Modeling of EGR Mixing in an Engine Intake Manifold Using LES

Abstract

and available online here Cet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 69, n°1, et téléchargeable ici D o s s i e rDOSSIER Edited by/Sous la direction de : C. Angelberger IFP Energies nouvelles International Conference / Les Rencontres Scientifiques d'IFP Energies nouvelles LES4ICE 2012 -Large Eddy Simulation for Internal Combustion Engine FlowsLES4ICE 2012 -La simulation aux grandes échelles pour les écoulements dans les moteurs à combustion interne Oil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 69 (2014) Re´sume´-Mode´lisation du me´lange de EGR dans la tubulure d'admission a`l'aide de la technique de LES -Nous e´tudions le processus de me´lange des gaz d'e´chappement avec l'air dans les moteurs ac ombustion interne. Dans ce but, une simulation des grandes e´chelles (LES, Large Eddy Simulations) de l'e´coulement compressible dans la tubulure d'admission d'un moteur Diesel ag rosse cylindre´e comptant 6 cylindres est re´alise´e. Le taux de recirculation des gaz d'e´chappement (EGR, Exhaust Gas Recirculation) est conside´re´comme un scalaire passif. Les re´sultats obtenus sont valide´s a`l'aide des mesures du taux de EGR effectue´es sur un moteur avec une sonde de mesure de CO 2 . Les conditions aux limites de l'e´coulement pulsatoire sont de´duites de simulations unidimensionnelles et de mesures de pression effectue´es sur le moteur. La qualite´du me´lange est e´value´e a`partir de la re´partition d'un cylindre a`l'autre et des moyennes quadratiques spatiales calcule´es au niveau des sections de sortie. Diffe´rentes me´thodes sont utilise´es pour le calcul des quantite´s moyenne´es. Les re´sultats montrent que les e´volutions spatiales et temporelles de EGR sont diffe´rentes d'un cylindre a`l'autre. La distribution de EGR dans l'orifice d'entre´e du cylindre n'est pas uniforme. Ces facteurs impliquent que les moyennes temporelles ne devraient pas eˆtre utilise´es pour de´crire l'e´volution de la teneur en EGR. De plus, les pulsations de l'e´coulement, au niveau de l'orifice d'entre´e de EGR, ont une forte influence sur la distribution de EGR. En comparant les re´sultats de simulations LES avec les re´sultats expe´rimentaux, nous montrons que les simulations LES permettent une meilleure et plus approfondie compre´hension du processus de me´lange lors d'e´tudes de tels e´coulements turbulents et pulsatoires.Abstract -Modeling of EGR Mixing in an Engine Intake Manifold Using LES -We investigate the mixing process of exhaust gases with fresh air in Internal Combustion Engines (ICE). For this purpose, the flow in an inlet manifold of a six-cylinder heavy-duty Diesel engine is computed using compressible Large Eddy Simulations (LES). The Exhaust Gas Recirculation (EGR) concentration is modeled as a passive scalar. The results are validated by on-engine measurements of the EGR concentration using CO 2 -probes. The boundary conditions for the highly pulsating flow are taken partly from one-dimensional simulations, partly from pressure measurements on the ...

Assessment of the numerical and experimental methodology to predict EGR cylinder-to-cylinder dispersion and pollutant emissions

“…24 The mixer studied in this work (see bottom side of Figure 3) can be included in the geometries that mix the air and EGR streams in a T-Junction upstream the manifold, like the manifolds that appear in Luján et al 12 and Hariganesh et al, 25 but these engines have four cylinders. All things considered, the manifold most similar to the one analyzed in this work is the geometry studied by Sakowitz et al 26 Nevertheless, the impact of different mixer geometries in the EGR distribution is out of the scope of this work.…”

“…Sakowitz et al 27 demonstrate that the turbulence structures in a T-junction have not been captured properly with the RANS approach, being too diffusive and with little mixing capacity. In spite of these commented discrepancies of RANS, a different work by Sakowitz et al 26 shows how the air-EGR mixing in the intake manifold at low frequencies ( ~ 60 Hz) the RANS approach and LES approach produce similar results, likely because the EGR dispersion in these conditions is more governed by the EGR pulses rather than the turbulence mixing. This behavior will be studied in sections Validation of turbulence models and Analysis of numerical flow field.…”

“…Regarding the LES approach, its ability to solve a significant fraction of the turbulent scales should allow an accurate prediction of mixing problems, ranging from simple geometries as T-junction 27,28 to EGR dispersion in intake manifolds. 26,27,29,30 RANS approach has been used as well in this type of problems. 31,32 Therefore, the decision of modeling turbulence in a more detailed way as LES or a more simplified as RANS needs to be addressed.…”

“…The air and exhaust gases have been modeled as different non-reactive, single gas components; instead of considering the EGR as passive scalar. 26 The main thermodynamical properties of EGR and air are variable with temperature but have been considered as alike, since the error of considering the actual exhaust gas composition is below 2%. 36 Indeed, replacing EGR by air is usual even for experimental facilities.…”

“…The number of engine cycles to average the results are variable depending of the works and the considered operating points. For example, in the works of Sakowitz et al, 26,30,38 the number of cycles vary between 4-10-20 cycles in LES calculations. On the other hand, in 3D RANS coupled with engine simulation software, the number of cycles calculated previously to the coupling are about 10 to 15 cycles.…”