Un modèle de combustion à allumage par compression basé sur la physique et la chimie tabulée : des modes de combustion contrôlés par la chimie jusqu’aux modes contrôlés par le mélange

International audienceThis paper presents a new 0D phenomenological approach to predict the combustion process in multi injection Diesel engines operated under a large range of running conditions. The aim of this work is to develop a physical approach in order to improve the prediction of in-cylinder pressure and heat release. Main contributions of this study are the modeling of the premixed part of the Diesel combustion with a further extension of the model for multi-injection strategies. In the present model, the rate of heat release due to the combustion for the premixed phase is related to the mean reaction rate of fuel which is evaluated by an approach based on tabulated local reaction rate of fuel and on the determination of the Probability Density Function (PDF) of the mixture fraction (Z), in order to take into consideration the local variations of the fuel-air ratio. The shape of the PDF is presumed as a standardized β-function. Mixture fraction fluctuations are described by using a transport equation for the variance of Z. The standard mixture fraction concept established in the case of diffusion flames is here adapted to premixed combustion to describe inhomogeneity of the fuel-air ratio in the control volume. The detailed chemistry is described using a tabulated database for reaction rates and cool flame ignition delay as a function of the progress variable c. The mixing-controlled combustion model is based on the calculation of a characteristic mixing frequency which is a function of the turbulence density, and on the evolution of the available fuel vapor mass in the control volume. The developed combustion model is one sub-model of a thermodynamic model based on the mathematical formulation of the conventional two-zone approach. In addition, an extended sub-model for multi injection is developed to take into account interactions between each spray by describing their impact on the mixture formation. Numerical results from simulations are compared with experimental measurements carried out on a 2 liter Renault Diesel engine and good agreements are found.Ce papier présente une nouvelle approche 0D phénoménologique pour prédire le déroulement de la combustion dans les moteurs Diesel à injection directe pour toutes les conditions d’utilisation usuelles. Le but de ce travail est de développer une approche physique en vue d’améliorer la prédiction de la pression cylindre et du dégagement d’énergie, avec un nombre minimum d’essais nécessaires à la calibration. Les contributions principales de cette étude sont la modélisation de la phase de pré-mélange de la combustion et une extension du modèle pour les stratégies d’injections multiples. Dans ce modèle, le taux de dégagement d’énergie dû à la combustion pour la phase pré-mélangée est relié à un taux de réaction moyen du carburant. Ce taux de réaction moyen de carburant est évalué à l’aide d’une approche basée sur un taux de réaction local de carburant tabulé et la détermination d’une fonction de densité de probabilité (PDF) de la fraction de mélange (Z). Cette PDF permet de prendre en compte la distribution de richesse existante dans la zone pré-mélangée. L’allure de cette PDF présumée est une β-fonction standardisée. Les fluctuations de la fraction de mélange sont décrites avec une équation de transport pour la variance de Z. La définition standard de la fraction de mélange, établie dans le cas de flammes de diffusion, est ici adaptée à une combustion pré-mélangée de type Diesel pour décrire l’inhomogénéité de la richesse dans le volume de contrôle. La chimie détaillée est décrite au travers de la tabulation du taux de réaction relatif à la flamme principale et du délai d’auto-inflammation relatif à la flamme froide, ces tabulations sont fonction de la variable d’avancement c, du taux de gaz brûlé ainsi que des grandeurs thermodynamiques telles que la température et la pression. Le modèle de combustion de diffusion est basé sur l’évaluation d’une fréquence de mélange qui est fonction du taux de turbulence dans la chambre et fonction de la masse de carburant vapeur disponible. Ce modèle de combustion est l’un des sous-modèles inclus dans le modèle thermodynamique de chambre de combustion basé sur une approche 2 zones différentiant gaz frais et gaz brûlés. De plus, un sous-modèle concernant la multi-injection a été développé pour prendre en compte les interactions entre les jets et pour décrire l’impact de la multi-injection sur le mélange air/carburant. Les résultats numériques ont été comparés aux mesures réalisées sur un moteur Diesel Renault de 2 litres. Pour l’ensemble des points de fonctionnement explorés, une bonne correspondance a été obtenue entre les résultats issus des simulations et les mesures expérimentales

Explicit-Ready Nonlinear Model Predictive Control for Turbocharged Spark-Ignited Engine

International audienceThe trend to reduce the engine size in automotive industry is motivated by more restrictive pollutant emissions standards. That is why engine technical definitions have become more and more complicated. The control challenge has also grown since engines are now considered as highly nonlinear multi-input multi-output systems with saturated actuators. In this context, the need for model-based control laws is bigger than ever. In this study we propose a nonlinear model predictive control strategy based on a physical engine model. Moreover, we also underline the benefit of using a thermodynamic engine term in the objective function. Finally, the design and calibration choices consciously fulfill the criterions of the use of an explicit approach for the real time implementation

Nonlinear Model Predictive Control of the Air Path of a Turbocharged Gasoline Engine Using Laguerre Functions

International audienceObjectives in terms of pollutant emissions and fuel consumption reduction have led car manufacturers to enhance the technical definitions of combustion engines. The latter should now be considered as multiple-input multiple-output nonlinear systems with saturated actuators. This considerably increases the challenge regarding the development of optimal control laws under the constraints of constant cost reductions in the automotive industry. In the present paper, the use of a nonlinear model predictive control (NMPC) scheme is studied for the air path control of a turbocharged gasoline engine. Specifically, a zero dimension physics-based model is combined with parameterization of the future control trajectory. The use of Laguerre polynomials is shown to increase flexibility for the future control trajectory at no cost in computational requirements. This increase in flexibility leads to an improvement of the transient response of the closed-loop with respect to traditional approaches. This practical application shows that this approach makes it easier to fine-tune the NMPC scheme when dealing with engine air path control

Explicit Nonlinear Model Predictive Control of the Air Path of a Turbocharged Spark-Ignited Engine

International audiencePollutant emissions and fuel economy objectives have led car manufacturers to develop innovative and more sophisticated engine layouts. In order to reduce time-to-market and development costs, recent research has investigated the idea of a quasi-systematic engine control development approach. Model based approaches might not be the only possibility but they are clearly predetermined to considerably reduce test bench tuning work requirements. In this paper, we present the synthesis of a physics-based nonlinear model predictive control law especially designed for powertrain control. A binary search tree is used to ensure real-time implementation of the explicit form of the control law, computed by solving the associated multi-parametric nonlinear problem

Clinical and molecular epidemiology of hospital Enterococcus faecalis isolates in eastern France

ObjectiveTo report on the occurrence of Enterococcus faecalis hospital isolates obtained during 1 year in hospitals in the Franche-Comté region of France.MethodsClinical isolates of E. faecalis of different antibiotic susceptibility phenotypes from hospitalized patients were characterized by pulsed-field gel electrophoresis. Patients with positive cultures were investigated by three case-control studies to identify risk factors for colonization/infection.ResultsThe crude incidence of colonization/infection was 2.37%, and 4-day and 7-day colonization rates after admission were 10.0% and 6.36%, respectively. The rates of high-level resistance to kanamycin (HLKR) and to gentamicin (HLGR) were 47.1% and 7.1%, respectively. No isolate was resistant to glycopeptides or produced β-lactamase. The 209 hospital isolates obtained during the study yielded 98 major DNA patterns, of which two were major epidemic patterns including HLKR isolates. No single factor was significantly associated with colonization/infection by HLKR isolates. The length of hospitalization before isolation was associated with colonization by HLGR isolates.ConclusionsThe isolation frequency of E. faecalis strains with acquired resistance to aminoglycoside antibiotics, and the wide dissemination of resistant strains with characteristics that allow them to persist and spread, argue for further large prospective surveys of clinical isolates of E. faecalis in hospitals

Transport processes in stars: diffusion, rotation, magnetic fields and internal waves

In this paper, I explore various transport processes that have a large impact of the distribution of elements inside stars and thus, on stellar evolution. A heuristic description of the physics behind equations is provided, and key references are given. Finally, for each process, I will briefly review (some) important results as well as discuss directions for future work.Comment: 50 pages, proceedings of the Aussois school "Stellar Nucleosynthesis: 50 years after B2FH

Données récentes sur l’occupation humaine dans les Alpes méridionales durant l’Antiquité

Parmi les nombreux travaux portant sur l’occupation du milieu alpin, très peu concernent la période antique. Les recherches, souvent anciennes, se sont focalisées sur des questions telles que les grandes voies transalpines, l’organisation administrative des régions alpines ou le développement urbain. L’occupation de ces régions était principalement appréhendée à travers quelques découvertes ou des fouilles anciennes, principalement dans les fonds de vallées des Alpes du Nord. Le développement de l’archéologie préventive a permis d’acquérir de nouvelles connaissances dans les zones basses mais ce sont surtout les recherches entreprises, depuis une dizaine d’années dans les Alpes méridionales, qui ont fait progresser les connaissances sur le peuplement de la montagne, en appréhendant ce milieu dans son ensemble, depuis les vallées jusqu’à la haute montagne.Amongst the many research projects dealing with the occupation of alpine landscapes, very few directly deal with the Roman period. Older research projects often emphasised the study of the major trans-Alpine routes, or the administrative organisation of the urban zones in the Alps. The settlement of these regions was primarily based on data from earlier excavations, mainly from the valley bottoms of the northernAlps. Rescue (or salvage) archaeology has enhanced our knowledge of lowland alpine archaeology, but it is the research undertaken during the past decade in the Southern Alps that increased our understanding of mountain populations covering all altitudes from valley bottoms to the high altitudes

Les Écrins, un territoire d’altitude dans le contexte des Alpes occidentales de la Préhistoire récente à l’âge du Bronze (Hautes-Alpes, France)

Les premiers témoignages d’une présence humaine en altitude reconnus dans les Alpes méridionales françaises, dès la Préhistoire, s’inscrivent au sein de travaux pluridisciplinaires et diachroniques menés, depuis 1998, sur le peuplement et les activités humaines en moyenne et haute montagne. Développés plus particulièrement sur les hauts massifs de l’Argentiérois/Vallouise et du Champsaur dans le Parc National des Écrins (Hautes-Alpes), ces programmes corrèlent sur le terrain données archéologiques et paléoécologiques d’altitude. Dès la seconde moitié du iiie millénaire et au cours du iie millénaire BC (fin du Néolithique-âge du Bronze), se distinguent des structures bâties à vocation pastorale, entre 2 067 et 2 360 m d’altitude, en relation avec l’essor démographique observé dans les zones basses. L’occupation de la haute montagne durant cette période paraît continue et le milieu, exploité de manière durable.The earliest evidence for a prehistoric human presence identified in the Southern French Alps has been revealed by a multidisciplinary, diachronic research project that started in 1998. This research assesses the natural and social dynamics of occupation in the sub-alpine and alpine zones. This work is focussed on the high mountains of the Argentiérois/Vallouise and Champsaur areas in the Parc National des Écrins (Hautes-Alpes), and combines archaeological and palaeoenvironmental evidence. The second half of the IIIrd millennium BC and during the IInd millennium BC (the Late Neolithic and Bronze Age) is marked by the appearance of the built pastoral structures between 2067 and 2360m, related to the development and increase in populations at lower altitudes. This high altitude activity appears to be continuous and sustainable throughout these periods