Stringent pollutant regulations on diesel-powered vehicles have resulted in the development of new technologies to reduce emission of nitrogen oxides (NOx). The urea Selective Catalyst Reduction (SCR) system and Lean NOx Trap (LNT) have become the two promising solutions to this problem. Whilst the LNT results in a fuel penalty due to periodic regeneration, the SCR system with aqueous urea solution or ammonia gas reductants could provide a better solution with higher NOx reduction efficiency. This thesis describes an experimental investigation which has been designed for comparing the effect NOx abatement of a SCR system with AdBlue urea spray and ammonia gas at 5% and 4% concentration. For this study, a SCR exhaust system comprising of a diesel particulate filter (DPF), a diesel oxidation catalyst (DOC) and SCR catalysts was tested on a steady state, direct injection 1998 cc diesel engine. It featured an expansion can, nozzle and diffuser arrangement for a controlled flow profile for CFD model validation. Four different lengths of SCR catalyst were tested for a space velocity study. Chemiluminescence (CLD) based ammonia analysers have been used to provide high resolution NO, NO2 and NH3 measurements across the SCR exhaust system. By measuring at the exit of the SCR bricks, the NO and NO2 profiles within the bricks were found. Comparison of the measurements between spray and gas lead to insights of the behaviour of the droplets upstream and within the SCR bricks. From the analysis, it was deduced that around half to three quarters of the droplets from the urea spray remain unconverted at the entry of the first SCR brick. Approximately 200 ppm of potential ammonia was released from the urea spray in the first SCR brick to react with NOx. The analysis also shows between 10 to 100 ppm of potential ammonia survived through the first brick in droplet form for cases from NOx-matched spray input to excess spray. Measurements show NOx reduction was complete after the second SCR bricks. Experimental and CFD prediction showed breakthrough of all species for the short brick with gas injection due to the high space velocity. The long brick gas cases predictions gave reasonable agreement with experimental results. NO2 conversion efficiency was found higher than NO which contradicts with the fast SCR reaction kinetics. Transient response was observed in both cases during the NOx reduction, ammonia absorption and desorption process. From the transient analysis an estimate of the ammonia storage capacity of the bricks was derived. The amount of ammonia slippage was obtained through numerical integration of the ammonia slippage curve using an excel spreadsheet. Comparing the time constant for the spray and gas cases, showed a slightly faster time response from the gas for both NOx reduction and ammonia slippage.

Higher atmospheric concentration of greenhouse gases (GHG) such as carbon dioxide and methane has contributed to an increase in Earth's mean surface air temperature and caused climate changes. This largely reflects the increase in global energy consumption, which is heavily dependent on oil, natural gas, and coal. If not controlled, the combustion of these fossil fuels can also produce high levels of nitrogen oxides (NOx) and soot emissions, which adversely affect the air quality. New and extremely challenging fuel efficiency and exhaust emissions regulations are driving the development and optimisation of powertrain technologies as well as the use of low carbon fuels to cost-effectively meet stringent requirements and minimise the transport sector's GHG emissions. In this framework, the dual-fuel combustion has been shown as an effective means to maximise the utilisation of renewable liquid fuels such as ethanol in conventional diesel engines while reducing the levels of NOx and soot emissions. This research has developed strategies to optimise the use of ethanol as a substitute for diesel fuel and improve the effectiveness of dual-fuel combustion in terms of emissions, efficiency, and engine operational cost. Experimental investigations were performed on a single cylinder heavy-duty diesel engine equipped with a high pressure common rail injection system, cooled external exhaust gas recirculation, and a variable valve actuation system. A port fuel injection system was designed and installed, enabling dual-fuel operation with ethanol energy fractions up to 0.83. At low engine loads, in-cylinder control strategies such as the use of a higher residual gas fraction via an intake valve re-opening increased the combustion efficiency (from 87.7% to 95.9%) and the exhaust gas temperature (from 468 K to 531 K). A trade-off between operational cost and NOx reduction capability was assessed at medium loads, where the dual-fuel engine performance was less likely to be affected by combustion inefficiencies and in-cylinder pressure limitations. At high load conditions, a Miller cycle strategy via late intake valve closing decreased the in-cylinder gas temperature during the compression stroke, delaying the autoignition of the ethanol fuel and reducing the levels of in-cylinder pressure rise rate. This allowed for the use of high ethanol energy fractions of up to 0.79. Finally, the overall benefits and limitations of optimised ethanol-diesel dual-fuel combustion were compared against those of conventional diesel combustion. Higher net indicated efficiency (by up to 4.4%) combined with reductions in NOx (by up to 90%) and GHG (by up to 57%) emissions can help generate a viable business case of dual-fuel combustion as a technology for future high efficiency and clean heavy-duty engines.

La pollution de l’air liée au trafic automobile constitue un problème de santé majeure et est reconnue comme un facteur de risque important pour les maladies cardiovasculaires. La contribution de la phase particulaire des émissions de moteur Diesel dans ces effets sanitaires a été bien établie. Cependant, les études portant sur la phase gazeuse sont peu nombreuses alors que l’évolution des systèmes de dépollution permettant un abattement des particules Diesel, ont conduit à un accroissement des polluants de la phase gazeuse tels que le Dioxyde d’azote (NO2),un polluant majeur et toxique. Par conséquent, l’objectif général de ce travail a été d’évaluer la part imputable de la phase gazeuse, et plus spécifiquement du NO2, dans les effets cardiovasculaires induits par des émissions Diesel représentatives du parc automobile actuel. Dans un premier temps, une étude comparative a été réalisée chez le rat Wistar exposé par inhalation au NO2 seul ou à des émissions Diesel, produisant du NO2, et prélevées en amont et en aval d’un filtre à particules(Fap). Afin de comprendre les mécanismes d’action mis en jeu, la fonction mitochondriale et le stress oxydant ont été évalués, parallèlement aux mesures de fonction cardiaque après une exposition unique (une seule exposition de 3h) et après une exposition répétée (3h/jour, 5jr/semaine pendant 3 semaines). Dans un deuxième temps, une étude portant plus spécifiquement sur les effets du NO2sur la fonction vasculaire et ses conséquences éventuelles dans un modèle d’hypertension artérielle a été réalisée en utilisant deux modèles expérimentaux : un modèle physiologique (rat Wistar) et un modèle d’hypertension artérielle (rat SHR). L’évaluation de la fonction vasculaire a été réalisée par une approche ex vivo à partir d’artères coronaires isolées après des expositions uniques et répétées chez le rat Wistar et uniquement après une exposition unique chez le rat SHR. Pour ce dernier, des expositions répétées ont également été réalisées pour explorer la fonction mitochondriale. Nos résultats montrent que l’exposition unique aux émissions, en amont et en aval du Fap induisent une légère altération de la fonction cardiaque, qui est cependant plus importante lors des expositions à 5 ppm de NO2 mais réversible. Après trois semaines d’expositions répétées, la dysfonction cardiaque persiste puisque le lendemain de la dernière exposition, les diamètres ventriculaires restent élevés, que ce soit après les expositions aux émissions Diesel, amont et aval, et au NO2. La dysfonction cardiaque est accompagnée d’une altération de la vasorelaxation des artères exposées au NO2. En parallèle à ces altérations, nous avons observé une dysfonction mitochondriale, plus particulièrement lors des expositions au NO2 indépendamment d’un stress oxydant myocardique ou systémique. L’exposition au NO2 aggrave la dysfonction mitochondriale préexistante au cours de l’hypertension artérielle, ce qui suggère l’aggravation de la fonction cardiovasculaire. L’ensemble de ces résultats démontre l’effet de la phase gazeuse, notamment du NO2 sur la fonction mitochondriale dans les deux modèles expérimentaux témoignant de l’importance de la prise en considération de l’action de la phase gazeuse dans les systèmes de dépollution à venir. / Air pollution from car traffic is a major health issue and is recognized as an importantrisk factor for cardiovascular disease. The contribution of the particulate phase of Diesel engine emissions to these health effects has been well established. However, studies on the gas phase are few in number, while the evolution of the depollution systems allowing a reduction of the Diesel particles, led to an increase in pollutants of the gas phases such as nitrogen dioxide (NO2) a major and toxic pollutant. consequently, the general objective of this work was to evaluate the attributable part of the gaseous phase, and more specifically NO2, in the cardiovascular effects induced by Diesel emissions representative of the current fleet. In a first step, a comparative study was conducted in the Wistar rat exposed by inhalation to NO2 alone or to Diesel emissions, producing NO2, and taken upstream and downstream of a particulate filter (PF). In order to understand the mechanisms of action involved, mitochondrial function and oxidative stress were evaluated, in parallel with cardiacfunction measurements after a single exposure (a single exposure of 3 h) and after repeated exposure (3 h / day, 5 days / week for 3 weeks). Second, a more specific study on the effects of NO2 on vascular function and its possible consequences in a hypertension model was carried out using two experimental models: a physiological model (Wistar rat) and a model of hypertension (SHR). Evaluation of the vascular function was performed by an ex vivo approach from isolated coronary arteries following single and repeated exposures in the Wistar rat and only after a single exposure in the SHR. For the latter, repeated exposures were also performed to explore mitochondrial function. Our results show that single exposure to emissions upstream and downstream of PF induces a slight alteration of cardiac function, which is more important at 5 ppm NO2 but reversible. After three weeks of repeated exposure, cardiac dysfunction persists as ventricular diameters remain high the day after the last exposure, both after exposures to upstream and downstream Diesel emissions and to NO2. Cardiac dysfunction is accompanied by an alteration in the vasorelaxation of the arteries exposed to NO2. In parallel with these alterations, weobserved mitochondrial dysfunction, particularly during NO2 exposures independently of myocardial or systemic oxidative stress. Exposure to NO2 aggravates pre-existingmitochondrial dysfunction during hypertension, suggesting worsening of cardiovascular function. All these results demonstrate the effect of the gaseous phase, in particular NO2, on the mitochondrial function in the two experimental models, indicating the importance of taking into account the action of the gas phase in the depollution systems to come up.

The concepts of engine downsizing and down-speeding offer reductions in CO2 emissions from passenger cars. These reductions are achieved by reducing pumping and friction losses at part-load operation. Conventionally, rated torque and power for downsized units are recovered by means of turbocharging. The transient response of such engines is, however, affected by the static and dynamic characteristics of the turbo-machinery. Recent advances in engine simulation and control tools have been employed for the purpose of the research reported in this thesis to identify and verify possible air-path enhancements. A systematic method for evaluating various turbocharger assistance concepts is proposed and discussed in this thesis. To ensure a fair comparison of selected candidate systems, an easily reconfigurable controller providing a close-to-optimal operation, while satisfying physical limits, is formulated. This controller is based on the Model Predictive Control framework and uses a linearised mean value model to optimise the predicted behaviour of the engine. Initially, the controller was applied to a 1D simulation model of a conventional light-duty Diesel engine, for which the desired closed-loop features were verified. This procedure was subsequently applied to various air-path enhancement systems. In this thesis, a turbocharger electric assistance and various concepts based on compressed gas injection were considered. The capability of these systems to improve engine response during third gear tip-in manoeuvre was quantified. This investigation was also complemented with a parametric study of how effectively each of the considered methods used its available resources. As a result, injecting compressed gas into the exhaust manifold was identified as an effective method, which to date has attracted limited attention from engine research community. The effectiveness of the exhaust manifold assistance was experimentally verified on a light-duty Diesel engine. The sensitivity of the improvements to compressed gas supply parameters was also investigated. This led to the development of the BREES system: a low component count, compressed gas based system for reducing turbo-lag. It was shown that during braking manoeuvres a tank can be charged to the level sufficient for a subsequent boost assistance event. Such a functionality was implemented with a very limited set of additional components and only minor changes to the standard engine control.