La réduction des émissions de CO2 et de polluants est un des enjeux essentiels pour faire face aux problèmes liés au changement climatique. Dans le secteur des transports, la technologie de recirculation des gaz d’échappement (EGR) est souvent utilisée dans les moteurs turbo-compressés à allumage commandé pour réduire la consommation de carburant, inhiber les risques de cliquetis et réduire les émissions de NOx. Cependant, des taux d’EGR élevés restent difficiles à atteindre car ils réduisent le dégagement de chaleur et la stabilité du moteur. L'augmentation du niveau de turbulence et la mise en oeuvre de systèmes à allumage commandé avancés n’apportant pas d'améliorations suffisantes dans des conditions aussi extrêmes, la chimie de la combustion pour les très hautes dilutions suscite un intérêt croissant. Le présent travail vise à comprendre la chimie de combustion des flammes prémélangées essence/air très diluées et à établir un mécanisme cinétique détaillé par modélisation multi-échelle afin de prévoir les caractéristiques de combustion avec une précision suffisante dans des conditions de forte dilution.Ce travail adopte une approche de modélisation multi-échelle et cible la vitesse de flamme laminaire (SL) d'un substitut d'essence, appelé TRFE et qui est constitué d'isooctane, de n-heptane, de toluène et d'éthanol. Pour la modélisation à l’échelle microscopique, la réaction entre le cétène et le radical hydroxyle, qui pourrait être importante pour la SL dans des conditions très diluées, est étudiée théoriquement à l'aide de méthodes de structure électronique ab initio pour la surface d'énergie potentielle (PES) et Rice -- Ramsperger -- Kassel -- Marcus Theory couplé à l'équation maîtresse (RRKM / ME) pour les coefficients de vitesse. Des PES détaillées sont obtenues, les voies dominantes sont identifiées et leurs coefficients de vitesse phénoménologiques sont dérivés pour être utilisés dans la modélisation de la combustion. Pour la modélisation à l'échelle macroscopique, les paramètres cinétiques, thermodynamiques et de transport importants pour la vitesse de la flamme laminaire dans des conditions très diluées sont d'abord identifiés à l'aide d'une analyse de sensibilité réalisée sur une version initiale du mécanisme TRFE de départ. Les réactions sensibles impliquent principalement HO2, les espèces C2 - C3 et des radicaux issus du carburant. Le mécanisme initial, via un travail spécifique à chacun des sous-mécanismes, est mis à jour à l'aide des paramètres cinétiques les plus récents issus de la littérature. Enfin, un mécanisme détaillé adapté aux calculs de vitesse de flamme laminaire dans des conditions de forte dilution est validé. Une corrélation mathématique de SL est établie pour l'utilisation dans des simulations numériques de la dynamique des fluides (CFD). / Reducing CO2 and pollutant emission is the essential challenge when dealing with climate change problems. In the transport sector, exhaust gas recirculation (EGR) technology is often used in turbocharged gasoline spark ignition (SI) engines to increase fuel economy, inhibit knock tendency, and reduce NOx emissions. However, high EGR ratios are still difficult to achieve, as they result in reduced heat release and engine stability. As increasing turbulence level and advance spark ignition systems could not bring sufficient improvements at such extreme conditions, growing interest is cast onto the combustion chemistry under high dilution. The present work aims to understand the combustion chemistry of highly-diluted gasoline premixed flames and to establish a detailed kinetic mechanism by multi-scale modeling to predict combustion characteristics with sufficient accuracy at highly-diluted conditions.This work adopts a multi-scale modeling approach, and targets on the laminar flame speed (SL) of a gasoline surrogate, which is named toluene reference fuel with ethanol addition (TRFE) and consist of isooctane, n-heptane, toluene, and ethanol. For micro-scale modeling, the reaction between ketene and hydroxyl radical, which might be important to the SL at highly-diluted conditions, is studied theoretically using ab initio electronic structure methods for the potential energy surface (PES) and Rice–Ramsperger–Kassel–Marcus Theory coupled with Master Equation (RRKM/ME) for the rate coefficients. Detailed PES is obtained, dominant pathways are identified, and their phenomenological rate coefficients are derived to be utilized in combustion modeling. For macro-scale modeling, firstly, important kinetic, thermodynamic, and transport parameters to the laminar flame speed at highly-diluted conditions, are firstly identified using sensitivity analysis based on a starting mechanism. Sensitive reactions are found to mostly involve HO2, C2--C3 species and fuel radicals. Secondly, in the sub-mechanisms where these reactions lies, diluted flames of the corresponding fuels are studied and chemical detail of the dilution effects are explored. The starting mechanism is updated by state-of-the-art kinetics parameters found in the literature for each sub-mechanisms. Finally, a detailed mechanism suitable for laminar flame speed calculations at highly-diluted conditions is established after validation. A mathematical SL correlation is generated for the use in computational fluid dynamic (CFD) simulations.

<p>Correlations between the coefficient of variations (COV) of ion current integrals and COV of indicated mean effective pressure (IMEP) are investigated. The investigations are made to see if there is a possibility to use ion sense technique for closed loop combustion control to maximize Exhaust Gas Recirculation (EGR) level with remaining combustion stability. The engine studied in this thesis is a stoichiometric natural gas engine with a three way catalyst working with different EGR levels. One way to increase the efficiency in a stoichiometric natural gas engine is to maximize the EGR level [3]. With a higher EGR level it is possible to open the throttle even further with a result of lower pumping losses. Also temperature losses to chamber walls will be smaller with high EGR levels. A closed loop system controlling the EGR valve against COV of IMEP around 5 % is used for this engine. For COV of flame peak integral in range from 0 to 15-20% of COV of IMEP a linear correlation was found for lambda less than 1.3. For COV of two peaks integral a linear correlation was found for the entire measured range. This correlation may not be used for a robust EGR control system due to a small increase of COV of ion integral and due to a high variance in COV of ion integral. Correlations are discussed for different ion integrals with different air/fuels ratios and EGR levels. A control strategy is also presented.</p>

I denna rapport studeras reglerbarheten hos ett pneumatiskt aktuerat vridspjäll. Spjället används på dieselmotorer från lastbilstillverkaren Scania CV för att reglera återflödet av avgaser till insugsröret, så kallat EGR-flöde, Exhaust Gas Recirculation. Arbetets mål har varit att identifiera och kravställa de hårdvaruparametrar som påverkar möjligheten till effektiv reglering. I det studerade systemet ingår spjället, dess pneumatiska ställdon samt den proportionalventil som reglerar lufttryck till ställdonet. De parametrar som studeras är bland annat spjällets och aktuatorcylinderns dimensioner, aktuatorns slaglängd, returfjäder och friktion. I syfte att analysera påverkan av hårdvaruförändringar skapas en modell av systemet i programvaran Simscape. Mätningar på ett isolerat spjällsystem används för att studera dess dynamik, uppmäta parametrar samt till modellvalidering. Från mätningarna framkom att systemets friktion domineras av en statisk friktion i aktuatorn, vilken ökade med trycket och därmed positionen hos aktuatorn. Det identifierades även ett antal olinjäriteter hos ventilen som komplicerar regleringen. I synnerhet uppvisar ventilens tömningsförlopp stora variationer med val av arbetsområde, något som sätter en stor begränsning på systemets stängningstider. Modelleringsresultaten visar att en neddimensionering av aktuatorns totala arbetsvolym är att föredra då det skulle minska tiderna för att dra in och skjuta ut dess kolv. Särskilda krav måste dock ställas på dimensioneringen för att behålla en god upplösning från insignal till spjällposition samt kompensera friktionens påverkan. Genom att betrakta överföringen av moment från spjäll till linjär aktuatorkraft konstateras det att en neddimensionering även kan göra systemet känsligare mot störningar från avgasflödet.

This study was directed at examining the effects of exhaust gas recirculation (EGR), water/N2/CO2 injections and oxygen enrichment on availability destroyed because of combustion in simple systems like those of constant pressure and constant volume. Higher cooled EGR fractions lead to higher availability destruction for reactant temperatures less than 2000 K. The availability destroyed for 40% EGR at 300 K for constant pressure and constant volume combustion was 36% and 33%, respectively. Neglecting the chemical availability in the products, the equivalence ratio and reactant temperature that corresponded to the lowest availability destruction varied from 0.8 to 1.0 and 800 K to 1300 K, respectively, depending on the EGR fraction. The fraction of the reactant availability destroyed increased with the complexity of the fuel. The trends stayed the same for the different EGR fractions for the eight fuels that were analyzed. Higher injected water fractions lead to higher availability destruction for reactant temperatures less than 1000 K. The availability destroyed for a 40% injected water fraction at 300 K for constant pressure combustion was 36%. The product temperature ranged from 2300 K to 450 K at a reactant temperature of 300 K for injected fractions from 0% to 90%. For a 40% injected fraction at a reactant temperature of 300 K, water injection and cooled EGR resulted in the greatest destruction of availability (about 36%) with CO2 injection leading to the least destruction (about 32%). Constant volume combustion destroyed less availability compared to constant pressure combustion at a reactant pressure of 50 kPa. At a higher reactant pressure of 5000 kPa, constant pressure combustion destroyed less availability compared to constant volume combustion for reactant temperatures past 1000 K. Higher fractions of oxygen in the inlet lead to higher product temperatures that lead to lower availability destruction. For 40% oxygen in inlet, the product temperature increased to 2900 K and the availability destroyed dropped to 25% at a reactant temperature of 300 K for constant pressure combustion.

Current research suggests resveratrol, a phytoalexin found predominately in grapes, may function as a chemopreventive and/or chemotherapeutic agent for various cancers, including colorectal cancer. However, the underlying mechanism(s) involved in these activities remain elusive. Thus, the objective of the studies discussed here sought to investigate the effect of resveratrol treatment on gene modulation in human colorectal cancer cells in order to identify and characterize novel molecular targets that contribute to the observed anticancer activities of resveratrol. Here, we identify activating transcription factor 3 (ATF3) and early growth response-1 (Egr-1) as novel targets of resveratrol and provide data to elucidate the mechanism(s) of regulation and how each target contributes to the anticancer effect of resveratrol in colorectal cancer cells. We demonstrate the involvement of resveratrol in ATF3 transcriptional regulation, which is facilitated by Egr-1 and Krüppel-like factor 4 interactions, and show that ATF3 contributes, at least partially, to resveratrol-induced apoptosis (Chapter 3). Moreover, we suggest that increased Egr-1 transcriptional activity by resveratrol requires posttranslational acetylation of Egr-1 in a SIRT1-independent manner. This acetylation by resveratrol may contribute to Egr-1-mediated expression of the pro-apoptotic protein nonsteroidal anti-inflammatory drug (NSAID)-activated gene-1 (NAG-1) induced by the phytoalexin (Chapter 4). Taken together, the work presented here provide (1) novel mechanisms by which resveratrol induces ATF3 and Egr-1 expression and (2) represent additional explanations for the anti-tumorigenic/anti-carcinogenic effects of resveratrol in human colorectal cancer cells.

Dagens förbränningsmotorer ställs inför allt högre krav på att minimera de miljöfarliga restprodukter som förbränningen av luft och bränsle ger upphov till. Efterbehandlingssystem har utvecklats i olika former för detta ändamål, där en utav dessa är EGR: Exhaust gas recirculation som bygger på att en del av motorns avgaser överförs tillbaka in i motorn och minskar bildningen av termiska kvävoxider. I detta examensarbete undersöktes ett EGR-system i AVL:s singelcylinder-provcell, där målsättningen var att kartlägga komponenternas inverkan på EGRflödet samt undersöka EGR-systemets begränsningar med fokus på att öka mängden EGR till motorn. Arbetet utfördes på AVL Motortestcenter AB i Södertälje för Karlstads Universitet i kursen Examensarbete för högskoleingenjörsexamen i maskinteknik MSGC17, fakulteten för natur- och teknikvetenskap under våren 2018. Kända metoder inom statistisk försöksplanering användes för undersökning av komponenterna i EGR-systemets inverkan, där resultaten ur testerna visade att komponenter i EGR-systemet som implementerats med anledning att erhålla högre EGR-flöden inte fungerade som önskat och bör därför uteslutas vid framtida körningar med provcellens EGR-system. Provningen var uppdelad i flera moment, där en utav testomgångarna bestod av att se hur EGR-systemet klarade av att leverera EGR till motorn vid höga laster och laddtryck. Utfallet av dessa tester visade att med dagens komponenter kunde EGR överföras till den grad att singelcylinder-motorn inte klarade av högre EGR-flöden än vad som undersöktes vid provningen.

Correlations between the coefficient of variations (COV) of ion current integrals and COV of indicated mean effective pressure (IMEP) are investigated. The investigations are made to see if there is a possibility to use ion sense technique for closed loop combustion control to maximize Exhaust Gas Recirculation (EGR) level with remaining combustion stability. The engine studied in this thesis is a stoichiometric natural gas engine with a three way catalyst working with different EGR levels. One way to increase the efficiency in a stoichiometric natural gas engine is to maximize the EGR level [3]. With a higher EGR level it is possible to open the throttle even further with a result of lower pumping losses. Also temperature losses to chamber walls will be smaller with high EGR levels. A closed loop system controlling the EGR valve against COV of IMEP around 5 % is used for this engine. For COV of flame peak integral in range from 0 to 15-20% of COV of IMEP a linear correlation was found for lambda less than 1.3. For COV of two peaks integral a linear correlation was found for the entire measured range. This correlation may not be used for a robust EGR control system due to a small increase of COV of ion integral and due to a high variance in COV of ion integral. Correlations are discussed for different ion integrals with different air/fuels ratios and EGR levels. A control strategy is also presented.

La recirculación de los gases de escape (EGR) introduce diferentes efectos sobre las prestaciones del motor debido a su influencia sobre los procesos de combustión y renovación de la carga del mismo. Los trabajos realizados en esta tesis doctoral se plantearon con el objetivo de profundizar en el conocimiento de los efectos que introduce la recirculación de los gases de escape en el proceso de renovación de la carga de un motor Diesel turbo-sobrealimentado. La metodología utilizada ha sido la combinación adecuada de resultados experimentales y modelados del motor sujeto a estudio. Se ha diseñado una serie de experimentos que permiten separar los efectos del EGR sobre el proceso de renovación de la carga, evitando y aislando el efecto que el EGR ejerce sobre la combustión. Del análisis de los resultados obtenidos se desprende, por un lado, la influencia que tiene la estrategia de EGR utilizada y los elementos que introducen dicha estrategia sobre las prestaciones del motor, y por otro lado, la influencia que ejerce el EGR sobre la sobrealimentación y el proceso de renovación de la carga. / Vera García, F. (2004). Efecto de la recirculación del gas de escape en el proceso de la renovación de la carga en motores turbo-sobrealimentados [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/62276

This thesis examines the effects of product composition, reactant temperature, reactant pressure, fuel-air equivalence ratio, diluent addition, and fuel composition on entropy generation in a constant internal energy/constant volume combustion process. Equilibrium product composition is shown to produce less combustion-generated entropy than frozen product composition. Using methane as the fuel, it is found that increasing reactant temperature by 100 K decreases entropy generation by 6 to 9 percent, while reactant pressure has little effect on entropy generation. Total entropy generation is increased with excess air and increased diluent addition. For the three fuels considered in this analysis (CH4, C2H5OH, C8H18), iso-octane uniformly exhibits the highest entropy generation, indicating the strong effect of fuel type and structure on combustiongenerated entropy.

No description available.