6 research outputs found
Simulation aux grandes Ă©chelles de l'injection de carburant liquide dans les moteurs Ă combustion interne
Les objectifs ambitieux, fixés aux acteurs du secteur automobile par les pouvoirs publics, en matière d'émission de polluants et de gaz à effet de serre rendent aujourd'hui indispensable une compréhension plus fine de la combustion dans les moteurs. La simulation 3D aux grandes échelles (LES) représente une voie prometteuse pour répondre à ces enjeux. Elle permet l'étude de phénomènes transitoires complexes inaccessibles avec des moyens expérimentaux ou des méthodes de calculs traditionnelles de type RANS. Ce travail de thèse est une première étape vers la simulation LES de l'injection de carburant liquide dans les moteurs à piston. Il a consisté à adapter le code de calcul aux particularités physiques de l'injection directe, technologie qui se généralise actuellement à tous les types de moteurs à piston. Dans un premier temps, et afin de s'affranchir du calcul 3D complexe en sortie d'injecteur, une méthodologie originale, consistant à initier le calcul en aval de l'injecteur, est proposée et validée sur différents cas. Pour la simulation 3D, l'approche Eulérienne mésoscopique, à laquelle est ajouté un modèle d'interaction particules-particules, est utilisée pour simuler le spray. Les simulations ont été premièrement validées par comparaison expérimentale dans des conditions proches de l'injection Diesel. De plus, une étude sur la dynamique du spray a permis de mieux comprendre son évolution et de dégager des points communs avec un jet de gaz turbulent. Des simulations complémentaires ont également montré la prédictivité de la LES sur des injections Diesel réalistes. Enfin, un premier calcul moteur à injection directe a été réalisé et a permis de valider les développements réalisés dans le cadre de cette thèse.Car manufacturers are facing increasingly severe regulations on pollutant emissions and fuel consumption. To respect these regulations, a better understanding of combustion processes is needed. Large Eddy Simulation (LES) is becoming a promising tool for such issues as it allows the study of complex unsteady phenomena which can not be analysed with RANS simulations or experiments. The present work is a step towards the LES of liquid injection in piston engines. The numerical code has been adapted to the specifications of Direct Injection which is more and more used in industry. Firstly, in order to avoid the difficulties linked to the 3D simulation of cavitation, primary break-up and turbulence in the near-nozzle region, an original methodology, based on an injector model, has been proposed. The idea is to initiate the spray physics downstream to the injector exit. Then LES 3D simulations of spray have been conducted using the Eulerian Mesoscopic approach extended to dense dispersed sprays by the addition of a particle-particle interactions model. The simulation results have been validated by comparison with experimental data in Diesel conditions with a low injection pressure. Furthermore a study on the spray dynamics has permitted to better understand its development and to find similarities with a turbulent gaseous jet. Additional simulations on realistic Diesel injection conditions have shown the good predictivity of LES in such cases. Finally, a first simulation of a Direct Injection Engine has been been carried out to assess the developments achieved in this work.TOULOUSE-INP (315552154) / SudocSudocFranceF
Coupling of a 1-D Injection Model with a 3-D Combustion Code for Direct Injection Diesel Engine Simulations
Modern diesel engines operate under injection pressures varying from 30 to 200 MPa and employ combinations of very early and conventional injection timings to achieve partially homogeneous mixtures. The variety of injection and cylinder pressures, as well as injector dynamics, result in different injection rates, depending on the conditions. These variations can be captured by 1-D injection models that take into account the dynamics of the injector, the cylinder and injection pressures, and the internal geometry of the nozzle. The information obtained by these models can be used to provide initial and boundary conditions for the spray modeling in a 3-D combustion code. In this paper, a methodology for coupling a 1-D injection model with a 3-D combustion code for direct-injected diesel engines is presented. A single-cylinder diesel engine has been used to demonstrate the capabilities of the model under varying injection conditions. Moreover, this coupling strategy opens a new methodology for 3-D calculations that do not need to fit initial conditions but use directly a 0-D model for intake/exhaust conditions and injection conditions. Using coupling strategy makes easier to run 3-D engine simulations, reduce engineering time and allows to investigate a large range of interesting phenomena
Towards the understanding of cyclic variability in a spark ignited engine using multi-cycle LES
International audienc
Towards large eddy simulation of combustion in spark ignition engines
Internal combustion engine simulations are commonly performed using the RANS (Reynolds averaged Navier–Stokes) approach. It gives a correct estimates of global quantities but is by nature not adapted to describe phenomena strongly linked to cyclic variations. On the other hand, large eddy simulation (LES) is a promising technique to determine successive engine cycles. This work demonstrates the feasibility of LES engine cycles simulation by using a flame surface density (FSD) approach. This approach, presented in a first section, combines an Eulerian spark ignition model derived from the RANS AKTIM model [J.M. Duclos, O. Colin, Arc and Kernel Tracking Ignition Model for 3D SI Engines Calculations, Comodia, Nagoya, Japan, 2001, pp. 343–350] and a Coherent Flame Model (CFM) [S. Candel, T. Poinsot, Combust. Sci. Tech. 70 (1990) 1–15; O. Colin, A. Benkenida, C. Angelberger, Oil & Gas Sci. Techn.—Rev. IFP 58 (1) (2003) 47–32] describing the flame propagation. The CFM model, commonly used in RANS simulations, is here formulated in a LES context. In a second part, the whole ignition-combustion model is validated against an experiment relative to the turbulent ignition and flame propagation of a stoichiometric propane-air mixture [B. Renou, A. Boukhalfa, Combust. Sci. Tech. 162 (2001) 347–371]. Finally, LES engine cycles simulations are performed on a real engine configuration. First, the sensitivity of the model to the LES combustion filter size ^D is examined, showing a weak dependence of the modelling approach to D. Then results are compared to those obtained with the algebraic model for the FSD proposed by Boger et al. [M. Boger, D. Veynante, H. Boughanem, A. Trouve´, Proc. Combust. Inst. 27 (1998) 917–925] and the need for non-equilibrium combustion models is demonstrated