESR-material, vars körsätt i ljusbågsugnen är längre och varmare än konventionellt stål, kan komma att leda till en ökad uppkomst av NOx i takt med att ESR-produktionen ökar. Rekommendation: Uddeholm bör vid nästa mätning välja att mäta specifika stålsorters körsätt, med speciellt fokus på ESR-material, för att säkerställa att de vid prövotidsutredningens slut kan yrka på ett realistiskt slutligt villkor på NOx från ljusbågsugn.

The overall aim of this thesis was to validate diffusive samplers for measurements of nitrogen dioxide (NO2) and nitrogen oxides (NOx). The Willems badge was validated for NO2 measurements both in laboratory tests and in field tests (Paper I-II). The sampling rate was 40.0 mL/min for ambient air concentrations and 46.0 mL/min for higher concentrations. No effects of different factors on sampling rate were found except for a reduced sampling rate at low wind velocity. The results of the laboratory validation were confirmed in field tests in ambient air and with personal sampling. The correlation between diffusive samplers and the reference monitor was good for ambient measurements. In conclusion, the Willems badge performs well at wind velocities down to 0.3 m/s, and this makes it suitable for personal sampling but less suitable for measurements in indoor air where the wind velocity is lower. Paper III reports about the field validation of the Ogawa diffusive samplers. Absolute humidity and temperature were found to have the strongest effect on sampling rate with lower uptake rates at low absolute humidity or temperature. The sampling rates above 0 °C were 8.6 mL/min for NO2 and 9.9 mL/min for NOx. NO2 and NOx concentrations that were determined using the manufacturer’s protocol were either underestimated or overestimated. The agreement between concentrations measured by the Ogawa sampler and the reference monitor was improved when field-determined sampling rates were used to calculate concentrations. Paper IV is based on a study with the aim of assessing the exposure of the Swedish general population to NO2 and some carcinogenic substances. The surveys were performed in one of five Swedish cities every year. In each survey, personal measurements of NO2 and some carcinogenic substances were conducted on 40 randomly selected individuals. In the study presented in this thesis, the NO2 part of the study is in focus and results were available for eight surveys conducted across the five cities. The estimated arithmetic mean concentration for the general Swedish population was 14.1 μg/m3. The exposure level for NO2 was higher for smokers compared with non-smokers, and the NO2 exposure levels were higher for people who had gas stoves at home or who were exposed at their workplace. The exposure was lower for those who had oil heating in their houses.

Industrial boilers that produce steam or electric power represent a large capital investment as well as a crucial facility for overall plant operations. In real applications, the operation of the superheater for producing high-pressure, high-temperature steam may result in problems frequently caused by ruptured superheater tubes. To make the boiler more efficient, less emission and less prone to tube rupture problems, it is important to understand the combustion and thermal flow behaviors inside the boiler. This study performs a detailed simulation of combustion and thermal flow behaviors inside an industrial boiler. The simulations are conducted using the commercial CFD package FLUENT. The 3-D Navier-Stokes equations and five species transport equations are solved with the eddy-breakup combustion model. Calculation of NOx is performed after obtaining a converged flow, thermal and combustion solution. The results provide insight into the detailed thermal-flow and combustion in the boiler and showing possible reasons for superheater rupture